Scipedia: Documents published in 2021

Parents' and children's perception on social media advertising

Scipedia content — Thu, 19 Jan 2023 13:52:26 +0100

This article presents the results of research that seeks to analyze the ability of minors to identify the advertising messages received through the most used social networks by this audience (YouTube and Instagram). Children’s aptitude to recognize persuasive intent was measured in a selection of examples taken for this study, as well as the perception that parents or guardians had about the minor's ability to recognize advertising on the platforms analyzed. Results were obtained from a survey applied to dyads in 501 homes in the Metropolitan Area of Santiago de Chile, to children aged 10 to 14 and to one of their parents or guardians. Main results include the notion that more than 50% of children were not able to detect advertising in examples containing ads. Lower recognition percentages were obtained in cases that combined persuasive content and entertainment and were not classified as advertising. For their part, adults perceived that their children recognize persuasive intent to a lesser extent than indicated by the children themselves. An explicit and clear signaling of advertising messages, as well as advertising literacy according to the age of minors could help them discern the content they consume on social networks.

Coping with distress among adolescents: Effectiveness of personal narratives on support websites

Scipedia content — Thu, 19 Jan 2023 13:51:49 +0100

Sharing, reading and responding to personal narratives on peer-to-peer support websites may provide adolescents with informational and emotional support to feel more confident in coping with stressful events. However, their use may also pose a threat to adolescents’ coping self-efficacy. Principles of expressive writing, social sharing of emotions, narrative persuasion and self-effects may provide insight in how these actions may both positively and negatively relate to coping self-efficacy. By using a cross-sectional online survey with 311 Dutch-speaking adolescents between the ages of 14 and 18, this article explores how these actions and social support motives (i.e. information-seeking and emotional support-seeking) are related to adolescents’ perceptions about the usefulness of these websites to their coping self-efficacy. The results showed a positive relation between adolescents’ social support motives and their belief in the usefulness of these websites to their coping self-efficacy. Therefore, we conclude that it may be an effective coping strategy for many adolescents. There was a negative relation between experience with sharing a personal narrative and coping self-efficacy, meaning that these users did not perceive the website to be helpful to their overall confidence in coping with stressful events. However, this negative relation was reversed when they were motivated to find emotional support with similar others.

Internet memes in Covid-19 lockdown times in Poland

Scipedia content — Thu, 19 Jan 2023 13:51:19 +0100

Poland was one of the countries that was hit by the Covid-19 pandemic in 2020, and its government imposed restrictions to combat the spreading of the virus. The Internet and social media became outlets for people’s reactions to the events that unfolded, including the lockdown. A part of this reaction came in the form of creating and sharing memes – an expression of digital participatory culture. This paper aims to analyze how Covid-19 was communicated and narrated through Internet memes and how they presented the pandemic and actors responsible for fighting it. 1,763 memes from six media platforms were analyzed using content analysis with framing elements and a comparative narrative analysis. The results show that the memes provided a form of commentary on the situation experienced by Poles. The most common category of memes was “bans and orders”, involving restrictions that were often criticized and ridiculed as pointless. The main characters within the memes were ordinary citizens, often portrayed in a comedic way as careless in regards to the virus and violating the restrictions. They were also presented as victims of the police and the government. Furthermore, the people responsible for fighting the pandemic were portrayed as incompetent and imposing needlessly severe restrictions and penalties for not abiding by them.

Cybergossip, cyberaggression, problematic Internet use and family communication

Scipedia content — Thu, 19 Jan 2023 13:50:42 +0100

Research into risky online behaviour among children and adolescents is on the rise, with more studies being conducted into the factors which can influence this phenomenon, above all in relation to school and family life. In the latter sphere, one relevant factor is the degree of genuine trust children have in their parents when using the Internet. The main objective of this study is to verify the effects of child disclosure about cyberaggression, in addition to the mediating role of problematic Internet use and cybergossip, and the moderating role of gender and age. A total of 866 primary school children (53% girls) between 10 and 13 years old (M=11.21; SD=0.90) were surveyed using self-reporting. The data processing followed a moderated serial mediation model using “Process”. The results revealed the effects of child disclosure about cyberaggression and the mediation of problematic Internet use and cybergossip. Unlike gender, age moderated the effects of the mediation model. The results highlight the need to foster a climate of trust and communication in the family environment to reduce involvement in risky online behaviour, in which children feel understood and supported by their parents, which in turn encourages open communication about Internet use.

Anxiety and self-esteem in cyber-victimization profiles of adolescents

Scipedia content — Thu, 19 Jan 2023 13:50:06 +0100

This study has two objectives: (1) Identify profiles of victimization in adolescence, depending on the levels of offline or online peer aggression suffered, along with the prevalence of each profile; and (2) Analyse the association of the victimization profiles with adolescents’ social anxiety and self-esteem. The sample was comprised of 3120 adolescents aged 12 to 18 (M=14.03; SD=1.40) from Asturias (Spain), who completed self-report questionnaires about traditional peer victimization and cyber-victimization, as well as social anxiety and self-esteem. We performed descriptive analyses, Latent Profile Analyses, and multivariate analyses of variance. We found a positive, moderate correlation between being a cyber-victim and being a traditional victim, along with four profile types: non-victims (77.8%), mainly cyber-victims (13.5%), mainly traditional victims (4.5%), and dual victims (4.3%). Traditional victims and dual victims exhibited greater social anxiety and less self-esteem than cyber-victims, who exhibited greater social anxiety and less self-esteem than non-victims. Dual victims and traditional victims do not differ in social anxiety and self-esteem. The results contribute to the identification of patterns of victimization in school-age adolescents, and their relationship with social anxiety and self-esteem.

Motivation and perception of Hong Kong university students about social media news

Scipedia content — Thu, 19 Jan 2023 13:49:31 +0100

With the prevalence of social media in a digital age, accessing news on social media has become a daily routine of university students’ lives. However, little research has been done to examine their social media news use in detail, especially in Asian countries. To fill this gap, we aimed to examine what motivated university students to seek news on social media, to what extent they perceived they were in control of the influences of news, and whether news motives were related to their levels of news media literacy across three domains: (a) authors and audiences; (b) messages and meaning, and (c) representation and reality. One hundred and forty-seven university students from a university in Hong Kong participated. Among the four news motives, socializing was the most powerful predictor for news use on social media. Most students believed they were in control of news influences and demonstrated a high level of news media literacy, and those who believed themselves to be in control of news influences showed a higher level of news media literacy. In this sense, high news-literate students were more likely to seek news for socializing as compared to their low news-literate counterparts. Insights on educating students to use social media in a positive and smart way were discussed.

Youths’ coping with cyberhate: Roles of parental mediation and family support

Scipedia content — Thu, 19 Jan 2023 13:48:56 +0100

Adolescents around the world are increasingly exposed to cyberhate. More knowledge is needed to understand howadolescents cope with cyberhate and how they can be supported when exposed. To this end, the present studyinvestigated the associations between parental mediation of Internet use and adolescents’ problem-focused coping strategiesfor hypothetical cyberhate victimization while considering family support as a moderator of these relationships. The sampleconsisted of 5,960 adolescents between 12-18 years old (M=14.94; SD=1.61; females: 50.7%) from Cyprus, Germany,Greece, India, Spain, South Korea, and Thailand. A structural equation model was used to investigate the relationshipamong parental mediation, family support, and coping with cyberhate. Findings showed a positive relationship betweeninstructive parental mediation and adolescents’ problem-focused coping strategies, and a negative relationship betweenrestrictive parental mediation and adolescents’ capability to cope productively with cyberhate. In addition, family supportstrengthened the positive relationship between instructive parental mediation and adolescents’ use of coping strategies andattenuated the negative relationship between restrictive parental mediation and adolescents’ use of coping strategies. Thefindings highlight the need for parental education training and underscore the importance of family support for increasingadolescents’ ability to cope productively with cyberhate.

Cyberostracism: Emotional and behavioral consequences in social media interactions

Scipedia content — Thu, 19 Jan 2023 13:47:52 +0100

This study focuses on the effect of cyberostracism on social networking sites. Based on the temporal need-threat model ofostracism, we examined a) reflexive reactions, specifically worsened mood and threats to the four fundamental needs (i.e.,belongingness, self-esteem, meaningful existence, and control), and b) reflective reactions, in the form of prosocial, antisocial,and avoidance behavior. We also focused on the role of social anxiety. Using the experimental tool Ostracism Online, weconducted an online experiment to manipulate ostracism, measure self-reported reflexive reactions, and measure reflectivereactions in a newly developed cooperative financial game. The participants were 196 young Czech adults (age 18-30; 62%women). T-tests showed worsened mood and higher threat connected to all four of the fundamental needs in the reflexivestage in ostracized participants. Regression models showed that social anxiety had a small effect on reflexive reactions, but itdid not moderate the effect of ostracism. The type of threatened need and social anxiety did not predict a reflective reaction.The only significant predictor of antisocial response was experienced ostracism. Even a mild form of ostracism such as thelack of reactions by strangers to a shared post can lead to negative emotional and behavioral consequences.

Meta-reflexivity for resilience against disinformation

Scipedia content — Thu, 19 Jan 2023 13:42:06 +0100

The rise of digital media contributes to fake news and disinformation being circulated on a larger scale and pace. The central aim of the work is to consider the potentials of individuals to actively respond to disinformation and fake news. In that regard, the authors rely on Archer’s theoretical framework of reflexivity and its modes. It is argued that a specific mode of reflexivity, namely meta-reflexivity, can enable people to take a critical distance towards media messaging. The method involves the Reflexivity Measurement Tool (RMT) to provide an approximate assessment of one’s reflexivity in terms of quantitative scores. The survey has been conducted in Slovenia on a representative national sample and path analysis is applied to identify the relationship between demographic features, media exposure, reflexivity and fact-checking. The results show how age and education affect media preferences, in terms of how frequently an individual is exposed to a particular type of media. Younger people, women and persons with tertiary education are more meta-reflexive, which contributes to their active response to disinformation. It is concluded that meta-reflexivity is essential but not sufficient to produce an active response of individuals to disinformation. Need for professional fact-checking-services and media education is discussed.

A study of the factors influencing air removal in Out-of-Autoclave processing of composites

Scipedia content — Thu, 31 Mar 2022 21:35:33 +0200

Nowadays, manufacturing of composite parts using out-of-Autoclave (OoA) processes is gaining importance because it allows a reduction of initial investments and recurring costs. Among these technologies, the consolidation of out-of-autoclave prepregs using vacuum bag only technologies (VBO) is proven to provide high-quality composite structural parts without the need of autoclaves. OoA prepregs are designed to be semi-impregnated creating engineered channels within the tows to evacuate internal air or volatiles generated during the cure cycle. The aim of this work is to understand and explain the void formation mechanisms, their spatial distribution and transport mechanisms during the consolidation of OoA prepregs using vacuum bag only methods. This work includes parallel studies carried out using X-ray computed tomography (XCT) to determine the most important factors for air removal process in laminated composites produced by hand lay-up (HLU) and automated fiber placement (AFP). A big challenge is the accurate monitoring of the evolution of porosity during composite curing, which has not been done so far and even less with a 3D visual technique. This combination of monitoring the dynamics of pore evolution by laboratory XCT and synchrotron tomography (SXCT) at different resolutions during a cure process will provide a profound understanding of the pore evacuation process which is strategic for the further development of OoA materials.

Multiscale Multiphysics Simulation in Composite Materials

Scipedia content — Thu, 31 Mar 2022 21:35:23 +0200

In the last decades, the improvements in terms of computational power provides the capability to analyze with more detail the materials behavior. On one hand, going deeper in the materials to study an increasingly smaller dimension and capture micro- or nano- changes. On the other hand, the increasing computational memory allows to perform finite elements analysis with millions of nodes, that permits to obtain more accurate results. In this scenario, the focus of this work is the numerical modeling of the microscale behavior of inhomogeneous materials, with special attention to composite materials under thermo-mechanical loading conditions. This work also proposes and implements optimization tools, at a constitutive law level, as well as the level of both, macro- and micro-structural algorithms. The study presents two computationally efficient multiscale procedures cables of predicting the mechanical non-linear response of composite materials. This is achieved, using an RVE Data Base (DB) calculated a-priori. Through the definitions of an equivalent damage parameter (deq), function of the global stress at the microscale, a series of strain controlled virtual tests of the RVE are performed storing in the DB the homogenized stress and strain state reached at certain levels of deq. Afterwards, the solution of the macroscale structure can be solved using the interpolation of the stored data.

Development of advanced methods to characterise the fracture behaviour of flexible bonded joints: An overview

Scipedia content — Thu, 31 Mar 2022 21:35:12 +0200

In some cases, the scope of bonded joint characterisation methods applied in laboratory may not be aligned with the bonded joints used in industry. Experimental results produce uncertainty and cause the bonded joints to be replaced by mechanical joints. Experimental procedures evidence a strong dependence on specimen dimensions, type of adhesive, ageing and crack measurement. They are suitable for bonded joints with thin adhesive layers and rigid behaviour while bonded joints in industrial applications have many different geometries and types of adhesive. Moreover, they must withstand external loads and environmental conditions simultaneously, while cracks may not be visible. The present work summarises the methodologies developed to overcome the limitations of current experimental procedures. An analytical method is developed to evaluate the fracture toughness of bonded joints with any width-to-thickness configurations. It is also demonstrated that external loads accelerate the degradation of bonded joints exposed to environmental conditions. Consequently, a new durability test has been developed for bonded joints that considers sustained loads during environmental exposure. Finally, it is demonstrated that the Acoustic Emissions technique is suitable for crack growth monitoring in bonded joints, providing a reliable alternative to locate the cracks when they are not visible.

Nonlinear response under several multiaxial loading states in fibre reinforced polymer laminates

Scipedia content — Thu, 31 Mar 2022 21:35:01 +0200

The present work includes a summary of the doctoral thesis entitled "Complexity of the structural response of fibre reinforced polymer matrix composites". This PhD thesis focused on analyzing the nonlinear mechanical response of a set of stacking sequences, with main interest in angle-ply laminates, to detail the stress-strain behaviour under a range of loading states: uniaxial tension/compression, loading-unloading-reloading tensile tests, three-point bending and plane stress states. The aim is to delve into the mechanisms of coupling and damage and their influence on the mechanical behaviour, in some cases highly nonlinear, aiming to achieve that the material withstands large strains with the consequent delay of the final failure and the increase in energy absorption capacity. Thanks to the characterization through standard testing, it is possible to calibrate material models based on progressive damage, providing two different numerical approaches which are tested against the different experimentally generated states of plane stress. In addition, it is worth mentioning the biaxial tests on cruciform specimens under different loading ratios, which provide experimental data closer to the actual response of composite structures in service. These tests, due to their greater complexity and lack of standardization, are analyzed in detail by applying numerical simulations and analytical models that ensure the validity of the results, highlighting the possible instabilities generated in the presence of compressive loads.

