Scipedia: Revista de Materiales Compuestos

Manufacture of a train carbody section using automatic lamination processes

María Ordóñez Muñoz — Fri, 19 May 2023 13:58:03 +0200

Within the European platform Europe's Rail, whose objective is to promote research and development activities in the railway sector, can be found the PIVOT-2 project (Grant Agreement no. 881807), which addresses the implementation on track of light and environmentally friendly vehicles, reducing energy consumption and therefore the CO2 emissions derived from the transport sector.

To meet these objectives, the project seeks to achieve the weight reduction of primary structures. This way, the use of composites materials appears as an interesting alternative in a sector where their use has been very limited to non-structural components, largely due to the need to comply with fire protection regulations (EN 45545) [1]. Thanks to the development of new resins, the possibilities of these materials are increasing, being necessary to evaluate their performance in new applications.

Similarly, the characteristics of the railway industry mean that the manufacturing processes of composite materials widely used in other sectors, such as the aerospace, must be adapted. Likewise, and due to the requirements of the final product, it will be necessary to adapt the materials to these new applications, developing materials with higher grammage or ply thickness than those currently used.

The project evaluates the automatic laying of different materials developed for the railway sector. The behaviour of flat laminates is analysed, as well as the lamination of the material on core structures. Finally, studies are validated with the manufacturing of a train carbody section, using automatic lamination processes (ATL).

Welding thermoplastic composites using resistive heating: tooling design, joining procedure and demonstrator manufacturing

Aroa Iriarte Legarreta — Thu, 18 May 2023 09:12:04 +0200

Thermoplastic welding technology is a long-established technology in the industry where the efficiency of the welded joint can be approached to the properties of the base material by fast, automated and reversible joining. The joining of two thermoplastic compounds can be done by fusion bonding and reconsolidation of the pieces in the joining line. The most promising fusion bonding techniques, and nowadays with more presence in the aeronautical sector, are resistance welding, induction welding, ultrasonic welding and laser welding. Among these methods, the advantage of resistance welding is that the heat is produced exactly at the interface to be welded, avoiding unwanted heating in other parts of the piece. This method is based on the application of an electrically conductive implant between the two parts to be welded under pressure that generates heat with the passage of current. The objective of this work was to develop a resistance welding system for the joining of a thermoplastic composite assembly. A demonstrator of a representative element of the aeronautical sector was manufactured in carbon fiber and PPS composite material consisting of a skin to which two L-shaped brackets made of the same material as the skin were welded. The welding process carried out and the electrical and thermal parameters obtained show the repeatability of this process. This technology could be easily scalable for the welding of larger elements and different geometries.

Integración de estructuras en material compuesto termoplástico mediante soldadura por inducción

Javier Ávila — Fri, 11 Apr 2025 12:17:33 +0200

Los materiales compuestos termoplásticos (TPCs) están transformando la industria aeroespacial gracias a su alta tenacidad, capacidad de reprocesamiento y reciclabilidad, alineándose con los objetivos de sostenibilidad y reducción de peso estructural para minimizar las emisiones de carbono. No obstante, las técnicas de unión convencionales, como remaches y adhesivos, presentan limitaciones significativas, como la pérdida de integridad estructural debido a perforaciones, el aumento de peso y procesos largos y costosos. La soldadura de TPCs es un proceso de unión para eliminar las superficies diferenciadas de las piezas a soldar mediante una nueva consolidación del material. El entrelazamiento de las cadenas poliméricas resultante en la zona soldada posibilita la transferencia de cargas a través de la interfaz. Esta técnica permite obtener uniones ligeras, sin necesidad de elementos adicionales, y con propiedades mecánicas comparables al material base. FIDAMC trabaja sobre un método de soldadura por inducción para material compuesto termoplástico, bajo el cual han sido fabricadas probetas a partir de paneles planos. Las probetas simulan el pie de un larguerillo soldado a un revestimiento como resultado de la puesta a punto del proceso. Las probetas han sido ensayadas obteniendo propiedades mecánicas por encima del 90% respecto del valor de referencia Este trabajo ha estado apoyado por un modelo numérico creado en COMSOL Multiphysics para modelar y simular la interacción entre los campos electromagnéticos y la distribución térmica a lo largo del material durante el proceso de soldadura.

Development of smart technology for monitoring the manufacturing process of composite parts in the aerospace industry

Maialen Garaigordobil — Mon, 14 Apr 2025 15:59:24 +0200

In recent years, the aerospace industry has seen significant advancements thanks to the incorporation of composite materials, which enable the design of lighter structures with excellent mechanical properties. However, the manufacturing process of these composites remains difficult to monitor and still lacks proper standardization. This has led to the need for the development of intelligent control technologies that can be implemented to efficiently oversee the production cycle. In this work, a detailed analysis of the various stages involved in the infusion-based manufacturing process of composite parts has been carried out, identifying weaknesses and defects that may arise during production. The technology developed aims to implement a wireless monitoring system using ferromagnetic microwires embedded in structural composite components, with the goal of improving process control and reducing potential errors. Although the knowledge gained from this project is focused on a specific manufacturing process, the results obtained could be extrapolated to other sectors operating under similar conditions. In this way, the quality and added value of the parts produced with this technology are enhanced, ensuring compliance with the stringent demands of the market.

AUTOMATED MANUFACTURING OF THERMOPLASTIC COMPOSITES FOR HYDROGEN STORAGE

Prasad Shimpi — Mon, 17 Mar 2025 11:45:34 +0100

The research work is focused on developing thermoplastic composites by automated tape laying process (ATL) having acceptable gas permeability levels to store hydrogen H2 in linerless composite material tanks at cryogenic temperatures. Carbon fibre (CF) with polyamide 11 (PA11) matrix was used to manufacture composites using automated tape laying process. The manufactured composites treated in autoclave and tested for hydrogen permeability at room temperature. The results show that autoclave cured CF/PA11 composites meet the set permeability requirements for composite hydrogen storage vessel designed for pressure of 6 bar.

Desafíos y estrategias de optimización en la soldadura ultrasónica continua robótica de CFR-TP

Maryam Ahanpanjeh — Sat, 17 May 2025 00:02:13 +0200

La soldadura ultrasónica continua robótica (cUSW) es una técnica prometedora para unir termoplásticos reforzados con fibra de carbono (CFR-TP), que ofrece alta eficiencia y tiempos de procesamiento rápidos. Sin embargo, mantener la calidad de la soldadura y la robustez del proceso presenta desafíos significativos. Las características de la soldadura, como la resistencia de la unión y el rendimiento a largo plazo, se ven fuertemente influenciadas por parámetros clave durante las fases de generación de calor y consolidación. Comprender las interacciones entre el sistema robótico y el proceso de soldadura ultrasónica es esencial, ya que impactan directamente en la calidad y consistencia de la soldadura. El robot debe controlar con precisión el movimiento del sonotrodo durante la fase de generación de calor para mantener una fuerza constante, precisión de trayectoria y uniformidad de velocidad, asegurando una transferencia de energía eficiente y una fusión uniforme. Durante la consolidación, tanto la velocidad como la fuerza son cruciales, controlando la disipación de calor para reducir la temperatura de la interfaz por debajo del punto de cristalización y prevenir defectos. Para abordar estos desafíos, es esencial la monitorización en tiempo real de los parámetros clave del proceso. La integración avanzada de sensores y las estrategias de control basadas en datos permiten ajustes dinámicos para optimizar las condiciones de soldadura y prevenir defectos. Este artículo explora los desafíos asociados con la soldadura ultrasónica continua robótica de CFR-TP y analiza técnicas de monitoreo y estrategias de control para mejorar la consistencia de la soldadura y la confiabilidad del proceso.

