Modeling of Coupled Behavior and Microcracking of Multifunctional Composite Structures for Energy Storage İ. Uyar∗, E. Gürses Department of Aerospace Engineering, Middle East Technical University, Ankara 06800, Turkey ∗ imren.uyar@metu.edu.tr Keywords: Fracture of Composites, Structural Batteries, Electro-Chemo-Mechanical Coupling, Phase Field Approach, Multifunctional Materials Energy storage and low thrust-to-weight ratios are major concerns for improving new designs in the aerospace and automotive industries. When these two concerns are considered together, the multifunctionality of structural load-carrying members, especially through adding energy storage capabilities, is a promising approach to realizing lightweight structural members for future transport vehicles. The high specific mechanical and electrical properties of carbon fibers make them ideal for multifunctional applications [1].This work presents a framework for coupled modeling of a multifunctional composite material, structured on the micro-scale, with the ability to function as a battery cell and carry a mechanical load.The microstructure consists of a single carbon fiber surrounded by a very thin solid electrolyte coating and is embedded in a polymer matrix which is a porous material containing active particles able to intercalate lithium. Therefore, the composite structure simulates the electro-chemo-elastic behavior under different electrochemical states (charging-discharging). At these states, a volume swelling caused by lithium-ion movement is observed, which is very similar to heat expansion, where pure volume expansion is produced under thermal load [2].The finite element simulation of monolithically coupled electro-chemo-elastic media is combined with the crack formation in the fiber region. Due to the high concentration gradient at the fiber surface, mechanical stresses are developed, which may lead to the initiation and growth of cracks in the fiber [3]. Crack evolution in the structure causes a decrease in the mechanical properties of fibers and a reduction in the charging properties of the battery by decreasing the diffusivity of lithium ions.The phase field fracture model [4] is implemented into the coupled system for modeling crack propagation and possible damage evolution scenarios. The crack geometry-dependent ion concentration distributions and the elastic stress distributions are investigated using an open-source finite element software FENICS. References [1] Adam, T.J., Liao, G., Petersen, J., Geier, S., Finke, B., Wierach, P., Kwade, A., Wiedemann, M. (2018) Multifunctional composites for future energy storage in aerospace structures. Energies, 11, 335. [2] Xu, J., Lindbergh, G. and Varna, J. (2018) Multiphysics modeling of mechanical and electrochemical phenomena in structural composites for energy storage: Single carbon fiber microbattery, Journal of Reinforced Plastics and Composites, 37(10), 701-715. [3] Pupurs, A., and Varna, J. (2014) Modeling mechanical stress and exfoliation damage in carbon fiber electrodes subjected to cyclic intercalation/deintercalation of lithium ions. Composites: Part B Engineering, 65, 69-79. [4] Miehe, C., Hofacker, M., Welschinger, F. (2010) A phase field model for rate-independent 80
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