Mechanics of deformation and failure of hybrid polymer composites

Scipedia content — Thu, 31 Mar 2022 21:34:40 +0200

High performance composites can be designed, and their properties tailored to enhance specific mechanical (or multifunctional) properties of the material. Fibre hybridization, which consists of combining multiple types of fibres in the same composite material, is a strategy that can lead to improved composite properties and performance, as it not only changes the material properties but also the damage propagation mechanisms leading to final failure. In this work, two numerical frameworks are proposed to analyse the mechanics of failure of hybrid polymer composites. Firstly, a FEM framework is used to analyse the mechanisms that lead to longitudinal failure of composite materials. The effects of superimposed hydrostatic pressure on longitudinal tensile failure is analysed and a generalized reduction in strength with increasing pressure is predicted. Secondly, a dynamic Spring Element Model is proposed and used to analyse the dynamics of the formation of clusters of broken fibres and the effects of fibre dispersion in hybrid composites, concluding that higher fibre dispersion leads to improved material performance. Additionally, an experimental campaign on two different hybrid materials (inter and intratow) is performed to understand the effect of hybridization on fibre dominated properties, namely longitudinal tensile strength and translaminar fracture toughness. The interply hybrid material is obtained by stacking alternating T800 and HR40 thin-ply layers, while the intratow is obtained by combining the two types of fibres in the same layer using spread tow technology. A change in the damage mechanisms through hybridization is observed, which can lead to improved material performance.

Development of a multifunctional self-sensing composite structure

Scipedia content — Thu, 31 Mar 2022 21:34:30 +0200

In the present work, a model of electrical properties of composites with inherent sensing properties is proposed. More specifically, the effect of both geometry and dispersion procedure is analyzed for carbon nanostructured polimers, exploring their influence in its electromechanical properties by developing simple analytical methods. In this context, it is observed that a better CNT distribution (by reducing the aggregate ratio) leads to a higher electrical conductivity as well as a higher electrical sensitivity to mechanical deformation. Therefore, the proposed model allows to get a deepr knoweledge about the influence of different processing parametrs in the final electrical properties of the nanocomposite. Moreover, the experimetal testing of self-sensing structures has been carried out by using a carbon nanotube doped adhesive film. More specifically, it has been observed that the proposed nanostructured adhesive presnts an outstanding capability for early damage detection and propagation, being a promising technique in order to complement other available inspection methods. This tests have been validated at coupon level, as well as a subelement one, by using stiffened panels. In addition, it has been proved a higher capability for detecting the presence of possible weak interfaces, demonstrating the applicability of the developed technique.

Theoretical and finite element approaches to model the phenomenon of high-velocity impact on GFRP plates

Scipedia content — Thu, 31 Mar 2022 21:34:20 +0200

New energy-based theoretical models that predict the ballistic behaviour of thin and thick woven composite laminates are presented. These models are formulated for high-velocity impacts, where the boundary conditions do not play a relevant role. This can be assumed as the local structural behaviour is responsible for the ballistic performance. A non-dimensional formulation is used to analyse the influence of material properties and geometrical parameters in the ballistic response of the laminate. The models are physically-based on the energy contribution of different energy-absorption mechanisms. Moreover, a 3D finite element model is also developed by means of a continuum damage mechanics model that takes into account the different failure mechanisms described in the theoretical models to simulate the performance of the laminate under high-velocity impacts and to validate the hypotheses of the theoretical models. A comparison between FE and theoretical models is performed by means of energy absorption mechanisms. The predictive capability of the proposed models is verified against experimental results, which were originally conducted in this work. The results obtained show the dependencies between the ballistic response and the non-dimensional physical parameters of the model. Furthermore, the proposed models can be used to see the relative importance of the different energy-absorption mechanisms involved and the comparison of these mechanisms between the theoretical and the FE models can reflect the different roles played by them, depending on the material properties and geometrical characteristics of the laminate. These results highlight the relevance of the in-plane and out-of-plane energy-absorption mechanisms, which rule the penetration process depending on the plate thickness.

Towards an improved compression after impact response of thin plies using ply grade hybridization and unsymmetrical laminate designs

Scipedia content — Thu, 31 Mar 2022 21:34:09 +0200

With thin structures used in the aircrafts, aeronautical manufacturers are worried about the response of these thin laminates towards impact and post impact loads. Thin laminates studied to show reduced compression after impact strengths with thin plies and hence continues to be a primary concern to the aeronautical industries. In this work, we aim to use ply grade hybridization (mixing different ply grades) and unsymmetrical laminate designs as an effort to improve the low velocity impact response and compression after impact strength of thin laminates. Using different materials, uni-directional and non-crimp fabrics, through experimental, numerical and optimization methods, we demonstrate that hybridization along with unsymmetrical designs can improve the CAI strength by upto 40% over the thin ply baseline laminates.

Development and manufacturing of heavily loaded suspension link based on one shot RTM, highly integrated and lightweight CF concept

Scipedia content — Thu, 31 Mar 2022 21:29:07 +0200

Fibre-reinforced polymer composite materials are leading candidates as component materials to improve the efficiency and sustainability of many transport modes and specially in new vehicles based on electric mobility where weight is also an important requirement. The advantages of high-performance composites are numerous: they include lighter weight and reduced assembly costs due to high level of integration potential. This translates into greater weight savings resulting in improved performance, greater payloads, fuel or battery energy savings and emissions reductions. However, the manufacturing processes to provide high level of integration are still a challenge as the process becomes more complex in terms of materials preparation (cutting, stacking, etc), 3D preforming and toolings involved. In this context, Tecnalia, Gestamp and other partners have recently developed a suspension link, with the following features: Lightweight CFRP concept despite of the very high demanding mechanical loads requirements Fast stacking, cutting and 3D net shape preforming including also the corresponding advanced toolings and equipment One shot RTM and highly integrated concept to optimize the mechanical performance and reduce the process steps and joining operations

Dynamic structural testing of a composite structure by 3D projected digital image correlation

Scipedia content — Thu, 31 Mar 2022 21:28:53 +0200

Complex composite structures have unexpected mechanical behaviour, specially under high dynamic loads or in bucking conditions. The complexity and the number of sensors of these types of structural testing require non-standard instrumentation in order to detect local phenomena before critical failure appears. The main problem introduced by accelerometers or strain sensors is the cabling, due to the weight and complexity introduced. Digital Image Correlation (DIC) is a strain and deformation measurement technique well know and extendedly applied in composite structural testing. In this paper it is proposed a new DIC methodology based on project the aleatory patter over the structure instead of paint it. Furthermore, an UAV wing full made of composite will be tested at high frequency and vibrations modes will be observed with a stroboscope and, simultaneously, the aleatory patter will be projected in order to measure the shape of the vibration mode applying the DIC technique. Additionally, strain and shape sensing at high frequencies will be validated with Distributed Fiber Optic at high frequency rates. In this paper, the different technologies will be tested and compared in order to validate their capabilities and limitations.

Structural monitoring of RPAS MILANO in the flight test phase

Scipedia content — Thu, 31 Mar 2022 21:28:40 +0200

The RPAS (Remote Piloted Air System) MILANO is the largest unmanned aerial system developed by INTA that aims to become a research platform capable of carrying out in-flight tests with many scientific payload, thus complementing the Air Research Platforms (PAIs) of INTA. At the structural level, the RPAS MILANO is made in its entirety in carbon / epoxy composite material that is cured out of the autoclave. Its design has been followed by the airworthiness regulations applicable to the aircraft type (STANAG-4671). In the month of December 2018, the RPAS MILANO flight test phase began and it’s Health and Usage Monitoring System (HUMS) is being used to collect data before, after and during flights, providing very useful information when evaluating and analyzing the state of the structure and the possible appearance of structural overloads not foreseen during the mission. Information about special events, such as forced landing or burst loading, can be provided to maintenance operators after each flight. The simulation model and its predictions have been validated in a real structure of the rear fuselage of the MILANO and in which real damage of larger sizes is introduced by eliminating rivets progressively. In our study, three different damage detection algorithms are used, based on a damage index, PCA and Artificial Neural Networks (ANN).

Hybrid and intelligent textile structures for composites structural health monitoring in automotive industry

Scipedia content — Thu, 31 Mar 2022 21:28:22 +0200

Automotive industry is a sector where the technologic development aims to fulfil high standard requirements regarding safety, energy efficiency and environmental pollution. The development and application of technical textiles as a reinforcement for polymeric matrixes to form high performance composite materials that comply with automotive industry standards has been increasing. Nowadays composite materials are an integral part of vehicles bringing advantages both in terms of mechanical performance and lightweighting. The current technical textiles applied in this sector focus on high mechanical performance through the application of fibres such as carbon fibre, aramid and glass fibre, these textiles combined with thermoplastic materials result in recyclable composites that reduce environmental pollution. This work was developed in the framework of TexBoost project co-financed by COMPETE 2020 – the Operational. Programme for Competitiveness and Internationalization, under Portugal 2020 through the European Regional Development Fund (ERDF). TexBoost PPS3 (AN1/AN2) main objective is the development of smart and hybrid textile structures that when integrated in the matrix result in not only high mechanical performance composites but also smart composites with structural health monitoring capabilities, allowing the evaluation of potential structural fails and necessity of vehicle part replacement (preventive maintenance of automotive parts). Therefore, different types of sensing fibres are being developed, characterized and weaved in a textile structure with carbon fibres to be further integrated in polymeric matrixes. All the developed composites are being characterized both in terms of mechanical and electrical performance.

Carbon nanotube adhesive films for crack growth detection under flexural load in composite structures

Scipedia content — Thu, 31 Mar 2022 21:28:10 +0200

Sensing capabilities of carbon nanotube (CNT) doped adhesive films under bending conditions were investigated. Standard Mode-II coupons and skin-stringer sub-elements were manufactured while their electrical resistance was monitored. Mode-II energy fracture was improved when adding CNTs in comparison to neat adhesive joints due to their toughening effect. Electrical monitoring showed a stable increase of the electrical resistance with crack length with lower sensitivity than Mode-I testing due to a lower crack opening effect. Monitoring tests on skin-stringer sub-elements subjected to bending load showed a similar behavior but some sharp increases were observed, especially in the last stages of the test, due to a less uniform adhesive distribution in the central region. Therefore, the proposed technique shows a high potential and applicability for Structural Health Monitoring of composite structures.

Cationic photopolymerizationand thermal post-curing of epoxy/TiO2 and epoxy/BN nanocomposites

Scipedia content — Thu, 31 Mar 2022 21:27:56 +0200

Cycloaliphatic epoxy resins containing cationic initiators which are activated by UV radiation give rise to thermoset networks when are exposed to UV light. On the other hand, due to its good mechanical properties, adhesive, thermal stability and electrical insulation epoxy resins are widely used in electrical and electronic applications.The inclusion of ceramic nanoparticles improves the properties of epoxy thermosets, but can influence the curing process. The objective of this work is to study the curing process of nanoparticle dispersions of boron nitride and titanium oxide in a cycloaliphatic epoxy curable epoxy resin. This study has been carried out using photo-calorimetry (UV-DSC) and traditional DSC. The effect of the presence of BN and TiO2 nanoparticles in the ultraviolet curing has been analyzed, finding that the UV curing is not complete, and a subsequent thermal post-curing stage is necessary. It has been found that TiO2 hinders the reaction reaching lower total conversions after both curing stages. Finally, in order to study the thermo-mechanical properties of the nanocomposites, thick specimens were prepared by applying the two stages of UV and thermal curing, the presence of nanoparticles leading to a more heterogeneous specimens. FTIR analysis of curing has shown that the surface of KBr support influences the curing reaction.

Mechanical properties of Al6005A-nTiC nano-composite obtained by milling, hot extrusion and FSW

Scipedia content — Thu, 31 Mar 2022 21:27:45 +0200

An aluminium matrix nano-composite (AlMNC) was obtained by a powder metallurgy (P/M) process, consisting of an ex situ reinforcement of pre-alloyed AA6005A powders with 3% vol. of TiC nanoparticles (nTiC), high-energy mechanical milling (HEMM) and hot extrusion powder (HEP). AA6005A powder was chosen as matrix because it is a heat-treatable medium strength Al alloy with excellent corrosion resistance, extrusion performance and good weldability; and the nTiC particles due to their low density, good chemical stability and excellent combination of hardness and elastic modulus. HEMM allowed obtaining an ultra-fine grained (UFG) matrix, a uniform dispersion of the nano-reinforcement and its proper incorporation in the ductile matrix. Simultaneously, the repeated plastic deformation of matrix powder led to a high density of crystal defects, and the large number of dislocation barriers produced by nTiC particles are responsible of the obtained nanostructured composites. HEP allowed obtaining high quality extrudates with an a homogeneous distribution of nanoparticles. The hardness of the nanocomposite is almost 43 % higher than that of the unreinforced AA6005A, showing important increases in yield strength and ultimate tensile strength with a 5% elongation. The extruded profiles were Friction Stir Welded (FSW) obtaining sound welds. The grain size refinement on the stir zone (SZ), led to a slight increase in hardness in the welds.

Application of ball milling in the synthesis of Al7075 composites containing carbon nanotubes.

Scipedia content — Thu, 31 Mar 2022 21:27:33 +0200

Through powder metallurgy techniques, it is intended to obtain a metal matrix composite (MMC) of 7075 aluminum alloy reinforced with 1% of multiple wall carbon nanotubes (MWCNTs), which after hot extrusion present mechanical properties similar or even superior to the conventional AA7075 alloy in condition T6. This MMC should be able to be welded by friction stir welding (FSW), thus avoiding the disadvantages presented by the hardenable alloys by precipitation in the welding process. This work focuses on the optimization of the dispersion stage of the MWCNTs in the prealloyed powders of the matrix. For this, three mechanical ball milling strategies are compared. In the first, the pre-alloyed powders and MWCNTs are milled together following a cycle of variation of low energy rotation speeds (LE) (300-200rpm). The second also performs the milling of the mix of powders and nanotubes by varying the rotation speed in a high energy cycle (HE) (1300-1200rpm). In the third one (H + LE), powders of 7075 are initially milled at high folowing a cycle of high rotation speed (high energy), followed by a low rotation speed stage (low energy) in which the MWCNTs are mixed. From the morphological characterization by SEM and determination of the crystallite size of the powders (XRD), a complete discussion of each of said pathways is carried out.

Foams with guest phases: multifunctional foam materials from multiphase composite materials

Scipedia content — Thu, 31 Mar 2022 21:27:24 +0200

Foam materials have characteristics that make them especially suitable for a multitude of technological applications. Currently, one of the most widespread techniques for the manufacture of foam materials consists of manufacturing a composite material formed by a matrix and inclusions of a certain nature, which can be afterwards eliminated under controlled conditions (dissolution, chemical reaction, etc.). This method is known as replication and leads to interconnected pore foams. So far, for more than 50 years since its original patent, the replication method has allowed the generation of foams of metals, polymers and even mesophase pitch, from which it has been possible to obtain high-performance graphite foams. The functionality of the foam materials that have been manufactured so far depends on the material from which the foam is made, as well as the size, shape and size distribution of its pores. Recently the author of the present work has developed a new family of multifunctional materials, formed by interconnected pore foams obtained from composite materials by the replication method in which in the pore cavities there are host phases that give different functionalities to the material. The present work presents preliminary results obtained from aluminum foams with guest phases of silicon carbide (SiC) particles for thermal management applications.

