The Influence of Crystallographic Orientations of Grains on Microstructurally Small Cracks Using Crystal Plasticity and Random Grain Structure

A plane-strain finite element crystal plasticity model of microstructurally small stationary crack emanating at a surface grain in a 316L stainless steel is proposed. The model consisting of 212 randomly shaped, sized and oriented grains is loaded monotonically in uniaxial tension to a maximum load of 1.12R_p0.2 (280 MPa). The influence that a random grain structure imposes on a Stage I crack is assessed by calculating the crack tip opening (CTOD) and sliding displacements (CTSD), considering also different crystallographic orientations. It is shown that certain crystallographic orientations result in a cluster of soft grains around the crack-containing grain. In these cases the crack tip can become apart of the localized strain, resulting in a large CTOD value. This effect, resulting from the overall grain orientations and sizes, can have a greater impact on the CTOD than the local grain orientation. On the other hand, when a localized soft response is formed away from the crack, the localized strain does not affect the crack tip directly, resulting in a small CTOD value. The resulting difference in CTOD can be up to a factor of 4, depending upon the crystallographic set. Grains as far as 6xCracklength significantly influence that crack tip parameters. It was also found the a larger crack-containing grain tends to increase the CTOD.