S.H.Ai
,
Y.B.Xia and J.F.Tian (State Key Laboratory for Fatigue and Fracture of Materials
,
Institute of Metal Research
,
The Chinese Academy of Sciences
,
Shenyang 110015
,
China)
金属学报(英文版)
The creep and fracture behavior of the cast K417 and forged GH4049 nickel-based superalloys were investigated in the temperature range of 700-900℃ C. Within the ranges of stress and temperature studied, the steady state creep rates exhibited a power law relationship with the applied stress and temperature. The time to rupture is inversely proportional to the steady state creep rate. Under all testing conditions, the creep fracture process was mainly controled by crack initiation and growth of the intergranular oxidation. Casting porosities, pores and carbides were also prefecentral locations of creep crack initiation in the cast K417 alloy. In addition, the intergranular fracture feature in the forged GH4049 alloy was apparently associated with the formation and coalescence of the cavitations on the grain boundaries.
关键词:
superalloy
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null
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null
ZHANG Hongxue XU Zhichao CHEN Guoliang University of Science and Technology Beijing
,
Beijing
,
China Professor
,
Faculty of Superalloy
,
University of Science and Technology Beijing
,
Beijing
,
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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null
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null
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null
WANG Xu
,
ZHANG Shouhua
,
CUI Peiyong Beijing University of Science and Technology
,
Beijing
,
China. Central Iron and Steel Research Institute
,
Beijing
,
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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null
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null
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null
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null
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null
GUO Chengbi ZHOU Weisheng Dalian Institute of Technology
,
Dalian
,
Liaoning
,
China Professor
,
Dept.of Shipbuilding
,
Dalian Institute of Technology
,
Dalian
,
Liaoning
,
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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null
,
null
Y.G. Cao
金属学报(英文版)
To investigate the causes that led to the formation of cracks in materials, a novel method that only considered the fracture
surfaces for determining the fracture toughness parameters of J-integral for plain strain was proposed. The principle of the
fracture-surface topography analysis (FRASTA) was used. In FRASTA, the fracture surfaces were scanned by laser microscope and the
elevation data was recorded for analysis. The relationship between J-integral and fracture surface average profile for plain strain
was deduced. It was also verified that the J-integral determined by the novel method and by the compliance method matches each
other well.
关键词:
FRASTA
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null
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null
HU Zhizhong WU Yusheng CAI Heping MA Lihua Xi′an jiaotong University
,
Xi′an
,
China Senior Engineer
,
Res.Inst.for Strength of Metals
,
Xi′an jiaotong University
,
Xi′an 710049
,
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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null
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null
Materials Letters
Quantitative measurements were carried out on the fatigue fracture surface of the SiC/Al composite by a sectioning method. It was shown that the cyclic plastic strain amplitude, SiC volume fraction and particle size have effects on fracture surface roughness R(S). The measured fracture surface roughness R(S) is closely related to the fatigue-crack propagation path and may corresponds to the fatigue life. Moreover, it was found that there is an obvious difference in the R(S) values for fatigue fractures which are due to different fracture mechanisms. These results show that it is possible to reflect the fracture mechanism using fracture surface roughness and relate it to the fracture properties of materials.
关键词:
composite;SiC/Al;fatigue fracture;roughness;fractal dimension;sectioning method;general-method;fractography
Physical Review Letters
We find that the failure of bulk metallic glassy (BMG) materials follows three modes, i.e., shear fracture with a fracture plane significantly deviating from 45degrees to the loading direction, normal tensile fracture with a fracture plane perpendicular to the loading direction, or distensile fracture in a break or splitting mode with a fracture plane parallel to the loading direction. The actually occurring type of failure strongly depends on the applied loading mode and the microstructure of the material. Extensive evidence indicates that the Tresca fracture criterion is invalid, and for the first time, three fracture criteria are developed for isotropic materials with high strength, such as advanced BMGs or the newly developed bulk nanostructural materials.
关键词:
amorphous-alloys;enhanced plasticity;zr-ti;flow;deformation;composite;strength;microstructure;ribbons;failure
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