Multicomponent materials for thermal dissipation with alternating Al foam structures and Al/D composite material

Scipedia content — Thu, 31 Mar 2022 21:27:12 +0200

The increasing advances in the electronics industry, which operates with increasingly powerful systems and with greater performances, needs the development of new materials able to dissipate the high amount of heat they generate and that, over 50% of the occasions, is the source of catastrophic failures. The two major approaches in the design and manufacture of heat sinking materials lie in what are called active dissipators and passive dissipators. The last advances in passive dissipation come from Al/diamond composites, which exhibit high thermal properties that can be modulated through the manipulation of interfaces. On the other hand, interconnected pore metal foams have been widely studied because of their active dissipation properties and potentiality as electronic heat sinks. These foams can be designed and manufactured using the well-known replication method. This method produces a composite material consisting of a matrix and inclusions of such a nature that they can be subsequently eliminated by dissolution or chemical reaction. In the present work we propose the manufacture and characterization of materials formed by alternating layers of Al/Diamond and aluminium foam Recorded thermal conductivities reached 435W/Mk and are discussed by models that consider a semi-infinite alternating layered system of composite material and metal foam. In addition, power dissipation densities were recorded under working conditions and values up to 65% higher than conventional aluminium foams were registered.

Mechanical and microstructural characterization of high reinforcement content aluminum metal matrix composites in extreme conditions

Scipedia content — Thu, 31 Mar 2022 21:26:59 +0200

The final motivation of the research in which is framed this work is to optimize the friction-stir welding, FSW, process and its implementation in conventional machining centers. The FSW process occurs in the solid state at high temperature and by severe plastic deformation (high deformation at high rate) of the material. In this work we have studied the behavior at high temperature and high deformation rates of metal matrix composite materials 2124Al-25%SiC and 6061Al-40%SiC. The plastic deformation capacity in the high temperature regime has been studied by tensile, compressive and torsion tests at temperatures in the interval 300-475ºC and high strain rates, at 1s-1 and above. Large plastic deformations have been obtained without the appearance of serious defects despite the high reinforcement content. The good behavior in the conditions studied presumes the good weldability by means of the FSW technique. On the other hand, the data of the microstructure have allowed determining some of the constants that appear in the creep equation. Finally, we have succeeded in explaining the creep behavior through models developed for this technique from the experimental results.

Mechanical characterization of advanced carbon fibre reinforced polymers for down selection of aero-structural materials

Scipedia content — Thu, 31 Mar 2022 21:26:47 +0200

Carbon fibre reinforced polymers are widely used in primary and secondary aircraft structures, mainly due to their excellent fatigue endurance and specific strength. Nowadays, improvements related to their manufacturing costs, impact resistance and fracture toughness are pursued through the investigation of new matrix-fibre combinations and the application of cutting-edge manufacturing technologies. This work presents the results of the coupons test campaign that has been conducted to assess the mechanical properties of different advanced carbon fibre reinforced polymers, being compared with those obtained for a composite material traditionally used in aero-structures. The effect of the introduction of innovative elements such as reinforcing-matrix Carbon Nanotubes or acoustic damping veil is evaluated. Moreover, the influence of ageing is assessed through the evaluation of the mechanical properties after specimen environmental conditioning. From the execution of this test campaign, a comprehensive knowledge base of mechanical properties has been generated, enabling the comparative analysis with reference composite and down selection of the materials that will be applied in the regional aircraft fuselage concept developed in Clean Sky 2 JU. The study shown here belongs to the scope of SHERLOC project. The purpose of the project is to perform a down selection of the most advanced composite materials, manufacturing processes and Structural Health Monitoring (SHM) systems that contribute moving towards a Condition-Based Maintenance.

Impedance spectroscopy applied to the study of conductive cements

Scipedia content — Thu, 31 Mar 2022 21:26:37 +0200

The addition of carbon fibers is the main alternative used for the manufacturing of conductive cements since, at a relative low price, provides a good combination of structural and functional properties. There are many different applications for this type of system, such as the manufacturing of heating elements or anodes for the cathode protection methodology. Most of the studies in this area are focused to the improvement of the dispersion of carbon fibers in the cement matrix. This objective is validated by measures of resistivity. According to this objective, there is no a universal method to verify these measures, but many alternatives can be found on the literature: measures with two or four electrodes, direct or alternating current testing…, impeding comparative analyses. This research offers the impedance methodology, already used for the characterization of common cement pastes without any reinforcements, as an option for the analysis of conductive cements. In this study, different variables are included, such as the type and quantity of dispersants to create a homogeneous mixture. The adjustment of the obtained results, following an equivalent electric model for this kind of systems, allowed us to determine the values of conductivity of different mixtures. With the use of this technique, it is possible to identify the polarization phenomena associated to the carbon fibers, being of interest in order to validate the dispersion of the fibers.

Natural fiber reinforced mortars to induce a specific mechanical amortization behavior in rupture as basis of seismic-resistant architecture

Scipedia content — Thu, 31 Mar 2022 21:26:24 +0200

The main focus of the actual research work was to define and study an emerging effective manufacturing process of producing natural fibers. It is also to insert them within the mortar or cement to preserve their mechanical behavior in terms of toughness, ductility, resistance... while extending their bending amortization following their possible rupture. Our objectives have been to: define a new process for manufacturing high quality long natural fibers using Instant Controlled Pressure-Drop DIC - assisted "organosolv"; design and build a specific laboratory-scale TRIPOLIUM DIC reactor devoted to such an operation by coupling the solvent treatment of various natural materials and DIC; identify correlations between the specificities of such natural fibers and the characteristics of the mortars intending to reinforce their anti-seismic aspect and behavior by inducing a non-linear large-time post-cracking behavior able to absorb the main amounts of breakage energy prior to collapse. The analysis of the mechanical behavior of the NATURAL FIBER REINFORCED MORTARS (NFRMs) was achieved in a well-detailed manner. Fiber distribution and fiber orientation were approached as the most critical parameters. The geometry of the structure shall ultimately dictate the NFRM composition that provides the best behavior for which fiber reinforcement is designed. Thus, this objective of producing Natural Fiber Reinforced Mortar (NFRM) should allow defining an interesting basis of seismic-resistant architecture.

Evaluation of the mechanical properties of biolaminates prepared by different manufacturing techniques

Scipedia content — Thu, 31 Mar 2022 21:26:13 +0200

Laminates are composite materials of thermoset matrix reinforced with long fibers. Natural fibers are a low-cost renewable resource, have a low density (which gives them a high specific resistance), are not irritating or toxic, have no abrasive effects such as glass fibers, and are completely biodegradable. However, natural fibers have certain disadvantages with respect to synthetic fibers, such as their low decomposition temperature and their high hydrophilicity. There are numerous lamination manufacturing techniques: infusion, resin transfer and autoclave. The autoclave provides an improvement in the mechanical properties of the laminates due to the control of the manufacturing parameters. However, this technique is very expensive, so not all industrial sectors can access it. Knowing the mechanical performance of biolaminates prepared from different manufacturing techniques will open a window of alternate possibilities to the use of an autoclave, which includes the development of nanoreinforced biolaminates.

Symmetrical and asymmetric dynamic characterization to fracture in mode III of epoxy composites-unidirectional carbon fiber

Scipedia content — Thu, 31 Mar 2022 21:26:01 +0200

The present work shows the results obtained after rehearsing fatigue in mode III a material composed of epoxy resin with unidirectional carbon fiber reinforcement. For the execution of the tests and has used a test device that has been previously designed and whose validity has been proven. The novelty of this work is that it is the first time that a study of fatigue to fracture is carried out according to mode III in this type of materials. In addition, this fatigue has been made in two different ways. First, it has been loaded in one direction until reaching a certain angle and returning almost to the starting point and, secondly, it has been loaded both in one direction and in the opposite. Hence the first case is called asymmetric fatigue and in the second, symmetrical fatigue. The results obtained are different since the case of loading is, in both cases, substantially different. In both cases, a statistical analysis of the results has been carried out in order to be able to compare the existing differences more properly.

Mode decomposition in DCB and ENF tests with geometric and material assymetry

Scipedia content — Thu, 31 Mar 2022 21:25:49 +0200

Mode decomposition in interlaminar fracture tests initially designed for pure modes I and II as Double Cantilever Beam (DCB) and End Notcehd Flexure (ENF) is analyzed. In the initial proposal of those tests crack arms have geometric and material symmetry and the crack advance occurs through the middle plane of the laminate. In the current study, the possibilty of crack arms of different materials or with different thickness is included. Two mode decomposition criterions are considered after the analysis of a slice near the crack tip. Those criterions are based on the stress and displacement state in the non-cracked zone near the crack tip. Two points that before the crack advance were the same point are named homologous. When the cohesive zone is developing, the stresses in homologous points are the same due to the principle of action and reaction. Nevertheless, relative displacement can be normal, related to mode I, tangential, related to mode II, or a combiantion of both, related to mixed mode I-II. In the present work the relative tangential displacement related to mode III is not considered. The contributions to the energy release rate corresponding to bending and shear in each mode are analyzed. The results obtained are applied to asymmetric DCB and ENF tests.

Experimental study of the appearance of the damage in composite laminates

Scipedia content — Thu, 31 Mar 2022 21:25:40 +0200

The scale effect in Composite Materials, consisting in the delay in the first damage appearance as ply thickness decreases, is, at present, a phenomenon under study due to the use of ultrathin plies (whose thickness may reach 20 microns) in the most leading industries. Based on this, the appearance of the first damage is experimentally analysed in this work for [04,90n,04] conventional laminates where n=1,2,4,8,16,32. The objectives are to study damage mechanisms occurrence as the thickness of the weakest layer varies when subjecting the laminate to uniaxial tension and to check if the scale effect is present. Acustical techniques have been employed for damage detection and optical and electronical microscopy have been used for its observation. The conclusions lead to well-diferenced mechanisms of damage for the different thicknesses analysed: high thicknesses show unstable damage resulting in an explosive failure of the whole laminate, whereas low thicknesses show a more stable damage, it being less significant for the laminate integrity. In addition, an scale effect is detected, since the load at which the failure is generated decreases as the thickness increases. In future works the same analysis will be presented for ultrathin plies.

Novel analytic solutions for edge stresses in symmetric laminates

Scipedia content — Thu, 31 Mar 2022 21:25:28 +0200

The “edge effect” problem in laminates is a redundant topic in the literature since the seventies because of its influence on the reduction of the laminate strength. In previous works analytic solutions for angle-ply and quasi-isotropic symmetric laminates were obtained. In this work, a new model for obtaining solutions in the general case of symmetric laminates is presented. It is based on a new assumed displacement field in which the transverse bending of the laminate is not constrained. An strategy for solving the system of differential equations is proposed, as well as different hypotheses for the boundary conditions. Different solutions for the interlaminar stresses can be derived from the proposed technique.

Scale effect in composite materials: Study of the intralaminar damage by means of a micromechanical model

Scipedia content — Thu, 31 Mar 2022 21:25:19 +0200

The scale effect in Composite Materials is known as the delay in the appearance of damage in the weakest laminas of a laminate (typically 90 degrees laminas). The availability of ultra-thin plies, of up to 20 microns of thickness, has attracted the attention on this effect, as the use of these plies can imply the delay of the onset of damage at a laminate in a significant manner. The frame of the present work is a micromechanical study of the different phases of damage assumed to lead to the failure of the weakest lamina. Thus, it is assumed that the damage starts by isolated debondings between fibres and matrix, then continuing by the abandon of the interphase, the debonding crack kinking into the matrix, and finally the damage progressing either through the matrix itself or along the interfaces between fibres and matrix, to generate a transversal crack in the 90 degrees lamina. The study is carried out using a multi-scale model based on the Boundary Element Method, with control cells in which the damage at micromechanical level previously described is allowed. Concepts derived from Fracture Mechanics and Interfacial Fracture Mechanics are applied in the analysis. The conclusions obtained with this study are compared with those that clearly manifest the scale effect based on a global energy balance from the pristine state to the final situation with the 90 degrees lamina having a complete transverse crack.

Composite materials in ICTS-CEHIPAR

Scipedia content — Thu, 31 Mar 2022 21:08:23 +0200

The Center for Hydrodynamic Research of El Pardo (ICTS-CEHIPAR) is a Unique Scientific and Technical Infrastructure (ICTS) part of the Deputy Directorate of Naval Systems (SGSN) of the National Institute of Aerospace Technique “Esteban Terradas” (INTA). A new research line to study the use of advanced composite materials in the naval industry has been recently opened in the Technology and Tests Department of ICTS-CEHIPAR. One of the main goals of this new research line is the monitoring of structural stresses in composite materials by means of fiber optical sensors in structural diffraction Fibers Bragg Gratings (FBGS). ICTS-CEHIPAR is enhancing the constructive procedures for the production of models of ships and naval devices made in composite materials. The implementation of instrumentation techniques for the monitoring of structural stresses in this kind of materials is necessary to detect possible damage due to different causes during the product lifetime. Results of scale model tests will be applied to the full scale ship construction and instrumentation methodologies, increasing ship safety and optimizing maintenance procedures.

Rheological modification of PET waste. Thermoplastic pultrusion as recycling technology

Scipedia content — Thu, 31 Mar 2022 21:08:11 +0200

Packaging sector generates 40% of the plastics consumption in Europe. Among Among the most consumed plastics Polyethylene terephthalate (PET) is still the material that undoubtedly continues to grow in the packaging sector. Because of that, there is a concern related to the recycling process, which today is only around 56%. This makes that at present, there are tons of thermoplastic material accumulated in landfills that could be a potential source of raw material (especially colored PET and multilayer). On the other hand, like PET waste (RPET), there are environmental problems associated with the disposal of composite materials in landfills, especially thermoset matrix composites. In this sense, due to the impossibility of recycling and reusing thermosetting composites, thermosets have composites are beginning to be replaced by thermoplastics. However, the main problem in the use of thermoplastic matrices in composite materials lies in the total impregnation of the reinforcement of the fiber due to the high viscosities of these materials. With the purpose of solving this limitation, and joining these needs, this work has been focused on obtaining new materials by modifying the less recyclable fractions of RPET. In this sense this material has been modified rheologically by reactive extrusion to replace thermosetting materials in the manufacture of composites, especially in thermoplastic pultrusion. From the first materials developed it has been possible to manufacture profiles from matrix 100% recycled material with adequate impregnation. The results of this study transform a waste into a product with high added value, reducing the carbon footprint and the costs of the process.

