Multifunctional Hybrid Fiber Composites for Energy Transfer in Future Electric Vehicles

Reducing the weight of electric conductors is an important task in the design of future electric air and ground vehicles. Fully electric aircraft, where high electric energies have to be distributed over significant distances, are a prime example. Multifunctional composite materials with both adequate structural and electrical properties are a promising approach to substituting conventional monofunctional components and achieving considerable mass reductions. In this paper, a hybrid multifunctional glass-fiber-reinforced composite containing quasi-endless aluminum fibers with a diameter of 45 μm is proposed for electric energy transfer. In addition to characterizing the material’s behavior under static and fatigue loads, combined electrical-mechanical tests are conducted to prove the material’s capability of carrying electric current. Light microscopy, thermal imaging and potentiometry-based resistance characterization are used to investigate the damage behavior. It is found that a volume fraction of about 10% work-hardened aluminum fibers does not affect the static fiber-parallel material properties significantly. Under transverse loading, however, the tensile strength is found to decrease by 17% due to the weak bonding of the aluminum fibers. The fiber-parallel fatigue strength of the multifunctional laminate containing work-hardened aluminum fibers is comparable to that of the reference material. In contrast, the integration of soft-annealed aluminum fibers decreases the tensile strength (−10%) and fatigue life (−21%). Concerning the electrical properties, electrical resistance is nearly unchanged until specimen rupture under quasi-static tensile loads, whereas under cyclic loading, it increases up to 60% within the last third of the fatigue life. Furthermore, the material’s capability of carrying currents up to 0.32 A/mm2 (current density of 4.5 A/mm2 in the aluminum phase) is proven. Under combined electrical-mechanical loads, a notable reduction in the fatigue life (−20%) is found at low fatigue loads, which is attributed to ohmic specimen heating. To the best knowledge of the authors, this is the first study on the electrical and mechanical material properties and damage behavior of glass-fiber-reinforced composites containing aluminum fibers tested under combined electrical-mechanical loads.