Simulation of Cleavage Crack Propagation in Steels with Anisotropic Crystal Orientation Distribution

A model to simulate cleavage crack propagation in steels with anisotropic crystal orientation is proposed. The model is based on a criterion that one of the three {100} planes having highest normal stress exceeding the critical stress is selected as a cleavage plane in a grain in front of a crack tip. The normal stress on {100} planes is calculated from linear elastic crack tip stress field and crystal orientation distribution. The crack tip stress field is calculated from mixed mode stress intensity factors derived from first-order approximations where crack surface irregularity and crack front non-straightness, crack closing force acting at ridges between cleavage facets are considered. The crystal orientation distribution is obtained by Electron Back Scattering Diffraction (EBSD) measurement. Using the model, we simulated cleavage crack propagations for different specimen directions in a steel with texture. First, we compared simulated fracture surface morphology with the actual fracture surfaces obtained from small crack arrest test specimens. Both morphologies showed good agreement. Next, we simulated crack propagation at different crack orientations with the use of the model and examined a dependence of crack propagation resistance on crack orientation. Anisotropy of arrest crack length simulated by the model corresponded to that observed in the small crack arrest tests. Therefore, the model can simulate cleavage crack propagation considering anisotropic crystal orientation distribution.