Advanced thermal control of VARI process with self-heating mold

Manuel Laspalas — Mon, 14 Apr 2025 14:49:35 +0200

Manufacturing liquid composites with thermoset resins requires precise temperature control throughout the process. In the specific case of vacuum infusion (VARI) in a self-heating mold, one side of the part is in contact with the mold, which is the one that incorporates the heating elements (resistors), while the other side is in contact with the consumables (peelable, bleeder, mesh, vacuum bag), which imposes a substantially different thermal condition that can create thermal gradients. In order to achieve the greatest possible thermal uniformity, not only throughout the length of the part, but also throughout its thickness, additional external heating elements are usually incorporated. In the present work, the thermal control of an infusion process of a leading edge section of a horizontal stabilizer of an aircraft is developed. This control has been developed using the MPC (Model Predictive Control) method, which allows applying the necessary power to the heat sources independently to control the temperature at the measurement points, based on predictions obtained from a reduced-order thermal model (MOR). This reduced representation has been generated using the POD (Proper Orthogonal Decomposition) technique from the thermal matrices obtained from a finite element simulation (FEM) model of the prototype mold, previously adjusted and validated. In order to detect and compensate for the nonlinear behaviors present in the system, mainly due to convection, a perturbation estimator using a Kalman filter is implemented. In addition, the reduced-order model allows a thermal representation of the complete system to be obtained, which facilitates the implementation of virtual sensors in a way that controls not only the temperature at the measurement points, but also at points of the part that would not be possible to monitor with physical sensors, helping to maintain a homogeneous temperature distribution in the material during the manufacturing process. The control scheme has been experimentally validated on the prototype mold, obtaining precise monitoring of the temperature profile and complying with the manufacturing standards of the part.

Process monitoring of aeronautical-graded materials using fiber optics sensors during liquid resin infusion: study on scalability methods

Cristian Builes — Tue, 15 Apr 2025 12:13:40 +0200

The main objective of the FLASH-COMP project is to develop an advanced and efficient quality control solution, operator oriented, capable of detecting defects early and accurately during the manufacturing process. This facilitates the implementation of in-situ corrective actions, aiming to achieve a zero-defect Liquid Resin Infusion (LRI) manufacturing process while significantly, reducing waste generation in composite material production. FLASH-COMP seeks to introduce new diagnostic methods that enable real-time process monitoring, providing relevant information during the process without compromising performance or the quality of the final component. Two embedded fiber optic sensor technologies are used: Fiber Bragg Grating (FBG) and Distributed All Grating (AGF), which are combined to collect process data during the preforming and resin infusion stages. Both technologies are integrated into a complex-geometry component to monitor different critical areas simultaneously. These technologies generate valuable process data, requiring an optimal strategy of sensor positioning, that can adapt to abrupt geometric changes without compromising sensor integrity or component quality. Both sensor technologies provide relevant information related to vacuum level and leaks, temperature, resin impregnation and part curing. This type of sensor requires prior training of the operator for its correct handling and analysis of the data generated. New strategies for manipulating sensors are proposed to facilitate their manipulation on an industrial scale.

Monitoring of process parameters during the forming of SMC materials, mechanical an thermal properties (COMPCERTO Project)

Paula Rodríguez Alonso — Wed, 14 May 2025 14:37:45 +0200

In recent times, polymer matrix composite material technologies have undergone a genuine revolution, driven by the surge in demand—particularly in the transportation and energy sectors. Composites are being increasingly incorporated due to the significant weight reduction they enable in structural components, which in turn leads to a decrease in energy consumption in transportation as a result of this weight savings. Ambitious EU sustainability policies (such as the EU Green Deal or the New Industrial Strategy) are further accelerating this shift toward efficient and sustainable solutions, with a significant impact on the transportation sector, especially the automotive industry—both in conventional and emerging propulsion systems (the use of lightweight materials is expected to increase from the current 30% to 70% by 2030, with composites accounting for approximately 20%). However, the automotive sector is one of the most demanding in terms of processing times. Therefore, the optimization and monitoring of processing parameters through embedded sensors in molds is presented as a valuable tool for adapting processing times and enabling continuous quality control of parts. This paper presents the results obtained within the framework of the COMPCERTO project, which aims to develop solutions that facilitate the optimized manufacturing of components with structural requirements through Sheet Molding Compound (SMC) thermoforming processes. To achieve this, the implementation of sensors for monitoring curing, pressure, and temperature in molds is proposed, enabling the acquisition of representative values at critical points and in real time for the phenomena occurring during the thermoforming of parts in the press. Preliminary tests are carried out to optimize the curing cycle in order to determine the most suitable manufacturing parameters, and based on the results, a Design of Experiments (DoE) is proposed. Finally, mechanical, thermal, and microstructural characterizations are performed on the tests defined in the DoE. This will generate a database that serves to correlate the real-time data obtained from the parts with potential defects in the SMC components.

Hybridisation of thermoplastic composite forging and continuous fibre additive manufacturing for automotive industry

Udane Olaziregi — Thu, 10 Apr 2025 09:59:54 +0200

Thermoplastic composites are becoming increasingly important in the automotive industry due to their high strength-to-weight ratio, recyclability and cost-effectiveness. Within these composites, continuous fibre-reinforced composites offer superior mechanical properties than discontinuous fibre-reinforced composites, but their design flexibility is limited. In contrast, discontinuous fibre composites allow more complex geometries. A promising approach to overcome these limitations and improve composite components is hybrid manufacturing, which integrates multiple manufacturing techniques. In this work, we have studied the feasibility of combining the additive manufacturing of composites with continuous glass fibre (cAM) and the forging of thermoplastic materials reinforced with discontinuous fibre (GMT). A topologically optimised cAM reinforcement has been inserted into forged GMT omega profiles. The results of microscopic analysis have confirmed that there is adequate compaction between the hybridised materials. Furthermore, the results of numerical simulations replicating a three-point bending test have demonstrated the potential of cAM as a local reinforcement in forged components, as the specific stiffness of the hybrid beams was increased by up to 42%. This hybridisation technique represents a significant advancement towards the development of innovative solutions in thermoplastic composite processes, with the potential to produce lighter, stronger components adapted to complex geometries.

Comparative life cycle assesment (LCA) of a boat hatch made of glass fibre and flax fibre reinforced composites

Alberto Lopez-Arraiza — Sat, 12 Apr 2025 13:26:23 +0200

The widespread use of glass fibre-reinforced composites in the marine industry is primarily attributed to their low cost, favourable mechanical properties, and high resistance to marine corrosion. However, their limited recyclability poses significant environmental concerns at end-of-life (EoL). Consequently, more sustainable alternatives such as biocomposites reinforced with natural fibres are being explored. This study presents a comparative Life Cycle Assessment (LCA) of the fore hatch of a small boat, currently manufactured by hand lay-up using glass fibre reinforced polyester glass fibre (GFRP), and a proposed alternative with flax fabric reinforced bio-epoxy (FFRB) produced by vacuum infusion. Initially, FFRB laminates were manufactured and mechanically characterised through three-point bending tests. Based on ISO 12215-5:2019 for small craft construction, the required laminate thicknesses for the FFRB hatch were determined, achieving a 14% weight reduction compared to the GFRP counterpart. Subsequently, a cradle-to-grave LCA was performed using OpenLCA software and the Ecoinvent v3.9.1 database. Results revealed that the FFRB hatch offers lower environmental impacts in fossil fuel depletion (ΔADP = –16%) and human toxicity (ΔHTP = –54%). However, terrestrial ecotoxicity (ΔTETP = +238%) increased due to pesticide and fertiliser use in flax cultivation. In conclusion, FFRB represents an environmentally sustainable alternative for marine component manufacturing, although further research is required to enhance its end-of-life performance.

