Chao Yu

Gradient nano-grained (GNG) metals have shown high synergetic strength and good ductility due to their unique gradient microstructure. In this study, the mechanical behavior of gradient nano-grained metals was investigated by three-dimensional discrete dislocation dynamics. The simulation results show a trend that the successive yielding and gradual “transmission” of dislocations along the gradient direction result in a gradient distribution of stress and plastic strain. The distribution of geometrically necessary dislocations is more inhomogeneous in the gradient nano-grained (GNG) sample compared with those homogenous counterparts. The non-uniform deformation response of component layers induces the synergetic-deformation-induced (SDI) strengthening in the GNG sample. The back stress originates from geometrically necessary dislocations that pile up near the interface of gradient layers and leads to a significant hardening while there is a slight softening in different gradient layers in the GNG sample. This study provides a deeper insight into the SDI strengthening in gradient structure from the submicron scale.

A series of stress-controlled uniaxial cyclic tension-unloading tests are discussed to investigate the ratchetting of a filled rubber at room temperature. It is shown that obvious ratchetting occurs and depends apparently on the applied stress level, stress rate, and stress history. Based on the experimental observations, a damage-coupled hyper-viscoelastic-plastic constitutive model is then developed to describe the ratchetting of the filled rubber, which consists of three branches in parallel, i.e., a hyperelastic, a viscoelastic, and a plastic one. The damage is assumed to act equally on three branches and consists of two parts, i.e., the Mullins-type damage caused by the initial tensile deformation and the accumulated damage occurred during the cyclic deformation. The developed model is validated by comparing the predicted results with the experimental data.