Papers by Author: Su Qing Jiang

Abstract: Residual stress field induced by laser shot peening (LSP) was simulated using Box-Behnken experimental design. Compressive residual stress field intensity (S) was introduced to estimate the effect of compressive residual stress field on fatigue performance. The effect of laser process parameters (such as laser shock wave peak pressure, spot diameter and peening number) on S was analyzed by response surface analysis (RSA), quadratic regression predicting model for S was established, and the rationality of that was verified. Finally, the optimal combination of laser process parameters oriented to anti-fatigue manufacture was optimized. The results indicated statistical analysis results agreed well with those of simulation, RSA for parameter optimization of LSP is feasible.

Abstract: Typical specimens of AZ31B Magnesium alloy were processed by single point and continuous laser shock peening (LSP). The selected laser energy was 25 J, spot diameter was 8 mm, peening spacing was 8 mm and peening times were 2. The obtained value of residual compressive stresses were -144.3 MPa and -230 MPa for single and continuous LSP respectively, and the magnitude of residual stress was in direct proportion to the depth of deformation in definite micro-deformation range. The average surface micro-hardness in the laser spot zone was 92.42 HV, which increased by 26% as compared to 73.2 HV of substrate, the depth of hardened layer was about 0.3 mm, and the maximum micro-hardness was about 109.86 HV beneath surface of 0.05~0.075 mm. Large amount of crystal chunks appeared at the crystal grain boundaries and inside the grains, and the average grain size decreased from the untreated 7 μm to the peened 4 μm. The results show that the nucleation of fatigue crack can be retarded and the mechanical properties of AZ31B magnesium alloy sheet can be improved greatly with LSP process.

Abstract: Numerical study on fatigue life of ZK60 magnesium alloy plate before and after laser shot peening (LSP) was carried out in this paper. Based on the FEA model, residual stress field induced by LSP was analyzed, the fatigue life and position of weak area were predicted with ABAQUS software and MSC.Fatigue code, respectively, and the processing parameters were optimized. The results show that the fatigue life of ZK60 sheet metal by single LSP with one side and both sides increased by 72.9% and 78.5% compared with the untreated sample respectively. The size and depth of compressive residual stress increase with the increment of peening number, but when the peening number gets to a certain value, the residual stress reaches saturation and the fatigue life increase no longer significantly.

Abstract: The optimization of processing parameters for laser cladding process based on Statistical Analysis System (SAS) software was investigated and the experimental investigation on Ni-based alloy components fabricated by laser cladding was carried out. The influences of the main processing parameters on the surface quality were analyzed, and the Ni-based components with superior surface quality were obtained by employing the optimum set of parameters. The surface morphology and microstructure of the components were analyzed. Results indicate that the surface of the cladding is rather smooth and the claddings have a unique microstructure consisting of primary dendrite. The laser cladding layer with integrated melt interface and without reheat cracking can be obtained by optimizing the process variables. The investigations show that the components fabricated by laser cladding process have better mechanical properties than that of the conventional manufacturing technology.

Abstract: In order to understand and control the process of laser peen forming (LPF) of sheet metal, a developed FEM model was established and the process of LPF was simulated by FEM code ABAQUS. Special emphasis was posed on the part of the model devoted to the analysis of 3D residual stress distribution under laser shock wave loading. With the aid of simulation method, the influence of laser parameters, number of shots, peening tracks and the characteristics of sheet bending were investigated. The results indicate that the bending deformation of metal sheet is relative to laser peening numbers, peening coverage and the plate’s thickness, both upper and back layers of the deformed sheet exists residual compressive stresses.

Abstract: By using 6061-T6 Aluminum alloy plate, the micro-plastic flow process of surface material induced by LSP was analyzed with FEM code ABAQUS/CAE, the change of residual stress distribution and micro-topography was shown dynamically. Based on the results of numerical simulation, factorial model of MINITAB was used to carry out response optimizer design to gain the optimum strengthening effects. After the creation and analysis of factorial design, contour plots and surface plots were output, the optimum strengthening effects were obtained by statistic results of response optimizer, and the influencing factors of correspondence were achieved. Finally, LSP experiments were carried out with the optimized laser parameters on 6061-T6 plate, good agreement was found between numerical and experiment results.

Abstract: The principle of laser peen forming (LPF) is introduced, the loading model of laser shock wave is established. This paper focuses on applying finite element analyses, instead of a complicated experimental procedure, to predict the development, magnitude and distribution of residual stresses induced by laser impacts on a metal plate, and dynamic process of laser continuous peen forming is realized with the FEM code ABAQUS. Based on the numerical analysis, the laser processing parameters can be optimized and the deformation contour of metal plate can be analyzed. The results calculated by the finite element method are correlated well with the available experimental results. The simulated results also reveal that adjusting the laser energy appropriately can result in an anticipated shape of plate in LPF process.