Mapping of crack tip strains and twinned zone in a hexagonal close packed zirconium alloy

This paper describes the use of synchrotron X-ray diffraction to map crack tip strain field evolution and initiation of twinning under applied load in a fatigue pre-cracked zirconium alloy. Compact tension specimens were machined in two orientations from a textured rolled plate and loaded along the normal direction and the transverse direction to rolling. Residual strains due to fatigue and the strains introduced at applied KI of approximately 10 and 30 MPa√m were measured for the two specimen orientations. Maps of the region of twinned material were determined. The experimental data is compared to finite element (FE) calculations for the crack tip strain fields and a prediction of the size of the twinned region using a multiscale model based on combining an FE approach with an elastoplastic self-consistent polycrystalline plasticity model.