ZANG Qishan LIU Kang KE Wei ZHU Ziyong Laboratory of Fatigue and Fracture of Sinica
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Materials
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IMR
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China.Institute of Corrosion and Protection of Metals
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Academia Sinica
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Shenyang
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China.
材料科学技术（英文）
The crack growth rates of A537 c1.1 steel and its weld metal have been investigated both in air and in artificial sea water.The effects of stress ratio,frequency,residual stress of welds as well as corrosion products on cor- rosion fatigue crack growth rate have been exa- mined.Some electrochemical reactions occurred during tests and models for describing the cor- rosion fatigue crack growth process in low strength of offshore structural steel were discussed.
关键词:
crack growth
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HU Zhizhong WU Yusheng CAI Heping MA Lihua Xi′an jiaotong University
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Xi′an
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China Senior Engineer
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Res.Inst.for Strength of Metals
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Xi′an jiaotong University
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Xi′an 710049
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China
金属学报(英文版)
Studies have been made of the torsional fatigue fracture life of notched specimens,the macroscopic fractography and microscopic fracture mechanism of steel 40Cr after various tempering treatments under different stresses,With the increase of stress,the fracture model changes from normal stress fracture to longitudinal shear one,and then transversal shear one. Under same stress,with the increase of strength,the fracture mode transfers from shear to normal stress fracture.The mechanism of normal stress fracture may be:transgranular frac- ture→striation+intergranular fracture→dimple+intergranular fracture,and of shear fracture may be:transgranular fracture→shear trace→dimple.Based on the experimental results,a fracture mechanism map of torsional fatigue has been drawn up.
关键词:
mechanism map
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WANG Xu
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ZHANG Shouhua
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CUI Peiyong Beijing University of Science and Technology
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Beijing
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China. Central Iron and Steel Research Institute
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Beijing
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China.
材料科学技术（英文）
Rolling Contact Fatigue(RCF) is a cumulative damage phenomenon when metals are subjected to repeated contact stresses. The fomation of pitting on the contact surface is the result of the rolling contact fatigue. The morphologies of rolling contact fatigue fracture of the har- dened steels (86CrHoV7, 42CrMo) show that strong resemblance in fractuye mechanisms exists between rolling contact fatigue and uni-axial fatigue. Since fatigue striations are hardly observed in hardened steels under uni-axial fatigue, it is interesting to note that the state of stress in rolling contact fatigue is more favor- able to ductile fractures than in uni-axial fatigue.
关键词:
rolling contact
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ZHANG Hongxue XU Zhichao CHEN Guoliang University of Science and Technology Beijing
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Beijing
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China Professor
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Faculty of Superalloy
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University of Science and Technology Beijing
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Beijing
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China
金属学报(英文版)
The relative ratio of fatigue resistance to creep resistance of materials varies with test temper- ature.As the temperature decreases,the creep resistance,since it is a thermal activation pro- cess,becomes relatively larger than fatigue resistance.Therefore the fatigue damage becomes predominant,and results in expansion of fatigue fracture region(region F),and shrinkage even complete elimination of creep fracture region(region C).A materials parameter Ω can be defined to estimate the temperature at which the creep fracture region is completely de- pressed.This phenomenon could be understood on the basis of the integrated model of compet- itive and cumulative models of fatigue creep interaction.
关键词:
creep fracture
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Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science
Tensile, compressive, cyclic tension-tension, and cyclic compression-compression tests at room temperature were systematically applied to a Zr52.5CU17.9Al10Ni14.6Ti5 bulk metallic glass for comprehensive understanding of its damage and fracture mechanisms. Under tensile loading, the metallic glass only displays elastic deformation followed by brittle shear fracture. Under compressive loading, after elastic deformadon, obvious plasticity (0.5 to 0.8 pct) can be observed before the final shear fracture. The fracture strength under compression is slightly higher than that under tension. The shear fracture under compression and tension does not occur along the maximum shear stress plane. This indicates that the fracture behavior of the metallic glass does not follow the Tresca criterion. The fracture surfaces show remarkably different features, i.e., a uniform vein structure (compressive fracture) and round cores coexisting with the radiating veins (tensile fracture). Under cyclic tension-tension loading, fatigue cracks are first initiated along localized shear bands on the specimen surface, then propagated along a plane basically perpendicular to the stress axis. A surface damage layer exists under cyclic compression-compression loading. However, the final failure also exhibits a pure shear fracture feature as under uniaxial compression. The cyclic compression-compression fatigue life of the metallic glass is about a factor of 10 higher than the cyclic tension-tension fatigue life at the same stress ratio. Based on these results, the damage and fracture mechanisms of the metallic glass induced by uniaxial and cyclic loading are elucidated.
关键词:
mechanical-properties;crack-propagation;zr-ti;enhanced plasticity;amorphous-alloys;high-strength;hydrostatic-pressure;matrix;composites;flow;deformation
Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing
In the present paper, the Fourier transform method (FTM) was applied in a study of fatigue fracture surfaces of commercial aluminum in order to relate the geometrical parameters on the fracture surface to the microstructure of the material. The results indicate that the power spectrum and the wave number are inversely related. An exponent n was indexed by curve fitting the power spectrum peaks of the fracture profile and was shown to correlate with the crack propagation rate da/dN, and da/dN can be inferred approximately from the correlation function.
关键词:
Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing
In this study the authors present and discuss the results of the investigation on the fatigue fracture behaviors in a series of as-soldered and thermal-aged copper/lead-free solder joints deformed under both monotonic and cyclic loadings. The observation results showed that fatigue cracks generally initiate around the IMC/solder interface when the loading axis is vertical to the interface. The intrinsic deformation behaviors are little different for different solder joints resulting from strain localization induced by the stain mismatch. Fracture surface observations revealed the crack propagation path and fatigue resistance of the solder joints to be affected by the yield strength and mechanical property of the solder. When the copper/solder interface is parallel to the loading axis, the interfacial IMC layer failed approximately perpendicular to the interface when the cumulative strain exceeded the fracture strain, then the cracks propagated to the IMC/solder interface, leading to the fracture along the interface. The failure mechanisms and factors influencing interfacial fatigue are discussed. (C) 2009 Elsevier B.V. All rights reserved.
关键词:
Lead-free solder;Fatigue fracture;Interface;Strain localization;Vertical cracks;lead-free solders;pb-free solders;deformation-behavior;joints;tensile;cu;embrittlement;temperature;sn-3.5ag;alloy
GUO Chengbi ZHOU Weisheng Dalian Institute of Technology
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Dalian
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Liaoning
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China Professor
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Dept.of Shipbuilding
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Dalian Institute of Technology
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Dalian
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Liaoning
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China
金属学报(英文版)
The in-phase and out-of-phase thermal fatigue,the C-P type and P-C type isothermal fa- tigue of grey cast iron were experimentally studied.The fatigue life was evaluated analytically by using the elastic-plastic fracture mechanics method(mainly J integral).The results of ex- periments and calculations showed that the lifes of in-phase and C-P type fatigue are longer than that of out-of-phase and P-C type fatigue respectively within the same strain range. This is in contrast to the results of other materials such as low carbon steel.On the other hand, the predicted lifes are consistent with experimental results.This suggests that J integral as a mechanics parameter for characterizing the thermal fatigue strength of grey cast iron and the mechanics model and the calculation method developed here are efficient.A parameter ΔW_1 was proposed from energy aspect to characterize the capacity of crack propagation. The isothermal fatigue life is the same as the thermal fatigue life for identical ΔW_1 values.
关键词:
grey cast iron
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