High-demand industrial applications with thermochemically recycled carbon fiber

Sonia García-Arrieta — Wed, 30 Apr 2025 10:39:35 +0200

The use of carbon fiber (CF) has increased in the last decade, shifting from the aeronautical sector to the leisure and automotive sectors. CF production requires high energy consumption and emits large amounts of CO₂. This increase in consumption generates a greater amount of CF composite waste, which must be properly managed to give it a second life. Deremco project aims to transfer and increase the TRL of different recycling technologies for composite from the wind and aeronautical sectors. The companies IDEC, BIRZIPLASTIK, and TECNALIA have focused on the recovery of post-production waste from the aeronautical sector to obtain recycled CF (rCF) through a thermochemical process. IDEC proposed the horizontal stabilizer of an aircraft's as a use case. This secondary structure requires a lower level of mechanical properties, so the introduction of rCF has proven feasible. BIRZIPLASTIK proposes developing a thermoplastic formulation with high technical requirements for automotive applications. Two formulations have been developed that meet these requirements, one of which is 100% recycled material. To carry out these success use cases, TECNALIA has worked on optimized the rCF sizing processes and integrating it into the compounding and Resin Transfer Molding (RTM) processes.

Comparison of stiffness and strength of flax, hemp and kenaf composites with other natural and synthetic fibers composites using fibre-specific parameters

Maria Asun Cantera — Wed, 21 May 2025 13:48:34 +0200

The increasing adoption of natural fibres as composite reinforcement is a promising development in materials science. These fibres have a low carbon footprint and are biodegradable, and they also have remarkable properties such as low density and high specific stiffness and strength. However, the mechanical properties of these composites are influenced by various parameters, which can complicate comparisons due to their diverse internal structures. This study focuses on two key normalised parameters: the Tsai modulus, which represents the trace of the stiffness matrix tensor; and the area of the Omni failure envelope in stress space. Our analysis of published data on unidirectional flax, hemp, jute, and kenaf composites shows that trace-normalised longitudinal Young's modulus can effectively facilitate stiffness comparisons between natural and synthetic fibre composites. A new and innovative way of measuring strength is suggested. This is based on the radius of a circle that matches the area of the Omni stress envelopes. This method is both robust and reliable for quantifying and comparing material strength. Although, extensive mechanical data on natural composites is available, it is difficult to establish design criteria for comparing them. Addressing this gap presents a significant opportunity to unlock the full potential of natural fibres in composite applications, paving the way for a more sustainable future in engineering materials.

Composite sustainability for aviation - Problem or solution?

Tamara Blanco Varela — Wed, 23 Apr 2025 14:21:14 +0200

Composite materials have highly contributed to the reduction of CO2 emissions of last generation aircrafts, due to their lightweight capabilities. However, the environmental burden during composite raw material production, part manufacturing and waste treatment versus aluminium alloys has become a priority during recent years and needs to be addressed asap. This applies to current aircraft but above all to ensure that composites are the best material choice for future more conventional or breakthrough products based on sustainable aviation fuel or liquid hydrogen propulsion.This presentation has the intention to be a general and comprehensive overview of the current situation and opportunities regarding composite sustainability for commercial aeronautical sector, including:

Problem understanding: composites are key for more sustainable aviation.
As-is situation: raw material and part production, composite scrap treatment.
Opportunities to develop more sustainable composites: biosourced composites and mass balance, substance compliance, industrial carbon footprint reduction, recycling technologies and recyclable resins.
Some tips and recommendations about how to approach the development of more sustainable composites and what to prioritize from a technical point of view.

Desarrollo de la tecnología de calandrado para la reutilización de residuos de pre-preg multiaxiales no curados procedentes del sector aeronáutico

María Ariño — Fri, 16 May 2025 17:19:14 +0200

Esta investigación se centra en aprovechar los residuos de pregreg multicapa sin curar generados durante la producción de componentes aeronáuticos, con especial énfasis en los procesos de AFP (Automatic Fibre Placement) y ATL (Automatic Tape Laying). Estos residuos, que presentan características repetitivas en cuanto a tamaño, forma y apilado, se procesan mediante un sistema mecánico de calandrado para darle una segunda vida al material. Este método desarrollado por FIDAMC está basado en preparar los residuos de ATL de prepreg sin curar en tiras longitudinales orientadas en la dirección predominante. Posteriormente, estas tiras se procesan mediante calandrado en condiciones específicas de temperatura, velocidad y ratios de reducción de espesor en diferentes pasos. Como resultado, se obtiene un material reusado intermedio manipulable para la fabricación de nuevas piezas. Este material se ha caracterizado física-química y mecánicamente para optimizar sus propiedades mecánicas y asegurar su viabilidad como material reusado. Aunque las piezas aeroespaciales de material compuesto deben cumplir estrictos requisitos de seguridad, existen aplicaciones no críticas donde se pueden emplear materiales más ecológicos y económicos, como la fibra de carbono reusada. Esto permite una reducción significativa del impacto ambiental y de los costes asociados. Para estudiar la viabilidad de fabricación con este material, se ha fabricado un demostrador de costilla de borde de ataque del elevador (elevator) del estabilizador horizontal (HTP) mediante el proceso de termoconformado. Este estudio pretende demostrar el desarrollo y aplicación de nuevos materiales reusados, los cuales pueden ser utilizados en piezas semi-estructurales en el sector aeronáutico, o bien, en el sector transporte, en general. Se ha estudiado el material mediante una caracterización físico-química (micrografía, DSC, digestión y porosidad) y mecánica (tracción, compresión, ILSS, G1C, IPSS, CAI, OHC y FHC), así como otros métodos de caracterización avanzada. También se ha estudio su viabilidad de fabricación mediante la producción de un componente de geometría compleja. Además, se han propuesto diferentes alternativas para mejorar la calidad el material y ampliar el abanico de aplicación. Los resultados obtenidos confirmaron el potencial del material reusado para aplicaciones no críticas, demostrando que cumple con los requisitos funcionales de este tipo de componentes y recorriendo el camino hacia una mayor sostenibilidad en el sector.

Design of a small sustainable wind blade

Rafael Carnicero — Wed, 26 Mar 2025 14:14:33 +0100

The European Union is committed to becoming the first carbon-neutral continent by 2050. To this end, member countries have outlined a long-term strategy to achieve this goal. Among the cross-cutting elements that will make this possible is the Circular Economy. In this context, the aim is to reduce raw materials by extending the useful life of products, reusing them, recycling materials, etc. In the wind energy sector, between 80 and 90% of wind turbines are currently recycled. Wind turbine blades, manufactured mainly from composites, are difficult to recycle in terms of economic efficiency. Even so, several technical solutions currently exist at varying levels of technological maturity.

The work presented is the design of a sustainable wind turbine blade, replacing the epoxy-type thermosetting resins used until now with a thermoplastic resin with similar mechanical properties, with the advantage that the composites produced are easily recyclable. This new liquid thermoplastic resin, AKELITE, patented by the CSIC group, is capable of producing sustainable and 100% circular composite materials.

