Secondary damage effect on stress redistribution in laminated composites

Intralaminar matrix cracking is recognized as the primary mode of damage appearing in laminates. Local Raman strain measurements in neighboring layers show that the distribution shape in the vicinity of the crack tip is smoothened with increasing magnitude of the applied strain. This behavior is attributed to secondary damage development in the neighboring supporting plies close to the transverse crack tip. In this article, an approximate analytical variational model, based on the principle of minimum complementary energy, is proposed for the investigation of the stress state in a glass/ epoxy cross-ply laminate with cracks in 90°layer and with homogenized damage (reduced elastic properties) in part of the 0° layer. The extent of damage (fiber breaks) is estimated combining modeling with measured local strain distributions. The model is applied in order to examine the effect of ply thickness on the magnitude of the secondary damage at the transverse crack tip.