Cold dwell behaviour of Ti$_6$Al alloy: Understanding load shedding using digital image correlation and crystal plasticity simulations

Abstract

Digital image correlation (DIC) and crystal plasticity simulation were utilised to study cold dwell behaviour in a coarse grain Ti-6Al alloy at 3 different temperatures up to 230 • C. Strains extracted from large volume grains were measured during creep by DIC and were used to calibrate the crystal plasticity model. The values of critical resolved shear stresses (CRSS) of the two main slip systems (basal and prismatic) were determined as a function of temperature. Stress along paths across the boundaries of two grain pairs, (1) a 'rogue' grain pair and (2) a 'non-rogue' grain pair, were determined at different temperatures. Load shedding was observed in the 'rogue' grain pair, where a stress increment during the creep period was found in the 'hard' grain. At elevated temperatures, 120 • C was found to be the worst case scenario as the stress difference at the grain boundaries of these two grain pairs were found to be the largest among the three temperatures. This can be attributed to the fact that the strain rate sensitivity of both prismatic and basal slip systems is at its greatest in this worst case scenario temperature.