A 3D CAD model was created from a series of cross-sections of the blade. This model describes the blade's aerodynamic surface, so that in the finite element design phase (ANSYS Workbench), the laminate is defined from the outside in. The laminate design prioritizes longitudinal stiffness, ensuring the presence of layers in all traditional layers (0°, 90°, and ±45°), maintaining symmetry, and progressively reducing thickness from root to tip. The blade was subsequently manufactured and finally tested. The blade is currently being recycled for subsequent life cycle analysis.

This work is part of a project under the call for "Projects aimed at the ecological transition and the digital transition" with the participation of three research groups: CIEMAT, the University of Girona, and the CSIC.

Eco-design in Automotive through 'Material Matrix Assessment': Use Case in the Salient Project

Vanessa Ventosinos — Fri, 11 Apr 2025 13:32:22 +0200

Eco-design in the automotive sector integrates environmental considerations into the product development process to minimize impact throughout the vehicle’s entire life cycle. This approach addresses aspects such as resource efficiency, emission reduction, and end-of-life options (recycling, reuse, etc.). In recent years, eco-design has gained relevance due to increasing regulations and growing user awareness of sustainability. However, its implementation is often based on Life Cycle Assessment (LCA), a complex and demanding method during early design phases, as it requires detailed data to deliver reliable comparative results. This can delay the development time of new components—a critical parameter in the automotive industry. To overcome this limitation, CTAG has developed its own methodology, the Material Matrix Assessment, which enables rapid preliminary analysis of multiple designs without requiring detailed specifications. This qualitative methodology can identify designs with the highest environmental potential using key metrics selected by a multidisciplinary team. Each category is scored and weighted according to its relevance, resulting in an overall score for each design concept. The Material Matrix Assessment was successfully applied in the European SALIENT project, using a front-end structure as a use case. In addition to facilitating the selection of the design with the lowest environmental footprint from the earliest stages of development, the methodology also enabled a system weight reduction of over 40%.

Environmental sustainability assessment of a recyclable wind turbine blade: Preliminary results

Ana Rosa Gamarra — Mon, 14 Apr 2025 17:39:30 +0200

Recycling wind turbine blades is a key element in ensuring the sustainability of the energy transition. Conventional wind turbine blades made of epoxy-based composite plastics cannot be recycled and are mostly disposed of in landfills. This paper presents the environmental sustainability assessment of a blade manufactured with a new recyclable liquid thermoplastic resin. A Life Cycle Assessment (LCA) methodology was applied to calculate the environmental footprint, including 16 impact categories, enabling a comparison between the environmental impact of a conventional blade and one based on the new recyclable resin. The results from the resin production stage showed that the innovative resin had a higher environmental impact than epoxy. For example, in the climate change category, the emissions were 7.89 kg CO₂ eq./kg compared to 3.99 kg CO₂ eq./kg. However, it is necessary to evaluate the full life cycle of the blade, including use phase, recycling process, resin recovery, and the manufacturing of new blades. The results of the full life cycle assessment of a blade manufactured with the recovered innovative material will be presented. The life cycle approach is essential for assessing novel material applications to support the sustainable deployment of renewable energy technologies, including circularity criteria.

Impact-Fatigue of Self-Reinforced Polyethylene Terephthalate

Jon Aurrekoetxea — Fri, 11 Apr 2025 15:22:23 +0200

The objective of this work was to characterise the impact-fatigue behaviour of self-reinforced polyethylene terephthalate (srPET). The impact characterisation results, covering the range of incident energies from subcritical to perforation, show that the main deformation mechanism is plastic deformation followed by tensile fracture of the PET fibres, and that the energy penetration threshold for a 1.1 mm thick specimen is 13.9 J. In single-impact scenarios, srPET has a specific penetration threshold of 3.24 J/g, which is worse than self-reinforced polypropylene (srPP). However, if the environmental goal is to reduce waste volume, srPET is a better option since PET has a recycling fraction of 18.2%, compared to 2.7% for PP. Additionally, srPET guarantees a lifespan of 100 impacts for incident energies up to 60% of its penetration threshold, while srPP cannot exceed 40%. Finally, the fatigue life loss of srPET is also more gradual, a key aspect from the structural integrity point of view.

Increasing Profitability in Wind Turbine Blade Recycling: A Pyrolysis-Based Approach with Thermal Treatment of Volatiles

Alexander Lopez-Urionabarrenechea — Tue, 15 Apr 2025 20:07:13 +0200

Pyrolysis is a technically suitable process for recovering fibres from reinforced plastic waste that may also contain other types of materials (wood, foam, lacquer, etc.), such as wind turbine blades at the end of their useful life. The economic profitability of the pyrolysis recycling process depends mainly on the value of the recovered fibres, since pyrolysis liquids currently have no industrial application (and are therefore hazardous waste) and the gases are usually used to partially supply the energy requirements of the process, which is endothermic. Given that the wind turbine blades currently being retired are mainly made of glass fibres, which have low economic value, the profitability of the pyrolysis recycling process for this type of blade is a critical issue. This paper presents an analysis of the increase in the profitability of a wind turbine blade pyrolysis process that includes a treatment stage to improve the properties of the liquid and gaseous products. To this end, the investment required for this treatment (additional process units) has been defined and the energy costs and liquid waste management costs have been quantified in scenarios with and without treatment, including in the latter case the income from the sale of hydrogen. With this information and the amortisation expense, the incremental income statements derived from carrying out the treatment have been prepared, obtaining the net cash flows (NCF). The NCF has been used to calculate the net present value (NPV) of the investment project, as this is the best criterion from a financial point of view for evaluating a project. Finally, a sensitivity analysis was performed taking into account deviations in the investment to be made, income and costs. The results show that the cost of managing liquid waste is the parameter with the greatest influence on profitability, meaning that implementing the treatment increases the profitability of the recycling process.

Buckling analysis of laminates subjected to biaxial loads using cruciform specimens

Maria del Carmen Serna Moreno — Fri, 28 Mar 2025 21:00:33 +0100

This study presents the compression-compression test with cruciform specimens (test CC) as a viable methodology to assess the geometric instability of a ∓45° symmetric laminate. The central region of the specimen, subjected to biaxial loading, exhibits a geometry similar to that of a square plate fixed along its entire perimeter. The bifurcation of the strains recorded at the top and bottom surfaces of the laminate is considered to be the threshold between the in-plane biaxial response and the response dominated by bending and torsional moments. The nonlinearities observed in the evolution of the stress-strain relationship in the region subjected to biaxial loading are confirmed to be independent of the response of the specimen arms. The bending-torsion coupling effects at the beginning of the bifurcation are observed experimentally in the deflection surface recorded by Digital Image Correlation. The results obtained suggest that the test CC is potentially suitable for the observation and measurement of buckling modes under various boundary conditions. However, more work is needed to reduce the quantitative dispersion. Specifically, the research should focus on minimizing geometric imperfections and load misalignments.

Analysis of Delamination Behavior in Mode I under Thermal Environment Exposure in Adhesive Joints of Carbon-Epoxy Composite Materials

Paula Vigón — Fri, 11 Apr 2025 19:25:45 +0200

This study analyzes the delamination behavior in mode I, under static and fatigue loading, in adhesive joints on a composite material with an epoxy matrix and unidirectional carbon fiber reinforcement (CFRP). The samples were exposed in a climate chamber at 60°C and 70% relative humidity for different periods (no exposure, 1, 2, and 4 weeks). Subsequently, standardized DCB tests were performed to evaluate the effect of environmental aging on interlaminar fracture toughness and adhesive strength. After an initial static characterization, reference parameters for fatigue tests were defined, obtaining initiation (ΔG–N) and crack growth (G–da/dN) curves. The initiation data were analyzed using a Weibull probabilistic model. The results show a change in the epoxy adhesive behavior with exposure time, evidenced by a reduction in the fatigue limit and an increase in crack propagation rates.

