Characteristics of crack-tip stress structure and crystal slipping in nickel-base single supperalloy CT specimens

Using compact tension (CT) specimens made of nickel-base single supperalloy DD3 in three crystal-lographic orientations ([001], [01l], [111]), the three dimensional elastic-plastic stress fields at the crack-tip have been analyzed by a crystallographic finite element program, which takes the effects of lattice rotation and finite deformation into consideration. The special attention is paid on the resolved shear stress and activating of slip system. The growth path of the crack is predicted by the crystallographic slip theory, which agrees with experiment exactly. The results show that the stress structure is dependent on the crystallographic orientation of specimen. The slip bands take place in specific sectors near crack tip in free surface, on which the initiation and growth of the crack are dependent. The crystallographic structure shows that the number and feature of slip bands are related to the crack orientation. The equivalent Mises stress and resolved shear stress along the thickness direction are nearly constant in the midsections and tend to decrease sharply near the free surfaces, which are experimentally confirmed to correspond to the smooth region and the shear lip on the fracture face respectively.