Improvement on out-of-plane impact resistance of CFRP laminates due to through-the-thickness stitching

The present study both experimentally and numerically investigated the damage process in the stitched laminates under the low velocity impact loading, and revealed the characteristic of the improvement on out-of-plane impact resistance due to stitching. First, we performed drop-weight impact tests and inspected the damage by using non-destructive inspection techniques. 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 revealed that impact damage resistance was improved more effectively when the impact energy was larger. The simulated results demonstrated that the increase of the number of stitch threads which located inside and near the delamination area caused this phenomenon.