Scipedia: Documents published in 2018

Viscoelastic models in green composites from PLA and hazelnut shell fillers with a natural plasticizer from epoxidized linseed oil

Scipedia content — Thu, 31 Mar 2022 20:36:29 +0200

In a same way to polymeric materials, some composite materials as it is the case of green composites, are characterized by a viscoelastic behaviour which plays a key role in their mechanical properties with time. The use of some engineering materials could be restricted as their mechanical properties could be highly affected by temperature or time. For this reason, this work is focused on the modeling of the viscoelastic behaviour of this biomaterial composite with a biobased polymer matrix from poly(lactic acid) and a lignocellulosic reinforcement/filler coming from hazelnut shell with different plasticizer content. In particular, a biobased plasticizer, namely epoxidized linseed oil (ELO) has been employed. A first approach to the viscoelastic behaviour of these composites is summarized in this work. The Maxwell model considers a series combination of the elastic reponse (represented by a spring) and the viscous contribution (represented by a dashpot). The Kelvin-Voigt model considers the same physical elements (spring and dashpot) but coupled in parallel. As these two basic visceolastic models show important restrictions regarding the real viscoelastic behaviour, this work also considers a series combination of the Maxwell model and the Kelvin-Voigt model, known as Burgers model. This works focuses on determining the different parameters of the Burgers model to fit experimental data from PLA-hazelnut shell flour biocomposites with varying plasticizer (ELO) content.

Weight optimization in composite fibre reinforced plastic fairings

Scipedia content — Thu, 31 Mar 2022 20:36:20 +0200

This abstract describes the weight optimization process followed by ALESTIS AEROSPACE in a secondary faring structure, designed and manufactured in composite material, focused in detail in the Belly Fairing structure of the A350 XWB A/C. The obective of this abstract is to enumerate and to decribe the weight optimization processes of this kind of structures, vieweing in detail following aspects: Optimum floatability definition in the joint between panels and structure Optimum design in sandwich panels Method to obtain out of plane loads for the joint between sandwich panel and structure Allowable determination for CFRP structure, based on finite element models correlated with mechanical tests It is also described in ths abstract the process followed to obtain test allowables and the methods developed to perform the weigth optimization in panels. Results obtained evidence that the Certification requirements are fulfilled for the complex design of a fairing such as Belly Fairing from A350XWB, manufactured with carbon fibre meterial with an optimum weigth.

Fatigue behaviour against delamination under mixed-mode I/II and ADCB test of a carbon/epoxy composite material

Scipedia content — Thu, 31 Mar 2022 20:36:10 +0200

Some composite morphologies are susceptible to loss of capacity due to the presence of interlaminar delaminations. The objective of this work is to experimentally evaluate the generation and propagation of these interlaminar cracks in a carbon-epoxy composite subjected to dynamic stress under mixed fracture mode I / II, using an ADCB type test methodology for this purpose. From a previous static characterization of the material the critical value of the energy release rate was obtained, from which the levels of the critical energy release rate to be applied in the fatigue tests were defined, the values considered were: 45, 50, 55, 60, 65, 70 and 75% Gcr. In all the dynamic tests, an asymmetry coefficient of R = 0.1 was used. From these experimental data the fatigue initiation curves DGN (number of cycles necessary for the nucleation of a crack, for a given rate of energy release) were obtained, observing fatigue life limits of the order of 38% of Gcr . In addition, the crack propagation velocity curves da / dN-G were shown, which showed the trend of the Paris law. On the other hand, a fractographic analysis of the delaminated surfaces was carried out, showing the typical fracture typologies of both modes, I and II, both in the initiation and propagation of the crack, showing the presence of mixed mode I / II in the ADCB type assay.

A stiffness-based phenomenological model to predict the fatigue life of unidirectional CFRP laminates under tensile fatigue loadings

Scipedia content — Thu, 31 Mar 2022 20:35:59 +0200

Fibre-reinforced composite materials can withstand large number of loading cycles compared to traditional materials. However, predicting the damage progress and strength loss in a composite structure due to fatigue is difficult because of the complex interaction of different failure mechanisms. This work investigates the decrease in the stiffness and strength in a high-performance undirectional CFRP laminate subjected to on-axis fatigue loads. A stiffness-based phenomenological model is proposed in order to evalute the damage growth due to fatigue through the longitudinal stiffness degradation. Assuming that the laminate ultimate strain is independent of the distributed damage caused by fatigue, the residual strength model can be deduced, or its integral form, the S-N curve. Thanks to this assumption, the residual stiffness model is related to the residual strength model, and thus it has reduced the experimental characterization of phenomenlogical-based approaches. The accuracy of the model is verified by comparing the experimental data against the derived S-N curves.

Accelerated fatigue life diagram characterization of CFRP

Scipedia content — Thu, 31 Mar 2022 20:35:36 +0200

There are several ways to obtain the fatigue life behavior of composite materials, such as the application of classical theories or complex progressive damage models. Recently, constant life diagrams have demonstrated good effectiveness in predicting the fatigue life of CFRPs. Nevertheless, the large number of tests required, and the time necessary for the characterization, makes this method very expensive in terms of time and resources. The aim of this work is the evaluation of accelerated characterization techniques in addiction with statistical methods, to obtain constant fatigue life diagrams of CFRPs, with a reduced number of tests and a shorter characterization time. The results show that, combining universal and accelerated testing techniques with statistical methods, it is possible to obtain constant life diagram for the whole range of tension-tension, tension-compression, and compression-compression loading modes, with a reduced number of tests. Moreover, it is observed that, the accelerated characterization techniques show a fatigue life limit similar to the conventional ones.

Mode III dynamic fracture performance of carbon-epoxy laminates

Scipedia content — Thu, 31 Mar 2022 20:35:25 +0200

The aim of this work is the development of a new test methodology for the characterization of delamination of composites under mode III of fracture and dynamic stress (fatigue). The phenomenon of delamination is one of the main failure mechanisms in composite materials configured by stacking several layers. The mode of fracture that has been studied is mode III to fatigue, with the difficulty that its simulation implies. The test device employed, which allows subjecting to the laminates to this loading mode, has already been previously tested in static tests. Characterization tests were performed on two different materials, both with different matrices and carbon fibers. An analytical model developed for the case of static fracture has been used and a statistical analysis of the results obtained has been carried out. A fractography of the fracture surface was also performed in order to determine the characteristics of this type of fracture in a dynamic regime.

Mode II cohesive law of adhesive joints

Scipedia content — Thu, 31 Mar 2022 20:35:14 +0200

A novel method is presented for the determination of mode II cohesive law for the characterization of delamination in thin adhesive joints The proposed method is based on the three point end notched flexure test. The data reduction method used is the Beam Theory including Bending Rotation effects method (BTBR), which includes the effect of local deformations, shear and bending rotations. By this method, the initial crack length, the apparent crack length during the crack advance, and the mode II resistance curve are determined. The relative shear displacement at the crack tip is determined as a function of the apparent crack advance that occurs when the generation of the fracture zone progresses. In order to determine the shear displacement an analytical analytical model based on the classical theory of beams is used. Finally, the fracture toughness versus the shear relative displacement is represented and the cohesive law is determined by numerical derivation.

Numerical analysis of composite-composite bonded joints. Fracture toughness determination

Scipedia content — Thu, 31 Mar 2022 20:35:01 +0200

Nowadays, the use of composite materials in primary structures has considerably increased, in particular in what refers to primary structures and bonded joints. Thus, numerical tools and experimental tests have to be implemented in order to understand failure modes and critical loads in this kind of structures. Usually, bonded joints quality is tested based on the interlaminar fracture test DCB (G1c). Nevertheless, these tests have some limitations. The aim of the present study is to create a feasible and accurate numerical model which allows the quality of a bonded joint as function of the peeling load to be determined. The idea is then an actual alternative to offer in-situ test by means of a transportable and easy to use device. In this study, a research analyzing two tests able to identify the quality of a bonded joints, as an alternative to the interlaminar fracture test, based on a classic peeling test on carbon laminates, is presented. The numerical simulation is based on a Finite Element Analysis using the commercial software Abaqus®. Onset and propagation of adhesive damage is taken into account by means of a cohesive zone model. A virtual test of the peeling test is done and its behavior is compared with the experimental results from an extensive laboratory test campaign. Numerical results will allow us to verify the feasibility to compute the value of G1c from experimental results.

Analysis of the tufting process, an alternative to suppress delamination. A mesomechanical approach

Scipedia content — Thu, 31 Mar 2022 20:34:52 +0200

Among the numerous strategies available for suppressing/decreasing delamination of laminated composite materials, the current work is focused on the tufting process. A literature study is carried out to underscore the advantages of this technology over alternative manufacturing techniques. The current paper presents with a mesomechanical composite modeling approach, based on a MMF (MicroMechanics of Failure) micromechanics scheme. The type of composite material analyzed here is a conventional ply laminate tufted along its thickness. In terms of mesomechanics, a new unit cell is described and formulated. In order to assess the accuracy of the current approach, three theory-experiment correlations studies have been carried out, the results obtained being quite accurate.

Influence of the particle geometry in reinforced epoxy resins

Scipedia content — Thu, 31 Mar 2022 20:34:41 +0200

In this work the mechanical behaviour of a epoxy resin reinforced with small particles has been studied. This study has been carried out by means of Finite Element Modelling (FEM). A number of models have been prepared with different volume fractions of particles and different particle geometry. The particles had different thickness to surface ratios. These particles were randomly distributed in the matrix with main surfaces parallel to the loading direction. In this study it was found that, as the thickness to surface ratio decreases, the stiffening effect of the particles is more effective. This behaviour was observed for all volume fractions studied. On the other hand, in mechanical tests carried out in parallel experimental programs it was observed that the addition of degassers and reducers of surface tension in the manufacture of the test pieces had an appreciable effect on the final mechanical properties. Due to this, the influence of the porosity on the aparent elastic modulus of the resins was also modelled.

Novel Discrete Multiscale Model (DM) for non-linear analysis in composite materials

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

In recent years, the study of the behavior of materials at the microscopic level has increased significantly in terms of design of high-performance materials. Despite recent advances in high-performance computers, the application of multiscale numerical methods to simulate large structures still requires prohibitive computational costs. The purpose of this work is to provide a procedure capable to predict the nonlinear mechanical response of composite materials under monotonic incremental load to reduce the computational cost required for the numerical analysis of complex structures. The solution of the macroscopic problem through the first order multiscale method (FE2) will be replaced by a Discrete Multiscale Model (DM) characteristic of the Representative Volume Element (RVE). Through the definitions of an equivalent damage parameter (deq), function of the global stress at the microscale, a series of virtual tests in deformation control will be carried out, storing the stress-strain state reached by certain levels of deq in a Database. Analyzing the evolution of the fracture in the composite materials can be observed as the non-linear regime is reached only in some elements of the structure. Therefore, a procedure, the Discrete Multiscale Threshold Surface (DMTS), in which the RVE analysis is used to obtain the surface at which the damage begins (deq>0) is proposed. This law allows to know if for a certain stress-strain state the material has damaged, without needing to solve the micro-model. Once the damage is initiated, it is proposed to generate an RVE only at the integration points that have been damaged. This work will demonstrate how the FE2 method can be replaced by a Discrete Multiscale Model, representative of the composite material, obtaining significant computational improvements.

Application of the Stiffness-Force method in the analysis of the fiber-matrix adherence in composite laminates

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

This work shows the analysis of the adherence of a fiber embedded in the matrix by the Stiffness-Force method (SFM) in Finite Elements. The formulation of the SFM method takes into account not only the equilibrium equations but also the compatibility conditions, obtained from the principles of the virtual work and complementary virtual work. For the finite element analysis using the SFM method a user subroutine (UEL) of a four node axisymmetric quadrilateral element has been formulated, and has been implemented in the commercial code Abaqus. In a first step the specimen has been analyzed by Abaqus, which uses the stiffness method in its formulation. Then the same model has been analized by the user subroutine which uses the SFM method. Finally, the results obtained by both analysis have been compared with varying degrees of discretization.

Micromechanical study of the Scale Effect on composite material laminates

Scipedia content — Thu, 31 Mar 2022 20:34:09 +0200

From the beginning of the application of composite materials, different theories to predict their behaviour and failure have been developed. The authors have already made a previous study, analyzing at the macroscopic level (both from an experimental and theoretical point of view), the failure of non-conventional laminates changing the thickness of the laminas that form it, in order to evaluate the “scale effect” (also known as “in-situ strength”) present in them. Results of this study proved the strength variation of the laminate with its configuration (scale effect) and it was found that the presence of laminas with fibres oriented in the direction of the load diminishes this effect. This paper is focused on the understanding of the aforementioned effect, conducting a study at micromechanical level (the level where the damages leading to the failure are generated) of the scale effect with an energetic approach, in order to progress in the understanding of this phenomenom. To this end, the Boundary Element Method (BEM) has been used. It has been applied to a laminate model with [0, 90n]S stacking sequence, where the influence of n at different stages of the generation and progression of damage has been studied: the beginning of the damage (that takes place when the debonding between fibre and matrix happens) and during the change of direction of the debonding crack towards the matrix (kinking). The models developed are multiscale, involving a mesoscale representation of the laminas of the laminates (modelled as homogeneous) and with micromechanics cells that simulate fibre and matrix and therefore with the capacity for collecting information about damage mechanisms observed experimentally.

