Prediction of stitch crack evolution and gas permeability in multidirectional composite laminates

Stitch cracks in multidirectional laminates were observed by many researchers in the literature. In the present work, the damage evolution in multidirectional laminates is investigated using the strain energy release rate concept. Two methods are used to compute the strain energy release rate. The effects of ply angle and ply thickness on stitch crack evolution are investigated. Then, a model based on Darcy's law for porous materials is developed for predicting gas permeability in composite laminates containing microcracks and delaminations. Gas permeability is presented as a function of crack density and crack intersection area. Then the intersection areas formed by crack opening displacements are computed using 3D finite element analysis. The progressive gas permeability in multidirectional laminates is predicted and compared with the gas permeability predicted in the cross-ply laminates in our previous work.