Papers by Author: J.B. Li

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Authors: M. Qin, Vincent Ji, S.Y. Ma, J.B. Li
Abstract: Investigation on the quasi-static residual stress relaxation is an important aspect of component design and life management. After taking into account the influence of transverse stress and strength distribution, this paper proposes a new criterion of residual stress relaxation under quasi-static load as follow: the surface residual stress tends to relax as long as the Mises effective stress anywhere exceeds the local yield point. In addition, by X-ray tensile test, a method of determining superficial yield strength based on the Von Mises hypothesis was applied at the shot-peened surface of a martensitic stainless steel 0Cr13Ni4Mo. The experimental results show that the yield strength of superficial layer is larger than that of core material. According to the experimental results, a simplified ladder-shaped model of the depth distribution of yield strength is proposed. On the basis of the above-mentioned relaxation criterion and the strength distribution model, a new method is presented to calculate the relaxation amount. The calculated results coincide with the experimental results.
Authors: J.B. Li, X.Y. Gai, D.L. Wang, S.Y. Ma, Vincent Ji
Abstract: The work hardening effect of the shot peening affected layer of hardened and low temperature tempered spring steel was investigated using the method for determining the yield strength of a metallic surface with biaxial residual stress. The results show that for the surface layer of the specimens, the microhardness and half-width values of X-ray diffraction lines is decreased, whereas the yield strength is increased during shot peening. Thus, shot peening leads the surface layer of steel in hard state to work hardening instead of work softening.
Authors: M. Qin, Vincent Ji, Y.N. Wu, S.Y. Ma, J.B. Li
Abstract: A new method is applied to investigate the relationship between the yield strength and annealing temperature for a Cu film. By Ion Beam Assisted Magnetron Sputtering (IAMS), Cu film with 2.4 µm thickness was deposited on a strip of super high strength steel 37SiMnCrNiMoV, and the specimens were treated by vacuum-annealing at different temperature. The X-ray tensile test was used to measure the longitudinal and transverse stresses and applied strain for Cu film. Based on the experimental results, the equivalent stress s and the equivalent uniaxial strain t e can be obtained. According to the s- t e relation, the calculated proof stress is acquired. The results indicate that the proof stress of the film decreases with the increasing of annealing temperature. When annealing temperature rises from 150ı to 300ı, the decreasing amplitude of proof stress is the largest. The phenomenon can be explained by the recrystallization and microstructure evolution in Cu film during the annealing treatment.
Authors: D.L. Wang, Tao Jin, S.Q. Yang, Z. Wei, J.B. Li, Zhuang Qi Hu
Authors: M. Qin, Vincent Ji, Jiu Hua Xu, J.B. Li, Ke Wei Xu, S.L. Ma
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