In situ optical observation of damage and failure process in adhesively bonded CFRP joints under mixed-mode loading

The effects of mode mixity on microscopic damage and failure process in adhesively bonded carbon fiber reinforced plastic (CFRP) joints were studied by in situ observation. Optical microscopy observation revealed that the damage and failure process were largely affected by the mixed-mode ratio of joints. The whitening of the adhesive resin due to cavitation was observed with an increasing mode I component, whereas the plastic zone length increased with an increasing mode II component. The damage and failure process observed by experiment were correlated with the stress state around the crack tip obtained by finite element analysis. The results indicated that the microscopic failure process well reflects the deformation and failure properties of epoxy resin depending on stress triaxiality.