Large rotations of the grain-scale stress tensor during yielding set the stage for failure

The stress-state within individual grains in a polycrystal determine the fate of the aggregate including mechanical failure. By tracking the evolution of the stress tensor throughout the elastoplastic transition, large rotations of the stressstate, which have long been theorized to occur, are observed experimentally for the first time. These stress rotations (similar to 15 degrees) are more than an order of magnitude larger than the concomitant crystallographic lattice reorientations (similar to 0.9 degrees) well-known to occur during metal plasticity. Furthermore, these rotations are accompanied by a decrease in stress triaxiality within certain grains, promote strain softening, and set the stage for failure at an early stage of deformation. These results provide a completely new perspective through which to contemplate the question of hot-spots responsible for failure of high-performance structural materials.

Automated summary

The study reveals that the evolution of stress state in polycrystals can lead to significant stress rotations and a decrease in stress triaxiality in certain grains, promoting strain softening and potential failure at an early stage.