Micromechanical experimental study on the inter-fibre failure under tension: Microscopical observations

Scipedia content — Thu, 31 Mar 2022 20:33:57 +0200

The study of the matrix/inter-fibre failure at micromechanical level by means of numerical methods predicts the appearance of differents stages in the development of this mechanism of damage; these numerical studies have also allowed the main features of each stage (such as the debond length at the interface and the kinking angle) to be identified. The development of experimental studies aiming to check the relevance of the aforementioned numerical results, the validity of the hypotheses assumed, as well as the identification of additonal parameters, is crucial for the advance in the knowledge of this mechanism of damage. Based on this, the research shown in this work focused on the tensile test (under different loading levels) of specimens manufactured from carbon-epoxy cross-ply symmetrical laminates. The microscopical observation of the 90º laminae of the tested samples, first results in the analysis of the appearance of the transverse cracks as a function of the load. Second, the study concentrates in the identification of the previously numerically predicted stages of the mechanism of damage and the measurement of key parameters such as the debond length, the kinking path and the influence of nearby fibres.

Wrinkle detection in carbon and glass fibre laminates using ultrasonic non-destructive evaluation

Scipedia content — Thu, 31 Mar 2022 20:33:43 +0200

Wrinkles (out-of-plane fiber waviness) are, unfortunately, a common phenomenon during the manufacture of composite materials. Because these internal defects affect the mechanical properties, all composite structures are inspected in order to ensure they meet the high quality standards that are demanded by the industry. During the desing process, parts are generaly oversized to mitigate the risk of undetected wrinkles and defects. Delaminations are widely characterized using traditional ultrasound techniques whereas wrinkles have traditionally been more difficult to detect using such techniques. This is due to the fact that wrinkles don’t represent a change in material density or a strong boundary for the elastic wave. The aim of this work is to detect and characterize wrinkles in thick laminates of composite material using ultrasonic non-destructive tests. Different parts with induced wrinkles have been inspected with ultrasonic techniques. The ideal frequency to perform the inspections was determined using an analytical model in MATLAB. The amplitude of the wrinkles was measured visually on the samples and compared with compared with the ultrasonic measurements to determine the accuracy of the proposed method.

Characterization of thermal protection elements for composites materials through thermal analysis

Scipedia content — Thu, 31 Mar 2022 20:33:28 +0200

Highest level automotive competition is one of the sectors that takes the materials to the limit of their specifications in their commissioning, creating in this way knowledge in new technological fields. An example would be the use of structures made in CFRPs in competition, being gradually movin on the general automotive industry. The objective of this work is to determine the effectiveness of thermal protection elements that have to be installed in those structures of vehicles manufactured in CFRP exposed to high temperatures, such as pontoons covering the power unit and its exhaust manifolds, treating to discriminate which of them offer better protection at the lowest possible weight. In this work, 3 different protection systems have been evaluated, subjecting them to 3 types of tests, such as adhesion, weight and effectiveness of thermal protection. The method described here has made possible to evaluate the different efficacy of the systems tested, yielding additional data on the weight, adhesion and cost of the protection system.

Optical fibre based sensors application to structural health monitoring in composite materials

Scipedia content — Thu, 31 Mar 2022 20:33:14 +0200

Structural health monitoring (SHM) by means of embedded fibre optic (FO) sensors is able to perform diagnosis and prognosis of structural damages and defects. SHM system monitor structural status based on the acquired data resulting in the detection and characterization of damages and defects without necessity for the aircraft to be on ground. Optical fibre sensors are permanently installed in the structure and trigger maintenance actions only when a damage or defect of a particular size is detected. To demonstrate the potential of FO sensors technology and their application by means of embedded sensors to composite material aerostructures, manufacturing trials have been performed and the influence in mechanical behaviour of the sensors’ embedding has been studied by performing tests campaings, at coupon level, for experimental validation. This study is within the scope of SHERLOC, a project belonging to the Clean Sky 2 JU aeronautical research and development program, and of which main objective is to combine advanced Structural Health Monitoring (SHM) and smart repair technologies with a probabilistic design philosophy, and hence to develop new maintenance concepts to reduce the direct operative costs without lowering the operational safety of a composite fuselage.

Manufacturing and characterization of graphene oxide reinforced composites

Scipedia content — Thu, 31 Mar 2022 20:33:01 +0200

The present work focuses on the mechanical characterization of polymer matrix composites reinforced with graphene oxide (GO) nanostructures. Firstly, the selection of the polymer matrix, the parameters for performing a proper curing and the fabrication of the composite material are carried out. The proposed procedure results in an adequate dispersion of the GO, without the need for solvents, which positively influences the mechanical properties of the resulting material. The epoxy resin selected as matrix is reinforced with different percentages of GO in order to study the influence of the reinforcement on the apparent mechanical properties. The composites obtained using such nanostructures are characterized by compression and three-point bending testing. Through the use of the Digital Image Correlation (DIC) technique is possible to evaluate the strain state of the material during the tests. This behaviour is combined with the analytical estimations developed to take into account in the results of the bending testing the difference of the tensile and compressive elastic properties of the material. In addition, numerical simulations are developed by applying both the Finite Element Method (FEM) and the eXtended Finite Element Method (XFEM) whose results are used to validate the experimental data and the analytical model.

Influence of the ply thickness and the stacking sequence on the edge stresses of quasi-isotropic symmetric laminates

Scipedia content — Thu, 31 Mar 2022 20:32:53 +0200

An analytic approach for determining interlaminar stresses in rectangular [θ/-θ]s laminates subjected to an axial load has been adapted to the case of [θ1/θ2/θ3/θ4]s laminates. The coupling effects of each part of the laminate are compensated by the adjacent parts. In a first step, a half of the laminate is considered for determining forces and moments per unit length that prevent the global deformation of the whole symmetric laminate. Then, interlaminar stresses are computed applying the stress equilibrium equations and imposing the continuity of the stresses in the layer interfaces. The influence of the ply thickness and the stacking sequence of the laminate on the edge effect is analyzed by the analytical approach.

Analisys of interlaminar stresses in composite laminates by finite difference method

Scipedia content — Thu, 31 Mar 2022 20:32:43 +0200

In this work, full stress tensor components regarding stress state for a simmetrical composite laminate under uniform uniaxial extension have been determined. Off-plane stresses are specially meaningful due to the fact that they are responsible for failure mechanisms such as delamination and shear stress cracking. A finite difference scheme has been used to solve internal equilibrium equations subjected to stress-free boundary conditions along boundary lines; moreover symmetry considerations have been made. In such way, we get an improvement in solutions in contrast with results obtained following bidimensional reasoning and using laminate based elements. Off-plane stresses for differents ply-sequences have been evaluated and maximum and minimum values for different fibers orientations were explored.

Study of the bending test, in two spans, of sandwich structures

Scipedia content — Thu, 31 Mar 2022 20:32:33 +0200

This paper presents a study of the flexural test, simply supported and two spans, necessary to establish the acceptance criteria of a sandwich panel of faces derived from wood, subjected to uniform load. Tests have been carried out on sandwich panels with CE marking and all of them have passed the European Technical Approval (ETA) evaluation process for the use for which they are specified. The results obtained in the experimental tests have been compared with analytical models and with finite element models. It has been observed that the finite element models coincide with the experimental results as long as the properties of the constituent materials of the sandwich panel are accurately known and the boundary conditions are suitably modeled. The analytical model also matches the finite element model when ideal supports are modelled.

Flexion in composite materials with different tensile and compressive response

Scipedia content — Thu, 31 Mar 2022 20:32:20 +0200

An analytical and experimental study of flexural testing on laminates formed by layers of unidirectional carbon-fibres pre-impregnated with an epoxy resin is presented. Among other stacking sequences, the configuration comprised by groups of ±45° is of interest in the transport industry in which often there are structural parts subjected simultaneously to bending moments and shear forces. Having as a reference the three-point flexural testing, the work is focused on taking into account the different response of the material under tensile and compressive loads. From the experimental point of view, the damage initiation and evolution of the material are proposed to be visualized by means of optical methods and microscopy techniques, comparing the experimental observations with the analytical estimations. The analytical model used is based on the technique of homogenized section and it allows to predict the initial failure mode that will occur experimentally depending on the thickness of the specimen.

Optimization of a resin with carbon nanotubes ink for printing by Inkjet technologies

Scipedia content — Thu, 31 Mar 2022 17:52:27 +0200

The main aim of this research is the development of a nanoreinforced thermosetting resin based ink to be used in injection printers for additive manufacturing processes. (inkjet tecnhnologies). Firstly, printing conditions have been optimized for the nanoreinforced epoxy resin at different MWCNT contents. Afterwards these inks have been used to print 2D circuits based on joined parallel straight lines. These printed materials were tested to evaluate their mechanical and electrical properties. MWCNT reinforced epoxy resin inks developed resulted in successful injection to produce the 2D circuits repetitively. The dispersion of the MWCNTs in the epoxy resin is adequate and the circuits containing 0.3 wt.% of nanoreinforcement were electrically conductive. Mechanical properties were similar for both materials.

Coated profiles in line: pultrusion process optimization (COALINE project)

Scipedia content — Thu, 31 Mar 2022 17:52:18 +0200

Composite profiles processed by pultrusion are replacing metallic profiles in sectors like building or automotive, due to two interested properties: lightweight (the gas consumtion of the vehicle will be reduced) and corrosion resistance. However, if the profile needs to be covered in order to achieve aesthetic properties or new functionalities, several drawbacks arise (high labour content and VOCs and small particles emissions), limitating its competitivness versus profile metals. In this work the results of COALINE project are described; pultrusion process has been enhanced achieving a coated profile inside the mould (with a gelcoat or a primer) thanks to the development and integration of a sensor system (needed to adjust the curing degree of the resin in each stage of the process), a MW technology curing (to faster the curing time of the resin and shorten the lenght mould) and a modular advanced die design. Two moulds have been manufactured and a covered profiled obained in-line has been achieved for the building sector. For the automotive sector a case study cargo bed has been manufactured using profiles covered with the primer and joined with an adhesive with debonding capability to provide a simple repair or recycling at the end life-cycle.

New composite fuselages manufacturing processes

Scipedia content — Thu, 31 Mar 2022 17:52:06 +0200

The present document describes a new concept of composite fuselages manufacture, oriented towards the minimization of manufacturing costs through the generation of a monocoque fuselage structure, that allows to reduce the number of rivets and also the components joining operations, by means in addition of a process that avoids the use of molds, finally producing a lightweight and adaptable structure. The process in turn facilitates a high level of automation in the manufacture of composite fuselages and opens the door to a greater acceptance of this application in the aeronautical sector. The document outlines the design of the manufacturing process and the implementation of that particular production process for the manufacture of a real-scale concept demonstrator within the MTorres facilities, showing the reduction of the production cycle and the general manufacturing costs based on the simplification of the structural design and the integration of components into just one piece. Other additional variables that can benefit the reduction of costs and cycle times of the production process are also evaluated.

Process for manufacturing carbon fiber composite structures by membrane-assisted compression molding

Scipedia content — Thu, 31 Mar 2022 17:51:52 +0200

The main objectives of this research work are to find new ways of reducing costs in the manufacture of composite materials, automate processes and improve energy efficiency by looking for alternatives to the use of autoclave, always meeting the quality requirements. For this, an out of autoclave curing process is studied through an innovative system of automatic and fast curing of composite parts for the aeronautic, automotive and construction sectors. The process allows the curing of prepregs of various materials and geometries. The process includes the provision of temperature by heating plate with electric resistances, pressure and vacuum adjustable through an air compressor, and cooling through circuit through mechanized plates. The main innovative feature of this system is the pressure supply with compressed air to the piece by means of a moldable and reusable silicone membrane, which allows to extend the field of study to complex elements saving the current limitation of hot plates presses, and without the need to place countermold. CFRP cured parts are manufactured in this new system, then their properties are compared with autoclave cured parts and similar properties are obtained, and auxiliary materials are considerably reduced. It can be concluded that this system improves energy efficiency, reduces costs and optimizes times.

Automated manufacturing process for omega stringers with high curvature

Scipedia content — Thu, 31 Mar 2022 17:51:42 +0200

This document describes an innovative manufacturing process for the production of omegas with high curvature. Starting from the shape of an omega in plane, the geometry of an omega with high curvature is obtained in a second manufacturing process, without appearance of wrinkles. With this manufacturing process, curved shapes that are currently made manually can be automated, with the consequent benefit of: Highly repetitive process. Great quality. Easily automated. Recurring cost reduction and Lead Time. This work shows the initial process of obtaining the omega with curvature, to later describe the final process easily industrializable, and the tests performed to validate the process. Although the work focused on obtaining an omega curve, it is easily extrapolated to other configurations, such as Z-frames.