Mechanical behavior analysis at low temperature of flax/epoxy laminates

Gabriel Enrique Sánchez Escudero — Sun, 13 Apr 2025 11:49:34 +0200

The growing environmental consciousness of recent years has driven the composite materials industry to increasingly adopt natural fibers as a sustainable alternative to synthetic ones, aiming to reduce the ecological footprint of manufacturing processes. Replacing conventional synthetic fibers with natural counterparts, such as flax, offers a significant decrease in energy consumption during laminate production, enhancing overall process sustainability. This study explores the mechanical performance of a flax fiber-reinforced epoxy laminate with a twill weave configuration. The material was tested under tensile and in-plane shear loading at both room temperature and subzero conditions (–40 °C and –70 °C). The laminate demonstrated a nonlinear stress–strain response, characterized by three distinct regions, suggesting that a trilinear model may be appropriate for its numerical simulation. The influence of temperature on the mechanical behavior was assessed in both the longitudinal and transverse tensile directions, as well as in shear. Results reveal that lower temperatures lead to increased stiffness and strength, although differences between –40 °C and –70 °C were not substantial.

Fracture characterization of hybrid composite laminates in modes I and II

Juan de Gracia Igelmo — Wed, 02 Jul 2025 09:27:53 +0200

In this work, the Mode I and Mode II interlaminar fracture toughness of a hybrid laminate composite consisting of carbon fiber-reinforced layers and glass fiber-reinforced layers was characterized. Unidirectional laminates were used for the tests, and the stacking sequence was chosen with the aim of achieving pure fracture modes in the tests. Mechanical characterization was carried out using three-point bending tests with different spans, taking into account the effects of indentation, shear, and support rotation. Mode I and Mode II interlaminar fracture tests were performed using the ADCB (Asymmetric Double Cantilever Beam) and AENF (Asymmetric End Notched Flexure) tests, respectively, also considering the effects of shear, local deformation, and rotations due to bending. The data were obtained using a recently published analytical model that allows the resistance curve to be found for each load-displacement data obtained from the testing machine.

Ballast Impact Damage Characterization. Determination of Acceptance/Rejection Criteria for Railway Components Made of CFRP.

Francisco José García Piñeiro — Fri, 11 Apr 2025 08:27:24 +0200

In recent years, the railway sector has been developing high-responsibility lighter components (such as the running gear frame), made from composites (mainly CFRP) to meet the new challenges of the sector. However, these components may be more sensitive to damage from impacts compared to conventional metallic ones. In high-speed train operations, elements located on the lower parts of the train are exposed to impacts with ballast stones that are lifted as the train passes (v > 200 km/h), leading to damage (sometimes internal and not visible) that can limit the use of these materials. During the development of CFRP components by Talgo, the damage caused by these types of low-velocity impacts has been analyzed and evaluated. These impacts can cause damage that requires more or less complex technologies (such as ultrasound) for evaluation, which are difficult to implement in maintenance operations. From the studies conducted on CFRP materials (compliant with the EN-45545 standard for fire, smoke, and toxicity), it has been found that acceptable approaches can be used, with easily implementable measures in routine inspections, to estimate the damage caused by ballast stone impacts. In these analyses, it was observed that: a) It is possible to estimate the impact energy level through the depth of the surface damage, b) it is possible to estimate the size of the internal damaged area based on the energy level, and c) it is possible to determine the residual strength based on the size of the internal damaged area. These results allow us to establish both acceptance requirements and criteria for the repair and rejection of materials

Experimental characterisation of the translaminar fracture toughness of an additive manufacturing c-CFRP composite

Alex Fernández — Mon, 14 Apr 2025 13:32:24 +0200

Fibre breakeage in composite materials is usually a determining damage mechanism for its structural integrity due to the high energy associated, in comparison with matrix cracking. For this reason, the assessment of the translaminar fracture toughness is relevant for accurate numerical predictions of composite structures. However, there are scarce investigations related to this topic for additive manufactured composites reinforced with continuous fibres. In this investigation, the translaminar fracture toughness of 3D-printed continuous fibre reinforced polymer (c-CFRP) composites was characterised using double-tapered compact tension (2TCT) specimens. The 2TCT geometric dimensions were obtained through a parametric study to prevent undesired failure modes. The results show a translaminar fracture toughness of 17.4 N/mm for the tested 0/90 laminates. The fracture toughness corresponding to the tensile failure of the 0° ply was derived using a rule-of-mixtures approach. Post-mortem micrographic and X-ray analysis indicated the presence of fibre pull-outs in the crack surface and confirmed the absence of any additional damage, validating the use of 2TCT geometry for the determination of the translaminar fracture toughness in additively manufactured c-CFRP composites.

Caracterización de las propiedades mecánicas de estructuras kirigami impresas en 3D y sus conexiones fabricadas con materiales compuestos

Montserrat Dolz — Mon, 14 Apr 2025 22:00:24 +0200

El avance de la tecnología de impresión 3D ha permitido la creación de estructuras complejas con formas únicas, como los diseños basados en kirigami, inspirados en el arte de cortar papel para formar estructuras tridimensionales. Estas estructuras ofrecen beneficios significativos, como una construcción ligera, despliegue rápido y la capacidad de soportar cargas mecánicas y absorber energía de deformación. Sin embargo, existe una investigación limitada sobre el comportamiento de estas estructuras y sus conexiones críticas cuando se fabrican con materiales compuestos mediante técnicas de impresión 3D.

Este estudio examina las propiedades mecánicas de estructuras kirigami impresas en 3D y sus conexiones, centrándose en mejorar el comportamiento de unión y optimizar el uso del material. Se emplea el marco Space Mapping para abordar la anisotropía inherente de los compuestos impresos en 3D, transformando el comportamiento direccional complejo del material en un dominio isotrópico equivalente. Este enfoque permite aplicar modelos no lineales isotrópicos ya consolidados, mejorando la precisión de la simulación y reduciendo el coste computacional.

Se utilizan simulaciones por elementos finitos para modelar el comportamiento de las estructuras kirigami, prestando especial atención a las propiedades del material, la adhesión entre capas, la dirección de impresión y la orientación de las fibras en el material compuesto. Se llevan a cabo ensayos mecánicos para validar las simulaciones, centrándose en la rigidez y resistencia de los pliegues y uniones bajo diferentes condiciones de carga. Mediante la mejora de los mecanismos de plegado y la optimización de la distribución del material en las zonas críticas, esta investigación busca demostrar cómo se comparan las estructuras kirigami frente a los diseños sólidos tradicionales en aplicaciones que requieren tanto resistencia como adaptabilidad.

Estos resultados son especialmente relevantes para sectores donde se necesitan diseños ligeros y flexibles, como la aeronáutica, la automoción, el transporte marítimo y la ingeniería civil. Combinando análisis numérico con validación experimental, el estudio ofrece aportaciones valiosas para la optimización de los puntos de plegado y conexión en estructuras kirigami impresas en 3D, con vistas a su aplicación en la ingeniería avanzada.

