The Effect of Interlaminar and Intralaminar Damage Mechanisms on the Quasi-Static Indentation Strength of Composite Laminates

This paper studies the effect of interlaminar and intralaminar damage mechanisms on the quasi-static indentation strength of composite laminates. To this aim, two carbon/epoxy laminates with a unidirectional lay-up of [024] (is named SU) and a cross-ply lay-up of [011/90]S (is named SC) were fabricated and subjected to quasi-static out-of-plane indentation loading. The ultrasonic C-scan, digital camera, and inverted microscopy images revealed that the dominant damage mechanism in specimen SU was a transverse matrix crack, while the damage of specimen SC included both transverse matrix crack and delamination. Although the load corresponding to the initial damage in both specimens was almost the same, the ultimate indentation strength of specimen SC was 1.6 times of specimen SU. The AE signals of the indentation tests were used to investigate the damage state of the specimens, and a Finite Element (FE) model based on the cohesive surface modeling was used to study the damage mechanisms in the specimens. The FE results were consistent with the AE results and the experimental observations.