Multifunctional Thin Film Lithium Ion - Graphite Composite Structural Laminates
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The consolidation of batteries and airframe into a multifunctional structure can theoretically reduce the aircraft weight by exploiting the battery components as load bearing elements and by enabling a distributed power supply. To realize this vision, a composite structure for load bearing and electrical energy storage comprised of thin film Li-ion batteries and carbon fiber/epoxy laminae was proposed. In this framework, the experimental characterization and finite element analysis of delamination growth and delamination buckling collapse response of the highly inhomogeneous laminates was conducted to support the design of the next generation of airborne multifunctional structures for load bearing and electric energy storage. The study assessed the technology readiness and showed that the low fracture toughness and the inhomogeneity of the material properties of a baseline battery packaging design led to critical unstable delaminations. Moreover, it demonstrated that the packaging design is a determining factor for the integrity of the multifunctional laminates. The study provided a design space for improving the limits of utilization of the next generation of structural thin film batteries by optimum materials selection. Based on these results, the use of thin film lithium ion technology seems to be possible for low stress applications and secondary structures with short lifecycle. This research also provided a general and novel automatic incremental solution algorithm for nonlinear static finite element equations, designed to compute local/global structural collapse by stable and unstable delamination propagation.