Mechanisms of air removal and void development in Out-of-Autoclave processing of laminates

Scipedia content — Thu, 31 Mar 2022 17:51:30 +0200

This study aim at understanding the void formation, transport mechanisms and porosity evolution during OoA consolidation process. The laminates were conformed by stacking and compacting of prepregs by two different technologies: manual (Hand lay-up, HLU) and automatic (Automated fiber placement, AFP). Subsequently the laminates were cured by the vacuum bag only (VBO) technique in an industrial oven at atmospheric pressure. The porosity characterization was performed using ultrasound and x-ray tomography technologies at different stages of the cure cycle. Ultrasonic inspections showed that the porosity is heterogeneously distributed, where the higher volumetric fraction of pores is located in the center of the laminate. X-ray tomography provided three-dimensional (3D) information of samples of the laminates and it allowed a quantitative and qualitative study of the pores within the tows of fibers and the porosity located between the layers of prepregs during the curing process. The prepregs designed for out of autoclave are partially impregnated in such a way to provide air evacuation channels in the fiber tows. The porosity of these channels was efficiently extracted and a volumetric fraction of pores entrapped between layers were evacuated during the curing process. The behavior of the evacuation channels and the porosity evolution for both stacking technologies were compared. An analytical model of the evolution of a pore was also developed.

Characterization of new generations of out-of-autoclave prepregs (OoA)

Scipedia content — Thu, 31 Mar 2022 17:51:19 +0200

New generations of out-of-autoclave prepregs, also known as VBP (vacuum bag only) are achieving a high maturity level that would allow the composite manufacturing with autoclave quality. These materials are characterized by its capability to allow air evacuation and minimize the presence of defects before its complete polymerization. To do this, it is necessary to control the factors which govern the phenomena that occur within it, such as compression, resin flow and void growth processes. Additionally, it should be considered fibers and resins properties, and curing cycle parameters such as temperature, vacuum quality and duration. In this work we have studied comparatively conventional and OoA prepregs.To do this, several panels have been laminated using hand lay-up method and cured only using vacuum bag and without autoclave pressure. Then, the panels have been characterized by optic microscopy, ultrasonic inspection and mechanical standarized tests. The results show that out-of-autoclave prepregs are achieving similar qualities to the conventional prepregs. Having completed this stage, new research and developments should be focused on, among other issues, guaranteeing manufacturing processes robustness and optimization of bigger structures with complex geometries.

Finite Element modelling of thermal deformations in composite aeronautical structures

Scipedia content — Thu, 31 Mar 2022 17:51:08 +0200

A comparative study of four different finite element (FE) models is presented, to determine the thermal deformations in a typical aeronautical structure. A detailed FE model with solid elements is used as a reference to determine the accuracy given by three FE model with shell elements. The component consists in four planar laminates with (relatively small) curved zones at the joints. The analysis shows that a correct modelling of the curved laminates is needed for obtaining accurate results. If the FE model with shell elements ignores the existence of the curved zones, as is typically done in models used for stress calculations under pressures and loads, unsatisfactory results are obtained. Precision is not significantly increased if the curved zones are modelled in detail and the properties of the shell elements are defined as in the planar zones. For this reason, a technique for modifying the in-plane thermal properties of the elements modelling the curved laminates, that forces them to follow the same shape changes observed in the real curved laminates is presented. The FE model with shell elements obtained with this technique provides the same accuracy than the FE model with solid elements, with a significantly lower computational cost.

Industry 4.0: Materials and CFRP manufacturing process control through digital laboratory

Scipedia content — Thu, 31 Mar 2022 17:50:58 +0200

Aerospace industry is well known to be one of the most demanding sectors to work with. It is strongly normalized, monitored and audited on behalf of airworthiness. In this scenario, continuous improvement is a must, to comply not only with requirements, but also lead times and costs. TITANIA, one of most recognized materials testing labs working for aerospace, moved to a tailor-made integral management system to deal with the high volume of data they deliver to their customers. After a two years effort, now is exploiting its results by offering better lead time compliances, robust test reports and new data analysis services. Digital transformation has pushed TITANIA into Industry 4.0. This paper presents the followed methodology and the first results obtained.

Simulation based design of single-shot RTM process for an integrated aircraft door structure

Scipedia content — Thu, 31 Mar 2022 17:50:46 +0200

One of the advantages of resin transfer moulding (RTM) is the ability to manufacture in one single step (one-shot) integrated structures having complex geometries resulting in a lower number of parts and reduced assembly costs. However, the design and optimization of the process and the associated tooling can be particularly challenging. This paper presents the approach for the production of a stiffened aircraft door structure using a single shot RTM process In this case, the simulation of the process is a necessary step to accelerate and reduce the cost of the development phase, providing rapid solutions for testing the preliminary design options, as well as refined analysis for process and mould optimization, and final design checking. The processing development has consisted of a complete material characterization and modelling followed by mould filling and curing simulations with PAM-RTM software. The results have been used to optimize the design of the mould and the RTM manufacturing process parameters. The paper also presents the results of the manufacturing of prototype components that validated the design obtained by the analysis.

Optimization of the CRTM process by means of monitoring techniques

Scipedia content — Thu, 31 Mar 2022 17:50:34 +0200

In this work the feasability of the monitoring system, composed of flow-rate and injection pressure sensors, in addition to the pressure sensors integrated in the mold, is demonstrated to determine the optimal process window of the CRTM (Compression Resin Transfer Molding). The sensors of the injector allow monitoring of the injection phase, while the pressure sensors integrated in the mold allow the phases of the compression and the curing to be followed. In order to relate the pressure sensor variations with the curing phase, an electric current sensor has been used. The increase of the resistance, associated with the beginning of curing, corresponds in time with the pressure drop, which in turn is justified by the contraction generated during curing. This pressure drop reaches a horizontal asymptote which corresponds to a conversion rate of 40%. Based on this behavior of the pressure sensor, it is possible to determine the minimum time for the demoulding of each of the pieces. Finally, the system has been used to monitor the manufacturing of prototypes with curing temperatures between 80-120 ºC, and it has been confirmed that the sensors identify the parts that are inside the process window and those that are not.

Development of preforming and RTM processes for highly integrated structures

Scipedia content — Thu, 31 Mar 2022 17:50:22 +0200

Landing gear doors / traps are usually composed of sandwich structures manufactured by hand lay up and cured in autoclave. In the present development, this type of construction and its associated manufacturing process have been replaced by a monolithic design manufactured by liquid composite moulding. Specifically, the selected process has been RTM (Resin Transfer Moulding) in a single process of impregnation / curing (one shot) with the objective of eliminating subsequent operations. In order to obtain a 3D integrated preform close to the final shape, pre-forming processes have been developed for the sub-elements of the part (skin, double T stiffeners, C stiffeners, etc.) as well as the processes of integration of the various preforms until obtaining an integrated preform. The preforming and manufacturing processes have been fully validated by obtaining real-size prototypes of the target part. This work is included within the ATEAERO project, with the support of the ETORGAI program (SPRI - Basque Government).

3D printed RTM prototype-moulds

Scipedia content — Thu, 31 Mar 2022 17:50:07 +0200

In the present work the feasability of 3D printintg, more specifically the FDM (Fused Deposition Modeling) technology, to manufacture moulds of RTM in the phase of prototyping has been demonstrated. The upper part of the mould for a side-intrusion bar of a front door of a car has been manufactured, since the bottom mould is the original metallic. Printing of the mould took 104 hours and 3.8 kg of plastic were used. For the employed PLA, it has been established that up to 5 mm thick the translucency is sufficient to observe the resin flow pattern during injection. In order to increase the rigidity of the mold, different geometries of vertical reinforcements have been analyzed by means of finite element simulations. Finally, the honeycomb-like structure has been selected. At the stage previous to the injection, when the vacuum is made, the presence of the glass fiber preform reduces the displacements measured at different points on the mould. Additionally, the tightness has been good even without applying any kind of surface treatment. However, when the resin is injected the intrinsic stiffness of the mould has not been sufficient to limit displacements and to make a good piece. This has been solved by using a 30 mm thick methacrylate plate to stiffen the mould, which in turn allows the visualization of the flow through the mould.

Modelling and predictive control for a RTM mold

Scipedia content — Thu, 31 Mar 2022 17:49:52 +0200

The objective of this work is the control of a Resin Transfer Moulding (RTM) mold trying to obtain a temperature in the whole cavity as much homogeneous as possible. This is a complex process, mainly because of two factors: temperature distribution in a complex geometry and variability of the system parameters. In order to solve these difficulties, a design procedure based on models is carried out. Firstly, the detailed modelling of the thermal system, discretized and solved by means of finite elements (FEM) and validated by thermal tests in the physical mold. Then, a simplified reduced-order model (ROM) is obtained by means of ARX approach based on the former model. Finally, the design of a robust MPC (Model Predictive Control) which is able to take the system variability, the geometry complexity and the limitations of the actuation systems (resistances) into account. In order to afford the nonlinearities intrinsically present in the system, in addition to the controller, a perturbation estimator is implemented, which evaluates the changes produced in the mold with regard to the expected behaviour according to the ROM. In this way, the control system is able to detect the variations and compensate them in real time. These algorithms are validated both by simulation and experimentally. From this verification, it follows that the application of these modelling, estimation and control techniques allows to control the mold with temperature variations much tighter than for PID standard controllers.

About the study of compounds incorporating rubber tires

Scipedia content — Thu, 31 Mar 2022 17:49:41 +0200

In this paper we have studied some physical characteristics of gypsum composites incorporated with two different tire rubber granulometry. The experimental program was formed by the following tests: consistency (mini-slump), compressive strength and scanning electron microscopy (SEM). The rubber used in the composites came from the retreading of tires with 5 and 10% incorporation in relation to the plaster mass and the two different granulometry used were denominated thicknesses (# 0.6 mm) and thick (# 1.19 mm ). The results were compared with the control paste, in which there was no incorporation of rubber. The rubbers of different granulometry stood out in different points. The thin rubber presented a compressive strength close to the value observed in the control, with an addition of 5% by mass, which may be due to its adherence to gypsum paste, which occurred in a less porous manner and with a closer interface between the rubber particles and pulp, observed through the SEM. The thick rubber presented the best results in consistency, contributing to the workability of the pulp, which was also observed in SEM, where the thick rubber presents less adherence to the gypsum plaster, compared to the composite with incorporation of fine rubber. It was possible to affirm, then, that rubber as residual material presented interesting characteristics in applications in plaster composites.

Recyclable thermoset composites derived from waste textiles

Scipedia content — Thu, 31 Mar 2022 17:49:28 +0200

The idea of recycling waste materials from such different sectors as textile or automotive has been popular for decades, but today's recycling methods often produce poor quality products that are difficult to reuse. In the specific case of thermoset composites the problem is even greater, since once the resin is cured its dissolution is not possible and therefore the recovery of the original fiber and resin becomes practically unfeasible. This work presents recyclable thermoset composites made with fabrics obtained from waste textiles and epoxy or polyurethane resins, whose crosslinking is based on reversible bonds, which confers them the ability to be dissolved in a specific agent, so that both the fiber and the resin can be recovered for subsequent reuse. Taking into account the particularities of the starting raw materials, the manufacturing parameters of the composites and the resin dissolution conditions have been studied and optimized. The work is part of the European project Trash-2-Cash, which proposes a new model in which waste from paper and textiles are recycled chemically,in order to obtain fabrics with the same quality as the initial ones, to manufacture innovative products such as recyclable thermoset composites that can be industrially produced and recycled at the end of life.

Influence of surface treatment on strength and adhesion between flax natural fibres and a thermoplastic matrix

Scipedia content — Thu, 31 Mar 2022 17:49:17 +0200

Composites of thermoplastics reinforced with natural fibres have been widely used in recent years. Natural fibres are considered as a greener substitute due to their advantages over conventional fibres such as low cost, low density, high availability, excellent mechanical properties, biodegradability and to be environmentally friendly. However, they present an important limitation, the weak interaction between fibres and matrix. Therefore, surface treatments on natural fibres are very common in order to increase wettability and surface energy and thus to promote good fibre-matrix adhesion. The objective of this work is to study adhesion between flax fibres, under different surface treatments, and LDPE matrix. Pull-out tests were carried out with flax fibres yarns treated with low pressure plasma, atmospheric pressure plasma torch,silane coating and different alkaline treatments as well as with untreated fibres. Afterwards, composites materials were manufactured using unidirectional flax fabric and LDPE in a hot plate press. Finally, mechanical properties of each composite material were evaluated by tensile tests using an universal test machine. In this way, a greater interaction between LDPE and flax fibres can be compared with the final properties.

Development of New Thermosetting Resins from Polyethylene Terephthalate (PET) Wastes

Scipedia content — Thu, 31 Mar 2022 17:49:04 +0200

In an attempt to cover the needs and requirements of consumers, packaging without good recyclability is sometimes introduced in the market. This is more evident in the case of polyethylene terephthalate (PET). PET is a highly recyclable material that results in a recycled product with enhanced quality. However, there are other type of PET multilayered packaging that are being introduced in the market. These packaging products include additional materials such as other type of polymers, metals, paper, etc., as well as different type of pigments, colouring agents and impurities confering a critical colour to the packaging. When this new packaging arrives to the recycler it generates problems, resulting in low quality products or even rejected, being deposited in landfill. This implies an important environmental reduction (mainly in the CO2 emissions) and in the economic affairs. For this reason, the recycling companies and, in general, waste management companies, are interested in alternatives that allow these residues to have a viable outlet. This development is presented as a solution to the problem of these particular PET multilayered residues. The main objective is the industrial development of thermosetting resins (alkyds and unsaturated polyesters) that include in their composition materials obtained from the chemical recycling of these multilayered packaging, at an affordable price and with reduced environmental impact.

