Impact morphology characteristics and damage evolution mechanisms in CFRP laminates for hydrogen storage cylinders

In instances of impact, the preeminent load-bearing framework for on-board hydrogen storage cylinders manifests in the carbon fiber reinforced polymer (CFRP) composite layer. Investigating the morphology of impact and elucidating the mechanism governing damage evolution in CFRP is crucial for optimizing the impact resistance of the cylinder. In this work, impact tests were performed on CFRP laminates with six types of interlaminar mismatch angles, under varying impact energies. The impact damage of laminates was characterized using an extended depth-of-field 3D microscopy. A numerical model, implemented in ABAQUS/Explicit, was devised to scrutinize the mechanical properties and damage mechanisms in laminates. A subroutine (VUMAT) was crafted to effectively predict intralaminar damage, while the application of a bilinear cohesive model served to capture interlaminar damage. In addition, this study delves into the ramifications of impact energy and interlaminar mismatch angles. The results reveal that the increase of impact energy leads to more irreversible damage and energy dissipation within laminates. Compared to damage depth (D) and cross-sectional area (Ac), the assessment of damage volume (V) and surface area (As) are more reflective of energy dissipation in laminates. The laminates with mismatch angle of 0 degrees and "helicoidal" lay-up sequence exhibit the worst impact resistance. Within the range of 24 degrees-90 degrees, laminates with a smaller interlaminar mismatch angle demonstrate better impact resistance. These findings lay the groundwork for optimizing the composite layer to enhance the impact resistance of hydrogen storage cylinders.