Many closed-cell foams exhibit an elongated cell shape in the foam rise direction, resulting in anisotropic compressive properties, e.g. modulus and strength. Nevertheless, the underlying deformation mechanisms and how cell shape anisotropy induces this mechanical anisotropy are not yet fully understood, in particular for the foams with a high cell face fraction and low relative density. Moreover, the impacts of mesostructural stochastics are often overlooked. This contribution conducts a systematic numerical study on the anisotropic compressive behaviour of low-density closed-cell foams (with a relative density <0.15), which accounts for cell shape anisotropy, cell structure and different mesostructural stochastics. Representative volume elements (RVE) of foam mesostructures are modelled, with cell walls described as Reissner–Mindlin shells in a finite rotation setting. A mixed stress–strain driven homogenization scheme is introduced, which allows for enforcing an overall uniaxial stress state. Uniaxial compressive loadings in different global directions are applied. Quantitative analysis of the cell wall deformation behaviour confirms the dominant role of membrane deformation in the initial elastic region, while the bending contribution gets important only after buckling, followed by membrane yielding. Based on the identified deformation mechanisms, analytical models are developed that relate mechanical anisotropy to cell shape anisotropy. It is found that cell shape anisotropy translates into the anisotropy of compressive properties through three pathways, cell load-bearing area fraction, cell wall buckling strength and cell wall inclination angle. Besides, the resulting mechanical anisotropy is strongly affected by the cell shape anisotropy stochastics while almost insensitive to the cell size and cell wall thickness stochastics. The present findings provide deeper insights into the relationships between the anisotropic compressive properties and mesostructures of low-density closed-cell foams.

Combining continuous unidirectional (UD) prepreg and advanced discontinuous long fiber-based sheet moulding compound (ASMC) in a hybrid component is advantageous for applications where cost and environmental impact of the manufactured part are of significance. Previous works have focused on the flow/compaction of ASMC and its interaction with continuous fibres at high pressures. However, little is known about the forming behaviour of such layups. This work investigates the formability of hybrid carbon fibre UD-ASMC composite layups. The deformation mechanisms during forming and their interactions are investigated experimentally. Forming simulations are conducted alongside experimental tests under varying layup configurations. The results show that the hybrid layup combinations investigated exhibited poor forming characteristics. This was due to the high interply friction properties of the UD-ASMC interface, which, in turn, restricted the intraply shear of the hybrid stack. A strong correlation between the numerically predicted forming outcomes and experimentally formed parts demonstrates that generic FE-solvers can provide a first estimate of the forming outcome when coupled with a good understanding of the underlying deformation mechanisms. However, these methods are computationally expensive and are better suited for detailed evaluations rather than for use in design applications.

The next generation of composite structures within aerospace is envisioned to evolve from a strictly mechanical to a multifunctional structure, adding functionalities to the structure by embedment of functional filler material or incorporation of foreign structures. The introduction of carbon nanotubes (CNTs) into the composite structure to achieve sensing capabilities is one example. In this paper, online cure monitoring of aerospace-grade glass fibre/epoxy prepreg laminates is performed by in-situ resistive measurements on embedded vertically aligned carbon nanotube (VACNT) forests. The measured resistance over the course of the cure cycle has a reproducibility in its shape, itself a reflection of the state of the embedded CNTs. The measured resistance is interpreted after studying the morphology of the VACNT forest, cure kinetics and viscosity of the resin, and volumetric changes of both resin and laminate during the cure cycle. The resistive signal is determined to detect the transition between the air-evacuation and consolidation regimes of the laminate compaction and the gel point of the epoxy. Unique observations after the gel point are recorded, theorised to be caused by the build-up of residual stresses in the laminate. The proposed cure monitoring sensor system offers great flexibility, being able to monitor the curing process locally anywhere in the laminate. Additionally, the proposed sensor offers a life-span multifunctionality to the produced component, possessing strain and temperature sensing capabilities in the cured state ideal for structural health monitoring.

In the transportation sector, any small changes in structural mass have a significant impact on the overall fuel and energy consumption of a vehicle over its lifetime. Thus, the pursuit of mass optimization has gained popularity to cut costs and lower energy usage. Notably, the railway bogie, a crucial component of a railway coach, accounts for more than a third of the coach's mass. Consequently, reducing the weight of the bogie can yield substantial reductions in the overall mass of the railway coach. Therefore, the utilization of materials with relatively higher performance-to-weight ratios, such as Carbon and Glass Fiber Reinforced Polymers (CFRPs/GFRPs), holds immense potential for mass reduction. However, it's crucial to adopt a holistic perspective when evaluating the energy consumption and environmental footprint of a structure due to the energy intensive nature of CFRP materials. In this research, we assess the environmental impact of a light-weight composite bogie frame using a Predictive Life-Cycle Assessment (PLCA) methodology. The impact category chosen for this cradle-to-grave assessment is the Cumulative Energy Demand (CED), with a special emphasis on evaluating the energy consumption during the EOL phase. The CED of the frame is evaluated over its service life with a comparison being made with a conventional metallic frame. The results show that using GFRPs in the composite side beam reduces the CED by approximately 25%. The break-even analysis performed showed that the steel structure has a lower energy consumption below a service life of 1,794,000 kms as compared to the GFRP side-beam manufactured by manual processes.