Cumare palm natural fiber biocomposite (Astrocaryum chambira) and bioepoxy resin, industrial applications

Scipedia content — Thu, 31 Mar 2022 17:48:55 +0200

This work is oriented towards the search of new materials friendly to the environment, for this the mechanical and thermal characterization of the natural fiber of Cumare (Astrocaryum chambira) was carried out by tensile and TGA tests, respectively. Subsequently, the biocomposite material was fabricated, using an artisan fabric made by the Tukano ethnic group of the Colombian Amazon, impregnated with bioepoxy resin using of the vacuum assisted resin transfer method (VARTM), obtaining in this way, specimens that were characterized by standards. The maximum tensile and flexural stress values of the cumare / bioepoxy biocomposite were compared with other composite systems with natural fiber, yielding values very similar to or higher than those reported by other authors. The values obtained in the validated the simulation for an industrial application of an interior opening handle for the door in a vehicle using finite elements. As a significant contribution in the present investigation, the cumare Colombian fiber is presented as an ecological alternative of low cost for the reinforcement of materials bicompuestos with industrial applications in the automotive sector.

Cross-WLF rheological modeling of a new composite material made with bioPE and Thyme

Scipedia content — Thu, 31 Mar 2022 17:48:43 +0200

Increased environmental awareness is driving the continuous search for new eco-friendly materials. Within the category of Wood Plastics Composites (WPC), a new "Green Composite" is proposed, whose matrix is a bio-polyethylene (bioPE) obtained from sugar cane and whose load, with reinforcing properties due to its fibrous structure, is Thyme, as a residue from the distillation of a liquor manufactured in a local company. Load concentrations of 10%, 30% and 50% %w have been studied. Since the polymers are processed in the molten state and the loads influence their visco-elastic behavior, it is necessary to know the rheological behavior of these new compounds, in order to evaluate their processability. The melt polymer viscosity is very sensitive to the temperature and the shear rate at which it is being processed. The Cross-WLF model, based on the experimental results obtained with a capillary rheometer, describes the rheological behavior of the materials, thus enabling the determination of the viscosity of these new bio-compounds under different conditions than those tested. In this way the processability of these new materials can be evaluated.

Reuse of CFRP material from Aircraft Manufacturing Parts. Industrial aplications and inverse logistic solution.

Scipedia content — Thu, 31 Mar 2022 17:48:34 +0200

The new Airbus A350XWB has the largest % of an aircraft primary structure elements made of composites ever. Thus, it has been a huge challenge to manage thousands of CFRP Tons per year in the part manufacturing plants, and consequently, several initiatives to reduce, reuse and recycle scrap material has been developed during last few years. Illescas Plant is introducing new processes to reuse and recycle CFRP material from wing covers and fuselage parts. Two initiatives are running these days: Reusing of CFRP (prepreg) end of spools and end of rolls to manufacture rowing for stringers that allows to decrease the purchased material in the Plant.

Recovering recycled carbon fiber by pyrolysis of cured prepregs

Scipedia content — Thu, 31 Mar 2022 17:48:22 +0200

Due to the rapid growth of the composite market, several European laws have emerged to minimize their environmental impact (EU 2000/53 / EC, End of life vehicles), as well as to make rational use of landfills (EU 1999/31 / EC). For example, in the aeronautical sector, composites can reach 50% by weight of the aircraft. Consequently, recyclability is a key issue. The objective of this work is the study of the recycling techniques of carbon fiber composites with thermoset polymer matrix in order to obtain fibers with similar properties to the original ones. In this way, the fibers could be reused in new composites by themselves or together with flass fibers in the manufacture of new hybrid composite materials. By this hybridization, materials with properties far superior to the GFRP would be obtained, but at much lower cost than the original CFRP. Therefore, this recycling and reprocesing strategies provides great economical attractiveness. The main objective of the project is to study and optimize the recyclability of cured carbon fiber / epoxy prepregs for use in hybrid materials. Starting from a pyrolysis in a controlled atmosphere reactor, followed by a oxidation, carbon fibers with properties similar to virgin fibers are obtained, with a loss less than 20% of the tensile strength. An evaluation of the different parameters of the recycling process has been carried out in order to optimize the procedure. The characterization of the fibers includes tensile tests, scanning electron microscopy and Raman spectroscopy.

Economic and energy benefit of a method for treating the vapors coming from the recycling of carbon fiber waste by pyrolysis

Scipedia content — Thu, 31 Mar 2022 17:48:11 +0200

The growing utilization of carbon fiber reinforced polymers (CFRP) in industry involves the generation of high quantities of this kind of waste. This tendency has fomented the investigation of different alternatives to recycle CFRP waste with the aim of reclaiming the carbon fibers, a material with high specific economic value. Among the alternatives, pyrolysis is the only one runnig at commercial scale nowadays. This process consists on heating the waste in an inert or oxygen-poor atmosphere, which causes the decomposition of the polymeric resin of the material and consequently the reclamation of the carbon fibers. The resin decomposes into organic vapors, which are normally incinerated and released to the atmosphere. The objective of this paper is to present the economic and energy benefit of a method for treating the vapors coming from the resin decomposition, through which high value chemicals can be obtained, avoiding the vapors incineration and emission. By means of this recently patented method a gas fraction with a higher energetic content than that of the vapors without treatment can be obtained. Besides, this gaseous fraction contains high quantities of hydrogen, which could be separated and sold. The commercialization of this hydrogen could increase 6 times the economic value of the gaseous fraction compared to the gas fraction without treatment.

Reuse of aeronautical uncured prepreg

Scipedia content — Thu, 31 Mar 2022 17:47:58 +0200

The content of this project is focused on the development of a process to reuse uncured A350 prepreg scrap obtained in production plants. The main aim is to reduce the current buy to fly ratio, which is the used raw material versus the material that will finally fly and, thus, to achieve clear benefits in terms of environmental aspects. The key properties of the new virgin material obtained after this reusing process have been evaluated in order to assess potential applications in aeronautical or other fields (e.g. automotive, sport, civil works…). Additionally, some aeronautical demonstrators or pilot cases with the reused material and process were produced. Regarding the key conclusions of this workt up to now: an effective process has been developed to reuse A350 uncured prepreg scrap, mainly mono-ply, based on chopping the prepreg to obtain a new virgin material, which will be used to produce a part by applying a compression molding process. Although the properties of the new raw material show high scatter, some of them stay close or even higher versus the reference (e.g. CAI). To end with, several aeronautical demonstrators with acceptable quality have been produced with the prepreg reuse process developed in this project (e.g. complex brackets, gaskets, manholes…).

Chemical Surface Treatments on aluminium films to prepare FML (Al-PP laminates)

Scipedia content — Thu, 31 Mar 2022 17:45:30 +0200

In this work, different type of surface treatments on aluminium films have been performed. The changes that these treatments produce in the nature, composition, functionality, morphology and free surface energy on the aluminium surfaces will be analyzed. First treatment has been performed in two steps, the first one consists on activating the aluminium surface with sodium metoxyde in methanol and the time and treatment conditions on the nature of the formed surface will be studied. The second treatment has been performed in three steps, so between the activation step and the sylanization, an intermediate treatment has been done in order to try to insert a polymer by "in situ" polymerization on the aluminium surface. Those treated aluminium film surfaces have been characterized using infrared spectroscopy by Fourier transform (FTIR), contact angle measurement, surface energy determination and Dynamic Mechanic Thermal Analysis (DMTA).

ZAero- Zero defect manufacturing of composite parts in the aerospace industry

Scipedia content — Thu, 31 Mar 2022 17:45:19 +0200

During the manufacturing process of a carbon fiber (CFRP) part in the aircraft industry defects occur. These defects are identified through inspections carried out in intermediate steps and even at the end of the manufacturing process. Due to these defects reworks need to be performed and even futilities. The aims of this project is the inline control of the defects that will be produced along the manufacturing of a stiffned surface panel. The ZAero control system consists on sensors integrated in the lay-up machine and sensors used during the infusion and resin curing processes. These sensors will detect defects that are outside the acceptance range and a response will occur. This response may be a rework as in the case of defects produced in the lamination stage or the variation of parameters produced in the infusion and resin curing stage due to the process monitoring. Three demonstrators will be manufactured. The degree of complexity will be increased in each demonstrator. The control system through sensors will make a quality control and when a defect that is outside the range of acceptance a response will occur.

PLATFORM: Study of the integration of new nanomaterials in a current processes of manufacture with prepreg materials in aeronautics

Scipedia content — Thu, 31 Mar 2022 17:45:06 +0200

PLATFORM appear for the need to improve non-intrinsic properties of composite materials, principally its mechanical and electrical properties. The main objective of the project is to analyze the possibility of introducing three new materials in development into the current manufacturing processes, improving the properties of the raw material, more concrectly prepreg unidirectional carbon fibre with epoxy resin. Several material developments are made with carbon nanotubes in three different formats: buckypapers, thermoplastic doped veils and CTN treated prepreg. The implementation of each materials has been studied in current infusion processes, more concretely manufacturing with prepregs and cure in an autoclave. The studied possibilities are: buckypapers incorporated and doped veils embedded in prepreg laminates or full manufacturing with treated prepreg. The obtained results at the 2nd year of the project are satisfactory, but it´s necessary to optimize the materials to automate the manufacturing and improve the final properties.

Comparison of lightning strike behavior between carbon fiber reinforced materials with thermoset resin matrix and thermoplastic resin matrix

Scipedia content — Thu, 31 Mar 2022 17:44:55 +0200

One of the weak points of the structures made of carbon fibre reinforced materials and thermosetting matrix is its mechanical impact behavior. In order to improve it, materials reinforced with carbon fiber and thermoplastic resin matrix are under study. In addition to the mechanical properties there are other factors to consider before introducing any structural material in the manufacturing of an aircraft, such as its lightning strike behavior. Materials properties that influence this behavior are mainly electrical, thermal and also mechanical; and these properties are modified from thermoset resins to thermoplastics. Within the Clean Sky program Airbus Defense and Space has carried out preliminary tests on flat panels manufactured by Fidamc with a carbon fibre reinforced material and thermoplastic resin matrix with two different configurations, both layout and additional (with and without metallization) The tests objective was the evaluation and comparison of the damages obtained after a lightning strike in flat panels made of traditional materials (thermoset matrix) with those made with new thermoplastic matrix materials. Both the mechanical damage and the temperatures generated in the material (using a thermal camera during the test) were analyzed in order to compare the thermal behavior of the thermoplastic matrix against the thermostable. This article shows the work done as well as results and conclusions.

Experimental analysis of high velocity impacts of carbon/epoxy composite fragments

Scipedia content — Thu, 31 Mar 2022 17:44:42 +0200

The aeronautical industry tries continuously to find different strategies to optimize structural components with the aim of reducing their weight and hence achieving a more sustainable transport. The new developments that will come in the following years, will probably use incorporate open rotor engines since they have lower consume. These engines have a series of counter-rotating blades made of composite materials, which could impact the aircraft fuselage in case of failure. Impacts on aeronautic structures can be caused by rigid (metallic fragments), or by highly deformable bodies (hail, bird). Apart from these, which have already been studied, there are other types of impacts, practically unexplored, which are the fragments of carbon/epoxy laminates. In this work, high speed impact tests of carbon/epoxy fragments have been carried out in a wide range of impact velocities, from 80 to 190 m/s. These tests have been monitored using high-speed cameras which, using a specific tracking software, could calculate their acceleration and therefore the force exerted. The erosion suffered during impact has also been quantified. In order to study the failure process, a simple analytical model has been proposed to evaluate the influence of the different mechanisms of energy absorption during the impact and hence predict the erosion of the fragment during the impact.

Experimental study of the influence of thickness and ply sequence on woven composite plates subjected to out of plane impact

Scipedia content — Thu, 31 Mar 2022 17:44:31 +0200

In this work the different failure mechanisms have been studied on 5HS woven composite laminates subjected to low velocity impacts. A large range of energies (5-75J) has been used to induce different failures: delamination, fiber failure, out-plane shear and perforation. In addition, different configurations of AGP 280-5HS woven coupons have been manufactured to analyze the influence of thickness ((0/90)4S, (0/90)6S and (0/90)8S) and ply sequence ((0/90)8S, (±45)8S, [(±45)/(0/90)]4S, [(±45)2/(0/90)2]2S, and [(±45)4/(0/90)4]S)). Laminates have been subjected to low velocity impact using an INSTRON-CEAST Fractovis 6875 drop weight tower according to ASTM standards (D7136). Each test has been recorded with two high speed video-cameras (Photron SA-Z 2100K) in order to analyze the plate behavior during the impact. In addition, a three dimensional high velocity digital image correlation (HV-DIC) analysis has been performed to measure the out of plane displacement. Once impacted, the damaged area of the composite laminates was evaluated by ultrasonic inspections. The analysis of the influence of the plate thickness and ply sequence have been made according to the Composite Structure Impact Performance Assessment Program (CSIPAP) proposed by Feraboli and Kedward using the peak force and the absorbed energy.

