Prediction of low-velocity impact damage in thin circular laminates

Clamped circular composite plates were analyzed for static equivalent impact loads. Three plate sizes—25.4, 38.1, and 50.8 mm radii—made of quasi-isotropic graphite/epoxy laminate were analyzed. The analysis was based on the minimum total potential energy method and used the von Karman strain-displacement equations. A step-by-step incremental transverse displacement procedure was used to calculate plate load and ply stresses. The ply failure region and modes (splitting and fiber break) were calculated using the Tsai-Wu and the maximum stress criteria, respectively. Reduced moduli were then used in the failed region in subsequent increments of analyses. The analysis predicted that the failure would initiate as splitting in the bottom-most ply and then progress to other plies. Larger radii plates had a lower splitting threshold (load or energy) and a higher first-fiber failure threshold. The size and shape of the ply damage regions were different for different plies. The bottom ply damage was the largest and elongated in its ply-fiber direction. Calculated splitting damage for a 25.4 mm radius plate agreed with reported test data.