Design of a sustainable and economical composite structure is challenging due to the often contradicting design drivers such as energy consumption and cost. Therefore, predicting the environmental and economic impact in the early stages of product design results in the significant reduction of energy consumption and cost. Consequently, the impact of contrasting objectives on an optimized carbon fibre reinforced polymer (CFRP) demonstrator is evaluated in this study. This evaluation is performed by integrating a predictive life-cycle assessment and costing framework in a multi-objective optimization methodology. The varying design configurations include designs with and without stiffeners. Furthermore, the impact of end-of-life allocation on the optimized design is also evaluated in this study. The results show a marked difference between the energy consumption of the various optimized designs with energy optimization producing the most efficient solution. However, the mass of the demonstrator increases by 7–9 kg across the different design configurations when the closed loop allocation model is implemented. Consequently, the results show the importance of selecting an appropriate EOL allocation methodology in evaluating the energy consumption of a product. The results also show that the parameters driving the energy consumption (mass and material configuration) and cost (complexity and manufacturability) are varied and often contrasting. The differences in mass, cost, and energy optimized designs further reinforces the importance of coupling cost and energy evaluation in design of sustainable products. Finally, the study demonstrates the need for a holistic life-cycle based assessment in early stage sustainable product design.

This work investigates the role of fibre orientation on interply friction. Interply friction tests were performed on a novel snap-cure unidirectional (UD) carbon/epoxy prepreg for five fibre orientations over a broad range of normal pressures and sliding speeds. The test method used closely mimicked the actual processing condition of the prepreg prior to forming including consolidation of the interface. The results show that fibre orientation of the prepreg has a large influence on interply friction. In fact, interply friction for various fibre orientation combinations varies substantially both in magnitude and behaviour of the curve. Further, the range of this variation is dependent on processing conditions such as consolidation, normal pressure and sliding speed. These findings make a strong case for including direction dependent friction models in forming simulations and presents opportunities to tailor the laminate stacking sequence for better forming outcomes.

The fatigue life of welded structures is dependent on the local geometry and imperfections of the welds. Therefore, optimizing the manufacturing processes to improve the local weld geometry and remove possible imperfections can considerably affect the fatigue life of the structure. Post-weld treatments such as burr grinding, and High Frequency Mechanical Impact (HFMI) treatment are commonly used techniques to extend the fatigue life of a weld by modifying the local weld toe geometry. However, employing additional manufacturing processes can have an adverse effect on the Life-cycle cost of a welded structure by increasing production costs. On the other hand, extending the fatigue life of a structure can result in lower maintenance and replacement costs. Therefore, a thorough yet predictive life-cycle cost assessment is required to assess the viability of such treatments and design economically efficient weld structures. This study assesses the life-cycle cost of welded joints. The fatigue life of the weld in this study is analyzed using the effective Notch Stress method (NS). Furthermore, the weld is post-treated with an automated HFMI treatment to prolong its fatigue life. Moreover, the effect of weld quality on the production cost is analyzed. The results show that every phase of the weld's life-cycle has a significant contribution to the life-cycle cost with the use-phase being the more dominant. The results also depict the impact of the changes in weld quality in the overall life-cycle cost.

In this paper, Vertically Aligned Carbon Nanotube (VACNT) forests are embedded into two different glass fibre/epoxy composite systems to study their sensing abilities to strain and temperature. Through a bottom-up approach, performing studies of the VACNT forest and its individual carbon nanotubes on the nano-, micro-, and mesoscale, the observed thermoresistive effect is determined to be due to fluctuation-assisted tunnelling, and the linear piezoresistive effect due to the intrinsic piezoresistivity of individual carbon nanotubes. The VACNT forests offer great freedom of placement into the structure and reproducibility of sensing sensitivity in both composite systems, independent of conductivity and volume fraction, producing a robust sensor to strain and temperature.

The design freedom of composite parts is often limited by the material and/or manufacturing process. When approaching the limits of the processing window, manufacturing robustness is lost, and defects occur. Most common defects are out of plane laminate wrinkles, voids, porosities, delamination, thickness deviations and fibre angle misalignments. The process settings resulting in defects needs to be translated into hard limitations. The research community has during the years added excellent contributions to the understanding of defect generation. In this work we will present the engineering adoption of these results into industrial practice to further improve the composite manufacturing. This work is focusing on corner thickness deviations during manufacturing of carbon/epoxy parts out of Uni-Directional prepreg.

In this paper, non-intrusive vertically aligned carbon nanotubes forests have been used to monitor the cure locally in a glass fiber/epoxy laminate. Deposited on a prepreg surface, the resistance evolution of the conductive vertically aligned carbon nanotube forests is monitored during curing of a laminate. Distinguishable phases of the resistance evolution are observed, correlating to the material characteristics during the heating up and curing. The consolidation of the prepregs is initially seen, followed by the reduction in viscosity, initiation of crosslinking, chemical shrinkage, and gel point of the matrix. Rheological and thermal experiments have been performed to correlate and interpret the resistance evolution in the glass fiber/epoxy laminate during curing. Applying this method, quality control of manufactured components and cure cycle optimization for increased production efficiency and energy savings are envisioned.