Polymerization kinetics of a recyclable thermoplastic as a matrix for structural composites

Jordi Farjas — Tue, 08 Apr 2025 18:57:23 +0200

In this contribution we have performed the kinetic analysis of the curing process and of its thermal decomposition. Due to the presence of a peroxide initiator, polymerization is a complex process involving an induction period for a fast cross-linking reaction. From the kinetic analysis, we have been able to characterize the induction time and the degradation kinetics. Finally, from the analysis of the volatiles we have determine that the main volatile generated during decomposition is the monomer.

Compensation of thermal and mechanical effects of a Lamb-Wave based SHM system in a composite aerostructure.

Jesús Sesé — Sun, 06 Jul 2025 23:08:53 +0200

Structural Health Monitoring has become one of the next challenges in the aeronautical industry in order to know the real-time status of structures and optimize their maintenance. The use of Lamb Waves for damage detection is proven; however, its effectiveness is affected by the boundary conditions in which the structure is located. To counteract this effect, it is essential to model its behavior in different environmental and operating conditions to ensure the correct detection of variations in the structure during its service life. This work presents the characterization of the Lamb wave behavior for a composite UAV supporting surface. By applying different load and temperature conditions to the structure, different conditions of the structure during flight will be simulated. The results obtained for the newly fabricated structure will be compared with the results obtained for the same structure damaged by impact. And finally, the main effects produced on the signal (arrival time, amplitude...) will be analyzed; and how they can simulate the presence of a damage that has not occurred (false positive) or camouflage the presence of existing damage (false negative).

Long-term performance of injection-molded isotactic polypropylene containing weld lines in unfilled and glass fiber-reinforced grades

Aitor Arriaga — Wed, 02 Apr 2025 10:06:44 +0200

The study of weld lines in polymers is far from settled, especially in predicting how materials perform over long periods under stress. While previous research has explored the behavior of isotactic polypropylene (iPP) in both its unfilled and glass fiber-reinforced forms, the focus has been largely on short-term behavior. However, this study shifts the lens to long-term performance under complex conditions, specifically looking at creep and fatigue. We take a novel approach by considering iPP with 30% glass fiber reinforcement, using tensile samples that induce weld line formation. Creep behavior is measured across a broad range of strain rates and temperatures, aiming to understand the underlying mechanisms that govern material failure. These short-term tests are then linked to more comprehensive long-term evaluations, including cyclic loading and creep-to-rupture tests. Crack growth is assessed using CT specimens, enabling us to capture failure modes that are otherwise difficult to quantify. The study goes further by proposing a new way to model deformation. Instead of relying on traditional methods, we turn to the Eyring equation for a more accurate prediction of failure times under cyclic stress, especially as materials transition to brittle fracture at higher temperatures. These predictions match experimental results, demonstrating the potential of linear elastic fracture mechanics (LEFM) in assessing long-term material performance. Ultimately, this research challenges conventional models and provides a pathway for more accurate long-term predictions, a crucial step for industries relying on polymer materials in demanding environments.

Development and integration of printed strain gauge-based sensors for structural health monitoring in composite material repairs of wind turbine blades

EDURNE TELLECHEA — Mon, 14 Apr 2025 11:00:23 +0200

Structural health monitoring is essential to ensure safety and extend the service life of critical components in renewable energy systems, such as repaired wind turbine blades. This study presents the development of strain gauges printed using advanced functional printing techniques, optimized for integration into composite materials and tailored to the mechanical characteristics of repaired areas to assess the effectiveness and durability of structural repairs. The integration of these sensors would enable real-time monitoring of key parameters, such as microstrains, during the operation of the blade after repair. The experimental work included the printing of strain gauges, evaluation of different substrates, and cyclic loading tests under controlled conditions to assess the accuracy and sensitivity of the printed gauges. Additionally, composite material coupons were characterized under tensile and compressive loads to analyse the impact of gauge integration on the mechanical properties of the composite. Preliminary results demonstrate the feasibility of this approach, although full validation is required, including aging studies, testing in real operational environments, and exposure to extreme temperature variations prior to industrial implementation.

Mechanical performance of continuous fiber-reinforced thermoplastic composites for structural applications

Jaime Lozano — Fri, 16 May 2025 07:47:23 +0200

Continuous fiber-reinforced thermoplastic composites are emerging as an efficient structural alternative to traditional thermoset materials, thanks to their recyclability, good impact resistance, and suitability for continuous processing. In this work, a manufacturing system was developed based on the thermoplastic pultrusion of unidirectional polypropylene (PP) and carbon fiber (CF) tapes, followed by hot compression molding. This approach enables the production of structural profiles with high fiber alignment and good consolidation. Experimental characterization included tensile, flexural, and impact tests to assess the structural applicability of the manufactured profiles. The results demonstrate a balanced combination of stiffness, mechanical strength, and impact performance, confirming the potential of this system for functional applications in sectors such as mobility or infrastructure, where lightweight, efficient processing, and sustainability are key requirements.

Experimental Evaluation of the Damping Factor in Laminated Composite Materials

Daniel Trias — Fri, 11 Apr 2025 18:56:56 +0200

The use of natural fibers in composite materials is gaining significant interest in the current context of emission reduction. In this regard, along with the fact that it is an eco-responsible material, it becomes a very attractive option, although its clear inferiority in mechanical properties such as stiffness and strength compared to glass fiber, and certainly carbon fiber, raises doubts about its use in structural applications. However, flax fiber's ability to absorb and damp vibrations is much greater than that of the aforementioned high-performance structural fibers. The experimental determination of the damping coefficient emerges as a key aspect that may allow for the consideration of natural fibers in structural applications requiring damping. Existing standards are very generic and do not account for some important details in the execution of the test. The present work presents the experimental method used for determining the damping coefficient of laminated composite materials using accelerometers and a vibration exciter (shaker), including consideration of the analysis of the effect of certain parameters such as the positioning of accelerometers, excitation methods, and data reduction methods.

Effect of Environmental Degradation on the Fatigue Resistance of Mode II Adhesive Joints in Carbon/Epoxy Composite Materials

Paula Vigón — Fri, 11 Apr 2025 17:06:23 +0200

This study analyzes delamination in CFRP adhesive joints under mode II loading in both static and dynamic regimes. The ENF test was used to evaluate the effect of exposure to salt spray and a climatic chamber over various periods—one, two, four, and twelve weeks—as well as for unaged specimens. Based on the experimental data, fatigue initiation curves (ΔG-N) and fatigue crack growth curves (G-da/dN) were constructed to analyze both degradation processes. In the fatigue initiation phase, the data were analyzed using a probabilistic model based on a Weibull distribution. The most relevant findings of this study are as follows: regarding the fatigue limits obtained for the adhesive joint under mode II fracture, a decrease in load-bearing capacity was observed due to degradation processes—around 20% under static loading conditions for salt spray exposure, and 25% for hygrothermal degradation. As for the fatigue crack growth phase, the crack propagation rates were found to depend on the specific environmental degradation process to which the tested specimens were subjected.

