In-depth Understanding of the Stability Response of a Novel 3D Fiber-Metal Laminate under Axial Impact Loading
De Cicco, Davide
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Environmental concerns have developed significant challenges for various industries, including the automotive industry. In fact, the industry has been challenged to halve vehicles’ fuel consumption by 2025. Considering the fact that engine efficiency has been approaching a plateau, the other effective means for reaching the set target is believed to be achieved by reducing the weight of various components of vehicles. It should be noted that, unfortunately, vehicles collisions occur frequently; consequently, vehicles must be designed in such a way to assure the maximum safety of the occupants, thereby generating an additional constraint to the weight-reduction approach. To address the latter design constraint, the automotive industry has been conducting an extensive series of research over the recent decades to explore the utilization of different light-weight metallic alloys and fiber-reinforced plastic composites (FRPs). However, relatively recently, it was proved that one could achieve optimal results by taking advantage of the marriage of the positive attributes of two distinctly different classes of materials (i.e., metallic alloys (preferably, the light-weight alloys), and FRPs). The aforementioned material combination is referred to as a fiber-metal laminate (FML) and was first used in aviation field (e.g., Airbus A380). The resulting hybrid combination enables one to take advantage of the unique properties of each constituent. Following this path, our research group recently developed a new class of three-dimensional FML that offers exemplary specific strength and stiffness, superior energy absorption capacity, and excellent damping properties compared to the traditional materials used throughout the industry, in a cost-effective manner. It takes advantage of a recently marketed 3D-knitted fiberglass fabric, infilled with a resilient foam, and sandwiched between thin sheets of light-weight magnesium alloy. The primary application target of this 3D fiber-metal laminate (3D-FML) has been transport vehicles’ body components, which are subjected to various loadings, including impacts. The superior energy absorption capacity of this new FML under a lateral impact, in comparison to traditional fiber-reinforced composite materials, has already been demonstrated by our research group. However, the targeted components may also encounter in-plane compressive loading applied at various loading rates, which could lead to the instability of the structural system. The overall aim of this work is to provide a deeper insight into the response of slender structural components made with the 3D-FML, when subjected to in-plane compressive load applied at various strain rates (particularly, to low-velocity impact loading). The task will be done by conducting a series of systematic and comprehensive experimental and numerical investigations. The finite element method is utilized to carry out the parametric studies, identifying and ranking the material properties that would most affect the response of the system. In addition, the interface bond strength (which will be shown to be the Achilles’ heel of the introduced hybrid system), is optimized, thereby improving the overall fabrication process of the FML in an efficient and cost-effective manner. In addition, the feasibility of graphene nanoparticles (GNPs) as a means of enhancing the interface bond strength of the system was explored. The results revealed that the lack of chemical bond between the GNP-reinforced resin and the magnesium skins of the hybrid material system significantly limited the potential influence of the GNPs. It is also well-known that composites’ performance is strongly affected by the existence of delamination(s) within them. Therefore, the effect of initial delamination on the performance of the material system is also systematically investigated. Finally, a set of simple semi-empirical equations is developed by which practicing engineers could quickly evaluate the buckling and maximum load bearing capacities of the 3D-FML subjected to in-plane static and low-velocity impact loading states.