Jianqiu Zhou

Modeling the strain-hardening effect and plastic deformation of nanocrystalline FCC metals dispersed with the finest grains

Abstract A mechanism-based plasticity model focusing on deformation and failure behavior of nanocrystalline (NC) FCC metals dispersed the finest grains (FGs) is proposed. The stress–strain relationship is derived by invoking the impeding effect of the FGs on the movement of grain boundary dislocations along the grain boundaries and the unique role of nanocracks into the constitutive model. A strain-based cumulative distribution function is also included in the present model to account for the contribution of grain boundaries to the local flow stress due to grain refinement during plastic deformation. It is found that the interaction between dislocations and the FGs contributes to the strain-hardening property and the failure behavior is attributed to the nanocrack evolution. Numerical results show that the proposed model can successfully describe the enhanced strength and ductility of the NC metals in previous experimental literatures. It is further noted that the strength and ductility are sensitive to the volume fraction of the FGs and the density of nanocracks. This quantitative continuum plasticity model can be utilized to optimize the mechanical properties of the nanostructured metals by tuning the material structure parameters.

Effect of electrochemical reaction on diffusion-induced stress in hollow spherical lithium-ion battery electrode

During the process of lithium-ion intercalation and de-intercalation, the electrode undergoes huge volumetric change. Diffusion-induced stress (DIS) has been investigated in solid and hollow spherical electrode. In this work, a new coupled model is established in a hollow spherical electrode to analyze the DIS with electrochemical reaction. The result shows that electrochemical reaction has a significant influence on the distribution of DIS, which can make the tensile stress decline and even convert the stress from tension to compression. The tendency to avoid the electrode fracture and failure induced by DIS is thus beneficial. Compared to stress evolution in solid and hollow sphere electrode, electrochemical-induced stress in solid electrode is much smaller than that in hollow electrode. Also, reaction-induced stress will keep increasing with the wall thickness decreases. Finally, a new strategy is put forward to optimize the reaction-induced stress and the electrode thickness, which may ultimately extend the overall battery life.

Finite element simulation on Cu/CuZr crystalline/amorphous laminate under three point bending test with a stationary notch

In this work, the fracture behavior of crystalline/amorphous laminate under three point bending and the effects of crystalline layers on the notch tip plasticity were studied. For this purpose, finite element simulations under plane strain, small scale yielding conditions were carried out. The numerical simulation results reveal that, the fracture toughness is significantly improved by the laminated composite microstructure when compared to the bulk metallic glasses. Moreover, the fracture toughness will increase with the increasing of the number of crystalline layers. The higher the notch length to specimen width ratio, the worse is the fracture toughness of crystalline/amorphous laminate. This simulation method can also provide a method to design a reasonable structure for required behaviors.