Examination of ply cracking in composite laminates with open holes: A moiré interferometric and numerical study

A moiré interferometric investigation of surface strain redistribution due to matrix cracking around open holes in two [0/45/90/-45]s composite laminates with differing ply thicknesses was conducted. Both tests revealed significant redistribution of strain as damage developed. The results from the thicker-ply specimen show strain redistribution mostly due to the cracking of the top 0° ply. This was verified by a mesh-independent displacement discontinuity modeling method based on higher order shape functions. Localized effects of sub-surface-ply cracking were not found. However, due to a thinner surface ply and more extensive damage, the thinner-ply specimen showed significant redistribution of strain as a result of the sub-surface-ply cracking as well as the 0° ply cracking. Evidence of cracking in the center −45° plies was present in the strain results. Examination of the strain redistribution and the failure surface of the thinner ply specimen led to the development of a failure scenario, where the initiation of critical 0° fiber cracking occurs slightly away from the hole edge. Future modeling efforts will attempt to verify this scenario.