Monitoring the evolution of the stiffness during the ultraviolet cure with air-coupled ultrasonics

Scipedia content — Thu, 31 Mar 2022 21:07:59 +0200

The ultraviolet (UV) curing process is gaining interest due to the curing speed, since it increases the production of the manufacturing processes. The high mechanical requirements of composite materials require the assurance of quality from the mechanical point of view. The inspection after processing is an additional operation that increases the costs and production times, so the monitoring of the mechanical properties, more specifically the evolution of the rigidity during the curing process, is strategic for the greater penetration of the composite materials in sectors dominated by the final price of the piece. Monitoring the elastic properties during curing, when contact between the piece and the sensor is not possible, is a challenge for rapid processes such as UV curing. The present work demonstrates the validity of the ultrasonic monitoring technique with air coupling (ACUS) for different UV curing conditions. Three conditions of UV curing (0.8, 1.6 and 2.4 W / cm2) were studied on a vinyl ester resin. The results of the ACUS are consistent with those of the direct current sensor with contact. The main conclusion is that the evolution of the rigidity with respect to the degree of conversion is similar for the different conditions studied.

Artificial vision system for the automatic inspection of preforms

Scipedia content — Thu, 31 Mar 2022 21:07:50 +0200

The preforming consists of processing the reinforcement to obtain a geometry of the dry fiber, close to that of the final product before being impregnated by the resin during the injection process. During the process, the fibers are manipulated to reach the desired shape are subjected to tensile, shear and torsion stresees that can cause changes in the orientation of the fibers, misalignments,or other defects such as wrinkles or fiber breakage that can affect the performance of the preform . In this work a solution for the automation of the quality control of the preforming process by artificial vision is investigated.. Two approaches are proposed, 3D vision for the geometric and superficial inspection of the fibers and machine learning aproach based on Deep Learning (DL) to detect irregularities in the orientation. The solution based on 3D vision automatically detects defects based on the comparison of a theoretical 3D model and a 3D reconstruction of the real part. A structured light system is used to generate dense and precise point clouds. Once aligned, the dissimilarities between both surfaces are analyzed. The solution is complemented by a 2D vision system based on DL that classifies the irregularities in the orientations of the fabric. The model is trained with images of classified fiber orientations to automatically identify areas of fiber whose orientation does not correspond to the expected one. The combination of both technologies allows to give a complete solution to the automated quality inspection of preforms for manufacturing or defects.

Study of the generation and evolution of damage in carbon fiber laminates subject to thermal cycling and corrosive agents

Scipedia content — Thu, 31 Mar 2022 21:07:39 +0200

The aeronautical structures manufactured by composite laminates experience damage as a result of the severe thermal and chemical conditions to which they are subjected during flight. Microcracks are one of the most common manifestations in terms of damage. Therefore, the study of its generation and propagation is fundamental in order to make improvements in design processes. In this work, the processes of microcrack generation and propagation in carbon fiber laminate samples, manufactured by resin transfer molding (RTM), subjected to different conditions of thermal cycling and immersion in corrosive agents, are studied. In this study, images of the specimens were obtained using the X-ray computed tomography (XCT) technique. Thanks to these images, geometric data from the microcracks was extracted, as well as their preferential trajectories, which helped to understand the aforementioned generation and propagation phenomena. This research has provided new insights into the complex interaction between different damage mechanisms.

Evaluation of the damage extension in laminates of glass fibers

Scipedia content — Thu, 31 Mar 2022 21:07:29 +0200

The study of the damage area extension in laminates made of composite materials that have been subjected to impacts, is a fundamental aspect in the evaluation of the residual properties of this type of materials. In the case of woven E-glass fibre/polyester laminates, the study of the damaged area extension by non-destructive techniques (NDT) can be carried out by visual inspection or ultrasounds. Within the techniques of ultrasonic inspection, the C-Scan type has been established as the primary inspection method. This technique is quite useful in composite laminates since it allows to quantify the total damaged area. However, this technique does not make possible the evaluation of evolution and location of damage along the thickness, which changes remarkably in thick laminates. For this reason, it is necessary to make use of the B-Scan technique of ultrasonic inspection, whichallows to evaluate the evolution of damage along the thickness. The aim of this experimental work is to study the evolution of damage in woven E-glass fibre/polyestes laminates for four different thicknesses. After being tested, these plates have been inspected through non-destructive inspection techniques (NDT) with ultrasounds (C-Scan and B-Scan) and visual inspection in order to evaluate qualitative and quantitative aspects.

Damage tolerance in repaired composite laminates

Scipedia content — Thu, 31 Mar 2022 21:07:18 +0200

In order to alleviate the adverse impact of the air transport on the environment, the UE has shown great interest in increasing the efficiency and safety of aircrafts, which covers the complete life cycle of aircrafts (design, production, maintenance, repair and update).Composite structures show high susceptibility to low-velocity impacts in the perpendicual direction to the plane of the laminate. The complete replacement of damaged components is not always possible due to the high level of integration of the structures and the large size of the components in many sectors (i.e. aeronautics). In this regard, the repair and subsequent put into operation of structures made of composite materials must be a cost-effective and time-saving process.Adhesive repairs present advantages in relation to mechanical repairs. There is a lack of knowledge in their behaviour under impact loads; therefore, the main goal of this work is to analyse the damage tolerance of composite repaired structures. To this end, an experimental study has been carried out on intact and repaired laminate specimens that allows comparing the structural response of both configurations.This study involves the generation of damage through low-velocity impacts (using a drop-weight tower), and subsequent compression tests in order to determine their residual stenght.

Axial crushing of auxetics tube manufactured by 3D printing of poliamide reinforced with short carbon fibre

Scipedia content — Thu, 31 Mar 2022 21:07:07 +0200

Additive manufacturing, and more specifically FFF (Fused Filament Fabrication), makes it possible to manufacture complex designs that are difficult to manufacture using conventional processes that improve the mechanical behaviour of the component. In the present work, the axial impact behaviour of cylindrical tubes with a reentrant auxetic structure has been characterized. The material used is a polyamide 6 reinforced with short carbon fibre. As a reference, a solid thickness tube with the same outer diameter and mass as the tube with the auxentic structure has been designed. The main result is that the auxetic structure not only improves the specific absorption capacity, but also allows a progressive collapse thanks to the design and location of fault initiators. For this reason, 3D printing technologies have very attractive properties for the design of impact absorbers in the transport sector.

Bending behaviour of composite sandwich beams manufactured by 3D printing with continuous fibre reinforcement

Scipedia content — Thu, 31 Mar 2022 21:06:57 +0200

Additive manufacturing with FFF (Fused Filament Fabrication) technology using continuous fibre, allows more complex structure designs with more technical materials than conventional manufacturing processes. The present paper is focused on analysing the bending behaviour of sandwich beams with unidirectional carbon fibre skins and honeycomb type core. The nobelty of the research is focused on printed materials (polyamide 6 reinforced with continuous carbon fibres) and the fact that the core has been manufactured directly in the printig process. The study variable consisted of the spatial arrangement of the beam; for the first type of beams the skins are positioned in parallel with the base plate, whereas for the second type of beams, the skins are placed perpendicullary with respect to the base plate. Thus, in both cases skins are obtained with the same fibre orientation, but with different manufacturing strategies. Otherwise, those configurations where skins are placed in parallel with respect to the base plate, the influence of reinforcing the hexagons of the core with carbon fibres following different strategies has been analysed. On the one hand, the hexagons are reinforced depositing continous carbon fibre following concentric deposition strategy, forming hexagonal rings in each hexagon independently. On the other hand, the overall core is reinforced toghether with continous carbon fibres following the external perimeter of the core. Results show that the beams whose skins have been manufactured in parallel with respect to the base plate have higher stiffness. In the same way, those structures with reinforced cores have a higher stiffnes compared to those with non-reinforced cores.

Calculation methodology of additive manufacturing processed parts

Scipedia content — Thu, 31 Mar 2022 21:06:48 +0200

Additive manufacturing technologies allow us the creation of 3D objects through layer overlay. This process is faster than other traditional manufacturing processes and it enables the customization of parts. Nowadays Fused Deposition Modelling (FDM) is the most used techonology. However, due to the nature of the process, resulting parts have complex mechanical behaviour, due to the fact that their properties vary according to the direction or the type of effort, which limits their applications in functional parts. To predict the behavior of a component Finite Element Analysis (FEA) are made. Although, the material models used by these analysis tools are not able to simulate the mechanical behavior of FDM products. Thus, a model supported by a finite element analysis tool, able to predict the behaviour of these materials has been developed. It works in the elastic and plastic region, for any geometry and load case. The model, feed by theoretical behavior models and experimental tensile, compression and shear tests, and implemented in FEA software, allows us to simulate the anisotropy of these materials in an easy and versatile way. The calculation methodology has also been experimentally validated.

Acoustic emission (AE) technology suitability for testing composite materials

Scipedia content — Thu, 31 Mar 2022 21:06:38 +0200

In this work the suitability of using Acoustic Emissions (AE) technology for evaluating the damage and location in composite materials during coupon tests has been analysed. The selected material for the evaluation tests is a carbon fibre reinforced epoxy composite material. Using coupon level tests, two permanent damage detection methods has been evaluated. The felicity ratio, in which applying load up to a known level and then discharging it, if in a subsequent load the sensors detects acoustic emissions before the 95% of the previous load is reached, it is indicative that damage has appeared in the sample. And the Palier effect, in which a structure is kept at a certain loading level, during the first 2 minutes some counts or hits can be emitted, but in the next 2 minutes period the material should not show acoustic activity, unless the structure is permanently damaged. During the same coupon tests, the damage location technique by acoustic emissions has been also evaluated on 1D and 2D samples. Results show that it is possible to detect damage with Acoustic Emissions technology, and to establish procedures able to predict the final failure before it happens. Moreover, the use of several sensors allows the damage to be located.

Multimaterial ballistic solutions for UAVs

Scipedia content — Thu, 31 Mar 2022 21:06:28 +0200

One of the main challenges for UAVs (Unmanned Aerial Vehicles) used in defence and military operations is to effectively conclude a flight mission in a harsh environment. The platform survivability is critical, therefore it is imperative that the vehicle is able to withstand ballistic impacts in flight and still be able to reach its destination. In the present work, the authors discuss the development of a lightweight ballistic armour to protect critical areas of the vehicle, such as the control systems and/or the payload. The structure response during and after a 9 mm bullet impact, shows that the proposed hybrid composite panels will be able to withstand high-energy ballistic impacts after optimization. The FEA (Finite Element Analysis) method is implemented to study the performance of ceramic protective plates attached to the CFRP (Carbon Fibre Reinforced Polymer) structural platform. An Eurelian-Lagrangian modelling technique is implemented with different damage models for the various materials involved in the impact event in order to properly capture each material response in this complex load scenario. Numerical studies are validated experimentally. The base structural CFRP is cured in autoclave followed by a post-cure to integrate the remaining components. Experimental tests were conducted at a shooting range where 9 mm projectiles are fired at a distance of 10 m of the target plates. Data is collected recurring to a chronograph/high speed camera combination apparatus to measure the impact and residual velocity and the projectile deformation/damage. Numerical models show good correlation with the experimentally measured data.

Mixed Mode Cohesive Law of Adhesive Joints

Scipedia content — Thu, 31 Mar 2022 21:06:18 +0200

This work presents an experimental method to determine the cohesive law of thin adhesive joints in mixed mode. The proposed method is based on the MMB (Mixed Mode Bending test). The Energy release Rate and Crack Tip Relative Displacement are determined based on a compliance variation data reduction method by processing the global load displacement curve, without monitoring the crack length and the crack tip relative displacement during the test. Representing the energy release rate versus relative displacement the cohesive law is determined by numerical differentiation. The method is validated numerically by virtual tests including the cohesive zone model. The results reveal that the proposed data reduction scheme is suitable to obtain the mixed mode cohesive law using only the load and displacement data obtained from the testing machine, without any external displacement measurement technique and without any assumption of the form of the cohesive law.

Analysis of bending-twisting coupling in angle-ply laminates

Scipedia content — Thu, 31 Mar 2022 21:06:09 +0200

The purpose of the present study is the evaluation of the bending-twisting coupling effect in the analysis of the DCB test by means of the analytical determination of the energy release rate of angle-ply laminated composites. The aim is to extend a previous work done by the same authors to new laminate configurations. Angle-ply laminates with symmetrical arms are analyzed, since in this case the application of a bending moment by means of the piano hinges causes a torsional rotation in each of the arms. That torsion is prevented by the hinges, due to the configuration of the test. Therefore, there is a non-uniform load distribution applied by the hinges, whose resultant is the applied load P and the resultant moment is an unknown twisting moment mt, which prevents rotation at the point of application. The resolution of the resulting system of forces and moments allows obtaining analytically the energy release rate, and analyzing the terms due exclusively to the bending-twisting coupling.

Dynamic characterization of interlaminar toughness in carbon fibre epoxy composite laminates

Scipedia content — Thu, 31 Mar 2022 21:05:58 +0200

In this work, the influence of the loading rate on the mode I interlaminar fracture toughness of carbon fiber laminates manufactured with prepregs of the second (IM7/8552) and third generation (IM7/M91) was investigated. The study has been carried out using to loading rates ranges, namely, quasi-static between 0.5 and 450mm/min, and dynamic between 100 and 2000mm/s. The latter tests were performed using a Gleeble 3800GTC hydraulic testing system. The dynamic tests were carried out using the WIF methodology (wedge insert fracture) by inserting at high speed a cylinder between the arms of the specimen. Two strain gauges were used to measure the maximum flexural deformation of the loading arms allowing the estimation of the opening force of the specimen to infer the dynamic fracture energy. The results showed that the IM7 / M91 laminate was sensitive to the speed of solicitation presenting a maximum value of the fracture energy for 500mm/s being the toughness more than twice than the one measured under quasi-static conditions.

Determination of the compressive and tendile moduli of the pultruited bars by bending tests

Scipedia content — Thu, 31 Mar 2022 21:05:49 +0200

Corrosion of the steel bars is the first cause of degradation of the reinforced concrete structures. This is the reason why in recent years non-corrosive materials are using to increase the useful life of these structures. Glass fiber reinforced polymer (GFRP) bars are an alternative to traditional steel bars. These bars are manufactured from continuous glass fiber embedded in a polymeric resin by the pultrusión process. Due to the great variability in the mechanical properties provided by manufacturers, it may be useful to define a test procedure to characterize the material in a simple manner. This work shows a procedure to determine the compression, tensile and flexural moduli of a GFRP bar by means of bending tests.