Matrix cracking effect in thermoset and thermoplastic CFRP: development of an analysis tool for the design of hydrogen tanks

Mayerlin Salgado — Thu, 12 Jun 2025 14:32:44 +0200

Liquid hydrogen (LH₂) is a promising alternative to reduce carbon dioxide (CO₂) emissions in the aeronautical industry. However, current tanks do not meet their rigorous design and safety requirements. Carbon Fibre Reinforced Polymers (CFRP) offer advantages over classic metallic materials, such as higher stiffness and toughness at low temperatures, as well as lower density. Nevertheless, matrix cracking in composites can cause leaks through the tank walls, compromising their tightness, even with a low crack density. Therefore, a deeper understanding of this phenomenon could prevent permeability loss and ensure the operational safety of the tank. Currently, thermoplastic composites are gaining distinction over thermosets in the aeronautical industry due to their better range of properties and the possibility of out-of-autoclave manufacturing. In this context, CF/PEEK composite has shown greater resistance to damage propagation compared to epoxy-based materials, positioning it as a promising candidate for LH₂ storage tanks. This research evaluates the initiation and propagation of transverse cracks in the matrix in specimens with 0º and 90º layer orientations of thermoplastic (CF/PEEK) and thermoset (M21E/IMA-12K) matrices under static loads and at room temperature. Two different stacking sequences, [0/90/0₂/90₂]s and [90/0/90₂/0₂]s, have been analysed. X-ray tomography images were captured at different deformation states. From these images, crack density was calculated using a digital processing method developed by the authors, which quantifies the number of cracks in each layer across the entire width of the specimen. This method allows for a three-dimensional (3D) visualization of the inspected area, facilitating the tracking of possible paths that could compromise the tightness of the tanks. These results contribute to the design of safer and more efficient tanks for liquid hydrogen storage in aeronautical applications.

Characterization of 3D-printed cordierite-rGO nanocomposites for aerospace applications

Maria Garcia-Martinez — Mon, 14 Apr 2025 23:00:45 +0200

One of the most critical challenges in the aerospace industry is the mismatch in the coefficient of thermal expansion (CTE) between optical components in satellites and their metallic supports, which limits system reliability and performance. Ceramic materials, due to their superior thermal properties, offer a potential solution; however, their adoption has been limited by the complexity of their geometries and conventional manufacturing constraints. Additive manufacturing has opened new opportunities for the development of advanced ceramics, including ceramic matrix composites (CMCs). Within the framework of the AERORECORD-3D project, funded by the Spanish Ministry of Science and Innovation, ceramic cordierite-based supports reinforced with reduced graphene oxide (rGO) have been developed for aerospace applications. In this study, cordierite nanocomposites with varying rGO contents were successfully fabricated via 3D printing. Their thermal, electrical, and mechanical properties were evaluated to assess their performance, exploring their potential as advanced materials for demanding space applications. This work represents a significant step toward the implementation of 3D-printed ceramic nanocomposites by combining innovative materials with advanced additive manufacturing technologies.

Development of dry fiber based on thermoplastic binders for aeronautical applications

GUILLERMO ULLDEMOLINS DE OLIVES — Thu, 15 May 2025 12:13:34 +0200

As part of the regional NEOCOMP project, funded by IVACE in the Valencian Community, AIMPLAS presents a comprehensive approach to the development of advanced composite materials by producing dry fiber through its own pilot line. This work focuses on the development of thermoplastic binders, dry fiber production, pre-consolidation and resin infusion, as well as the study of mechanical properties. The main objective is the development of thermoplastic binders and the subsequent production of dry fiber. The binders will be formulated using compounding technologies with co-rotating twin-screw extruders to ensure proper dispersion and distribution of the additives. The dry fiber will be produced using a pilot plant system designed and developed by AIMPLAS, equipped with the necessary technology for binder adhesion onto continuous reinforcement. Finally, the materials will be validated for processing with AFP (Automated Fiber Placement) equipment to achieve pre-consolidated panels. After pre-consolidation, resin infusion will be carried out to obtain high-performance structural materials. The binder materials will be characterized through powder granulometry analysis, while the dry fiber will be studied using scanning electron microscopy (SEM) to evaluate binder-to-fiber distribution and adhesion. The project concludes with a thorough tensile analysis of the infused panels, following standards for mechanical performance evaluation. The results obtained not only highlight the potential of the developed materials but also demonstrate the feasibility of this approach for the industrial production of high-performance composite materials for key sectors such as aerospace.

Development of thermoplastic composites with energy storage capacity for aeronautical applications

Fernando Ramos Saz — Fri, 16 May 2025 20:23:22 +0200

The RE-CELL project proposes a comprehensive approach to developing multifunctional structural composites capable of energy storage for non-critical aeronautical applications. The project is rooted in the recycling and valorization of carbon fiber waste through solvolysis, promoting environmental sustainability and circular economy principles. Recovered fibers are functionalized with conductive materials such as carbonaceous particles and MXenes, enabling them to serve as both structural reinforcement and electrodes. Solid electrolytes are produced by incorporating thermally stable ionic liquids and BaTiO₃ as a dielectric enhancer into a polycarbonate matrix via extrusion. The resulting films function simultaneously as electrolytes and separators. Finally, the structural cells are assembled by compression molding and subjected to mechanical (tensile, flexural, delamination) and electrochemical (electrochemical impedance spectroscopy, cyclic voltammetry) characterization. The project aims to scale up the most promising multifunctional laminates and validate their performance through a demonstrator based on the geometry of an actual aircraft fuselage component.

Manufacturing of new composites with a polypropylene matrix and latxa sheep wool reinforcement

Ander Larruscain — Fri, 11 Apr 2025 18:29:23 +0200

The development of new sustainable materials is key to meeting growing demand without compromising the planet’s future. To achieve this, it is essential to reduce environmental impact through strategies like those of the circular economy. One example is the use of Latxa sheep wool, a breed associated with Idiazabal cheese in the Basque Country. This wool has interesting physical, chemical, and mechanical properties, but currently lacks industrial applications. Therefore, it could be used as reinforcement in composite manufacturing, also supporting the local economy. In this study, polypropylene (PP) was used as the matrix—one of the most widely used thermoplastic polymers due to its versatility, good barrier properties, and chemical resistance. However, PP has few functional groups, which limits interaction with other materials. This may lead to poor adhesion at the fiber-matrix interface, affecting the cohesion and properties of the composite. To address this, composites of PP with Latxa wool fiber (PPWF) were prepared, analyzing the effect of modifying the PP with maleic anhydride (MAPP) to enhance compatibility between the matrix and the protein-based fiber. MAPP was added in a proportion of 10% relative to the wool fiber. The results show that adding 20% wool to the modified matrix significantly improves both the strength and modulus of the PP.

Flame retardant polyurethane nanofibers based on the Diels-Alder reaction

Arantxa Eceiza — Tue, 10 Jun 2025 18:03:24 +0200

In this study, a halogen-free flame retardant containing maleimide groups was synthesized and incorporated into a polyurethane solution containing pendant furan groups (PUF), with the aim of producing nanofibres via electrospinning. The furan groups of the polyurethane and the maleimide groups of the flame retardant readily react with each other via the Diels–Alder (DA) reaction. The resulting nanofibre membranes were characterized before and after crosslinking through DA reaction. Microscopy images of the membranes showed morphologically homogeneous and defect-free nanometric fibers. The crosslinked membranes exhibited higher solvent resistance and superior mechanical properties compared to the uncrosslinked ones. Thermal analysis showed that the flame retardant promotes the formation of a protective carbonaceous layer that gives the membranes fire-resistant properties.

