Dislocation evolution at a crack-tip in a hexagonal close packed metal under plane-stress conditions

Understanding the stress state and microstructural features at a growing crack-tip is critical to understanding the failure mechanisms of engineering structures. To investigate the strain and dislocation evolution at a crack-tip, electron backscatter diffraction and geometrically necessary dislocation analysis were performed on fully annealed zirconium foils at room temperature. Different levels of macroscopic plastic strain were applied: 0.0%, 0.22%, 0.84%, 1.2%. Based on their different Burgers vectors and line vectors, prismatic , basal , screw , screw and pyramidal geometrically necessary dislocation densities were estimated during crack blunting and subsequent propagation. Most of the plastic deformation was accommodated by screw and pyramidal dislocations. Screw dislocations were found to be dominant over the as might be expected. Instead of twinning, pyramidal slip accommodated the strain along the c-axis caused by contraction at the crack-tip. Dislocation densities at the crack-tip were plotted according to the angle relative to the applied tension direction and the distance from the tip, and were compared with plastic strains simulated from a 3D static finite element model. Crack-tip singularity was observed and total geometrically necessary dislocation densities were in qualitatively good agreement with the equivalent plastic strain distribution predicted by the finite element method (FEM). (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.