Damage and delamination modeling of multifunctional composite structural batteries

Structural battery composites are capable of storing and delivering electrical energy and bear structural loads. It is important to analyze the stiffness and strength of these composites, particularly in bending loading configurations. Damage of structural batteries is of particular importance in structural batteries due to the energy storage component. Two structural battery material systems were considered. The first battery cell uses copper and aluminum foils as electrodes and carbon paper as current collectors. The second material system incorporates carbon fiber fabric coated with nickel and iron through electrodeposition as the multifunctional electrodes. These stiff carbon fiber fabrics provide excellent mechanical properties. For sufficient electrical energy capacity storage for use as the chassis of a CubeSat, it was calculated that seven layers per panel would be required. Multi-layer panels consisting of seven battery layers as a core with external structural reinforcement were tested. Physical and virtual three point bend tests were completed on these material systems. Prototype Cu-Al panels were fabricated and tested in a 3 point bend test configuration until ultimate failure. The damage initiation and propagation was analyzed through qualitative and quantitative analyses. Damage morphology took the form of layer delamination and material cracking within the battery layers. Computational finite element simulations matching the mechanical testing geometry were completed to further understand the mechanism involved in the damage of these composites. Simulated Cu-Al panels showed a larger stiffness, however the progression of damage was well represented in the models. The Ni-Fe carbon fiber battery was superior in stiffness and strength. Overall, these composites show promise that these can be utilized as structural materials that store electrical energy.