Papers by Author: Xue Ren Wu

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Authors: Xiang Yang Huang, M. Lang, Xue Ren Wu, H. Döker
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Authors: J.Z. Liu, Xue Ren Wu, L.F. Wang, B.R. Hu, B. Chen
Abstract: Analytical studies were made on effect of size and location of a weld defect on fatigue life for argon-arc welded titanium alloy joint. In the analyses, a weld defect was assumed as an initial crack, and the crack growth life was taken as total fatigue life. By using the Isida and Noguchi’s stress intensity factor solution for a plate containing an embedded elliptical subsurface crack under tension, the life prediction code FASTRAN3.9 was revised. A small crack methodology based on the plasticity-induced crack-closure concept and the effective stress intensity factor range, Keff , was used to predict the total fatigue life of welded joint, and to study the effect of the size and location of weld defect on fatigue life by means of the revised FASTRAN3.9 code. Limited amounts of experimental data were used to make comparison with the predictions. The predicted fatigue lives are in reasonable agreement with experiments, and the effect of both the size and location of the weld defect on fatigue life was found to be significant.
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Authors: B.R. Hu, J.Z. Liu, B. Chen, L.F. Wang, Xue Ren Wu
Abstract: Experimental and analytical studies were made on the fatigue behavior and life prediction for argon-arc welded titanium alloy joints, TA15. High cycle fatigue tests at two stress ratios, R=0.5 and 0.06, were carried out on smooth specimens with the argon-arc weld joint located at the specimen center section. Through macroscopic observation and SEM fractographic analysis, it was found that most of the cracks were initiated at weld defects such as voids and inclusions at the edge of weld and in the heat affected zone (HAZ). A small crack methodology based on the plasticity-induced crack-closure concept and the effective stress intensity factor range, ΔKeff , was used to predict the total fatigue life of the weld joints. Large crack growth curve for cracks in the HAZ area was employed as the da/dN-ΔKeff base-line of the TA15 alloy. From fractographic measurements, an average defect size of 100 microns was assumed as the initial small crack size in the life predictions. Predicted total fatigue life by solely considering small crack growth stage agreed well with the experimental data.
157
Authors: Hui Chen Yu, Bin Zhong, Xue Ren Wu, Hui Ji Shi
Abstract: The fatigue behaviors of a directionally solidified (DS) nickel base superalloy, coated with a MCrAlY coating (NiCrAlYSi) were studied. Two kinds of tests were performed. One kind of tests are low cycle fatigue (LCF) test under strain control at different temperatures, another kind of tests are stress controlled LCF test with SEM-servo hydraulic testing machine for in situ cracking observation. The results show that the effect of coating on LCF life of coating/substrate system was rather different according to different strain levels and temperatures. The coating has no or less effect on LCF life under high strain range and the LCF life is governed by fatigue behavior of substrate in spite of the difference of temperature. However, when strain range is smaller, crack initiation and propagation are observably affected by temperature, which leads to a shorter LCF life of coating/substrate system at 500°C and a longer LCF life at 760°C or 980°C. This means the failure of coating/substrate system is dominated by the cracking of surface coating under low strain range. The brittleness at 500°C lower than DBTT results in rapid stage II crack propagation. The crack initiation from coating surface was in situ observed at room temperature and 700 °C and it was found that cracks usually initiated from the surface roughness of coating and then propagate to failure. The brittleness and surface roughness are the basic acceptable causes leading to the early damage of a coating/substrate system.
229
Authors: Y. Zhou, G.J. Yuan, X.N. Lu, H.Q. Li, Jian Feng Tong, Da Ming Chen, Xue Ren Wu
403
Authors: Yu Kui Gao, Xue Ren Wu, Feng Lu, Mei Yao, Qingxian Yan
Abstract: The characteristics of compressive residual stress fields induced by shot peening in 40CrNi2Si2MoVA, 16Co14Ni10Cr2Mo, 30CrMnSiNi2A and 0Cr13Ni8Mo2Al ultra-high strength steels, which are used widely in aeronautical industry were investigated, and the change of surface integrity including surface residual stress, surface roughness as well as its effects on fatigue properties were investigated. The results show that the fatigue limits of ultra-high strength steels can be increased by shot peening because the surface integrity can be ameliorated by shot peening, and that for a given steel there is a appropriate peening intensity under which the fatigue property of this steel is optimum. Finally, a judgement for the optimization condition of shot peening process is proposed based on a theory of micro-meso processes of fatigue crack initiation and experimental results. The technique should be considered to be optimum, if the fatigue crack source of shot peened specimen has been moved to the internal matrix metal region beneath the hardened layer; and its apparent fatigue limit has been improved and got to a value, which is near to that predicted according to the concept of surface/internal fatigue limit.
448
Authors: Hui Chen Yu, Bin Zhong, Xue Ren Wu
Abstract: The isothermal low cycle fatigue (LCF) behaviors of a directionally solidified (DS) nickel base superalloy, coated with a NiCrAlYSi coating were studied. The study concerned NiCrAlYSi coating formed by an arc-discharged physical vapor deposition (PVD) process for protection against high-temperature corrosion and oxidation of gas turbine blades. The effect of protective coating on LCF life of coating/substrate system was investigated at high temperatures and compared with uncoated alloy. The test results show that coating has no or less effect on LCF life under high strain range and the LCF life is governed by the fatigue behavior of substrate at different temperatures. However, when strain range is smaller, crack initiation and propagation are observably affected by temperature, which leads to a shorter LCF life of coating/substrate system at 500°C and a longer LCF life at 760°C or 980°C.
203
Authors: Ying Li, Hui Chen Yu, Xue Ren Wu, Xiao Guang Yang, Duo Qi Shi
Abstract: Tensile creep tests were conducted at 980°C under a constant stress on a single crystal nickel base superalloy. Some tests were interrupted at different stages during the creep process. The strain-time curves indicated that this alloy exhibited conventional primary, steady-state and tertiary stages at this temperature. The transmission electron microscope (TEM) observations of foils taken from the gauge sections of specimens were made to interpret the microstructural evolution that occurred during the creep process. It was found that the γ′ particles were rafted in the direction perpendicular to the applied stress. The acceleration of the creep rate was related to the change of the dislocation density.
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