Papers by Author: Shu Huang

Abstract: The ABAQUS software was used to analyze the residual stress of TiN film treated by the single point micro-scale laser shock peening (μLSP). In view of the multi-factor effect of μLSP, the response surface methodology (RSM) of Design-Expert software was utilized to analyze the influence of laser process parameters on the residual stress in TiN film, based on the Box-Behnken experimental design methods, as a result, optimal combination of the laser process parameters was obtained. The results showed that μLSP can transform the tensile residual stress in the TiN film into the compressive residual stress, the compressive residual stress was gradually increasing with the increased laser power density, when the laser power density was 8 GW/cm2, the maximum compressive residual stress of the film surface was up to -350.48 MPa. In addition, as the laser power density increased, the maximum compressive residual stress was moving away from the spot center. The optimal combination of the laser process parameters of μLSP was obtained by the RSM, the laser power density was 7.6 GW/cm2, laser spot diameter was 283 μm, and the number of shocking was 2 times. Simulation results of the average residual stress was -248.76 MPa, while the predicting result of regression model was -245.31 MPa, the error was just 1.38 %. The results showed that μLSP was feasible for improving the residual stress distribution of TiN film, and the RSM can effectively optimize the process parameters of μLSP.

Abstract: In order to analyze effect of processing parameters on Laser Shock Peening(LSP), a novel numerical model integrated with FEM and statistical optimization algorithm was established, and the numerical simulation of LSP process was carried out. In simulation, laser pulse energy, beam diameter and center distance were considered as control parameters, while the compressive residual stress and the deformation value as output aim parameters,. The results indicates that the laser pulse energy has the strongest impact on the surface residual stress, while the spot diameter affects the section residual stress and the surface deformation. Moreover, the response surface function was applied to predict and optimize laser parameters. Lastly the presented method was verified by experiments.

Abstract: Micro-scale laser shock peening (μLSP) is a flexible and precise process that can potentially be applied to metallic structures in micro devices to improve strength and reliability performance. In order to understand the mechanism of μLSP process, a typical experiment was carried out for copper foils specimen with various process parameters. Surface morphology, deformation and hardness of the specimens were observed and characterized by 3D microscope system and situ nano-mechanical test system respectively. It was found that overlapping rate of laser spot has a little effect on microscopic deformation depth which increases slowly with the increasing of laser energy, and micro-hardness of the laser treated specimens was improved significantly.

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: Microscale laser shock peening (μLSP) can generate beneficial compressive stress distribution in the targets, as the used beam diameter in μLSP is at the order of micron equivalent with grain size, the treated material must be considered as anisotropic and inhomogeneous, this causes an asymmetrical distribution of residual stress. In this paper, shape factor σSF was introduced and defined to characterize the asymmetrical distribution of stress, optimum conditions of factors and the influence degree were explored based on Taguchi design with the optimal object of stress characterization values. The results show that shape factor is a significant characteristic of residual stress induced by μLSP, crystal orientation is the most important influence factor, but laser energy and peening number have significant influence on stress characterization values.

Abstract: Laser shot peening (LSP) has recently received more and more attention as a viable laser processing technology, since it can obtain the desirable residual compressive stress to improve fatigue life of the material by precisely controlling laser parameters. The purpose of this paper is mainly to explore the optimal residual compressive stress in the surface layer during LSP by statistical optimization algorithm. Based on the finite element analysis software ANSYS, Multi-island Genetic Algorithm (MIGA) is adopted to find the best solution of design requirements, the control parameters are laser pulse energy and spot diameter, while the aim parameters are residual compressive stress and deformation values, respectively. The results indicate that the optimal residual compressive stress obtained by integrated optimization technique can significantly improve the mechanical properties of the target after LSP. It provides a guiding importance for parameters optimization in future experimental research and practical application.

Abstract: Micro-scale laser shock peening (μLSP) is a novel surface modification technique utilizing mechanical effect of shock wave induced by high intensity pulsed laser with micron spots. μLSP can introduce the beneficial residual compressive stress distribution in surface layers of metal with micron-level spatial resolution, and thus enhance wear resistance and fatigue performances of metallic micro-structures. The characteristics and influence factors of μLSP were briefly introduced, and progress in μLSP research fields was reviewed and presented, including laser induced shock pressure, material constitutive relation, changes of mechanical properties and microstructure evolution of materials. Finally, proposals on further investigations of μLSP were brought forward. The systematical characterization will lay the ground work for better understanding the effect of μLSP in microlength level and developing a more practical simulation method.