An optimisation methodology is developed and applied on a FRP sandwich body of an electric vehicle – ZBee, where single-objective and multi-objective optimisation studies are performed stepwise using ...a commercially available software package. The single-objective optimisation allows the identification of the load paths within the composite body, according to the loading conditions previously defined. Within the multi-objective optimisation, the optimum thickness and distribution for each of the layers that form the composite body are searched within the design space so as to obtain the best performance with respect to weight, material cost, global and local stiffness. Strength requirements are also considered as constraints within the optimisation. A conflict situation appears when several objectives are considered within the optimisation, meaning that an increased performance in one objective may often lead to a decreased performance for the others. Therefore, a trade-off between objectives is needed. The interpretation of results is partially made by using trade-off plots, the so-called Pareto frontiers. A method for the overall selection of the most beneficial solutions is proposed and applied in order to choose between the best obtained solutions according to the importance of the objectives.
Most products today have several functions, but these are achieved by integrating different monofunctional devices and/or materials in a system. Having several functions simultaneously in one single ...material has many potential advantages, such as a structural material that can also store energy, have self-sensing or self-healing capability or any other physical function. This would lead mass and resource savings, being more energy efficient and thus more sustainable. This paper presents a mini review on how carbon fibres can be used for integrating several functions simultaneously in a high-performance load carrying structural material using the electrical and electrochemical properties of carbon fibres. Through this carbon fibre composites can also store energy like a lithium-ion battery, be used as a strain sensor, have electrically controlled actuation and shape-morphing, and be used as an energy harvester.
•An efficient manufacturing route to produce a thermoplastic lattice is presented.•The influence of core geometry on the mechanical properties have been investigated.•Thermoplastic carbon fibre ...structures show competitive mechanical performance.•Thermoplastic single polymer structures show better performance than foams.•Single polymer lattice cores have good recyclability and energy absorption.
A novel manufacturing route to efficiently produce fibre composite lattice structures has been developed. By using thermoplastic composite materials, flat sheets have been continuously folded, cut into a lattice shape and joined into a sandwich structure. Carbon fibre reinforced poly-ethylene terephthalate (CPET) and poly-ethylene terephthalate fibre reinforced poly-ethylene terephthalate (SrPET) materials have been used to explore two different core options; a carbon fibre option which gives high performance but low recyclability and a single polymer PET option which gives lower performance but full recyclability. Parametric numerical simulations have been used to investigate how the various manufacturing parameters affect the mechanical performance of the core. The carbon fibre composite cores have mechanical performance on-par or better than existing metallic and composite lattice cores presented in literature. Single polymer PET cores show better performance compared to high-end foam cores but have considerable lower performance than carbon fibre lattice cores.
A structural lithium ion battery is a material that can carry load and simultaneously be used to store electrical energy. We describe a path to manufacture structural positive electrodes via ...electrophoretic deposition (EPD) of LiFePO4 (LFP), carbon black and polyvinylidene fluoride (PVDF) onto carbon fibers. The carbon fibers act as load-bearers as well as current collectors. The quality of the coating was studied using scanning electron microscopy and energy dispersive X-ray spectroscopy. The active electrode material (LFP particles), conductive additive (carbon black) and binder (PVDF) were found to be well dispersed on the surface of the carbon fibers. Electrochemical characterization revealed a specific capacity of around 60–110 mAh g−1 with good rate performance and high coulombic efficiency. The cell was stable during cycling, with a capacity retention of around 0.5 after 1000 cycles, which indicates that the coating remained well adhered to the fibers. To investigate the adhesion of the coating, the carbon fibers were made into composite laminae in epoxy resin, and then tested using 3-point bending and double cantilever beam (DCB) tests. The former showed a small difference between coated and uncoated carbon fibers, suggesting good adhesion. The latter showed a critical strain energy release rate of ∼200–600 J m−2 for coated carbon fibers and ∼500 J m−2 for uncoated fibers, which also indicates good adhesion. This study shows that EPD can be used to produce viable structural positive electrodes.
Structural batteries (SBs) are a growing research subject worldwide. The idea is to provide massless energy by using a multifunctional material. This technology can provide a new pathway in ...electrification and offer different design opportunities and significant weight savings in vehicle applications. The type of SB discussed here is a multifunctional material that can carry mechanical loads and simultaneously provide an energy storage function. It is a composite material that utilizes carbon fibers (CFs) as electrodes and structural reinforcement which are embedded in a multifunctional polymer matrix (i.e., structural battery electrolyte). A feasible composite manufacturing method still needs to be developed to realize a full-cell SB. UV initiated polymerization induced phase separation (PIPS) has previously been used to make bicontinuous structural battery electrolytes (SBE) with good ionic conductivity and mechanical performance. However, UV-curing cannot be used for fabrication of a full-cell SB since a full-cell is made of multiple layers of nontransparent CFs. The present paper investigates thermally initiated PIPS to prepare a bicontinuous SBE and an SB half-cell. In addition, the effect of curing temperature was examined with respect to curing performance, morphology, ionic conductivity, and mechanical and electrochemical performance. The study revealed that thermally initiated PIPS provides a robust and scalable process route to fabricate SBs. The results of this study are an important milestone in the development of SB technology as they allow for the SB fabrication for an actual application. However, other challenges still remain to be solved before this technology can be introduced into an application.
