Residual stress provides significant strengthening and ductility in gradient structured materials

Residual stress exists extensively in biological and engineering structures. Here we report that residual stress can be engineered to significantly enhance the strength and ductility of gradient materials. In-situ synchrotron experiments revealed that the strongest strain hardening occurred in the layer with the highest compressive residual stress in a gradient structure. This layer remained elastic longer than adjacent layers during tension, producing high hetero-deformation induced stress to increase strength and enhancing work hardening even after the disappearance of the compressive stress to increase ductility. This finding provides a new paradigm for designing gradient structures for superior mechanical properties.