Decomposition kinetics and lifetime estimation on natural fibre reinforced thermoplastic composites

Scipedia content — Thu, 31 Mar 2022 21:05:39 +0200

Through this study two different natural fibres composites were characterized from the point of view of decomposition kinetics comparing two kinetics models, Kissinger and Model Free Kinetics in order to estimate the lifetime of the composites. Composite materials were prepared with low density polyethylene as matrix and as reinforcements, plasma treated and untreated natural fibres with 20 and 30 wt.% of fibre content. Composites were manufactured using a rotor mixer and a hot plates press. Afterwards, thermogravimetric analysis was carried out for each material at six different rates with a coupled Mass Spectrometry device to identify detached elements in a specific temperature range. The influence of the low pressure plasma treatment, as well as the fibre type, was taken into account to evaluate the activation energy of the decomposition processes of each material. Besides, lifetime was estimated from the obtained decomposition energies and the Toop equation. It was found that plasma treatment does not have a meaningful influence on decomposition kinetics but, the main composition of the natural fibres is decisive in this aspect, giving rise to much longer lifetimes when the cellulose content of the fibre is higher.

Influence of the test methodology on the fatigue behaviour of a composite subjected to a mixed fracture mode I/II

Scipedia content — Thu, 31 Mar 2022 21:05:27 +0200

Composite materials manufactured by means of the superposition of layers and some specific morphologies, are susceptible to losing part of their resistant capacity due to the presence of delaminations between their layers. The objective of this work is to evaluate experimentally the generation and propagation of these interlaminar cracks in a carbon-epoxy composite subjected to dynamic stress under mixed fracture mode I/II, using for this purpose two different test methodologies, on the one hand the standardized MMB (Mixed-Mode Bending) and on the other hand the ADCB (Asymmetric Double Cantilever Beam), with the intention of exploring the viability of the ADCB test as a simpler alternative of execution, especially in fatigue tests, to the MMB test. For this purpose and after a previous static characterization of the material in which the critical values of the energy release rate were determined in both test methods, the energy release rate levels to be applied in the fatigue tests were defined for two GII/Gc mixed mode grades of 0.2 and 0.4(0,33 ADCB) and a ratio of stress levels to fatigue of R= Gmin/Gmax=0.1.DG-N fatigue initiation curves were obtained from these experimental data. The most relevant result of the work is that, in general, the MMB mixed mode provides different fatigue limits depending on the degree of mixed mode, whereas in the ADCB type test the fatigue limits tend to have the same value.

Study of the influence of the skins in the behaviour of sandwich structures subjected to high-velocity impact

Scipedia content — Thu, 31 Mar 2022 21:05:16 +0200

Sandwich structures made of composite materials, namely glass fibre/polyester, are widely used in the naval, ground transportation, aerospace and telecommunication industries. Due to the combination of key factors: the good mechanical properties of this kind of materials together with their low specific weight and their permeability to electromagnetic waves. These structures are often subjected to impulsive loads during its service life. Therefore, in order to obtain a safer structural design, a better knowledge of the impact response must be accomplished. It has been demonstrated that the composition of the skins plays a fundamental role in the behaviour of sandwich structures against high-energy ballistic impacts. The structures studied in this work are composed by two E-glass fibre/polyester skins and a PVC core. With the objective of optimising this kind of structures when they are subjected to high-energy impact, a numerical study in the finite element code Abaqus has been carried out. In this study, the number of plies in the front and rear faces varies in order to find the configuration that presents better ballistic performance. To this aim, a VUMAT subroutine previously developed has been used for the skins. The core has been modeled with the crushable foam constitutive model available in the software Abaqus. The influence of the thickness of the skins can be tested by means of this numerical model. The results obtained show that the residual velocity disminishes the more the number of layers in the rear skin increases.

3D printing of multidirectional composite materials reinforced with continuous fibres: impact damage behaviour

Scipedia content — Thu, 31 Mar 2022 21:05:05 +0200

3D printing is a promising additive manufacturing technology capable of producing functional parts of continuous fibre reinforced thermoplastic composites (CFRTPCs). Thus recyclable parts having complex geometries are obtained in a simple manner [1]. In addition, the use of thermoplastic polymers significantly reduces the manufacturing costs because, unlike thermoset polymers, autoclave is not required for curing purposes. This is one of the greatest opportunities for 3D printing as an alternative to conventional manufacturing processes [2, 3]. Pieces obtained from both, conventional manufacturing methods and 3D printing technology, consists on a sequence of stacked sheets. Although greater automation and the possibility to optimize the design of each sheet are advantages of 3D printing, the adhesion between the matrix and the reinforcement fibres is insufficient and consequently, parts with inferior mechanical properties are obtained. Some studies have been interested in the effect of different process parameters on the mechanical performance of the printed parts, however, further research is required. A fundamental challenge is to get good consolidation between the fibres and the polymer matrix, with control of the fibre orientation and low cost [4, 5]. The aim of this work was to evaluate the mechanical properties of multidirectional 3D printed continuous carbon, glass and Kevlar fibre reinforced nylon composites, manufactured by FDM technique. Special attention was paid to the impact damage resistance and tolerance. [1] L. Nickels, Strengthening the 3D printing composites field, Reinforced Plastics, 62 (2018) 298-301 [2] L.G. Blok, M. L. Longana, H. Yu and B. K. S. Woods, An investigation into 3D printing of fibre reinforced Thermoplastic composites, Additive Manufacturing, 22 (2018) 176-186 [3] T. Liu, X. Tian, M. Zhang, D. Abliz, D. Li and G. Ziegmann, Interfacial performance and fracture patterns of 3D printed continuous carbon fibre with sizing reinforced PA6 composites, Composites Part A: Applied Science and Manufacturing, 114 (2018) 368-376 [4] R. Velu, F. Raspall and S. Singamneni, 3D printing technologies and composite materials for structural applications, Green Composites for Automotive Applications, chapter 8 (2019) 171-196 [5] Q. Hu, Y. Duan, H. Zhang, D. Liu, B. Yan and F. Peng, Manufacturing and 3D printing of continuous carbon fiber prepreg filament, 53 (2018) 1887-1989

Thermal ageing effect on the mechanical properties of carbon fibre-reinforced epoxy laminates

Scipedia content — Thu, 31 Mar 2022 21:04:55 +0200

Thermostable matrix are extensively used in structural components because of their good mechanical properties [1]. The region of stability of these polymers is defined by the glass transition temperature (Tg) [2]. The typical service temperature of these materials should be lower than Tg but in some cases operating temperatures can exceed Tg which causes a variation in the properties of the polymer and consequently, modifies the mechanical properties of the composite material [3]. Therefore, it is important to understand the effect of temperature on the failure mechanisms that occur in the material in order to ensure stability and durability [4,5]. The objective of this work was to evaluate the effect of temperature and time of exposure on the mechanical properties of carbon/epoxy composites. For that purpose, samples were aged at different temperatures and periods of time and then, impact and flexural tests have been performed. It was observed that thermal ageing caused notable variations in the glass transition temperature of the epoxy resin. In consequence, two different effects were observed: in most cases, thermal ageing causes a reduction on the mechanical properties of the composites due to the thermo-oxidation of the epoxy resin and the loss of adhesion in the matrix/fibre interface, especially at higher temperatures; however, at temperatures below the Tg, there is an increase of the maximum strength because of a post-curing effect. [1] E. Selver, P. Potluri, C. Soutis, Impact damage tolerance of thermoset composites reinforced with hybrid commingled yarns, Compos. Part B 91 (2016) 522-538. [2] E. Ernault, E. Richaud and B. Fayolle, Origin of epoxies embrittlement during oxidative ageing, Polymer Testing 63 (2017) 448-454 [3] A. Mlyniec, J. Korta, R. Kudelski and T. Uhl, The influence of the laminate thickness, stacking sequence and thermal ageing on the static and dynamic behaviour of carbon/epoxy composites, Composite Structures 118 (2018) 208-216 [4] A. P. C. Barbosa, A. P. P. Fulco, E. S. S. Guerra, F. k. Arakaki, M. Tosatto, M. C. B. Costa and J. D. D. Melo, Accelerated ageing effect son carbon fibre/epoxy composites, Composites Part B, 110 (2017) 298-306 [5] S. Marouani, L. Curtil and P. Hamelin, Ageing of carbon/epoxy and carbon/vinylester composites used in the reinforcement and/or the repair of civil engineering structures, Composites Part B, 43 (2012) 2020-2030

Dams Bibliography: A Disruptive Step Forward From Past Knowledge

Alessandro Calvi — Wed, 29 Dec 2021 16:43:02 +0100

This paper is aimed to analyze how a bibliographic work should be considered not as rigid collection of publications but as an opportunity to discover knowledge which often turns into the development of new technical ideas and finally it translates into innovation.

Design of an Arduino shield for ota programming

Javier Mora — Thu, 16 Dec 2021 10:33:02 +0100

The International Center for Numerical Methods in Engineering (CIMNE) is a research organization, created in 1987, that does research in many areas, one of them is Information and Communication Technologies. In this area there is a line specialized in Wireless Sensor Networks (WSN) that uses many of existent technologies or devices to gather data from the real world and sent it to CIMNE server to feed simulation systems. CIMNE participates in many research projects with other companies and institutions.

This project was born from the need of some research projects in ICT group of CIMNE as well as one of their associated companies. Research projects that lead to this project are relative to WSN. CIMNE used to use MicaZ sensor mote from Crossbow but its high cost

made CIMNE to look for alternatives.

One of the alternatives used in WSN is Arduino, a versatile board that have a microcontroller digital and analogic inputs and outputs to gather data from sensors and interact with actuators or other gadgets. Arduino is easily programmable and is open hardware. It has

not the capability of wireless communications but it has the feature of using shields, boards that connect to Arduino, to expand its functionalities.

Arduino is a growing technology that is used in many different fields; from domotics to professional applications to use it with educational purposes to teach students from high school to university. This grow is due to its low cost, its easiness to use and program.

Since Wireless Sensor Networks usually are deployed in remote places, such as a vineyard or a highway bridge, it is very important to be able to manage and reprogram the sensor nodes remotely. Arduino has not this feature and after doing some research on the state of the art of wireless shields and not finding any shield with this feature. CIMNE has identified the needing of designing a Wi-Fi shield with Over-The-Air (OTA) programming feature. We have done a short review of applications, some of CIMNE, that will need this feature.

Wi-Fi shield with OTA programming capabilities is also important to CIMNE since nowadays the Internet of Things is growing fast and with shield CIMNE can provide Internet to many objects, such as speakers.

To design the shield we have used Cadsoft Eagle software since is one of the best circuit design software available in the market nowadays.

At the end of the project we want to obtain a working Wi-Fi Arduino Shield with OTA capabilities.

OPENFOAM COMPUTATIONAL FLUID DYNAMICS SIMULATIONS OF THERMAL WIND GENERATION IN MOUNTAIN/VALLEY CONFIGURATIONS

Adeline Montlaur — Wed, 15 Dec 2021 11:52:03 +0100

Thermal winds appear in mountainous areas and valleys due to temperature gradients caused by the buoyancy effects associated with the diurnal heating-cooling cycle of the lower atmosphere. These winds develop over complex topographies of multiple scales, and reverse their direction twice a day, driven by formation and dissipation of temperature inversions. Winds may flow up-slope (anabatic winds), up-valley, or from the plain to the mountain massif during day-time. Conversely, during night-time, winds may flow down-slope (katabatic winds), down-valley, or from the mountain massif to the plain. Previous investigations have shown that such winds can reach relatively high speeds [1], which can be interesting for wind energy applications. Moreover, thermal winds showing higher regularity and periodicity than synoptic winds [1], can thus be more predictable, which is of special interest to the current energy market, aiming to match the energy demand with the renewable energy production, given the fact that wind energy and solar energy production cannot be controlled at will.

In this work, thermal wind generation is analysed using OpenFOAM, which is an open source computational fluid dynamics software. For this analysis, an idealized numerical model of a mountain-valley system with a mountain slope angle of 20º is used. Anabatic and katabatic winds are generated imposing altitude-dependent temperature boundary conditions on the slope. OpenFOAM’s solver buoyantBoussinesqPimpleFoam is used, and validation of different turbulence models and initial conditions is done by comparing OpenFOAM simulations with results from the literature. The effects of the fluid domain height and of the valley width on the flow behaviour are also discussed. Conclusion on anabatic and katabatic wind formation and on their possible application to wind energy generation is finally drawn.

English as a Foreign Language Teachers’ Perceptions of their Unique language acquisition device Construction in Second Language Acquisition Process: (Grounded Theory)

L1-Educational Studies in Language and Literature — Sun, 12 Dec 2021 21:45:03 +0100

In this study, the perceptions of selected experienced EFL teachers about the construction of their unique LAD in the SLA process is investigated. The grounded theory and constructive design were employed and open, axial, and selective coding after semi-structured interviews ranging from 30 to 90 was used. The teachers' perceptions showed seven categories related to the construction of their unique LAD, namely, (a) unique environment; (b) individual uniqueness; (c) Unique Socio-emotional factors; (d) entertainment; (e) Psychological problems; (f) genetic factors; and (g) cyberspace. Perceptions showed that the following mentioned factors have been affected uniquely by those mentioned categories separately and uniquely. Factors such as motivation, interest, self-confidence, self-esteem, attitude, viewpoint, opinion, intentions, learning styles and strategies, exposure to the TL, rate of acquisition, acquisition progress, IQ and intelligence, social interaction, mental status, memory capacity, concentration, learning potential, metaphorical thinking, and ideology so that they would be equipped with the ULAD in SLA.

A NUMERICAL SIMULATION OF THE 1991 LIMÓN, COSTA RICA, EARTHQUAKE

Benjamin Colucci — Wed, 08 Dec 2021 21:36:02 +0100

Synthetic strong motion records for the 1991, Mw 7.6, Limón, Cosa Rica earthquake were computed for several hundred different source models. The rotd50 (response spectra) was used to compare synthetic and observed data at seven stations that recorded the event. The source model that minimized the misfit was selected to calculate new synthetic records at present-day stations. The result indicated that the fault length reached some 100 km long by 40 km deep. The largest peak ground acceleration would have been recorded in the stations located along the Caribbean coast, close to the epicenter. A post-earthquake bridge inspection calculation using our scenario earthquake predicted a high level of damage to several bridges that collapsed in 1991.

