Damage mechanism in open hole carbon textile reinforced epoxy composites

In this experimental investigation the damage mechanisms and the damage evolution were observed during tensile quasi-static and cyclic loadings of open hole carbon balanced plain weave reinforced epoxy laminates. The initiation and propagation of the damage in open hole (diameter 5 mm) notched specimens were studied measuring the full field strain by the digital image correlation (DIC) and observing damage modes by X-ray micro-CT. The DIC maps of the strain components and the X-ray micro-CT observations highlighted similar damage concentrations and damage mechanisms for both loading conditions. In the beginning of the fatigue life (about 10%) and for a static load of almost 70% of the strength, the damage was localized between three different strained zones and limited in a very narrow area at the edge of the hole. A slow increase of delamination was observed from the hole edge up to 90% of the fatigue life and for a static load approaching 90% of the ultimate stress. Finally, the fast diffusion of the strain concentration and delamination led to the complete failure of the tows at the hole edge.