Numerical study of the surface-hardening effect on surface phenomena in 3D polycrystalline specimens

Surface hardening effect on the mesoscale surface deformation in polycrystalline specimens subjected to uniaxial tension is numerically studied. Basing on the experimental findings, three-dimensional microstructure-based constitutive models of the unhardened and surface-hardened polycrystalline specimens are constructed. The mechanical behavior of the polycrystalline models is analysed numerically by the finite-difference method. The grain structure is shown to be responsible for the free surface roughening under uniaxial loading. Microscale stresses acting in the bulk of the material across the free surface give rise to the formation of surface ridges and valleys. The hardened layer in a surface-hardened specimen moves the grain structure away from the free surface, thus smoothing out the microscale folds caused by displacements of individual grains. The thicker is the modified layer, the smoother is the surface relief.