Haijian Chu

Mechanical properties for irradiated face-centred cubic nanocrystalline metals

In this paper, a self-consistent plasticity theory is proposed to model the mechanical behaviours of irradiated face-centred cubic nanocrystalline metals. At the grain level, a tensorial crystal model with both irradiation and grain size effects is applied for the grain interior (GI), whereas both grain boundary (GB) sliding with irradiation effect and GB diffusion are considered in modelling the behaviours of GBs. The elastic-viscoplastic self-consistent method with considering grain size distribution is developed to transit the microscopic behaviour of individual grains to the macroscopic properties of nanocrystals (NCs). The proposed theory is applied to model the mechanical properties of irradiated NC copper, and the feasibility and efficiency have been validated by comparing with experimental data. Numerical results show that: (i) irradiation-induced defects can lead to irradiation hardening in the GIs, but the hardening effect decreases with the grain size due to the increasing absorption of defects by GBs. Meanwhile, the absorbed defects would make the GBs softer than the unirradiated case. (ii) There exists a critical grain size for irradiated NC metals, which separates the grain size into the irradiation hardening dominant region (above the critical size) and irradiation softening dominant region (below the critical size). (iii) The distribution of grain size has a significant influence on the mechanical behaviours of both irradiated and unirradiated NCs. The proposed model can offer a valid theoretical foundation to study the irradiation effect on NC materials.

Texture evolution and mechanical behaviour of irradiated face-centred cubic metals

A physically based theoretical model is proposed to investigate the mechanical behaviour and crystallographic texture evolution of irradiated face-centred cubic metals. This model is capable of capturing the main features of irradiated polycrystalline materials including irradiation hardening, post-yield softening and plasticity localization. Numerical results show a good agreement with experimental data for both unirradiated and irradiated stress–strain relationships. The study of crystallographic texture reveals that the initial randomly distributed texture of unirradiated metals under tensile loading can evolve into a mixture of [111] and [100] textures. Regarding the irradiated case, crystallographic texture develops in a different way, and an extra part of [110] texture evolves into [100] and [111] textures. Thus, [100] and [111] textures become dominant more quickly compared with those of the unirradiated case for the reason that [100] and [111]-oriented crystals have higher strength, and their plastic deformation behaviours are more active than other oriented crystals. It can be concluded that irradiation-induced defects can affect both the mechanical behaviour and texture evolution of metals, both of which are closely related to irradiation hardening.

Interface Dislocation Core-Spreading Simulation and Corresponding Response

Dislocation can spread its core at an interface especially at a weak shear interface associated with shearing the interface. Such core-spreading dislocation can significantly reduce stress/strain concentration compared with the compact dislocation and thus trap the dislocation in the interface, correspondingly strengthening materials. Employing the Green’s function for a compact dislocation, we derived analytical expressions for the elastic fields of a dislocation with core spreading in anisotropic bimaterials. We proposed a conic model to mimic the spreading core of a dislocation at an interface. The accuracy and efficiency of the conic model are validated by the boundary conditions of both traction and displacement across the interface. Numerical simulation is calculated in the Cu/Nb biomaterial. The results of displacement and stress fields show that: (1) core-spreading dislocation can greatly reduce the stress intensity near the dislocation compared with the dislocation with a condensed core; (2) dislocation core spreading has a great influence on the elastic fields near the core region, while the influence can be negligible when the distance of a field point from the center of the dislocation core is greater than 1.51 times the width of the spreading core; (3) near the core region, Peach-Koehler force induced by the core spreading dislocation is larger than that of the compact dislocation.