Residual strength of stitched laminates after low velocity impact

Tests were conducted with stitched laminates in order to calculate CAI (compression after impact) strength and TAI (tension after impact) strength for stitched laminates. Two levels of low velocity impact energy were used. All the specimens were made of two different types of lay-up sequence laminates with three different stitching directions of 08, 458, and 908. FEM model was developed using MSC/PATRAN software to predict the CAI and TAI strength of stitched laminates. PS criterion (point stress) and FD criterion (fiber breakage in damage zone) were applied to predict CAI strength. It showed that the predicted residual strengths were in agreement with the test results. Stitching improves the residual strength of the laminates.