Sensor integration and data explotation of Structural Health Monitoring Network integrated on a Unmananned Aerial Vehicle (UAV)

Scipedia content — Thu, 31 Mar 2022 17:44:18 +0200

Unmanned Aerial Vehicles (UAVs) are flying robots that require little or no human control while flying. The number of UAV has growth exponentially due to rise in applications such as video taking, surveillance and delivering cargo to customers. Despite the promise of the technology, UAV are not very reliable currently, either civil or military. They lack of sensing mechanisms to detect issues in operation, such impacts, hard landings and overload, together with the difficulties to detect structural problems during the UAV operation could compromise not only the safety of the UAV, also all along the entire flying area. This paper presents the design, development implementation, and validation of a Structural Health Monitoring (SHM) system applied to the rear fuselage of the UAV developed by INTA for R&D activities (MILANO). The rear fuselage, a 2.5 meters carbon/epoxy structure with frames and stringers, was instrumented with fiber optic sensors and PZT. Two different types of fiber optic sensors were considered: Fiber Bragg Gratings and distributed fiber sensing based on Rayleigh backscatter. The objective of the fiber optic sensor network is to detect the changes induced on the strain field due to damage appearance. This information will be employed to train a neural network which provides the self-diagnosis of the structural integrity. Additionally, the PZT network will be used as active system for structure interrogation through elastic waves.

Damage detection in Composite laminates by Fiber optic sensors

Scipedia content — Thu, 31 Mar 2022 17:44:05 +0200

Fiber optic sensors, both FBG point sensors and distributed sensors based on OFDR, are accepted and validated as temperature and strain sensors, enjoy a high TRL and are already in use in many industrial applications. The determination of occurrence of damage from strain measures is a technique still not mature, its TRL can be 2-3. A local crack can greatly weaken a structure, it will be the point of initiation of the catastrophic failure, but until the failure has occurred, the crack only causes very small changes in the overall behavior of the structure (stiffness, natural frequencies, strain field, etc.). Therefore, and unless the position of the crack coincides with the predetermined position of the sensors, it is not easy to detect the existence of damage from strain measurements. In this work two parallel techniques, experimentally validated, are presented. The first one is to use distributed measurement, with an optical fiber placed in the area where the damage is expected. It is verified that a delamination causes residual strains in the delaminated area, of significant value, and that will be detected by the fiber, if it crosses the delamination zone. The second technique is to compare the strains measurements obtained at different points, when the structure subjected to external loads. Although the changes are going to be very small, local damage causes a redistribution of the rigidity of the structure, and of the load paths, and therefore the strains readings, may be slightly different. Results of the application of the model are presented to actual composite elements, such as an isogrid structure, and a small wind turbine blade.

Synergy effect in the addition of nanoreinforcements in matrix and onto the continouos fiber for composite structural health monitoring

Scipedia content — Thu, 31 Mar 2022 17:43:54 +0200

The aim of the research is focused on the manufacture of multiscale reinforced composites with self-monitoring capabilities. In order to achieve it, reference material based on epoxy resin and glass fiber fabric has been modified by the addition of carbon nanotubes which allow the creation of a nanoreinforcement electrically conductive percolation network. The registration of electrical resistance variations due to strain or damage can be used to monitorize these effects caused by the mechanical loads. The research also studies the modification of the electrical properties (electrical conductivity measured in both transverse and longitudinal directions) and interlaminar mechanical properties caused by the use of nanoreinforced resins or surface modified fabrics. Multiscale reinforced composites manufactured allow the detection and partial location of damage caused during the interlaminar strength test. Moreover, differences in sensitivity due to manufacturing method and nanoreinforcement used have been clarified.

Electrical properties in polyester resins: comparison of the use of carbon nanotubes (CNT) and carbon black (CB)

Scipedia content — Thu, 31 Mar 2022 17:43:43 +0200

This work presents a comparison in the production of electrical conductivity polyester resins by doping it with two types of carbonous fillers; carbon nanotubes (CNT) and carbon black (CB). These polyester resins are used to obtain electrical conductivity powder gel coat. This type of coating reduces cycle times in the manufacture of composites due to the fact that significantly decrease curing time of the gel coat and eliminate secondary operations for the application of the final coating in the composite. Electrical conductivity with different fillers content and percolation thresholds obtained in the simulation phase are detailed. The results obtained in the simulation are validated at the pilot plant level taking into account the influence of the loading percentage on the resin processing. Finally, a comparison between the results obtained with the different percentage of CNT and CB is made. The results of the simulation show that the value of the percolation threshold is much lower in the case of CNT (about 3% in the case of CNT versus 35% in the case of CB). The experimental results indicate the strong dependence of the electrical properties on the production process obtaining variations of up to two orders of magnitude in the experimental results using the same percentage of CNT but different type of polyester resin.

Passive damped deployment of full composite structures

Scipedia content — Thu, 31 Mar 2022 17:43:31 +0200

A new material, currently used in non-spatial applications, with interesting properties has been identified: a flexible epoxy resin with lower stiffness and higher damping than the space used resins and that is miscible with these ones. Such a mixed material could be used in CFRP components which properties (stiffness and damping) could be customised. One possible application has been selected for this study: the deployment of full CFRP structures composed of thin-walled composite deployable booms with tape-spring hinges on them. These kind of passive springs have been shown to be very powerful, but they have also shown a hard dynamic behaviour that can produce damages to the deployed items or their hosting structure. The partial use of flexible epoxy resins in the CFRP hinges can introduce an efficient damping in the deployment and relief of this dynamic effect. The objective of this activity is to verify the feasibility of the use of a mixture of rigid and flexible epoxy resins for obtaining better dynamic performances of CFRP tape springs. The results of this study are very promising. They show that it is possible to customise the properties of some components by finding the adequate mixture of resins. However, additional studies are necessary to assess good performances in space environment. The validation of this material can open the door to new space applications where the proper combination of stiffness and damping is crucial.

Modular deployable structures

Scipedia content — Thu, 31 Mar 2022 17:43:20 +0200

Large aperture antennas and telescopes, long baselines and long focal lengths in space have important applications for Telecommunications, Earth Observation and Science missions. Within this context, an ESA TRP activity is currently under development, carried out by COMET Ingeniería, PROSIX Engineering and Airbus DS (CASA Espacio), with the aim of designing overall structural assemblies based on unit cells developing representative parts of deployable masts (linear structures) and rings (antenna or radiotelescope aperture). This paper presents the current status of this project and the results obtained until the date of presentation of this paper. The results of these paper will be confirmed during next PDR to be celebrated at ESA-ESTEC.

Development of a software for calculation of optimised pressure vessels according to ASME X

Scipedia content — Thu, 31 Mar 2022 17:43:10 +0200

The methodology for calculating pressure vessels made of composites is included at the Secion X of the ASME Code. These vessels are more common in aerospatial engineering, or in medical gas industry, but lately are being introduced in automotive, naval, energy and petrochemical industries. The development of a software tool to calculate pressure vessels according to ASME Code sec. X is proposed. Technically, the goal is to develop a software tool to aid in and speed up the process of designing pressure vessels according to the ASME Code Sec. X. With this software, and considering the entered data (diametres, lengths, design pressures, design temperatures, etc…), dimensions and final laminates of a pressure vessel can be obtained in order not to surpass the failure criteria for the considered composite.

Improvement of the mechanical properties in hybrid structures by polyurethane rigid foams reinforcement in aluminium profiles

Scipedia content — Thu, 31 Mar 2022 17:42:58 +0200

One of the biggest challenges in transport industry is weight reduction. The objective is both economic and environmental: cost reduction together with a reduction in the use of fuel and CO2 emissions. Multi-material design, with rigid foams as local reinforcements, suppose a great opportunity to success this challenges, being a versatile solution for cost and weight saving. Among them, polyurethane rigid foams (PUR) not only present structural and energy absorption advantages, but also improveme other properties, as corrosion resistance and vibration and noise reduction. In the present work, extruded profiles (series 6xxx-T6) were reinforced with PUR foams manufactured by CETEC. The influence of the next factors on the structural strength has been evaluated: profiles wall thickness (from 1.6 to 4 mm), filling method (manual or injection), PUR density (from 100 to 300 kg/m3), amount of material inside the profiles (from 70 to 90%) and influence of the temperature in the PUR foaming. Improvement in the structural strength (maximum load and energy absorption) was characterised by 3-point bending test. In conclusion, it has been observed an improvement in the load and energy absorption with the inclusion of PUR, with a dependence on the wall tickness and foam density. Furthermore, injected profiles presented improved structural results due to the better control over the manufacturing process.

Lightweighting of PP/GF: foamed composites for automotive applications

Scipedia content — Thu, 31 Mar 2022 17:42:46 +0200

Lightweight construction is one of the main strategies conducted by carmakers in order to reduce fuel consumption and greenhouse gas emissions. Since the demand of plastic and composite materials for automotive applications is continuously growing, lightening approaches like foaming techniques are being introduced with the aim of decreasing their weight. The present work aims to compare the morphology and mechanical properties of plastic foams obtained by two different foaming technologies: MuCell® and IQ Foam®. Solid and foamed plates of glass fiber reinforced-polypropylene (PP/GF) were injection molded by using MuCell® and IQ Foam® processes combined with the complementary tool technology Core Back expansion molding. The morphology analysis of the obtained plates was carried out through Scanning Electron Microscopy (SEM) and Computed Tomography (CT) techniques, and the mechanical properties were assessed by means of tensile, flexural and impact tests. The morphology analysis revealed the presence of solid skin-foamed core structure in the foamed samples. The mechanical properties decreased gradually with the apparent density of the microcellular plates. By increasing the thickness of the part because of the expansion of the cavity, the apparent density decreased but the flexural stiffness was greatly enhanced. Foamed samples obtained by IQ Foam® technology exhibited lower cell density than that of the MuCell® ones, but consequently higher resistant area, and thus, slightly higher mechanical properties. The new IQ Foam® technology is able to produce foamed parts with properties comparable to that of the MuCell® process, offering additional benefits such as cost-effectiveness, easy to use and machine-independence.

Design and manufacture of a self-supporting racing motorcycle seat made on carbon fiber

Scipedia content — Thu, 31 Mar 2022 17:42:36 +0200

This work presents the design and manufacture of the structural tail (subchassis+seat) of a racing motorbike which has participated in the MotoStudent 2016 edition, held in October 2016 on the Alcañiz circuit, representing the University of Malaga. Two motorcycles were presented, one inside the Petrol category (4 stroke engine and 250 cc) and another one in the Electric category. It is a self-supporting structure that replaces the use of the traditional subchassis and seat, in order to save weight. As a material we selected a 2x2 twill carbon fabric 3K, 200 g/m2 and Resoltech 1070/1074 epoxy resin. The selected manufacturing process has been manual molding and vacuum bag. Taking into account the estimated fiber percentage, the properties of the elemental sheet of composite material have been estimated using micromechanical models. These properties have been implemented in the finite element program Patran-Nastran for the optimization of the part. Once it has been designed, a model of the part has been fabricated on MDF wood which has been used to manufacture the mold of the piece in fiberglass. The designed part was homologated by the organization of the competition. The developed part is 50% lighter that previous solution. The manufactured mold allows to produce more pieces with the consequent cost reduction.

Development of vehicle chassis manufactured by 3D pultrusion

Scipedia content — Thu, 31 Mar 2022 17:42:25 +0200

The present work presents a preliminary study on the development of a tubular chassis design for automotive industry manufactured with ultraviolet (UV) 3D pultrusion. The use of straight profiles for energy absorption elements and the advantages and feasibility of using curved profiles in other structural areas have been analysed. For the straight profiles, the energy absorption cabability of the material (specific energy absorption, SEA) has been evaluated performing quasi-static compression tests, showing high energy dissipation values, over 50 kJ / kg. On the other hand, the manufacturing of curved profiles by UV pultrusion have been analysed, evaluating the influence of the processing parameters (emitting intensity and pulling speed) and the influence of the reinforcement type on the geometry of the profile. It has been observed that the roving reinforcement allows an easier manipulation and allows to obtain curves without wrinkles with complex sections, due to the free movement between yarns; while the tape reinforcement may present wrinkles during the curving stage. In addition, based on a design with straight profiles, it has been shown that using non-rectilinear profiles, a significant reduction of the necessary connection nodes can be achieved, reducing up to 75% the number of connection nodes based on the analyed design.

Design and manufacture of automotive components in thermoplastic composite (Part II)

Scipedia content — Thu, 31 Mar 2022 17:42:13 +0200

The thermoplastic RTM process (T-RTM) is currently one of the most demanded process for R&D in the automotive sector. This sector tries to lighten the weight of the vehicle with highly resistant non-metallic components and with efficient manufacturing in cycle-time and cost. In the framework of the BIHARKONP project, EDERTEK-TECNALIA proposes the migration of a suspension arm, currently manufactured by means of metal stamping, to high mechanical requirements composite materials, obtaining a weight reduction of 30%. For the manufacture of this component it was proposed to redesign the component in carbon fiber (CF) and polyamide 6 matrix (APA6). The redesign (Part I) consisted in a mechanical calculation of the loads that the component had to support. The geometry has been changed with the aim of fulfilling the part specification and the peculiarities of the T-RTM process. For the manufacture of the component, a CF/APA6 composite laminate was defined and characterized and a specific CF for thermoplastics was selected. Subsequently, a T-RTM mold was designed and manufactured with inserts for fiber compaction and eight thermal control zones. The geometry of the control arm involves the manufacture of CF preforms by means of a thermal forming process with thermoplastic veils. Caprocast technology has been used to manufacture the prototype by caprolactam injection and its polymerization inside the heated mold. The prototype was subjected to bearing test, bushing insertion-extraction test and bushing strength test. The component was validated.

