Characterization of out-of-plane impact damage in stitched CFRP laminates

The present study experimentally and numerically investigated the damage progress in stitched and unstitched CFRP laminates under the low-velocity out-of-plane impact load. First, we performed drop-weight impact tests for both stitched and unstitched specimens, and inspected the damage by using the soft X-ray radiographs and micro-focus X-ray CT We then conducted damage-extension simulation using a layer-wise finite element model with stitch threads as beam elements, in which the damage (ply cracks and delamination) was represented by cohesive elements. A detailed comparison between the experimental and simulated results confirmed that stitching effectively suppressed the out-of-plane impact damage. Furthermore, we demonstrated that the improvement effect of impact damage resistance became greater when the impact energy was larger.