Papers by Keyword: Residual Stress

Abstract: Based on the estimation of the critical hydrogen pressure and concentrations required for hydrogen-induced delayed cracking in high-strength steel, the conclusion that welded joints are hydrogen pressure microcracks body can be drawn under certain conditions. Through the analysis of the relationship between the microstructure evolution of welded joints, diffusion enrichment of hydrogen and cracking behavior, the formation mechanism of hydrogen-induced delayed cracking in weld center of high-strength steel joints is analyzed and the mechanism that stress induced the residual diffusion hydrogen gathered to promote the hydrogen pressure microcracks propagation is proposed. The research shows that the initation and propogation of hydrogen-induced delayed cracking in weld center can be divided into two stages, i.e. irreversible hydrogen damage stage and reversible hydrogen damage stage. In irreversible stage hydrogen pressure is the main causes of the initation of microcracks, while in reversible stage welding residual stress and residual diffusible hydrogen are necessary conditions for microcracks growth. The microcracks growth can be controlled by regulating welding residual stress.

Abstract: Residual stresses in green compacts have a significant influence on the quality of the compact and post-compaction processes like part handling. In this study, the latest European and American standard for residual stress measurement by X-ray diffraction have been used to obtain more exact residual stresses in surface of green compacts as experimental evidence for simulation. The influence of kinds of powders, compacting pressure and friction on residual stresses in green compact has been studied.

Abstract: In the article the results of the design and analysis of mathematical model for determining residual stresses in the surface of layer at parts processed by plastic surface deformation (PSD) in which the rollers having an arbitrary shape and size. It is shown that for the calculation of stresses in the surface of layer it should not be defined by them at a forcing point but by a function of contact stresses. Integral equations are obtained for calculating the stresses in the body parts at the processing of PSD rolls of arbitrary size and shape of the stress distribution over the contact area. We found that the tangential and radial residual stresses depend on the magnitude of the force F and its distance from the point at which the voltage is considered in detail. There is a sharp decrease in the influence of forces on the stress in the surface of the part of the distance to the point in question.The calculated data generated by the proposed method are highly matches with data during the experimental investigations. Maximum deviations of the calculated values do not exceed the errors of the experiments and adequate treatment of each other at a significance level of 0.05.

Abstract: The residual stress introduced in the thin-film process may caused some problems, especially after removing of the sacrificial layers below, the suspended structure may be bended due to the release. In this articles we will develop a new in-situ residual stress detection method based on flexible hinges for thin-film materials, then described the detection principle theoretically and simulated its properties by FEA method.

Abstract: The changes in residual surface stress state significantly affect the mechanical behaviour of the materials. In this paper, the effect of cryogenic treatment on grinding residual stress of ultra-fine grained WC-Co hardmetals has been investigated by measuring the residual stress of ground carbide surfaces before and after cryogenic treatment. The results show that the cryogenic treatment can relieve the residual stresses of ground carbide surfaces. Relaxation degree of residual stresses is highly dependent on the process parameters of cryogenic treatment, such as soaking temperature, cooling rate and warming rate. The relaxation rate of residual stresses decreases with the decreasing of soaking temperature, warming rate or increasing cooling rate, and does not change obviously with the soaking time.

Abstract: The laser shock processing(LSP) is a new surface treatment technique that induce a significant compressive residual stress field on the metal and alloys. The developed compressive stress field is beneficial to improve surface properties such as fatigue, wear, and corrosion. To improve the understanding of the shock process, investigation into the physical processes and its variability involved is necessary. This work examines the effect of LSP at different input variability to induce its compressive stress. Various factors that affect the compressive stress of the LSP are tested with a serial experimental using 30CrMnSiNi2A as workpiece. It was found that the in-depth residual stress induced by LSP were a function of laser power density,laser beam spot size, laser pulse width and pulse repetition.

Abstract: Grain growth simulations considering heat treatment process were carried and the change in microstructure on the surface was regenerated. Stress-dependency of the phase transformation from original phase to precipitate was introduced into the conventional multi-phase-field model, and stress distributions were calculated. Volumetric dilatation was considered as a source of the stress generation, and a slight variation in the dilatation coefficient was applied for each grain. As a result, a mosaic pattern in the stress distribution correlated to the polycrystalline microstructure was obtained. The residual stress distribution was also calculated under three different conditions, and revealed to vary depending on the microstructure obtained.

Abstract: Numerical simulation based on MSC.MARC was applied to predict the residual stress in double-sided double arc welding (DSDAW). The distribution of residual stress field in the welding seam was simulated and the actual situation in experiment of the residual stress was also measured. It shows that the calculated results are in good agreement with the experimental ones. The residual stress of conventional welding (CW) or a single arc welding (SAW) is calculated too. Moreover, the welding residual stress field of thick metal plates welded by DSDAW was carried out and compared with that of the CW method with back chipping. The result shows that the DSDAW technology had some excellent characteristics of smaller angular deformation, lower residual peak tensile stress, and well-proportioned stress distribution, which testifies that the welding procedures in DSDAW are reduced and the welding efficiency and quality of the welding joint are improved in great margin.

Abstract: The mechanism of healing fatigue damage was investigated by pulsed laser surface irradiation for polycrystalline copper film, X-ray Diffraction(XRD), optical microscopic and scanning electron microscopy(SEM). The results indicate that surface melting and grain refinement were found in the melted surface layer. Tensile residual stresses were introduced in the resolidified surface layer due to laser surface melting which produced deleterious effect on fatigue property. Remelting and grain refinement in the surface layer is mainly responsible for healing fatigue damage and fatigue life improvement. The fatigue damage could be healed completely or partly by laser surface irradiation under the proper parameters of laser treatment for the specimens.

Abstract: The paper presents a study on analysis of thermal elasto-plastic stress during pulsed laser heating a K418 alloy plate. Based on elasto-plastic constitutive relationship, a spatial finite element model was established to simulate the whole process. The distribution and evolutions of temperature and stress field was calculated. The stresses induced during the process are highly heterogeneous because of the recurrent changing temperature field. The stresses during the process fluctuate as the temperature field changes. High level tensile residual stresses reside in the fusion zone after the laser process. Compared to all other stress components, longitudinal stress is the highest and will have considerable influences over the distortion level and failure of the material.