Damage mechanism of hybrid composites with nonwoven carbon tissue subjected to quasi-static indentation loads

Damage mechanisms of hybrid composites with nonwoven carbon tissue (NWCT) are investigated under a quasi-static indentation loading condition with a steel ball as an indentor. The damage level corresponds to an initial stage of damage due to an indentation loading, which leads to a strength degradation of the composite. The hybrid composites consist of the CFRP prepreg and the NWCT prepreg, which are made by interleaving the NWCT prepreg into the CFRP layer interfaces. Four kinds of cross-ply laminates are studied; i.e., CFRP laminates ([0₅/90₅/0₅] and [0₃/90₃/0₃/90₃/0₃]) and hybrid laminates ([0₅//90₅//0₅] and [0₃//90₃//0₃//90₃//0₃]). Here, the symbol "//" means that the NWCT prepreg is located at an interface between CFRP layers. The hybrid effect is examined by investigating the delamination area and the absorption energy of two cross-ply laminates. As it has been recognized that the quasi-static indentation damage agrees well with the low-velocity impact test results, the present static test results can then be used to understand the damage mechanism of low-energy impact. The damaged parts of the specimens were observed by the deply technique and the cut method which used a microscope. The NWCT interleaving's effect was clarified based on the observation of the damage for the hybrid specimen's cross-sections after indentation testing. The delamination area of the hybrid composites was reduced to about a half of the CFRP's by indentation loading. It was clarified that the Mode II interlaminar fracture is predominant in the delamination by the impact.