Papers by Author: L. Zhang

Abstract: A mathematical model for the Cu/ZrW2O8 functionally graded films was established using a finite element method. The effects of the parameters, such as the layer number (N) and composition distribution index (P), on the thermal stress fields of the Cu/ZrW2O8 functional graded films were discussed. It shows that when N=5 and P=2, the maximum thermal stress in the functional graded films is decreased. And the maximum value of thermal stress appears in the internal layers of the functionally graded films. The phase composition, the surface morphology and the thermal stress of the films were analyzed by the XRD, SEM and X-ray stress tester, respectively. The results show that the thermal stress distribution is similar to that from the numerical calculation. The maximum value of the thermal stress decreases to 72% of the original coating without the functionally graded films, and appears in the internal layers of the functionally graded films.

Abstract: The strain-rate sensitivity of LY2 aluminum (Al) alloy subjected to laser shock processing (LSP) was investigated according to the fracture morphology at strain-rates ranging from 0.00001 s-1 to 0.1 s-1. The fracture morphology was observed by the scanning electron microscopy (SEM). Fracture morphology at different strain-rates suggested that LY2 Al alloy after LSP seemed to evolve towards a more ductile dimple fracture mode with increasing the strain-rates. The relations underlying the fracture morphology and strain-rate sensitivity were also addressed.

Abstract: In the present investigation, the effects of processing parameter on three-point bending fatigue pergormance of TC4 alloy are examined, particular emphasis is devoted to the question of appropriate LSP processing parameters for improving the fatigue properties. Based on cyclic deformation and stress/life (S/N) fatigue behavior, it was found that there was the optimal shock number of overlapped spots for three-point bending fatigue pergormance of TC4 alloy. By comparing with the as-received specimen, the fatigue performance of TC4 alloy has the most obvious improvement by LSP with two impacts.

Abstract: Laser shock processing (LSP, also known as Laser shock peening) is applied by using a high energy pulsed laser to create a high amplitude stress wave or shock wave on the surface to be treated. LSP is proved to be superior to conventional treatments such as shot peening in many engineering products. This paper focuses on Laser shock processing and its effects on mechanical properties of material AISI 8620 alloys steel. Experiment results indicated that compared with base material, the surface hardness increased by 13.8%, and compressive residual stress increased by 521%. Statistical method was introduced to analyze hardness and residual stress change before and after the LSP.