Design and manufacture of automotive components in thermoplastic composite (Part I)

Scipedia content — Thu, 31 Mar 2022 17:42:00 +0200

Due to the increasing demands in environment regulations related to gases emissions, the automotive sector has gradually increased the plastic consumption in vehicles.The objective is to introduce in the market structural components made in latest generation composite materials in a serial and competitive way with the functionality of the present metallic parts. In this work the redesign of two automotive metallic components that will be produced via thermoplastic RTM (Part II) is presented. This technology allows the manufacturing of high performance long fibre composite materials with shorter cycle times. Based on the specifications of the components and the actual metallic solutions performance a new concept of a brake pedal and a control arm consistent with the manufacturing via a RTM thermoplastic process is adressed. For the calculations of both components, carbon or glass fibre with poliamide matrix (APA6) based solutions are used.

Applicability of Short Carbon Fiber technology to aeronautical structural parts of low responsibility

Scipedia content — Thu, 31 Mar 2022 17:41:48 +0200

The development of structural parts optimized in weight and cost has always been a key aspect in the aeronautical industry. Nevertheless, these premises also appears in other industries. A specific study focused on the automative industry showed the possibility of re-studying a technology analyzed in the past: Short Carbon Fiber injection. The technology offered low recurring costs, high rate possibilities and reliable repetitivity of the processes. Based on these statements, aeronautical parts from the Horizontal Tail Plane (THS) with low structural responsibility were defined as target options. After defining the scope, different engineering and manufacturing studies were performed. The conclusions from both investigations, together with weight and cost estimations, confirmed the potential application of the technology for a present and future implementation. The previous project was included in the project FACTORIA, funded by the Ministerio de Economía y Competitividad, by means of the Centro Tecnológico Industrial (CDTI), in the Strategic Programme CIEN 2016.

Design and Manufacturing of a small wind turbine with biodegradable composite material

Scipedia content — Thu, 31 Mar 2022 17:41:37 +0200

The awareness for developing an eco-friendly industry based on green materials, sustainable technologies and optimum process with less environmental impact are a general societal consciousness, but it is still a considerable challenge to achieve. The biodegradable structural materials can contribute to reduce the CO2 emissions, the carbon footprint and increase the concept of recyclability for structural applications. In terms of performances, the natural fiber reinforced composite material could become in worthy alternative to E-Glass composite, wood reinforced materials and aluminum alloys because of their good ratio between mechanical properties, density and cost. However, the structural engineering applications are still very limited mainly because the lack of a robust manufacturing process. For that purpose, it has been developed an innovative mechanical extraction methodology based on the morphology of two species of bamboo, along with the optimization of the melting parameters to manufacture a fully biodegradable Bamboo-PLA composite. Furthermore, in order to define the future applications, the mechanical properties have been analyzed under different thermal cycling conditions.

A novel reinforcement structure in tire treads compounds: organo-modified octosilicate as additive

Scipedia content — Thu, 31 Mar 2022 15:12:14 +0200

Only 3phr of octosilicate (OCTO), swollen with cetyltrimethylammonium ions (CTA), used as an additive in a rubber tire tread compound (80phr of highly dispersible silica, HDS) improves the end properties. The presence of the organo-modified synthetic layered silicate increases vulcanization rate, while the analogue natural silicate, montmorillonite, did not show the same effects.[1-3] The reinforcing filler network is modified as a result of the incorporation of the SLS, therefore, the values of fractal exponents which characterize the reinforcing filler network were found to be different when comparing sillica-only compounds to silica/SLS compounds.[4] The substitution of CTA ions by dimethyldioctadecylammonium ions (2HT) increases the interlaminar space (from 2.7nm to 4.3nm), improving the exfoliation of octosilicate. Therefore, mechanical effects similar to those of OCTO-CTA can be obtained with lower OCTO-2HT concentration. Nevertheless, as a result of the change in the organic modifier and concentration levels, variations of the mixing process have also been necessary in order to obtain comparable results.[5] Systematic studies of our research will be expounded and discussed in this publication.

In Situ polymerization of isotactic polypropylene nanocomposites with metallocene catalysis

Scipedia content — Thu, 31 Mar 2022 15:12:03 +0200

The family of polyolefins are materials with a high demand, due to thermoplastics are structurally simpler and economical in their production and processing. Within the polyolefins, the commercial use of polypropylene began with the rise of the catalyzed reactions, in this way it was possible to control its specific conformation and with it, the final properties. In order to improve their properties, these materials are usually reinforced, specially with nanometric loads. So far, three methods have been developed for obtaining nanocomposites: In situ polymerization, melt intercalation and solution mixing. In order to solve the existing problems, in terms of charge dispersion, molecular weight control of the synthesized matrix and the complexity of the immobilization processes of the metallocene catalysts, this research uses In situ polymerization of polypropylene-Sepiolite, using the nanoclay as support of the catalytic system. This study proposes a method of immobilization that contemplates the use of the density of the polar groups that has the surface of Sepiolite, to fix the co-catalyst. In addition, the resulting polymerization process defines the reaction temperature as a variable which will provide a mechanism for controlling the molecular weights of the polypropylene. The proposed method has allowed the polypropylene to be added in its own synthesis process, besides controlling its structure in terms of its stereo-specificity and molecular weight, thus improving its final properties.

Study of the nanostructure and the local mechanical properties of polypropylene multifunctional materials

Scipedia content — Thu, 31 Mar 2022 15:11:52 +0200

Polymer-based multifunctional materials reinforced with graphene represent a step forward due to the combination of good structural properties with others of different nature such us electrical conductivity. These new systems are good candidates for applications in the transportation industry provided that the nanofiller is well-dispersed within the matrix and there is a good interaction between the fibre and the polymer. The aim of this work is the study of the nanostructure and the mechanical properties of polymer nanocomposites based on polypropylene (PP) and graphene with concentrations in the range of 0.9 to 2.6 vol.%. The nanostructure of the composites was investigated by wide angle x-ray scattering and the local mechanical properties were assessed by nanoindentation. On the one hand, nanoindentation studies revealed a good distribution of the nanofiller within the polymer matrix. On the other hand, an enhancement of the mechanical properties by the incorporation of graphene was found. This mechanical improvement was attributed to the intrinsic properties of graphene while there were no clear differences in the nanostructure of the nanocomposites compared to that of neat PP. Finally, comparison of the moduli from nanoindentation and tensile testing allowed the understanding of the mechanism of deformation of these materials under external stresses of different nature.

Friction stir welding, FSW, of metal matrix composites, MMCs, with high reinforcement content

Scipedia content — Thu, 31 Mar 2022 15:11:41 +0200

To a large extent, the promising expectations that were set in the 1980s in metal matrix composites, MMCs, have been diluted in recent decades. One reason for this frustration lies in the impossibility of joining these materials by conventional welding methods: these methods (involving fusion) destroy the homogeneous distribution of the reinforcement and give rise to reaction products detrimental to the properties of the joint. Friction stir welding, FSW, however, does not involve fusion, it occurs by a severe plastic deformation process, avoiding the drawbacks of traditional welding techniques. Therefore, recent years have witnessed a growing interest in the study of welds by this technique, not only of MMCs but also of dissimilar welds MMC-monolithic metal. joining MMCs by FSW is not simple, particularly if the reinforcement content is high,> 20 vol%. This paper discusses the most important difficulties facing this welding process and summarizes the recent results of CENIM-AIMEN studies on joints of MMCs with up to 40%vol. of reinforcement, and dissimilar joints. The most relevant correlations between the different mechanical stresses required under different advancing and rotational velocities are presented. This will allow an analysis of the energy balance of the work necessary to produce the deformation of the material and to heat it. In summary, it is emphasized the importance of measuring these efforts to deepen the severe plastic deformation process that takes place, always at high strain rates.

Evaluation of crystallite size and micro-strain during mechanical milling process of composite material AA6005A+ 10% nano-TiC

Scipedia content — Thu, 31 Mar 2022 15:11:28 +0200

Powder metallurgy process (by high-energy mechanical milling) was used to obtain a nanostructured aluminum matrix composite. Powders of the AA6005A alloy (particle size <63 μm) was utilized as matrix, and 10% by weight of nano-sized TiC particles (20-30 nm) as reinforcement. Composite powder was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Microstructural changes produced during the milling process, such as modification of crystallite size and micro-strain of matrix lattice were determined using the three Williamson-Hall (W-H) analysis models: UDM (Uniform Deformation Model), USDM (Uniform Stress Deformation Model) and UDEDM (Uniform Deformation Energy Density Model). The results show that crystallite size decreases and micro-strain increases sharply in the first few hours of milling and then both parameters remain stable until 10 hours. The three W-H models present a coefficient of determination R2 close to the unit indicating that are suitable to determine crystallite size and lattice micro-strain of nanostructured composite obtained.

Application of ultrasounds to improve the dispersion of nanoparticulates in a Al-Si7Mg0.6 alloy reinforced with 0.5 wt. % of nanodiamonds

Scipedia content — Thu, 31 Mar 2022 15:11:18 +0200

One of the most important technical barriers that hinders the development and implementation of nanoparticulate reinforced aluminium alloys is the difficulty to avoid the formation of clusters and to obtain their homogeneous distribution. The present work summarises the results obtained with the use of an ultrasound probe that was immersed into the melt alloy containing nanodiamond particulates just before the casting step. The microstructure and tensile properties of the obtained specimens are compared with nanoreinforced samples obtained with conventional stir cast process. The materials used in the study are the Al-Si7Mg0.6 casting alloy and nanodiamond particulates obtained by detonation synthesis. Samples containing up to 0.5 wt.% of nanodiamonds have been obtained. The use of the ultrasound probe results in the elimination of nanoparticulate clusters and provides an improvement of mechanical properties in comparison to properties measure with the unreinforced alloy and also with the conventionally stir cast composite.

Design and manufacture of a granular hybrid material with high energy dissipation capacity

Scipedia content — Thu, 31 Mar 2022 15:11:08 +0200

Obtaining lighter materials, with more toughness and higher impact resistance, is getting larger is becoming of high interest in the current industry. It is possible to find lots of examples of different materials inspired in nature with gradient properties that are used for the development of hybrid materials. Also, various studies in granular materials show the possibility of confinement of the impact energy inside the material itself, allowing the decomposition of the initial pulse into several weaker pulses, the energy dissipation through several mechanisms and the gradual release of the non-dissipated energy. This article congregates the results of a preliminary design process and the fabrication of a granular hybrid material (ABS polymeric matrix and 0.25% of carbon nano layers as a reinforcement) initially in the form of a filament, subsequently utilised in the fabrication of viscoelastic layers. These layers will be fabricated using 3D printing techniques and will be introduced inside the structural material to improve its behaviour against impacts and to increase its energy dissipation capacity, which indeed is the main goal of this investigation. In the study, several non-destructive tests are shown for the morphological characterisation of the nanoreinforcement (SEM analysis) and for the examination of the reinforcement homogeneity in the hybrid material filament (Micro-CT analysis), as well as the application of a mathematical method via Voronoi diagrams to complement the results. By the realisation of mechanical tests, the improvement of the mechanical properties of the granular hybrid material is checked up.

Analysis of ILSS tests of continuous fiber reinforced composite specimens produced by 3D

Scipedia content — Thu, 31 Mar 2022 15:10:56 +0200

3D printing technologies are one of the major current trends in the manufacturing and prototyping of structural elements, with recent developments focused on the production of polymer matrix composites. The objective of this study is to analyze the results of interlaminar shear tests performed on monolithic composite materials of thermoplastic matrix reinforced with continuous fiber. The test specimens were manufactured with a MarkOne 3D printer using different filaments reinforced with glass fiber, aramid fiber and carbon fiber, which were later cut and tested according to EN2563. In the case of the carbon fiber specimens, results from the ILSS test have been obtained, which will be used to carry out comparative analysis. However, for the glass fiber reinforced specimens no valid results have been obtained, undergoing plastic deformation during the test. The aramid fiber reinforced specimens could not be tested since they suffered softening due to the heat generated during the cutting process. These activities are included in the FACTORIA project, financed by the Ministerio de Economía y Competitividad a través del Centro Tecnológico Industrial (CDTI) within the framework of the Strategic Program CIEN 2016.

Removing stress singularities in standard tests of composite materials

Scipedia content — Thu, 31 Mar 2022 15:10:46 +0200

In many standard tests involving composite material, specially those needing tabs at the ends of the sample, configurations of multimaterial corners, with abrupt changes in geometry and material properties, typically appear giving rise to stress fields which achieve very high stresses and theoretically are unbounded. These stress intensifications may promote premature failures, or simply, alterations of the uniform stress state which is expected to occur in the specimen, and the test strength, calculated as a certain load divided by a certain failure area, may not be representative of the real strength of the material under analysis. In the present work three examples are presented, in which, by means of an addecuate selection of the geometrical parameters defining the test configuration which do not affect the mechanical property to be measured, the stress singularities at these multimaterial corners are removed (or at least reduced to a minimum). The three cases are: a) tests in tension and shear (Iosipescu) in bimaterial coupons, b) the off-axis test for the intralaminar shear strength in composite materials and c) a compression test of thick laminates in composite materials. In two of the three cases experimental results are available to corroborate that the removal of the stress singularities gives rise to higher strength values than those obtained in the original test configurations.