WIDESPREAD SHALLOW MASS WASTING DURING HURRICANE MARIA: LONG-TERM SIGNIFICANCE OF SEDIMENTATION IN THE TROPICS

Benjamin Colucci — Wed, 08 Dec 2021 21:22:01 +0100

Hurricane María was an extreme atmospheric event that impacted Puerto Rico in 2017. As a result of the passage of hurricane María over the island more than 70,000 landslides were triggered, with the highest density of mass wasting found in the mountainous center of the island. This area is highly susceptible to slope failure given the local soils that form as a result of continuous tropical chemical weathering of the bedrock material. Copious amounts of sediment from these soils were mobilized and transported by the landslide-triggering event. The results of our study reveal the soil types that are most susceptible to mass wasting loss in order to better understand their susceptibility to failure and contribution to sedimentation across the rugged interior of the island. A preliminary analysis of area volume scaling statistics for thousands of landslide sites in the important Lago Dos Bocas basin reveals that Hurricane María likely liberated at least 1.7 million cubic meters of mostly superficial sediment in the lake’s contributing area (not including the Caonillas sub-basin). In an effort to determine the efficiency of the fluvial system to transport these sediments during and after the catastrophic hurricane event, bathymetric surveying was carried out in Lago Dos Bocas, where much of the sediment is hypothesized to have been deposited. This reservoir is a vital piece of infrastructure in the island as it supplies water to the San Juan metropolitan area. Based on the 2021 bathymetric survey and the historical data, the excess sediment deposition to the reservoir related to Hurricane María is estimated at approximately 2.1 million cubic meters. When compared with data from 1999-2010, this volume represents the equivalent of 18 years of background sedimentation. At present, the reservoir capacity loss since construction is at 64%. These analyses are pertinent to understand how the local sediment budget has been affected and to re-calculate the useful life of the reservoir and highlight the vulnerability of Caribbean infrastructure systems, given the forecasted likelihood of increased tropical cyclone activity in the years to come.

COMPOSITE SOILS USING SYNTHETIC LIGHTWEIGHT AGGREGATES TO PREVENT SLOPE COLLAPSES AND FOR SETTLEMENT CONTROL

Benjamin Colucci — Wed, 08 Dec 2021 21:00:22 +0100

The Synthetic Lightweight Aggregates (SLA) is a patented aggregate composed of fly ash and high-density polyethylene (HDPE). It is considered as an eco-friendly material because its use would contribute to reduce the amount of waste going to landfills. One of most promising applications of SLA is related with the geotechnical engineering field because of its low density that when combined with natural soils may produce a composite backfill material with adequate mechanical properties. This research focuses on testing SLA material properties, including material characterization, trial mixes of SLA with natural aggregates, and compaction tests to obtain the optimum dry density. The composite soil meets the AASHTO classification standards for A-2-4 soils. The validation of the observed behavior lead to propose at least three basic applications related with natural disasters prevention: a) efficient design of retaining walls with lower lateral pressures, b) control of settlements using low density composite soils over compressible soils, and c) slope stability problems.

DEVELOPMENT OF SPECTRA ELASTIC DESIGN FOR DIFFERENT MUNICIPALITIES OF PUERTO RICO

Benjamin Colucci — Wed, 08 Dec 2021 20:54:13 +0100

The most recent update of the Seismic Hazard Map of Puerto Rico was carried out in 2003 when the first active seismic fault within the island, in the Cabo Rojo area, was considered. Since then, several geophysical studies have been carried out on various seismic faults within the island that have helped to expand the knowledge of these faults and, in some cases, to recognize their high seismic activity. The Seismic Sequence that began in December 2019 produced more than thirteen thousand earthquakes in 2020, with a large percentage of them having their epicenter within the Island. The overwhelming evidence of active seismic faults within the Island urges the prompt update of the Seismic Hazard Map. However, multiple studies are needed to determine with accepted precision the location, size and slip rate of these faults so that they can be included in the Seismic Hazard Map. In the meantime, engineers urgently require a proper estimate of the seismic loads that these faults, not thoroughly studied, can apply to the structures to be designed or rehabilitated. In this paper we use the current knowledge of the existing earthquake fault zones and the deterministic methodology of ASCE 7-16 to develop design spectra for twelve municipalities of Puerto Rico taking into consideration all the earthquake fault zones that constantly threaten the Island. In average, the proposed spectra almost double the design seismic loads required by the current 2018 IBC code.

QUANTITATIVE RISK ANALYSIS OF GAS PIPELINES IN CÓRDOBA, ARGENTINA

Benjamin Colucci — Wed, 08 Dec 2021 20:42:01 +0100

A quantitative risk analysis is presented for a gas pipeline system in the province of Córdoba, Argentina. This is a part of a project on the vulnerability of infrastructure and physical environment associated with the storage and transport of combustible fluids. The developed model considers the identification of threats to the integrity of the pipelines, an estimate of the probabilities of failure of the identified threats, an estimate of the consequences of a failure, the determination and evaluation of the quantitative risk according to acceptance criteria, and the adoption of risk mitigation and control measures. For this study, the main data from the existing backbone network and the recently built gas pipelines in the province of Córdoba are used. This is complemented with a survey of the constructions near the route of the sections under study, as well as the crossings of roads and watercourses, based on available satellite images. The work is focused on establishing the individual and social quantitative risk levels of the gas pipelines with the highest qualitative risk level, already defined by previous work. Finally, and in the necessary cases, the adoption of mitigation measures is considered to adjust the risk levels to the international acceptance criteria. A quantitative risk analysis is presented for a gas pipeline system in the province of Córdoba, Argentina. This is a part of a project on the vulnerability of infrastructure and physical environment associated with the storage and transport of combustible fluids. The developed model considers the identification of threats to the integrity of the pipelines, an estimate of the probabilities of failure of the identified threats, an estimate of the consequences of a failure, the determination and evaluation of the quantitative risk according to acceptance criteria, and the adoption of risk mitigation and control measures. For this study, the main data from the existing backbone network and the recently built gas pipelines in the province of Córdoba are used. This is complemented with a survey of the constructions near the route of the sections under study, as well as the crossings of roads and watercourses, based on available satellite images. The work is focused on establishing the individual and social quantitative risk levels of the gas pipelines with the highest qualitative risk level, already defined by previous work. Finally, and in the necessary cases, the adoption of mitigation measures is considered to adjust the risk levels to the international acceptance criteria.

FAILURE ANALYSIS OF THE ARECIBO OBSERVATORY M4N AUXILIARY CABLE

Benjamin Colucci — Wed, 08 Dec 2021 20:30:29 +0100

Structural and forensic analysis concluded that the Arecibo Observatory M4N socket joint failure in August 2020 was due to a socket joint design with insufficient design criteria that did not explicitly consider socket constituent stress margins or time-dependent damage mechanisms. The socket attachment design was found to have an initially low structural margin with a finite service life, notably in the outer socket wires, which degraded primarily due to long-term zinc creep effects that were activated by longterm sustained loading and exacerbated by cyclic loading. Additionally, HAC and wire defects were found in a few outer wires that may also have contributed to initial outer wire failures. The design did not explicitly consider the time-dependent effects of creep and cyclic loading on design capability, account for a worstcase build condition traceable to in-service inspection of features (e.g., zinc creep/extrusion), specify an end-of-life capability requirement associated with service life degradation, or explicitly set service life inspection intervals with pass/fail inspection criteria. In-service inspections showed evidence of progressive zinc extrusion on several Arecibo sockets, which in hindsight were evidence of cumulative damage and effectively a missed opportunity to prevent cable failure. Open spelter sockets of this type are used throughout industry in stay cables. The following recommendations are proposed to prevent failures of similar socket joints: (1) Verification of positive stress margins in socket joint wires for all failure modes, (2) Periodic visual inspections with acceptance criteria for zinc extrusion that are tied to structural qualification, (3) Revisiting civil codes and industry standards based on lessons learned from this analysis.

Vulnerability Assessment of Italian Unreinforced Masonry Churches Using Multi-Linear Regression Models

Scipedia content — Tue, 30 Nov 2021 14:57:27 +0100

The extensive damage occurred to the Italian historical and architectural heritage during the 2016-2017 earthquake sequence, and particularly to unreinforced masonry churches, highlights the need to better recognize the vulnerability of religious buildings. A sample of 158 churches belonging to the four stricken regions is studied and their performance analysed statistically. Structural behaviour of these churches is described in terms of mechanisms affecting the so-called macroelements, being portions of the building behaving more or less independently. In order to define fragility curves correlating the damage related to each collapse mechanism against ground motion intensity and churches’ specific characteristics, the observed behaviour of the sample is herein analysed by means of statistical procedures accounting for possible local collapse mechanisms. Several regressions strategies are considered, accounting for vulnerability modifiers increasing/reducing the vulnerability of each macroelement, since the severity of shaking alone is not capable to fully explain the observed damage, strongly influenced by structural details that can worsen the seismic performance or improve it through earthquake-resistant elements. A synthetic damage index, purely based on observed data, is used to summarise the overall severity of damage related to relevant mechanisms, highlighting the contributions of ground shaking and building vulnerability. Results show the relevance of the proposed multi-linear regression models for the national heritage of churches and the advisability of extending mechanism-based regressions to other countries besides Italy. The proposed global damage index can be used as predictive tool to support seismic vulnerability mitigation at a territorial scale.

Vulnerability Assessment of Italian Rationalist Architecture: Two Case Studies

Scipedia content — Tue, 30 Nov 2021 14:57:18 +0100

The work is focused on the structural vulnerability assessment of two historical constructions, chosen as case-studies representative of a recurrent typology of Italian rationalist architecture, dating back to the Fascist period, often hosting public offices. Both examined buildings have similar dimensions and geometry, being characterised by five/six storeys and by an almost square plan with an inner courtyard, and are located in EmiliaRomagna, in zones of medium seismic hazard. The older building, dating back to the Thirties and located in Ravenna, has a mixed masonry-reinforced concrete structure, while the other one, built in the late forties and located in Parma, is characterised by an unreinforced masonry structure with some limited reinforced concrete elements. For the vulnerability assessment of the two buildings, a multi-disciplinary approach was followed, including the historical documents search concerning both the investigated buildings and the surrounding areas, the detailed geometrical and structural survey, the identification of materials, and in situ and
laboratory tests to evaluate materials mechanical properties. These activities allowed reaching an adequate level of knowledge about the present conditions of the structures and their critical deficiencies. This knowledge path is not only necessary for the subsequent numerical analyses, but is also important as it allows targeting the repairing interventions, possibly reducing their final costs, in agreement with the “minimum intervention” approach for heritage buildings.

Vulnerability Assessment of Dwellings in the Historic Center of Cusco (Peru)

Scipedia content — Tue, 30 Nov 2021 14:57:05 +0100

The seismic vulnerability assessment of the historic center of Cusco (Peru), an important UNESCO world heritage site, is dealt with in this paper. First, historical development of the city is presented through an in-depth historical analysis of its transformation over time, from the Inca empire to modern days. Then, an extensive in-situ survey activity, that allowed to collect several information about the main structural features concerning ordinary residential buildings, is shown.
Based on the collected data, an empirical method calibrated on Italian historic centersfrom the authors is applied. It allowed to obtain Damage Probability Matrices and Fragility Curves for different earthquake intensities, as well as to assess the probability of exceeding certain levels of damage when seismic events of different intensities occur.
Based on these predicted damage frequencies, it is possible to prevent irremediable losses and to propose retrofitting interventions which can lead to the seismic vulnerability mitigation for the whole historic center

Using the Ultrasonic Tomography Method to Study the Condition of Wooden Beams from Historical Building

Scipedia content — Tue, 30 Nov 2021 14:56:57 +0100

The need to evaluate the integrity of wooden structural elements is constantly increasing. Non-destructive methods are becoming more popular in this field of research. One type of non-destructive testing is the ultrasonic imaging method, which allows the analysis of internal wood structures without disturbing their state and integrity. In this study, we are interested in assessing the effect of wood condition on the ultrasound time of flight (TOF). The research was carried out on wooden beams, which were obtained from a historical building. The images obtained from ultrasound tomography were compared with results of a visual inspection.Places of discontinuities, voids and cracks in wood caused a much lower velocity of wave propagation.The location of the wood core was illustrated by the places with the highest velocity. The article proved the validity of using ultrasonic tomography to assess the technical condition of historic wooden beams.

Using Information Technologies for Bridge Management in Mexico‘s Royal Roads Built Between XVI and XVIII Century

Scipedia content — Tue, 30 Nov 2021 14:56:48 +0100

After the establishment of the Viceroyalty of New Spain in the 16th century, the interest in precious metals and the mining activities would influence the emerging economic activities and the communications network of the New Spain. All the communications were built based on two mutually perpendicular axes. The first axis, East to West, between Veracruz-Mexico-Acapulco and the other axis, north to South, linked the northern region of the Viceroyalty with Mexico City and to Oaxaca and Guatemala. As part of the road infrastructure needed to get a continuous flow of goods, bridges were very important for crossing rivers, cliffs, and mountains. The fabrication of these structural elements were mainly made using the roman old school. The geometry, length, and materials used were varied, depending on the technical improvements of the time, and local labour
expertise. The Vice-regal bridge vestiges are now scattered in the 2 million square km of the Mexican territory. Most of them are still in use, but others were forgotten in the old Royal Roads when they went out of use. This investigation deals with the methodology used (based on information technologies) to create a web-based management system for Viceregal bridges, that is now available to be used in Mexico by the three government levels (Municipality, State, and Federal) and research institutions.

Unreinforced Masonry Structures‘ Seismic Improvement with F.R.C.M. : the Experience of the Vanvitellian Palazzo Murena of Perugia

Scipedia content — Tue, 30 Nov 2021 14:56:39 +0100

The aim of the contribution is to illustrate strengthening design in regard to the conservation of Palazzo Murena in Perugia, designed in the eighteenth century by the prominent Architect Luigi Vanvitelli. Starting from an accurate historical analysis and taking into account experimental campaign and results of numerical analysis, the vulnerable elements of the construction have been highlighted. A local reinforcement intervention is proposed with the aim of retain the historical value of the architectural characteristics; this consists of the application of plaster with Fiber Reinforced Cementitious Matrix, F.R.C.M., to achieve an adequate strength, without adding supplemental weight to the masonry structure and therefore avoiding an increase of the seismic vulnerability. The benefits of the application of F.R.C.M. materials, also with respect to different reinforcement techniques are broaden.

Understanding Traditional Anti-Seismic Strategies Beyond Their Disappearance and Distortions: Yazd Qajar Architecture Case Study

Scipedia content — Tue, 30 Nov 2021 14:56:29 +0100

Understanding traditional seismic strategies is necessary to conduct appropriate restoration of historic buildings and city centers located in earthquake-prone areas. But, the fast disappearance of vernacular built heritage and of the associated popular knowledge and know-how, along with the spread of inappropriate maintenance works, make it very difficult. To overcome these obstacles, it is suggested to broaden the scope of observations by including both larger geographical areas and elements that do not appear as seismic features at first consideration. This paper illustrates the relevance and the limits of this approach by applying it to the case study of Yazd historic city center. Yazd is located in a moderate seismic area and is famous for its well-preserved historic city center, with a high number of Qajar adobe buildings in various conditions. The authors combined literature review, direct observation of numerous buildings and a deeper study of four Qajar houses to conduct the first part of their research. The data collected mainly relates to the geometrical features, the materials used and the interconnections between elements at different scales. Their analyses led to the elaboration of several assumptions on the seismic behaviour of the studied adobe buildings and vaults and on the distortions some features may have suffered. To validate these assumptions, two methodologies were used. Both are illustrated in this paper through the study of the insertion of baked bricks in adobe vaults. The first one is based on observation campaigns on damaged houses. The second one is based on experimental works, with tests conducted on the shear strengths of masonry made with mud mortars and adobes or baked bricks to better understand how builders benefited from mixing these materials in an adobe vault. Finally, the authors discuss the limits of the method and the extent to which restoration projects can benefit from it.

