Experimental determination of grain stresses and critical resolved shear stresses by neutron diffraction

This study investigates the plastic deformation behaviour of the AZ31 magnesium alloy under various uniaxial loading conditions using in-situ neutron diffraction, the crystallite group method (CGM), and crystal plasticity modelling. A key novelty of this work is the direct, model independent determination of resolved shear stress (RSS) values for individual slip and twinning systems, as well as their critical values (CRSS), derived from lattice strains in grains with preferred orientations. The experiment was extended beyond the conventional loading paths along the normal direction (ND) and rolling direction (RD) to include compression at angles of 30 ° from the ND (NDC30). The NDC30 test, combined with diffraction measurements, was specifically designed to activate basal slip in the majority of grains while minimizing twinning, enabling clear identification of this slip system and accurate determination of its CRSS. For the first time, hardening parameters were determined by comparing the model predicted values of RSS with those obtained from diffraction measurements for each active system. These data, together with the results of macroscopic tests, were used to calibrate an elastic-plastic self-consistent (EPSC) model, which accurately reproduced stress partitioning under applied load, texture evolution, and twin activity.