Damage-mechanics analysis of matrix cracking in cross-ply CFRP laminates under thermal fatigue

Microscopic damage development in high-temperature CFRP, AS4/PEEK cross-ply laminates under thermal cycling has been investigated. Two types of laminate configurations were tested to discuss the effect of ply thickness. Matrix cracks initiated in both 0 and 90° plies and the number of cracks increased as the number of cycles increased. The number of cracks in the stable growth region were twice as great as in a 90° ply. To discuss these experimental results, a damage-mechanics analysis was used to evaluate the energy-release rate associated with cracking and thermal residual stress in cracked ply. It was clear that a modified Paris law approach is effective for thin plies and an average-stress approach is effective for thick plies.