Functionally Graded Foamed PLA Cores for Optimized Vibratory Behavior in Sandwich Panels

Jon Rodriguez — Thu, 10 Apr 2025 11:40:34 +0200

Fused filament fabrication of foamed PLA enables lightweight structural parts with adjustable density and stiffness. This material expands during printing, making it ideal for functionally graded materials. It can serve as a sandwich core, enhancing lightweight properties. These panels can be a promising type of panel, as their behavior, such as vibracoustic, can be customized. However, their effectiveness in vibration attenuation remains unexplored. This study designs, manufactures, and tests 3D-printed foamed PLA sandwich panels with variable stiffness and density to improve vibroacoustic performance. The material’s Poisson’s ratio and elasticity modulus were characterized as a function of density, controlled by hot-end temperature and extrusion flow rate. A finite element model with spatially variable mechanical properties was developed for optimization. A genetic algorithm determined the optimal core properties to maximize the first two natural frequencies of a plate with one fixed edge and three free edges. The best designs were fabricated and tested, showing significant increment in the first two natural frequencies. This work advances the design and manufacturing of 3D-printed foamed PLA sandwich panels and contributes to high-performance, functionally graded components for enhanced vibroacoustic behavior.

Ionic conductive bio-based composite aerogels

Miguel Sanchez-Soto — Sun, 06 Apr 2025 00:50:23 +0200

In the realm of energy transition, significant advancements are essential on the improvement of energy storage performance as well as in sustainability and safety. Aerogels are lightweight materials that can be endowed with mechanical strength, thermal insulation capability, and fire resistance. These characteristics make them promising for electrochemical devices such as composite polymer electrolytes (CPE). Silica-based aerogels have been used as scaffolds for solid polymer electrolytes (SPE). In these applications, the aerogel not only provides structural support but also creates additional conduction channels that improve ionic conductivity (IC). In this work, we present a bio-based aerogel composed of gelatin, montmorillonite clay, and tannic acid, synthesized using water as a solvent. By employing an ice templating strategy, we achieved a 1D pore orientation, which provides more direct conduction pathways. This aerogel exhibits an axially oriented honeycomb porous structure with high porosity (92.9 ± 0.1%) and low density (0.130 ± 0.002 g/cm³). It is also categorized as a self-extinguishing material. This aerogel was infiltrated with a SPE consisting of Polyethylene glycol (PEG) and Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). With partial pore coverage, we achieved IC at room temperature on the order of 2 × 10^-7 S/cm. This led to promising results, resulting in a porous (76%) ionic conductive aerogel that opens new perspectives. It enables the creation of a low-density solid electrolyte, which can increase the specific capacity of the final device. Alternatively, it can serve as an active, fire resistant, scaffold for a liquid or gel electrolyte, enhancing and maximizing IC.

Nanocomposites based on PVDF-HFP and piezoelectric nanoparticles fabricated by solvent-casting and electrospinning techniques for sensing applications

Esther Arribas Yuste — Mon, 14 Apr 2025 23:24:13 +0200

This work deals with the development of flexible piezoelectric nanocomposites based on PVDF-HFP copolymer reinforced with ZnO nanoparticles (NPs) for biomedical sensing applications. Two fabrication techniques are analyzed: solvent casting and electrospinning. The films obtained by the solvent casting technique, characterized by FTIR-ATR and Atomic Force Microscopy (AFM) in PFM mode, show a significant increase of the piezoelectric coefficient (d₃₃) for ZnO NPs concentrations equal or higher than 12% by weight, with respect to the unreinforced polymeric matrix. FTIR analysis estimated an electroactive phase content close to 60% in the reinforced samples. On the other hand, the preliminary study of optimization of electrospinning parameters, evaluated by Scanning Electron Microscopy (SEM), demonstrates the feasibility of forming mats with high fiber content and homogeneous nanofiber diameters between 110-140 nm, whose morphology depends on parameters such as the speed of the collector. These preliminary results are promising for obtaining flexible piezoelectric fabrics by both fabrication routes.

Optimization of a car hood using natural fiber composite and 3D-printed PLA foam

Aritz Esnaola — Fri, 11 Apr 2025 15:23:13 +0200

Thanks to the wide range of available cores and skins, the design and manufacture of sandwich structures allows for many variations, but conventional manufacturing processes limit design freedom when it comes to geometries. In recent years, interest in sustainable materials, such as plant-based resins and natural fibres, has grown. Furthermore, recent advances in 3D printing have opened up new design possibilities, including the use of biodegradable foams and functionally graded structures. This study presents the development of a 1:6 scale car bonnet, where the skin is made of bio-epoxy resin reinforced with flax fibre and the core is a PLA foam produced via additive manufacturing. Two variants were considered: in the first, the core was distributed homogeneously across the entire bonnet surface, and in the second, it was distributed in areas selected through topological optimisation simulations. As both bonnets have the same mass, the density of the homogeneous bonnet had to be lower. This was achieved by programming different 3D printing parameters. Quasi-static load test results show that the bonnet with the optimised distribution is 25% stiffer. The study's main conclusion is that manufacturing cores using 3D-printed foamed PLA enables a wide range of densities and design possibilities that are not feasible with conventional materials and manufacturing processes.

Thermal and flame retardant properties of recyclable disulfide based epoxy vitrimers

Alaitz Rekondo — Thu, 10 Apr 2025 09:20:33 +0200

The development of flame-retardant epoxy vitrimers which are suitable for use as a composite matrix material is essential for the transition to a sustainable circular economy. In this work the thermal and flame-retardant properties as well as the rheological characteristics of epoxy vitrimers based on 4-Aminophenyldisulfide (4-AFD) hardener and with different reactive and additive Phosphorus based flame retardants (FR) with different oxidation states were studied. The use of 4-AFD as curing agent imparts vitrimeric properties to the material and allows repairing, reprocessing and recycling. A series of epoxy vitrimers (EV) were prepared aiming to improve the flame-retardant properties while maintaining dynamism and reprocessability. The neat EV (T_g ∼125 °C) showed a limited oxygen index (LOI) of 20.9 ± 0.4 %O₂ and no classification and heavy dripping in the UL-94 vertical burning test. With 1.5 wt% of Phosphorous (P) in the EV, LOI values up to 38.5 ± 0.4 %O₂ and V-0 classification with excellent self-extinguishing behavior was achieved. Especially gas phase active FRs with lower oxidation states showed better flame-retardant properties in the LOI and UL-94 vertical burning tests with identical phosphorus content. In cone calorimeter test the EVs with 1.5 wt% P reduced the peak heat release rate (PHRR) up to 43 %. The addition of reactive phosphorous-based FRs did not influence the dynamism and recyclability of the material in dynamic mechanical analysis. After mechanical recycling >73 % of the mechanical strength was recovered and the flame retardant EVs do reach as well a V-0 classification in the UL-94 vertical burning test.

Lightweight, very high-speed bogie frame. CFRP in high-responsibility railway components

Diego Escobar Redondo — Fri, 25 Apr 2025 16:50:14 +0200

In recent years, the railway sector has been demanding lighter, high-responsibility components made from composites due to the incorporation of new technologies to improve passenger comfort and experience, as well as to address new environmental challenges (reducing emissions, energy consumption, increasing capacity, etc.). With this objective, Talgo introduces a high-performance composite bogie frame (CFRP) for very high-speed trains, traditionally made of metal (steel), which allows for weight reductions of over 30%. Additionally, this new bogie leverages the fatigue properties of these materials to incorporate the first stage of suspension into the frame itself. The reduction of bogie elements, as well as infusion manufacturing, improves competitiveness throughout the lifecycle compared to a traditional bogie, complying with the EN-45545-2 HL2 standards for fire, smoke, and toxicity. The project for this lightweight frame will be completed with manufacturing and bench testing in accordance with EN 13749 standards, as well as ballistic impact tests with ballast stones.