Compression strength of stitched laminates after low-velocity impact

Tests are conducted using stitched laminates in order to calculate the unnotched failure stress and the compression after impact (CAI) strength of the stitched laminates. Unnotched laminates, laminates with a hole, and laminates with impact damage are used in the tests. All the specimens are made of two different types of layup sequence of laminates with three different stitching directions - 0, 45, and 90 degrees. In this paper, an FEM model is developed using the MSC PATRAN software to predict the CAI strength of stitched laminates. Two failure criteria are applied to the model to predict the CAI strength, the point stress criterion (PS) and the fiber breakage in damage zone (FD) criterion. The influence of the moduli retention ratio (Mr) is investigated. The predicted CAI strengths show a good agreement when compared with the test results.