Typological Classification and Observed Damage Patterns of Masonry Churches After the 2016 Central Italy Earthquake

Scipedia content — Tue, 30 Nov 2021 14:56:19 +0100

The seismic protection of cultural heritage is an important topic that has been faced by several researchers in the last decades. Seismic events of the past have highlighted the need of achieving a proper knowledge of the vulnerability of cultural heritage, in particular of churches, in order to put in the field proper mitigation measures at the large scale. According to this premise, this paper deals with the damage scenario observed on eighty seven churches hit by the 2016 Central Italy earthquake. In a first stage, the most important structural features of the studied churches are discussed and threated by the statistical standpoint. The reported information have been collected through the A-DC form, adopted by the Civil Protection Department and by the Ministry of Heritage and Cultural Activity and Tourism (MiBACT), which was used in the framing of the damage reconnaissance activity carried out by the ReLUIS Italian consortium in the aftermath of the earthquake. Also, the form has been used in order assess the damage of each macro-element and, then, to assign a damage index to each church. The presented work is framed in a wider research activity that aims at providing a predictive methodology for the vulnerability assessment of churches at the regional scale. This methodology was already calibrated on the basis of the 2009 L’Aquila seismic event. The outcomes presented in this paper will serve to further prove the reliability of the proposed model.

Typological Characterization of Ancient Town Walls for Disaster Prevention and Mitigation. The MO.M.U. Project

Scipedia content — Tue, 30 Nov 2021 14:56:10 +0100

The problem raised by the steadily increasing number of failures in ancient town walls has recently attracted much interest. This typology of cultural heritage has always played a critical role in shaping local identities and still holds great potential as a cultural resource but poses substantial challenges in management terms. In fact, multi-disciplinary methodologies for their study and analysis are missing. The MO.M.U. project aims to safeguard ancient town walls in Tuscany (Italy) by introducing an integrated framework for their knowledge, diagnostic, assessment, monitoring and management. The proposed approach employs innovative non-invasive technologies and introduces a multi-hazard risk prioritisation methodology to address preventive conservation and programme interventions.

TRM-Strengthened Timbrel Cross Vaults Subjected to Vertical Settlements

Scipedia content — Tue, 30 Nov 2021 14:55:58 +0100

Two full-scale timbrel cross vaults subjected to vertical settlements in one of their supports were tested at the ICITECH laboratories of the Universitat Politècnica de València. In one of the vaults a support was moved downwards, while the other was subjected to upward-downward displacements in one support. Both tests are described and analysed in detail in Torres et al. [1,2]. Both vaults presented certain levels of post-test damage in the form of cracks and significant displacements. In order to analyse the effectiveness of the reinforcement of previously damaged vaults, both were strengthened with TRM and subjected to further testing in which vertical settlements were applied to one support. The TRM strengthening comprised an extrados layer composed of a 25x25mm glass grid embedded into two approximately 5 mm thick layers of cementitious matrix. The TRM strengthening was able to withstand higher peak loads and prevent the formation of cracks along the extrados surface of the structure, while as expected, ductility increased. A 3D macro-modelling FE strategy on Abaqus commercial software was also adopted to study the behaviour of the vaults during the tests.

Treatment for Rising Damp and Natural Hydrodynamic Equilibrium in Masonry Walls

Scipedia content — Tue, 30 Nov 2021 14:55:50 +0100

The water absorption, in the Historic Heritage Restoration, through porous materials of the different constructive elements, is certainly one of the factors that constitute the basis for most pathologies and degenerative phenomena on plastering and masonry walls. Particularly, the most critical humidity comes from the soil, because it contains salts (chlorides, sulphates, nitrates). Those salts impregnate the masonry and unleash humidity rises up to several meters. Humidity varies the physical and chemical behaviour of the wall, increasing the thermic conductivity and limiting the isolation power. In addition, due to surface crystallization of the salts, early disintegration of the building materials and rapid destruction of the wall are generated. A wall saturated with water diminishes its isolation power and favours the formation of mould and bacteria, worsening the healthiness of the environments and the well-being of the people who habit them. In nature, a natural hydrodynamic balance is established between the water absorbed by building materials through capillarity and osmosis, and the water transferred to the atmosphere through evaporation. The constant components within this equilibrium are the absorption of water through capillarity and osmosis of the building materials, and the chemical nature of the aqueous solution absorbed. The variable components are the temperature and relative humidity of the atmosphere. The evaporation surface, composed by masonry mortar, plastering, scraping and painting are the constructive elements on which we might make an intervention. The traditional constructive systems, exclusively based on using natural lime for the manufacture of masonry mortars and rendering, and on using lime paste for coatings and paints, used to create the natural effects of the breathable hydrodynamic balance of the masonry. The challenge is to reproduce today, on site, a range of natural lime products in order to carry out interventions completely comparable to the original construction techniques. The range of naturals products, ensures a natural balance between rising damp and surface humidity evacuation, exploits the natural qualities of microporosity and hygroscopicity of the NHL, and natural pozzolan. The lack of reaction with the salts ensures chemical stability of the rendering and the duration of the entire dehumidifying system. The aim of the paper is to present real cases.

Towards a Methodology for Use of Sonic and Ultrasonic Tests in Earthen Materials

Scipedia content — Tue, 30 Nov 2021 14:55:41 +0100

In many regions around the world, earth has been used through history as a traditional building material. Nowadays, there is a significant revival of its use due to its ecological value and architectural performance. However, there is still a significant lack of knowledge about its actual mechanical properties and behavior. This work aims at the development of consistent methodologies for the characterization of this building material based on non-destructive tests, NDT's. Ultrasonic and sonic tests on prismatic rammed earth specimens and adobe bricks were carried out. The paper presents an optimized method for estimating S-waves and P-waves based on direct and indirect non conventional sonic testing methods. Finally, the paper discusses methodological issues for estimating the earthen material properties through the propagation velocity of sonic waves.

Towards a Digital Architectural Heritage Knowledge Management Platform: Producing the HBIM Model of Bait al Naboodah in Sharjah, UAE

Scipedia content — Tue, 30 Nov 2021 14:55:32 +0100

This paper explores the methodology for the production and integration of Heritage Building Information Modeling (HBIM) into the museum management system of the Emirate of Sharjah, United Arab Emirates (UAE). The historic Bait Al Naboodah Museum is documented as a pilot study using terrestrial laser scanning (TLS) technology. The scanning and modelling processes are explained in a seven-stage workflow: preliminary data acquisition, site surveying and terrestrial laser scanning, processing of the captured cloud point data, post-processing and modelling, quality control, final delivery of the digital model, and its validation. The architectural elements and details of Bait Al Naboodah have been reconstructed in a multilayered 3D digital model, and its accuracy has been tested. This HBIM model has been conceived as the basis of a shared inter-institutional platform for the Museum's management.

To Reach the Light: The Monumental Byzantine Stairs of Caesarea, a Conservation and Restoration Project

Scipedia content — Tue, 30 Nov 2021 14:55:22 +0100

Ancient Caesarea has founded in the years 25-10 BC and named after Emperor Augustus. Throughout history, from the early Roman until the Byzantine period, Caesarea was a major city and one of the largest and most important port cities in the Mediterranean. During the Byzantine period, the city encompassed an area three times larger than that delimited by the Herodian wall and became an important center of Christianity. The monumental stairs led to the Byzantine Octagonal Church built upon giant arch above the remains of the enormous Roman stairs of Augustus temple. Stairs led a large number of people from the vast harbor, to the Temple platform. The Byzantine arch located 17 meters from the ancient quay, is 8 meters width and 4-meter long, built with specific technology from local sandstone named Kurkar. The arch fall after the Byzantine period and the staircases severely damaged due to the long exposure of almost 1500 years and environmental conditions such as capillary rise, daily winds carrying sand, high temperature, moisture, salts, and deliberate destruction, for instance, stones robber and collapse parts from the wall. The characteristics of the Kurkar with sustained deterioration and this environmental condition have led to different conservation problems, at various levels of severity erosion, the disintegration in both bonding materials and stones. The conservation measures' purpose is to stop the ongoing weathering process and prevent a deterioration state of the staircases, to restore the arch and stabilize the structure of the stairs to carry 48 tons of the restore arch. The findings of the project show that a suitable solution to ensure effective and sustainable protection of complicated staircases structure from destruction and various weathering condition to carry new massive arch depends on understanding the ancient application of building technologies and techniques, the use of original bonding material, integrated monitoring, and ongoing maintenance.

Timber Reinforcements: Local Construction Techniques in Italian Historical Buildings

Scipedia content — Tue, 30 Nov 2021 14:55:14 +0100

The role of timber connections as reinforcement for vertical masonry walls is well known but still requiring a systematic study. Considering the main sources coming from the architectonic treatises, a real identification of the use of wooden poles as binding elements between walls is not recognized. Several important authors belonging to the 15th and 16th century recommended avoiding the use of timbering elements into the section of the walls, arguing that the perishability of this material cannot provide a long durable solution. Nevertheless, since the 17th century also some indications from the so called “high knowledge” seem to identify a reliable technique in the timber reinforcements for masonry walls. This work explores the contraposition between theoretical approaches and the building site practice, focusing on the mechanical function of orthostatic timbers inserted into masonry structures. Recent contributions based on archive studies indicated that the use of wooden reinforcements was widely diffused in Italy, but rarely documented by the architectural theorists. The technical documentation discovered into archives is instead a rich source of information concerning the persistence of timbers inside walls as a solution against the vulnerability of masonry structures to shear forces. The case of the building site documentation for the realization of Volpi Palace in Como offers an important occasion for improving the studies on a building practice that did not meet official credits by the theoretical experts in architecture.

Thermal Behavior Assessment of Two Types of Roofs of the Dominican Vernacular Housing

Scipedia content — Tue, 30 Nov 2021 14:55:05 +0100

The Dominican vernacular architecture, based on the indigenous bohio with Spanish influence, is built with natural materials, such as the royal palm (Roystonea Hispaniolana) and the cana palm (Sabal Dominguensis). This model of housing has remained practically unchanged for five centuries, responding adequately to the Caribbean tropical climate. In the twentieth century, start to replace the traditional palm leaf roof by a corrugated sheet zinc, significantly affecting the temperature inside these houses and altering the conditions of living comfort. For this reason, the aim of this research is to evaluate the thermal behavior of two roof types of vernacular housing. One type is a cana palm leaf roof and the other is a corrugated sheet zinc roof. The houses are in the towns of Villa Sombrero and Sabana Buey, Peravia Province, in the southwest of the Dominican Republic, a region with a Tropical savanna climate (Aw) according to the Köppen-Geiger climate classification. The climate is characterized by temperatures from 20°C to 38°C, with rainfall below 500 mm per year. The technique and tools used for this research are: Infrared Thermography (IRT) and digital thermometer for measure of thermal properties of roof materials, a thermometer and hygrometer to measure the relative humidity and temperature inside and outside of the houses, and carbon monoxide (CO) and carbon dioxide (CO2) meter. Passive IRT is used to measures the temperature differences of a structure that are generated under normal conditions. The results indicate that there is a difference in temperature between one type of roofing material and the other. Finding that houses with palm leaf roofs have lower temperature than corrugated sheet zinc roof and present a temperature difference between the interior and exterior

The Use of a Building Information Model to Support Seismic Analysis: Application to the National Palace of Sintra, Portugal

Scipedia content — Tue, 30 Nov 2021 14:54:53 +0100

This work presents an application of a Building Information Model (BIM) to the National Palace of Sintra, Portugal, a large and complex building composed of different unreinforced masonry buildings that is included in the Cultural Landscape of Sintra, classified under the UNESCO World Heritage list in 1995. The developed H-BIM (Heritage Building Information Modelling) model has the ability to provide the geometric information of the structure of the building, together with its descriptive attributes, such as the mechanical characterization of the building materials, as inputs to the seismic structural analysis. The results of such analyses are also stored as attributes within the H-BIM model, providing an integrated platform usable by the building management. Geometric data was acquired using a Faro FocusS70, together with a Topcon Falcon 8+ UAV. The methodology applied in the construction of the H-BIM model was implemented with Autodesk Revit® software. Since the Palace is very complex, its seismic behaviour was studied for the different building units, considering the effect of the adjacent ones, and performing nonlinear static analyses through 3Muri software.

The Unbuilt Musmeci Parabolic Cross Vault Reinvented as a Dry-Masonry Structure

Scipedia content — Tue, 30 Nov 2021 14:54:40 +0100

This paper investigates the unbuilt Musmeci parabolic vault, reinventing the original reinforced concrete structure as a dry-masonry vault. In the framework of rigid no-tension constitutive model with no sliding, the equilibrium analysis is conducted with the aim ofevaluating the design thickness of the masonry vault, respecting the original Musmeci shape. A parametric survey is performed to assess the minimum thickness of the vault, and its structural capacity under spreading supports. Attention is focused on the different collapse mechanisms and the corresponding crack patterns. For a better insight into the behaviour of the parabolic vault, the relevant case of the parabolic arch is first analysed and discussed. The numerical results show the feasibility of the project, with a thickness comparable with that proposed by Musmeci.

The Structural Function of the Dutch Buttressing of the East Curtain Wall of Elmina Castle, Elmina, Ghana

Scipedia content — Tue, 30 Nov 2021 14:54:31 +0100

Elmina Castle is the first of a series of European trading bases along Africa’s west coast, and it is the oldest and best preserved early European building in Sub-Saharan Africa. The structure shows a combination of mud-mortared and lime-mortared sandstone masonry macro elements and has undergone reconstructions and modification throughout time under Portuguese and Dutch occupation. This study focuses on the structural analysis of Elmina Castle’s east curtain wall, which features two massive masonry buttresses built only alongselected portions of the wall. The hypothesis that these buttresses were built in correspondence of deep voids in the foundation bedrock platform is numerically evaluated using pushover analysis. The lateral capacity is determined based on energy considerations using nonlinear FE models in Abaqus/CAE Explicit and concrete damaged plasticity. Results indicate that, at a later Dutch stage of structural modification, loose soil filling might have caused rotational instability of the curtain wall, requiring the addition of the buttresses.

The State and Condition of Historical Buildings Located on Partisan Hill in Wroclaw

Scipedia content — Tue, 30 Nov 2021 14:54:21 +0100

The paper presents fragments of original archival documentation, which are used to identify the historical outline of the colonnade building and the peristyle pavilion located on Partisan Hill in an old part of Wroclaw. Traces of these buildings date back to the Middle Ages. The state of preservation of these objects was presented on the basis of conducted assessments, drilling cores, and non-destructive and semi-non-destructive tests. Much attention was devoted to the brick walls, brick and reinforced concrete ceilings in flat roofs, as well as to the elements of architectural detail. The presented results include tests of the moisture content and salinity of walls, tests of the compressive strength of concrete and distribution of reinforcement in ceilings. They constitute the first stage of activities that aim to restore the buildings to their former glory.

