Papers by Author: Hong Yan Ruan

Abstract: In order to enhance mechanical property and restrain crack growth of 6061-T6 aluminum alloy, laser shot peening (LSP) was employed to induce compressive residual stress and plastic deformation on the surface of metal. The FEA code ABAQUS and MSC. Fatigue were used to simulate crack growth of Compact tension (CT) specimens treated by LSP. The numerical simulation results showed that LSP can effectively inhibit the crack growth, decrease the crack growth rate as well as increase the final crack size, and as a consequence, fatigue life was extended. Adding peening times could get deeper compressive residual stress field which strengthen material surface and restrain crack growth, but the fatigue stress intensity factor threshold decreases.

Abstract: After the mechanisms of laser peen forming (LPF) were analyzed, the effect of sheet metal’s thickness on LPF was discussed in theory. The analysis model that residual stresses brought sheet bending was established, and the relationship between thickness and arc height of sheet metal was obtained. The process of laser shock wave loading during LPF was modeled, and then the residual stresses and deformation of the peened sheet were simulated by ABAQUS software. The results indicated that LPF use bending moments caused by residual stress to induce deformation, which was agreed with the theory analysis. The curvature of sheet metal induced by LPF decreased as the thickness increased, the arc height formed by bending was inversely proportional to thickness square of sheet metal on the whole. This research also has significance for the control of LPF and the investigation of further experiment

Abstract: The gas jets from the conical and new designed supersonic nozzles on different working pressure are simulated by a computational fluid dynamics code, FLUENT, using standard k-ε model and unstructured grid finite volume method with compressible axis-symmetry N-S equation. Under the same condition of pressure-inlet, the distribution of symmetry velocity and that of static pressure are compared. The result of the analysis indicates that conical nozzle outlet can reach subsonic or sonic flow. It is fit for low speed and low pressure situation. The gas jet from the new design supersonic nozzle working at design work pressure has better properties than those of other nozzles. So it is better for thick-plate and or high-speed laser cutting. It is obvious that the results of CFD numerical analysis are consistent with the shadowgraph. Thereby it is an effective way to optimize the nozzle according to the performance of flow field.

Abstract: The existing studies based on 2-dimension cutting model are partial investigations on tool wear. In order to get close to the true cutting conditions, the Lagrangian thermo-viscoplastic cutting simulations were conducted and the tool wears were predicted under different cutting speeds using 3-dimension finite element models. The simulation results indicate that when the cutting speed increases the cutting forces will reduce accordingly while the wear depth will be deeper. As a result, different factors should be considered at the same time when the speed range is selected. This study has shown that the finite element method is a valuable approach to understand the tool wear mechanism in machining and the influences of different cutting speeds.

Abstract: Based on premixed high pressure water jet cutting, five kinds of nozzle models were established, and the control equations and closed equtions of liquid-solid two-phase were given. The inside-outside liquid-solid two-phase flow characteristics of the nozzles were simulated by Hybrid Finite Analytic Method (HFAM). The results indicate that the taper-beeline nozzle has better convergence characteristic, good hydraulic characteristic and lower radical velocity, thus it is more suitable for premixed high pressure water jet cutting nozzle.