Narrow Results

Adhesive interaction in the presence of plastic deformation may be crucial in additive manufacturing, pharmaceuticals and powder metallurgy. Only limited studies on adhesive contact accounting for plastic deformation had been conducted mainly on the basis of the linear elastic fracture mechanics model where the singular distribution of traction is involved, which is believed to be applicable to softer materials. In this work, an analytical model for elastic–perfectly plastic contact during unloading has been proposed for different adhesion effects, where the effect of yield on normal traction in the cohesive zone has been taken into account. The adhesive contact behaviors during unloading are then illustrated by the proposed model and compared with the predictions of the existing models.

Magnesium alloys exhibit significant inelastic behavior during unloading, especially when twinning and detwinning are involved. It is commonly accepted that noteworthy inelastic behavior will be observed during unloading if twinning occurs during previous loading. However, this phenomenon is not always observed for Mg sheets with strong rolled texture. Therefore, the inelasticity of AZ31B rolled sheets with different rolled textures during cyclic loading-unloading are investigated by elastic viscoplastic self-consistent polycrystal plasticity model. The incorporation of the twinning and detwinning model enables the treatment of detwinning, which plays an important role for inelastic behavior during unloading. The effects of texture, deformation history, and especially twinning and detwinning on the inelastic behaviors are carefully investigated and found to be remarkable. The simulated results are in agreement with the available experimental observations, which reveals that the inelastic behavior for strongly rolled sheets is very different than the extruded bars.

Rock burst is a multiscale dynamic fracturing process induced by unloading. To further investigate the dynamic fracturing mechanism of rock burst, a grain-based discretized virtual internal bond (GB-DVIB) method is developed. The Voronoi diagram is used to discretize the background discretized virtual internal bond (DVIB) mesh to generate the micro-structure of rock. The bond cell within a Voronoi diagram is termed as the grain cell, characterized by the linear Stillinger–Weber potential. While the bond cell cut by the Voronoi polygon edge is termed as the interface cell, in which both the tension and the shear failure are considered. The simulation results suggest that this method can reflect the contact and friction between grains and reproduce the confining pressure-dependency of compressive strength of rock. With this method, the unloading effects of the in situ stress, the grain size and the heterogeneity on rock failure are studied. The simulated results show that more tensile cracks and less shear cracks are generated when unloading a higher confining stress. When the axial stress is fixed, the total created crack area is almost a constant. The tensile crack area is basically a constant while the shear crack area increases under the condition of a higher axial stress. With decreasing the grain size, more cracks are generated, but the area ratio of the shear to the tensile cracks is almost a constant. It is suggested that GB-DVIB is an effective method for the rock burst simulation. The findings provide deep insight into the rock burst from the standpoint of dynamic fracture.