Research of ductile damage in large crystal pure aluminium at crack tip under mixed mode loading

An in situ tensile experiment with SEM was carried out to investigate the plastic deformation, and the behavior of ductile damage in the immediate vicinity of crack tip in commercial large crystal pure aluminium under mixed mode loading, and the mechanics analysis of mixed damage was made by using the result of finite element calculation. It is shown that the model of a mixed crack tip deformation is a sharpening-blunting because an opposite kind of deformation carried out at the upper and the down side of the crack tip, and it results from successive activation of a number of slip systems. The ductile damage occurs in the blunting region (which is the uniform slip zone) but not in the sharpening region (which is the concentration slip zone). The crack initiates at the place where the effective strain is maximum and propagates along the direction of the maximum gradient of effective strain, which agrees well with that of maximum stress triaxiality in the blunting region under mixed mode loading. The deformation of the mixed crack tip investigated by SEM was also proved by FEM.