Papers by Author: Judith C. Yang

Abstract: In this paper, it has been studied that the thickness of the free confinement medium in the Laser Shock Processing. Then the relationships are analyzed between the peak pressure induced by laser shock and the properties of the free confinement medium. On the basis, the optimum thickness of the free confinement medium is obtained, which ensure not only the optimum LSP effect but also the elimination of the remains of free confinement medium at a time. In the experiments, a kind of materials of free confinement medium was invented successfully, which is applicable to laser shock processing. The estimation of the free confinement medium theoretical thickness is accorded with the result of the experimental.

Abstract: The conventional forming of sheet metal is realized by the Die and Mould, this method usually give rise to high cost, long production periods and little flexibility. In order to adapt to the changing requirements of the market and make small batch production of three-dimensional parts of shallow stretching economically, a flexible forming technique of sheet metal based on laser shock waves is presented in this paper. After the forming mechanism and process are introduced, a finite-element analysis method is applied to simulate the shock forming process to obtain the optimized laser parameters and the shocking tracks. The experimental are carried out for the overlapped shock-forming, and the forming contour is measured and compared with the FEA simulation. The investigation provides the theoretical foundation for the selection of forming locus and processing parameters of flexible forming of sheet metal.

Abstract: With the advent of high-power pulsed lasers, laser peening has emerged as a new and very promising technique to improve the resistance properties of materials to fatigue, wear and corrosion. In this paper, the effect of laser peening on the surface performance of QT700-2 materials was investigated, the parameters of laser peening were optimized by an artificial neural network (ANN) method. A series of experiments was carried out by using a high-power, Q-Switched, pulsed neodymium-glass laser. The microstructure features were analyzed with SEM and the hardness and residual stresses at the surface and in-depth were measured. The results indicate that the depth of hardened layer was about 0.31ı1.40mm for a different shot number of 1-4 times and the compressive residual stress at the surface increases with increasing laser pulse energy, from -165MPa for the low energy 12J to -410MPa for the higher energy 20J. Laser peening can restrain nucleation of fatigue cracks and improve the fatigue life of nodular cast iron materials.