STUDIES ON LOW-VELOCITY IMPACT DAMAGE OF STITCHED COMPOSITES

A 3D dynamic finite element method with stitching threads is described by the space bar element and combined with experiment work to study the damages of the stitched composites induced by the low-velocity impact in this paper. Impact induced contact forces by modified Hertz contact law are obtained, the dynamic equations are solved with NewMark direct integral scheme, and strain and stress during impact are obtained. A modified delamination criterion considering fibre failure is proposed based on that of Chang and Hou, and the method to analyse the impact induced failure area is developed. Impact tests on the stitched and unstitched composite laminates with the same ply sequence are performed. Good agreement is found between experiment and finite element computing results, and the results indicate that stitching greatly reduces the extent of the impact damage area at the same impact energy level.