Most products today have several functions, but these are achieved by integrating different monofunctional devices and/or materials in a system. Having several functions simultaneously in one single ...material has many potential advantages, such as a structural material that can also store energy, have self-sensing or self-healing capability or any other physical function. This would lead mass and resource savings, being more energy efficient and thus more sustainable. This paper presents a mini review on how carbon fibres can be used for integrating several functions simultaneously in a high-performance load carrying structural material using the electrical and electrochemical properties of carbon fibres. Through this carbon fibre composites can also store energy like a lithium-ion battery, be used as a strain sensor, have electrically controlled actuation and shapemorphing, and be used as an energy harvester.
A structural battery is a multifunctional battery that can carry a load while storing energy. Structural batteries have been a cutting-edge research focus in the last decade and are mainly based on ...polyacrylonitrile (PAN)-carbon fibers (CFs). In this work, positive electrodes based on PAN-carbon fibers were manufactured with powder impregnation (siphon impregnation) technique using a water-based slurry containing lithium iron phosphate (LFP) as the active electrode material and the water-soluble binder polyethylene glycol (PEG). Different coating compositions, electrode-drying temperatures, and coating parameters were investigated to optimize the coating uniformity and the electrochemical performances. Scanning electron microscopy results showed that the electrode materials coat the CFs uniformly, conformably, and individually. Electrochemical characterization of pouch cells shows that the electrodes containing 6 wt% PEG dried at 140 °C have the best battery performance, delivering a first discharge capacity of 151 mAh g−1 and capacity retention higher than 80% after 100 cycles. Moreover, excellent capacity reversibility was achieved when the electrodes were cycled at multiple C-rates attesting to their stability. The results demonstrate that CFs perform excellently as current collectors in positive electrodes.
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•Powder impregnation was a successful method to coat carbon fibers uniformly in a tow.•Water-based slurry of LiFePO4 (LFP) was used for coating.•LFP-coated carbon fibers are used in Li-ion batteries as the positive electrode.•Coated carbon fibers performed perfectly in electrochemical cyclings.
A novel manufacturing route for fully recyclable corrugated sandwich structures made from self-reinforced poly(ethylene terephthalate) SrPET composites is developed. The dynamic compression ...properties of the SrPET material and the out-of-plane compression properties of the sandwich core structure are investigated over a strain rate range 10−4–103s−1. Although the SrPET material shows limited rate dependence, the corrugated core structures show significant rate dependence mainly attributed to micro-inertial stabilisation of the core struts and increased plastic tangent stiffness of the SrPET material. The corrugated SrPET cores have similar quasi-static performance as commercial polymeric foams but the SrPET cores have superior dynamic compression properties.
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•Life cycle based material selection approach for lightweight design.•The approach is applied on a truck roof sandwich panel.•Assessment of different material, use-phase and ...end-of-life alternatives.•Environmental assessment of self-reinforced polymer composites.
Weight reduction is commonly adopted in vehicle design as a means for energy and emissions savings. However, selection of lightweight materials is often focused on performance characteristics, which may lead to sub optimizations of life cycle environmental impact. Therefore systematic material selection processes are needed that integrate weight optimization and environmental life cycle assessment. This paper presents such an approach and its application to design of an automotive component. Materials from the metal, hybrid and polymer families were assessed, along with a novel self-reinforced composite material that is a potential lightweight alternative to non-recyclable composites. It was shown that materials offering the highest weight saving potential offer limited life cycle environmental benefit due to energy demanding manufacturing. Selection of the preferable alternative is not a straightforward process since results may be sensitive to critical but uncertain aspects of the life cycle. Such aspects need to be evaluated to determine the actual benefits of lightweight design and to base material selection on more informed choices.
Tow-based discontinuous composites are an attractive alternative material to conventional continuous composites as they offer in-plane isotropy, enhanced manufacturability allowing to achieve complex ...3D shapes with high curvatures and local reinforcement in critical areas, while also maintaining high strength and stiffness, therefore expanding the design space significantly. In addition, the use of ultra-thin tapes and optimised manufacturing methods can increase the mechanical properties even further and change the damage mechanisms. Fatigue, however, could be a limiting design factor, as the fatigue behaviour of these materials has not been fully characterised. This work presents a complete study on the fatigue response of ultra-thin tow-based discontinuous composites: fatigue S–N curves are measured, and the damage and failure mechanisms are characterised utilising optical and scanning electron microscopy. Finally, a critical interpretation of the results is also presented by comparing the performance of ultra-thin tow-based discontinuous composites against other similar fibre reinforced composites and metals. It is shown that the optimised manufacturing methods combined with low tape thickness leads to enhanced quasi-isotropic fatigue performance. In addition, the fatigue limit was raised significantly compared to other discontinuous composites, and the tow-based discontinuous composites outperformed their metal counterparts when the results were normalised with density.
•Ultra-thin TBDCs were manufactured and tested under fatigue loading reaching a fatigue limit of at least 380 MPa.•Different damage mechanisms were observed between the static, low cycle, and high cycle fatigue loading.•The ultra-thin TBDCs outperformed similar discontinuous composites and QI laminates.•The ultra-thin TBDCs outperformed conventional metals when the S–N curves were normalised against the materials' densities.
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