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

•Rotations of the stress tensor in individual grains are experimentally quantified.•These stress rotations are an order of magnitude larger than lattice reorientation.•The stress state rotates mainly about rather than towards the loading axis.•The stress tends to rotate towards the yield surface vertices.•These stress rotations reduce triaxiality in certain grains and determine 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 (∼15°) are more than an order of magnitude larger than the concomitant crystallographic lattice reorientations (∼0.9°) 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.