Chunsheng Lu

A finite element study of the temperature rise during equal channel angular pressing

Abstract The temperature rise and temperature distribution in the workpiece during equal channel angular pressing were investigated by using the finite element method for Al–1%Mg and Al–3%Mg at different pressing speeds. The simulated temperature rise was compared with published experimental and analytical results.

Crystallization of amorphous alloy during isothermal annealing: a molecular dynamics study

The crystallization process of a Ti–Al amorphous alloy during isothermal annealing was studied with molecular dynamics simulations. The structural development and phase transformation were analysed based on the variations of the internal energy, cell volume, radial distribution function, bond pairs, and atomic configuration. The crystal nucleation, grain growth, and grain coarsening during the crystallization process were studied. The three-stage feature of the crystallization process was identified. The simulation results also show that there are transformations from a metastable crystal phase to a more stable crystal phase during the crystallization.

Nanoindentation-induced elastic–plastic transition and size effect in α-Al2O3(0001)

The mechanical properties of α-Al2O3(0001) have been investigated using the technique of nanoindentation with a Berkovich indenter. Coupled with the Hertzian contact theory, a theoretical shear strength of 28 ± 2 GPa was determined from the onset of pop-in events on load–displacement curves during loading, and the intrinsic hardness 30 ± 3 GPa was obtained by analysis of the so-called indentation size effect, based on the concept of geometrically necessary dislocations. The predicted values of the shear strength, hardness and elastic modulus are in good agreement with available experimental data. The importance of experimentally calibrating the area function over the contact depth range prior to nanoindentation tests is emphasized.

Evolution induced catastrophe

Abstract Fracture due to coalescence of microcracks seems to be catalogued in a new model of evolution induced catastrophe (EIC). The key underlying mechanism of the EIC is its automatically enlarging interaction of microcraks. This leads to an explosively evolving catastrophe. Most importantly, the EIC presents a fractal dimension spectrum which appears to be dependent on the interaction.

A sudden drop of fractal dimension : a likely precursor of catastrophic failure in disordered media

The variation of fractal dimension and entropy during a damage evolution process, especially approaching critical failure, is investigated. The results show that, as damage evolves, the fractal dimension and entropy of the spatial distribution of microcracks/voids decrease. A sudden drop of fractal dimension can be viewed as a quantitative indicator of damage localization or a likely precursor of an impending catastrophic failure. Using mining-induced rock bursts as an example, the complexity and difficulties of prediction are discussed.

A linked stress release model for historical Japanese earthquakes: coupling among major seismic regions

A linked stress release model is proposed for the analysis of spatial interaction of earthquake occurrences through stress transfer within a large area of the Earth’s crust. As an example, the model is used for statistical analysis for the Japanese historical earthquakes in central Japan and offshore in the Nankai and Sagami troughs with magnitude M ≥ 6.5 during the period from 1400 to 1997. This area is divided into four smaller regions of roughly comparable size and activity. Based on the Akaike information criterion (AIC), the results demonstrate the existence of coupling between certain of the regions. With the evidence that the crust may lie in a near-critical state, this has implications for the possible triggering of earthquakes at long distances from the origin event. In particular, we find evidence for the dependence of Nankai trough events on the Chubu/Kinki triangle region, whose events are themselves dependent on the the Fossa Magna/Sagami trough. Evidence for the validity of the model includes simulation results indicating that the model had a higher forecast hazard post-1991 for an event in the Chubu/Kinki triangle region than did models not incorporating regional coupling.

Influence of microstructures on mechanical behaviours of SiC nanowires: a molecular dynamics study

The tensile behaviours of [111]-oriented SiC nanowires with various microstructures are investigated by using molecular dynamics simulations. The results revealed the influence of microstructures on the brittleness and plasticity of SiC nanowires. Plastic deformation is mainly induced by the anti-parallel sliding of 3C grains along an intergranular amorphous film parallel to the plane and inclined at an angle of 19.47° with respect to the nanowire axis. Our study suggests that the wide dispersion of mechanical properties of SiC nanowires observed in experiments might be attributed to their diverse microstructures.

Strengthening brittle semiconductor nanowires through stacking faults: insights from in situ mechanical testing.

Quantitative mechanical testing of single-crystal GaAs nanowires was conducted using in situ deformation transmission electron microscopy. Both zinc-blende and wurtzite structured GaAs nanowires showed essentially elastic deformation until bending failure associated with buckling occurred. These nanowires fail at compressive stresses of ~5.4 GPa and 6.2 GPa, respectively, which are close to those values calculated by molecular dynamics simulations. Interestingly, wurtzite nanowires with a high density of stacking faults fail at a very high compressive stress of ~9.0 GPa, demonstrating that the nanowires can be strengthened through defect engineering. The reasons for the observed phenomenon are discussed.

Monte Carlo simulation of grain growth in two-phase nanocrystalline materials

The normal grain growth in volume-conserved two-phase nanocrystalline materials is studied using a modified Potts model, in which the grain boundary migration is driven by the interfacial energy between two phases and the grain boundary energy inside each phase. Monte Carlo simulation results show that the grain growth of one phase is constrained by the presence of the other phase. The power-law grain growth kinetics with an almost temperature-independent exponent of 0.16±0.01 (0.5 in a pure single-phase system) is predicted for two immiscible phases, which is in agreement with experimental observations.

A kinetic model for diffusion and chemical reaction of silicon anode lithiation in lithium ion batteries

In this paper, a kinetic model is proposed that combines lithium ion diffusion through a lithiated phase with chemical reaction at the interface between lithiated amorphous and crystalline silicon. It is found out that a dimensionless parameter, relating the concentration distribution of lithium ions to the movement velocity of phase interface, can be used to describe the lithiation process. Based on the stress distributions and lithium ion diffusion profiles calculated by an elastic and perfectly plastic model, it is shown that, as lithiation proceeds, the hoop stress that changes from initial compression to tension in the surface layer of silicon particles may lead to surface cracking.