“Hot Forming” Process vs Cycle Parametrization: Ancillary Materials, Risks by Contamination and Prepreg Aging

Scipedia content — Thu, 31 Mar 2022 15:10:37 +0200

Aeronautical process globalization and the growth in number of composite materials suppliers have allowed the development of creativity since processes parametrization point of view as well as the use of ancillary materials that guarantee the product quality in the currently available resin systems in the composites world. Hot-forming process optimization in order to provide the development of high thickness parts and complex shape must meet a minimum parameters (temperature, time and vacuum) which are determinated by experimental methods and are in relation with: 1) Prepreg Material (tape / resin system); 2) Ancillary Materials, particulary the release film due to contamination risk of un-cured prepreg during hot-forming process; 3) Indication and control systems of temperature. Nowadays, the new thermoset resin systems are more complex due to an increase of the requirements from OEMs to manufacturers of composites in order to obtain a products optimization (functional and structural) in a more effective way.This aspect, joined to the study and the industrial capability analysis of a determinated equipment, allowed us the development of a tests campaign on structural parts of unidirectional prepreg (UD) to define the maximum and minimum temperature, time and ancillary materials to be used in a “hot-forming” process. Non contamination of the part and no material aging are guaranteed, as well as the internal quality after a process of consolidation by co-curing process in autoclave for any thermoset resin system available in the composite world.

GFRP laminates modified with a viscoelastic layer for improvement of the response under low velocity impacts

Scipedia content — Thu, 31 Mar 2022 15:10:24 +0200

High speed crafts made of glass fibre reinforced polymers (GFRP) suffer in-service structural damage due to the slamming impacts, when the bottom surface impacts against the water. It is important to quantify the extend of the damage and progression during the service life of the ship. In this work, it is presented a methodology using non-destructive evaluation for the assessment of the level of damage in the laminated panels. It is also investigated the effect of the introduction of a viscoelastic layer, composed of two polymeric material with different stiffnesses, designed specifically to dissipate the impact energy. The combination of these polymers with different deformation response under compression, and due to the confinement of the elastomer in small cell surrounded by the rigid polymer, constitutes an effective mechanism of energy dissipation due to impacts, protecting the plies beneath the viscoelastic layer and minimizing the damaged generated in the laminates due to slamming. Test specimens have been prepared using GFRP prepregs cured Out-of-Autoclave (OoA) and impacted using a specifically designed device that apply pressure peaks in the laminates that resemble very closely those that appears in the hull due to slamming loads, and compared with and without viscoelastic layer in the laminate. Changes in panel compliance are used for monitoring the evolution of damage in the material, as a function of the number of repeated impacts imposed on the panel for every load condition. Drop weight tests have been also used to understand the percentage of the income energy that is generating damage in the material, and to establish threshold levels for damage initiation both for unprotected panels and those with viscoelastic shielding layer.

Integral methodology of materials and dimensional optimization adapted to product design

Scipedia content — Thu, 31 Mar 2022 15:10:15 +0200

This paper describes the development of an integral methodology for the material selection and dimensional optimization adapted to product design. The methodology proposes the use of genetic algorithms in order to approach the optimization of materials and dimensions in multi-material structures. Three innovative aspects are included in this methodology: pre-treatment of the material data and its clustering, definition of objectives and post-processing of the results obtained on the possible solutions in order to select the best one according to additional opinions imposed by the designer. The methodology has been implemented on a specific case study: the base of an elevator cab. In order to achieve this goal, a parametric model of the structure was built and several load cases were included. With these models, an optimization problem was created, subjected to goals and restrictions. The results obtained show the validity of the methodology proposed

Study of the manufacturing process of laminated composites of polypropylene reinforced with continuous fibres

Scipedia content — Thu, 31 Mar 2022 15:10:04 +0200

The aim of the study was to define the composition and methodology for manufacturing laminated composites of polypropylene and continuous fiber reinforcement. These composites are designed with the aim of being integrated into high mechanical performance lightweight parts obtained by high production rate manufacturing processes such as compression molding or the overinjection. The complete cycle of production of the polypropylene textile laminate composites has been analyzed, going from the selection and additivation of raw materials, treatment of the reinforced fibers and fabrication and characterization of the composite laminates. The study has focused on composites based on polypropylene resins and twill 2/2 reinforcements of fiberglass fabric.

Strategy of the manufacture of veils by electrospinning for the improvement of fiber reinforced polymeric composites properties

Scipedia content — Thu, 31 Mar 2022 15:09:49 +0200

In the last decades the fiber-reinforced polymer composites, FRPC, have undergone a spectacular development in applications where high performance of resistance and tenacity with a minimum weight are required. However, due to their laminar structure and the brittleness of their resin matrix, they show a great tendency to fracture as a failure mode. At the moment, technologies are being studied to improve their behavior to the fracture, doping or modification of resins and treatments of the reinforcing materials. However, the trend with the greatest potential is the use of interleave veils arranged as an interface between the matrix and the fiber, which have shown important improvements in the final mechanical properties of the composite material. This is due to adhesion phenomena between the polymer matrix and the reinforcing fiber. Initial studies were performed with interleave veils not specifically developed for this use; custom-made veils are currently being developed for use in laminated composites. The electrospinning technology is taking a positioning of relevance in this field, due to its great capacity of production and its low cost. High specific surface of electrospun veils , make electrospinning a good candidate to manufacture interleave veils to improve the mechanical properties of laminated composites. This work shows the fabrication of electrospun veils of PA6 polyamides for their integration into the composite by varying the number of veils in order to analyze their influence on the flexural strength of the composites.

Obtaining electrospun mats from waterborne polyurethanes containing cellulose nanocrystals

Scipedia content — Thu, 31 Mar 2022 15:09:38 +0200

Cellulose nanocrystals (CNC) have attracted great interest as nanoreinforcement due to their excellent mechanical properties. Furthermore, their dispersibility in water makes them suitable for their incorporation in many aqueous systems such as waterborme polyurethanes (WBPU). WBPUs have gained attention due to their versatility and ability to ajust their properties to a wide range of applications, in addition to their non-toxicity, non-flammability and environmental sustainability. Therefore, in this work a waterborne polyurethane has been synthesized for the preparation of nanocomposites with different contents of cellulose nanocrystals, incorporated by different routes, the classical mixing by sonication once the waterborne polyurethane has been synthesized, and the alternative in-situ by adding the CNCs in water during the WBPU synthesis, just in the phase inversion step. The obtained dispersions have been used in the preparation of films by casting and mats by electrospinning. The films and mats have been characterized from the point of view of their physical-chemical, morphological and superficial properties.

Metal/Graphite flakes foams for heat sink applications

Scipedia content — Thu, 31 Mar 2022 15:09:30 +0200

Materials combining a certain degree of macroporosity and high thermal conductivity are interesting for current active thermal management applications. In this work a new class of multiphase composite porous materials have been fabricated. The materials are inspired by a recently developed family of high thermally conductive composite materials formed by combination of graphite flakes, ceramic particles and a metal matrix. Replacing the ceramic particles by NaCl particles allow obtaining an interconnected pore structure in the material after dissolution in water. Materials with aluminum matrices have been obtained by gas pressure infiltration of preforms conformed by mixtures of graphite flakes and NaCl particles. The thermal conductivity has been calculated and experimental results are discussed in accordance with two mathematical models based on ideal microstructures: i) alternated layers of semi-infinite continuous graphite flakes and metallic foam, and ii) a metallic foam with oriented graphite flakes in the struts.

Development of carbon foams with hierarchical porosity

Scipedia content — Thu, 31 Mar 2022 15:09:20 +0200

Mesoporous carbon materials (pore size ranging 2-50 nm) have been used in applications as membranes, filters, catalyst supports or electrodes in electrochemical devices. Their problems related with diffusion of reactants/products and heat leading off from or supplied to the reactors have motivated the efforts directed to obtain new materials capable of combining pores in different scales. In this work a double templating method is used to generate carbon foams with hierarchical pore structure. The mixture of mesophase pitch (MP) and polystyrene (PS) allows infiltrating preforms of packed NaCl particles which afterwards can be removed away by dissolution in water, forming the large pores in the material. Posterior heat treatments allow removing an interconnected fine microstructure created by the PS, which is able to create the fine porosity in the material. The success of the process depends on the solidification conditions of the infiltrating mixture and the careful removal of the templates. By this method a new class of materials with hierarchical porosity (pores in the range 500 mm-20 nm) has been obtained.

Development of light rigid polyurethane foams containing thermoregulating microcapsules

Scipedia content — Thu, 31 Mar 2022 15:09:08 +0200

During the past years the incorporation of PCMs in building materials has been extensively studied.The combination of isolation and thermal storage properties that rigid polyurethane foams containing PCMs exhibit allows to reduce the losses during the warming and cooling at the same time that they store energy, making these composites an ideal element for the increase of the energy efficiency of buildings. In order to combine both properties in an optimal way, in this work the development of rigid polyurethane foams (RPU) containing up to 30 wt% of thermorregulatory microcapsules at 700, 800 mbar and atmospheric pressure has been studied. The used thermorregulatory microcapsules have been obtained in a spray-drying pilot plant at the Instituto de Tecnología Química y Medioambiental (UCLM). Obatined foams have been physically (density), thermally (thermal energy storage capacity and thermal conductivity) and mechanically (modulus of elasticity in compression) characterized. As a result of this research, a RPU foam synthesized at 800 mbar, containing 30 wt% of microcapsules, with a latent heat of 21.3 J/g and a thermal energy storage capacity of 1.43 kWh/m3 has been obtained. In addition, this foam keep the isolation property of the polyurethane. The final composite presents a proper resistance to compression with a density that fulfills the Spanish regulation for the RPU foams application in buildings.

Photocurable nanodoped resins

Scipedia content — Thu, 31 Mar 2022 15:08:56 +0200

This work is focus on the development of photocurable resins doped with nanoparticles of very diverse nature, diamond, barium oxide, hydroxyapatite and silver. These nanoreinforcements are being investigated, and even applied industrially, as nanofillers of thermosetting resins, due to the different enhancements and new properties, including increased mechanical, thermal and chemical properties, high electrical and thermal conductivity, improved biocompatibility and antimicrobial properties, among others. The reinforcement of photocurable thermosetting resins can be complex since the added charge can exert shielding to the radiation, limiting to reach high curing degree. For it, it is necessary to use catalysts and sensitizers of UV radiation. In addition, in order to limit this negative effect, a high degree of dispersion of the nanofillers is required, avoiding the presence of micrometric agglomerates. An epoxy system has been selected, whose is commly used for dental applications, and differente contents of nanofillers have been added. Once the dispersion process has been optimized, the effect of the different fillers on the degree of curing of the photocurable resin, measured through its glass transition temperature, has been studied. The degree of curing achieved has been explained through transperance measurements to the visible light of the samples, as well as the morphology of the cured and doped resins.

Reprocessable, repairable and reciclable thermoset composites

Scipedia content — Thu, 31 Mar 2022 15:08:46 +0200

Composites based on epoxy resin are a class of high performance structural materials with great potential in a wide variety of industrial sectors. However, being thermoset resins, despite their great benefits in lightness and mechanical performance, they present the great disadvantage that once cured they can not be reprocessed, repaired or recycled. This is hindering the rapid growth of composite materials in applications such as automotive. In order to overcome the disadvantages of thermosetting resins, this paper presents the development of a new generation of dynamic thermoset epoxy resins able to be reprocessed, repaired and recycled thanks to the incorporation of reversible bonds within its reticulated structure. As resins containing dynamic bonds, the cured material presents new properties previously unthinkable for thermosetting materials. These new resins have been developed for the manufacture of composite materials reinforced with both glass fiber and carbon fiber. It has been shown that these new composites have mechanical properties equivalent to those of conventional thermosetting composites, but unlike the latter, they are recyclable, repairable and reprocessable, which is a step forward and the creation of new opportunities for sectors such as automotive .

Utilisation of sugar cane straw ash (SCSA) as pozzolan in partially replacement of Portland cement

Scipedia content — Thu, 31 Mar 2022 15:08:33 +0200

Sugarcane production in Brazil considerably increased in the last 10 years. After the mechanized harvesting, it is generated a waste called by sugar cane straw. This straw presents good calorific value and it can be utilised in energy production as a biomass. However, after the energy generation, it is obtained another waste, which does not have a suitable destination, known as the sugar cane straw ash (SCSA). A destination to this material can be as pozzolanic material. Therefore, the SCSA was physically and chemically characterised. The ash presented amorphous silica that can be used in partial replacement of the Portland cement. The ash reactivity was assessed by thermogravimetric analysis (TGA) of lime/pozzolan pastes. Also five replacement percentages of the Portland cement by SCSA in mortars were evaluated: 0 (control), 15, 20, 25 and 30%. Specimens were moulded in order to be assessed by compressive strength after 3, 7, 28 and 90 days of curing at 25 ºC. All mortars presented similar compressive strength after 90 days of curing of approximately 45 MPa. It can be concluded that the SCSA can be used in partial replacement of the Portland cement.

