Crystallographic Orientation and Spatially Resolved Damage for Polycrystalline Deformation of a High Manganese Steel

In-situ neutron diffraction investigation on a high manganese steel, which was stretched before or after the fatigue loading, renders a meso-scale damage criterion: the {111} and {422} lattice strains along the transverse direction violating the Poisson effect signifies severe damage. They either showed no more lattice contraction corresponding to increasing of the tensile stress or transversal expansion during the plastic stage of tension. Distribution of the damaged grains was further investigated by the full-width at half-maximum pole figures. The crystal plasticity simulations justify the rationality of the damage criterion, and it could relate to the orientation distribution of the damaged slip/twinning planes. The cracks mainly distributed at the transverse surface. It is shown that the strong interaction between twin boundaries and slip dislocations could result in heavy damage at the surface, with a morphology of curved twin boundaries. Also, grain boundaries and the narrow deformation twins often correspond to different amplitudes of transversal contraction and expansion than other surface areas during the tension-compression fatigue loading, which may trigger the surface cracks. It is due to large crystallographic orientation gradients. The present paper provides a sound routine to identify criterions of the plastic damage for face-centered-cubic (FCC) polycrystals.