Optimal stress and deformation partition in gradient materials for better strength and tensile ductility: A numerical investigation

Inspired by recent progress in developing gradient materials with excellent performances, here we report a systematic finite-element based investigation to show how the strength and tensile ductility of gradient crystalline metals depend on their microstructure characteristics. We reveal that the yielding strength of polycrystalline metals with gradient grain size can be significantly enhanced at no reduction in ductility. By employing a representative 3D voronoi gradient sample, we demonstrate that the redistribution of stress and deformation in the gradient structure - stronger grains carry more load and ductile ones share more deformation - accounts for the realized optimal property in strength and ductility. In addition, the hardenability of the ductile domain is beneficial to circumvent pre-mature plastic instability in gradient samples.