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 [0(24)] (is named S-U) and a cross-ply lay-up of [0(11)/90](S) (is named S-C) 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 S-U was a transverse matrix crack, while the damage of specimen S-C 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 S-C was 1.6 times of specimen S-U. 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.

Automated summary

This paper investigates the effect of interlaminar and intralaminar damage mechanisms on the quasi-static indentation strength of composite laminates. Two types of carbon/epoxy laminates were fabricated and subjected to quasi-static out-of-plane indentation loading. The results showed that the dominant damage mechanism in one specimen was a transverse matrix crack, while another specimen exhibited both transverse matrix crack and delamination. The ultimate indentation strength of the latter specimen was 1.6 times higher than the former, despite similar initial damage loads. Acoustic emission signals and finite element modeling were used to study the damage state and mechanisms, which were consistent with the experimental observations.