PLA and P3HB-3HH-based bio-composites made with cotton fabric

Scipedia content — Thu, 31 Mar 2022 15:08:23 +0200

Composite panels were produced using film stacking procedure: a dry layer of fabric and two layers of matrix were piled up alternately and compression molded. The matrices used were PLA or PHB and the fabric was a cotton twill fabric without any chemical pre-treatment or treated with an epoxy functional oligomeric acrylic polymer (J). The PLA-based composite had clearly better mechanical properties than the pure matrix, namely +75%, +39% and +45% for elastic modulus, elongation at break and tensile strength, respectively. The PHB gave dramatic results reaching increases of +103%, +83%,+104% of the same three parameters. The J additive employed in the PLA gave no substantial changes but reduced the elongation at break. The same J additive in the PHB-based composite apparently increased the adeshion between matrix and fabric, showing an modulus and strenght increase with a reduction of elongation at break.

Approach to the Weight Estimation in the Conceptual Design of Hybrid-Electric-Powered Unconventional Regional Aircraft

Scipedia content — Tue, 23 Mar 2021 07:10:46 +0100

The present work deals with the development of an innovative approach to the weight estimation in the conceptual design of a Hybrid-Electric-Powered (HEP) Blended Wing Body (BWB) commercial aircraft. In the last few decades, the improvement of the environmental impact of civil aviation has been the major concern of the aeronautical engineering community, in order to guarantee the sustainable development of the system in presence of a constantly growing market demand. The sustained effort in the improvement of the overall efficiency of conventional aircraft has produced a new generation of vehicles with an extremely low level of emissions and noise, capable of covering the community requirements in the short term. Unfortunately, the remarkable improvements achieved represent the asymptotic limit reachable through the incremental enhancement of existing concepts. Any further improvement to conform to the strict future environmental target will be possible only through the introduction of breakthrough concepts. The aeronautical engineering community is thus concentrating the research on unconventional airframes, innovative low-noise technologies, and alternative propulsion systems. The BWB is one of the most promising layouts in terms of noise emissions and chemical pollution. The further reduction of fuel consumption that can be achieved with gas/electric hybridisation of the power-plant is herein addressed in the context of multidisciplinary analyses. In particular, the payload and range limits are assessed in relation to the technological development of the electric components of the propulsion system. The present work explores the potentialities of an energy-based approach for the initial sizing of a HEP unconventional aircraft in the early conceptual phase of the design. A detailed parametric analysis has been carried out to emphasise how payload, range, and degree of hybridisation are strictly connected in terms of feasible mission requirements and related to the reasonable expectations of development of electric components suitable for aeronautical applications.

Document type: Article

A Robust Optimization for Designing a Charging Station Based on Solar and Wind Energy for Electric Vehicles of a Smart Home in Small Villages

Scipedia content — Tue, 23 Mar 2021 07:03:11 +0100

In recent years, integration of electric vehicles (EVs) has increased dramatically due to their lower carbon emissions and reduced fossil fuel dependency. However, charging EVs could have significant impacts on the electrical grid. One promising method for mitigating these impacts is the use of renewable energy systems. Renewable energy systems can also be useful for charging EVs where there is no local grid. This paper proposes a new strategy for designing a renewable energy charging station consisting of wind turbines, a photovoltaic system, and an energy storage system to avoid the use of diesel generators in remote communities. The objective function is considered to be the minimization of the total net present cost, including energy production, components setup, and financial viability. The proposed approach, using stochastic modeling, can also guarantee profitable operation of EVs and reasonable effects on renewable energy sizing, narrowing the gap between real-life daily operation patterns and the design stage. The proposed strategy should enhance the efficiency of conventional EV charging stations. The key point of this study is the efficient use of excess electricity. The infrastructure of the charging station is optimized and modeled.

Document type: Article

Stochastic Electric Vehicle Network Considering Environmental Costs

Scipedia content — Tue, 23 Mar 2021 06:50:50 +0100

In recent years, many countries have published their timetables to promote electric vehicles. Many researches have focused on the benefits of electric vehicles. Compared with gas vehicles, electric vehicles are more suitable for modern cities, because they are considered to be environment-friendly by the public. Hence we pay attention to the environmental costs of electric vehicles. In this paper, an electric vehicle network is established. To analyze this electric vehicle network, we define environmental costs for the network and propose a stochastic user equilibrium model to describe drivers’ route choice behavior. An algorithm is proposed to solve this model. The model and the algorithm are illustrated through a numerical example. We test the calculation feasibility of the proposed model and the computational efficiency of the proposed algorithm via this numerical example. A comparative analysis is conducted to show the benefits of introducing electric vehicles into traffic networks. With the sensitivity analysis, we also reveal the relationship between people’s environmental awareness, the quantity of electric vehicles and the environmental costs of the overall traffic network.

Document type: Article

Decade-Long Changes in Disparity and Distribution of Transit Opportunity in Shenzhen China: A Transportation Equity Perspective

Scipedia content — Tue, 23 Mar 2021 06:39:00 +0100

Efficiency and equity have always been the two points of focus of transport projects. Compared with efficiency, equity is easily overlooked in the evaluation of transport projects. Many studies emphasize that defining and operationalizing costs and benefits and the distributive principle are critical parts in the assessment of transportation equity. However, the scope and time frame of the assessment target are also critical. In this paper, we took China’s fastest urbanizing city, Shenzhen, as a case study to assess transport equity by comparing accessibility among groups. First, the public transport system was divided into bus and subway, and the residents were divided into two groups: urban village and nonurban village. Second, we adopted an enhanced potential opportunity model to measure residents’ bus and subway accessibility and summarized them as transit opportunity. Third, we used the Dagum Gini coefficient decomposition and kernel density estimation method to explore the fair distribution of transit opportunity among groups and districts from 2011 to 2020. Decade-long changes in disparity and distribution of transit opportunity gave us a clear picture. On the one hand, the development of Shenzhen public transport system had a positive effect. All populations are benefiting, and their accessibility is increasing. On the other hand, it also had a negative effect to exacerbate inequality between populations. For the absolute value of the opportunity, Shenzhen’s urban village populations do have fewer transportation opportunities than nonurban villages, and this gap between them will be wider more and more. The public transport system is more inclined to improve the population with high initial opportunity and make them higher. The results illustrated the importance of examining transportation equity over an extended period and could provide information on urban development strategies.

Document type: Article

Methodology to Design an Optimal Rule Based Energy Management Strategy Using Energetic Macroscopic Representation: Case of Plug-In Series Hybrid Electric Vehicle

Scipedia content — Tue, 23 Mar 2021 06:10:43 +0100

International audience

Document type: Article

Asymptotic approximations of transient behaviour for day-to-day traffic models

Scipedia content — Tue, 23 Mar 2021 06:08:16 +0100

We consider a wide class of stochastic process traffic assignment models that capture the day-to-day evolving interaction between traffic congestion and drivers’ information acquisition and choice processes. Such models provide a description of not only transient change and ‘steady’ behaviour, but also represent additional variability that occurs through probabilistic descriptions. They are therefore highly suited to modelling both the disturbance and subsequent ‘drift’ of networks that are subject to some systematic change, be that a road closure or capacity reduction, new policy measure or general change in demand patterns. In this paper we derive analytic results to probabilistically capture the nature of the transient effects following such a systematic change. This can be thought of as understanding what happens as a system moves from varying about one equilibrium state to varying about a new equilibrium state. The results capture analytically the changes over time in descriptors of the system, in terms of link flow means, variances and covariances. Formally, the analytic results hold asymptotically as approximations, as we imagine demand increasing in tandem with capacities; however, our interest is in general cases where such tandem increases do not occur, and so we provide conditions under which our approximations are likely to work well. Numerical results of applying the methods are reported on several examples. The quality of the approximations is assessed through comparisons with Monte Carlo simulations from the true underlying process .

Document type: Article

Intelligent personalized ADAS warnings

Scipedia content — Tue, 23 Mar 2021 06:05:54 +0100

Purpose Advanced Driver Assistance Systems (ADAS) have been among the key innovations in the automotive market for over a decade, since they promote traffic safety. This tendency is strengthened even more lately, with the introduction of the autonomous vehicles. A plethora of ADAS exist in the market today, using common warning thresholds for all drivers. However, since we are not all driving the same way, by offering common systems for all the drivers, neither the acceptance nor the effectiveness levels of ADAS are optimal. This manuscript attempts to optimize the Collision Avoidance System (CAS) warning, through intelligent personalized algorithms. Methods Starting with the identification of the dynamic parameters for driving behaviour modeling on the longitudinal road axis, the personalization parameters for ADAS are derived that form the basis for the algorithms developed. Also, based on literature studies, the safety boundaries for warning provision by the CAS are set and implemented in the algorithms. Results Specific personalized algorithms for the longitudinal road axis behaviour are developed, based on Time to Collision and Time Headway. The proposed algorithms based on Time Headway were assessed on-road with 10 drivers and were positively evaluated by the majority of the participants, with a varying degree of reliability and usability. Conclusions Based on the results obtained, it can be concluded that with the proposed algorithms, the initial hypothesis of the paper is verified, i.e. personalised warnings would get a greater acceptance by the drivers, of course without braking the safety limits. Further improvements of the algorithm could be achieved, possibly through a better determination of the car following event, since its definition includes a few assumptions.

Document type: Article

Speed prediction models for car and sports utility vehicle at locations along four-lane median divided horizontal curves

Scipedia content — Tue, 23 Mar 2021 06:01:11 +0100

Sites with varying geometric features were analyzed to develop the 85th percentile speed prediction models for car and sports utility vehicle (SUV) at 50 m prior to the point of curvature (PC), PC, midpoint of a curve (MC), point of tangent (PT) and 50 m beyond PT on four-lane median divided rural highways. The car and SUV speed data were combined in the analysis as they were found to be normally distributed and not significantly different. Independent parameters representing geometric features and speed at the preceding section were logically selected in stepwise regression analyses to develop the models. Speeds at various locations were found to be dependent on some combinations of curve length, curvature and speed in the immediately preceding section of the highway. Curve length had a significant effect on the speed at locations 50 m prior to PC, PC and MC. The effect of curvature on speed was observed only at MC. The curve geometry did not have a significant effect on speed from PT onwards. The speed at 50 m prior to PC and curvature is the most significant parameter that affects the speed at PC and MC, respectively. Before entering a horizontal curve, drivers possibly perceive the curve based on its length. Longer curve encourages drivers to maintain higher speed in the preceding tangent section. Further, drivers start experiencing the effect of curvature only after entering the curve and adjust speed accordingly. Practitioners can use these findings in designing consistent horizontal curve for vehicle speed harmony.

Document type: Article

Predicting Work Zone Collision Probabilities via Clustering: Application in Optimal Deployment of Highway Response Teams

Scipedia content — Tue, 23 Mar 2021 05:47:27 +0100

This paper proposes a clustering approach to predict the probability of a collision occurring in the proximity of planned road maintenance operations (i.e., work zones). The proposed method is applied to over 54,000 short-term work zones in the state of Maryland and demonstrates an ability to predict work zone collision probabilities. One of the key applications of this work is using the predicted probabilities at the operational level to help allocate highway response teams. To this end, a two-stage stochastic program is used to locate response vehicles on the Maryland highway network in order to minimize expected response times.

Document type: Article

Self-Organizing Traffic Flow Prediction with an Optimized Deep Belief Network for Internet of Vehicles

Scipedia content — Tue, 23 Mar 2021 05:42:28 +0100

To assist in the broadcasting of time-critical traffic information in an Internet of Vehicles (IoV) and vehicular sensor networks (VSN), fast network connectivity is needed. Accurate traffic information prediction can improve traffic congestion and operation efficiency, which helps to reduce commute times, noise and carbon emissions. In this study, we present a novel approach for predicting the traffic flow volume by using traffic data in self-organizing vehicular networks. The proposed method is based on using a probabilistic generative neural network techniques called deep belief network (DBN) that includes multiple layers of restricted Boltzmann machine (RBM) auto-encoders. Time series data generated from the roadside units (RSUs) for five highway links are used by a three layer DBN to extract and learn key input features for constructing a model to predict traffic flow. Back-propagation is utilized as a general learning algorithm for fine-tuning the weight parameters among the visible and hidden layers of RBMs. During the training process the firefly algorithm (FFA) is applied for optimizing the DBN topology and learning rate parameter. Monte Carlo simulations are used to assess the accuracy of the prediction model. The results show that the proposed model achieves superior performance accuracy for predicting traffic flow in comparison with other approaches applied in the literature. The proposed approach can help to solve the problem of traffic congestion, and provide guidance and advice for road users and traffic regulators.

Document type: Article

Is Road Pricing a Sustainable Policy? Jakarta Case

Scipedia content — Tue, 23 Mar 2021 05:40:07 +0100

Urban road pricing involves direct charging of drivers for the use of the road network, usually during peak periods. The main objectives for the introduction of a road pricing scheme, in a congested city network, include reduction of delays, environmental improvement and revenue increase. These objectives are closely associated with the concepts of sustainable mobility in urban areas with respect to social equity, economic efficiency, and environmental responsibility. There have been intensive discussions about sustainable transportation in Indonesia. In tune with the issue of climate change and the decline in the ability to provide fuel, this paper is intended to look at the perspective of road pricing from the standpoint of traffic flow, travel speed, emissions reduction, and energy consumption as well as pricing scheme. As pricing will be imposed for the Moslem community, it should conform with Islamic tax income which is for the benefits of poor, needy and less privileged people in the society. The conclusion drawn is that the frenzied application of road pricing will be able to improve traffic in Greater Jakarta but the sustainability of pricing should be adjusted with Islamic tax income.

Document type: Article