The Safety of Masonry Arches Subject to Vertical and Horizontal Forces. A Numerical Method Based on the Thrust Line Closest to the Geometrical Axis

Scipedia content — Tue, 30 Nov 2021 14:54:14 +0100

In this paper the topic of the safety assessment of masonry arches based upon their geometry is investigated. The theoretical background is the Heymanian master safe theorem along with the no-tension assumption of masonry. The continuous arch is analyzed considering a discrete pattern of vertical loads, such as those of the self-weight and superimposed loads. Among all the lines of thrust contained within the profile of the arch, the one closest to the geometrical axis can be considered to be the best one thanks to the minimum bending moment and shear force present in each cross section. A numerical procedure for computing the line of thrust closest to the geometrical axis of an arch subject to its self-weight has been recently formulated by the authors. This procedure accounts for this line of thrust by minimizing the distances between the geometrical axis of the arch and the thrust line. In order to consider the action of both vertical loads and horizontal forces proportional to the vertical ones, such as those provoked by an earthquake, an extension of this procedure is herein presented. The safety of the arch is finally assessed by computing a domain of equilibrium thrust lines within the profile of the arch which provides, in analogy with the Heymanian geometrical factor of safety, the full range factor of safety. The procedure is described in the paper and illustrated with
regards to the analysis of arches subject only to vertical loads and arches subject to also horizontal forces.

The Safety Level of Concrete Pile Foundations under Industrial Monuments

Scipedia content — Tue, 30 Nov 2021 14:54:07 +0100

Prefabricated concrete piles have been used for the foundation of bigger buildings for about a century. Often a change in function, an addition (also vertically) or another type of alteration is required, resulting in different loads on the foundation.
There are several complicating factors that return regularly in these assessments. The first one is a lack of data. Often drawings are missing or incomplete, e.g. showing only pile head dimensions or maximum calculated load but not the pile length, pile tip shape or material properties. Inspection is hard and only possible for the part directly under the pile head. And a third complication is that in The Netherlands there have only been official codes for piles since 1992.
Various calculation and design methods from WWII until 1985 are discussed to see if there is any consistency that might lead to an indication of the load bearing capacity of piles in The Netherlands from that era.
It is concluded that design rules for the load bearing capacity of concrete pile foundations in The Netherlands have been inconsistent over time. If the original detailed geotechnical calculations and/or structural drawings cannot be found in archives then the given ultimate loads cannot only not be exceeded; even if the load on a pile is currently less than stated on the technical specifications designers are advised not to increase the load.

The Reuse of Housing Buildings in Barcelona. The Versatility of Old Constructive Structures

Scipedia content — Tue, 30 Nov 2021 14:53:59 +0100

There are 1,463 buildings in Barcelona, from different times from the first century to the present day, that have changed their functions once or more times throughout their life. This paper analyses those cases in which changes in use relate to housing and it does it in two opposite ways: In one way, examining houses –mostly with building structures of bearing walls– that have endured functional modifications without losing its main attributes. In the opposite way around, studying buildings with other uses than housing – many of them built with isotropic structures or large structural spans– that have been converted into dwellings. On the other hand, and in both cases, the analysis addresses how the urban situation of the building conditions the use to which it will tend to be transformed.

The Restoration of the Medieval Walls of San Ginesio: a Dedicated Study for the Conservation, Repair and Enhancement of an Important Military Fortification

Scipedia content — Tue, 30 Nov 2021 14:53:49 +0100

The seismic events that occurred in central Italy in 2016 severely damaged the rich cultural heritage system present in the area hit by the earthquake. Particularly significant is the situation of the Marche Region, here it is necessary to intervene quickly and effectively in order to preserve and secure the damaged historical architectural heritage. Following the agreement signed in 2019 between the administration of the Municipality of San Ginesio and the Marche Polytechnic University, a collaboration has been established, which is the basis of the present research work, aimed at studying and deepening the possible actions to be undertaken to be able to repair, preserve and enhance the medieval walls of the city. The city walls, dating from the fourteenth century A.D., almost completely surround the historic center of the city and are characterized by the presence of a large part of the ancient fortifications such as towers, access doors, defensive walkways, loopholes, etc. Since there is no complete survey of the planimetric configuration and of the elevations of the medieval walls, updated to the situation created after the earthquake, the first phase of the research focused on data acquisition. Combining DJI Spark MMA1 photogrammetric UAV images with cloud point by Mobile laser SLAM Kaarta Stencil, the 3D-dimensional modelling of the walls was obtained with the accuracy related to the output scale of 1:200 and with a detail and complexity useful for the following conservative analysis. Once the data was acquired and processed, it was possible to carry out a complete analysis of the walls structure, identifying the materials and construction techniques, the state of preservation of the materials, the damage situation to the structures, the various construction phases with the consequent relative dating. The analytical phase was concluded, therefore, with the identification and cataloging of the types of walls present. Each of these has been characterized both from a typological and a technical construction point of view, defining the wall quality (IQM) and the consequent mechanical parameters through the calculation process of the Wall Quality Index.

The Restoration Interventions of “Forte Marghera” in Venice

Scipedia content — Tue, 30 Nov 2021 14:53:39 +0100

In the framework of the Strategic Masterplan Cultural Heritage 2014-2018 of the Italian Ministry of Culture, a specific attention for the strengthening and constitution of relevant urban cultural centers is sought through the restoration and re-use of structural complexes of great architectural and historic value such as the case of Forte Marghera (Marghera Fort) of Venice. The need to build a fortress at the point where the mainland approached Venice was understood, after the fall of the “Serenissima” Republic (1797), by the Austrian Empire. The fort was therefore built in a marshy area on the edge of the Venice lagoon, crossed by a maze of canals. The works started in 1805. On the area there was already the old village of Malghera, home to warehouses and customs, which was incorporated into the Fort. However, the return of Napoleon's troops in 1806 surprised the works still in a early stage. The fortified work was then revised according to the plans of the French architect Marescò and conducted under the guidance of the general and military engineer François-Joseph Chaussegros de Léry and later the Chasseloup. The most significant buildings still present in the fortress – object of the current restoration works - are the two French barracks (1805-1814), located on the front near the dock. They are two-storey brickwork masonry structures with a 83x15 m rectangular plan and perimeter walls reaching a 3 m thickness, provided with decorative elements made of Istria stone. Visible decay is present in both two massive buildings, due to differential settlements mainly visible the long sides of both buildings, especially affecting the West one, also partially subjected to local collapse. A wide investigation campaign, aiming to the adequate characterization of the constituting materials and building techniques, was carried out in order to properly feed the design of conservative restoration interventions. Results indicate the use of good quality materials and proper layout also in the foundation system, indicating in the poor soil mechanical characteristics the main structural deficiency leading to the visible settlements. To date, the detailed design stage was reached for just one of the three buildings involved in the restoration, while the two remaining buildings are still in a preliminary design phase.

The Plaster Ceilings of Buckingham Palace and Windsor Castle: Their Construction, Condition and Conservation

Scipedia content — Tue, 30 Nov 2021 14:53:28 +0100

Alan Conisbee & Associates and Richard Ireland were engaged by the Royal Household Property Section to inspect and assess the historic plaster ceilings and their supporting structure within Buckingham Palace and Windsor Castle. Following the partial collapse of the Apollo Theatre ceiling in London in 2013 great importance has been placed on the inspection and certification of all historic plaster ceilings throughout the United Kingdom. This paper presents the key challenges of the project included the facilitation of access to constrained spaces, asbestos removal and cleaning of delicate fabric, surveying, digital monitoring, structural and plaster defects. Furthermore we discuss the key project outcomes including lessons learnt and best practice methodologies and practicalities behind inspections of this kind. The paper concludes with an outline of significant discoveries and ongoing laboratory testing of undernailed historic timber connections.

The NDT Investigations Carry out at the Arudj Cathedral, Armenia

Scipedia content — Tue, 30 Nov 2021 14:53:18 +0100

Arudj Cathedral, Armenia, is an example of early-Christian domed-hall that dates 671-672. A deep structural analysis of the building was developed by Politecnico di Milano, during the II° Level Master for Architects and Archaeologists named “Restoration Training and Support to Local Institutions for the Preservation and Conservation of Armenian Heritage”. The preservation project mainly focuses on deepen the knowledge level of the building in relation to the architectonical and structural aspects in order to offer a working method with the aim to propose and teach alternative solutions for static and seismic consolidation.
This paper reports the NDT investigations of the surveys carried out at the Cathedral of Arudj and the results obtained at the laboratory of the Politecnico di Milano.
The NDT investigations were carried out by the Authors and here following are briefly described. Sonic investigations on masonry structures were applied for a qualitative comparison of the walls, based on the variation of the sonic velocity values in the presence of areas with lower density, voids or cavities. The passive thermographic technique was applied to identify the distribution of capillary ascent in masonry structures. In order to offer a longterm verification of the evolution of the crack pattern, after having identify the cracks present on the masonry structures some displacement transducers have been fixed to state their evolution hourly.
Finally, a series of laboratory tests were carried out to determine the main mechanical characteristics of the constituent stone.

The Modern Impossibility of Making Art like That of the Past. Intervention Proposal for the Temple of San Juan Bautista, Tochimilico, Puebla, Mexico

Scipedia content — Tue, 30 Nov 2021 14:53:10 +0100

Restoration proposal for the Temple of Saint John the Baptist in Tochimilco, Puebla, México, damaged by the earthquake on September 19th, 2017. This proposal is based on the restoration article by the Mexican architect José Villagrán García, his arguments are based on the modification of the architectural values after a restoration project. This must take into account the respect for the authenticity of the original element but must also seek to adapt to the time and requirements of its current environment. Taking these points, a recovery of the space is proposed, consolidating the ruin and using modern materials to fill the gaps left by the earthquake. It is sought that this line of restoration be followed more and more in order to identify the historical stages in the life of the monuments.

The Iscarsah Guidelines on the Analysis, Conservation and Structural Restoration of Architectural Heritage

Scipedia content — Tue, 30 Nov 2021 14:53:02 +0100

The paper introduces the main concepts and criteria presented in the Guidelines on the Analysis, Conservation and Structural Restoration elaborated by the ICOMOS/ISCARSAH committee. The guidelines have been developed with the aim to provide guidance to experts and practitioners working in the study and conservation of structures or the architectural heritage. The guidelines are based on the ICOMOS Charter on the Principles for he Analysis, Conservation and Structural Restoration of Architectural Heritage elaborated by ISCARSAH and adopted by ICOMOS in 2003. The guidelines are intended to assist the multidisciplinary teams involved in the management of historical structures across all the stages of the study and operation, including the investigation and documentation works, the structural verification and the selection and design of appropriate minimum interventions.

The Influence of the Passive Earth Pressure and other Factors on the Stability of the Underground Masonry Vaults of the Paris Metro

Scipedia content — Tue, 30 Nov 2021 14:52:54 +0100

The Influence of External Climate on Church Internal Microclimate

Scipedia content — Tue, 30 Nov 2021 14:52:46 +0100

This paper deals with monitoring microclimate in the area of church and describes influence of exterior microclimate to interior microclimate, changes during one year. The basic parameters of the interior space (temperature, relative humidity, dew point and specific air humidity) were monitored in the long-term in the selected sacral building. These parameters were monitored at the same time as monitoring the surroundings in the exterior. The long-term monitoring of the internal microclimate of ossuary showed significant instability of the interior environment during the annual cycle, where the appropriate limits of humidity of the environment (excessive moisture in the spring and over-drying in the winter) are significantly exceeded. The microclimate behavior of ossuary is also different in different height levels, where the lower space acts as a pool with heavy cold air and vice versa, the space under the vault is moistened with vapor. The fact that under no circumstances of the exterior climate in winter is the temperature of the interior below freezing point is specific. The negative phenomenon of the internal environment of ossuary is the fact that in certain periods optimal conditions are created for condensation of water on the surfaces of walls and interior equipment of ossuary and also for the creation of ideal conditions for the formation and development of mold. Monitoring of the internal microclimate of ossuary during everyday operation has become the basis for the subsequent design of the reconstruction of the building. The remediation proposal must address several issues at once. It has to solve the issue of reducing moisture in the peripheral and inner walls of the building, restoring original materials while maximizing their preservation, stabilizing the internal microclimate in terms of humidity, creating optimum conditions for the natural drying of residual structural moisture and, last but not least, ensuring the mode of future operation with minimal effect on changes in the internal microclimate. Due to the historical value of the building and its layout, it is possible to use forced air treatment only to a limited extent, and great emphasis must be placed on addressing this issue by using the natural physical properties of air and phenomena involving its natural flow and controlled temperature exchange between spaces.

The Influence of Civil Works on Heritage Architecture, El Vergel, Cuenca - Ecuador

Scipedia content — Tue, 30 Nov 2021 14:52:36 +0100

In urban and rural areas of the Andean cities of Ecuador, construction based on earthen technologies has been an important alternative, which are carried out through ancestral customs, such as the minga, which benefit the cohesion of the community. Against this background, the World Heritage City Project of the University of Cuenca (Ecuador) has since the year 2011 undertaken interventions in heritage buildings inspired by the minga, so called Maintenance Campaigns, where the collective efforts of various actors (community, academy and organizations) are joined to recover buildings in highly vulnerable heritage neighborhoods, promoting preventive conservation, maintenance and monitoring of vernacular buildings.
The fourth campaign, which was carried out in 2018, took place in the Las Herrerias Street in the historical El Vergel neighborhood of Cuenca, a World Heritage City since 1999. The methodology applied in the previous campaigns was essentially maintained, gaining experience and innovating at every opportunity. As a special aspect, the Las Herrerias Campaign was characterized by the existence of buildings with structures that were already affected by civil works previously carried out, such as re-pavements, drinking water installations, various services, etc.
This research proposes to establish conservation strategies of vernacular heritage buildings and to mitigate the effects of poorly carried out civil works. The buildings intervened in the 2018 campaign are taken as reference, specifically those whose damages are the result of civil works. First, a review of bibliographic sources is undertaken to reveal historical data about the neighborhood and the civil works that have been carried out. The research continues with a diagnosis of the condition of the buildings before the Maintenance Campaign. Next, the daily maintenance records and the experience of the participants of the Campaign are investigated to identify and analyze those buildings affected by bad civil works practices and their impact on the damages of their structures. Subsequently, the condition of the buildings after the Campaign is evaluated.
Finally, strategies are proposed that must be considered for the interventions of vernacular heritage architecture, built with traditional earth and wood systems. Furthermore, civil works guidelines are defined for these types of interventions. Accordingly, the preservation for future generations of the wealth of material as well as immaterial heritage is encouraged.