材料期刊网

STUDY ON FATIGUE DAMAGE BELOW THE FATIGUE LIMIT AND THE COAXING EFFECTS

WU Zhixue , LU Wenge and XU Hao1)(Fushun Petroleum institute , Fushun 113001 , China)2)(State Key Laboratory for Fatigue and Fracture of Materials , Institute of Metal Research , ChineseAcademy of Sciences , Shenyang 110015 , China)3)(Institute of Mechanical Engineering , Northeastern University , Shenyang 110006 , China)Manuscript received 19 July 1995 , in revised form 11 April 1996

金属学报(英文版)

Rotary bending fatigue tests were carried out for smooth specimens of a mediumcarbon steel with two different grain sizes near the fatigue limit. The process of fatigue damagewas observed by replication method, and the effects of grain size,stress level and microstructure on surface damage were studied. The effect of following cycle stress level on the coaxing effects was also discussed. The fatigue limit is the maximum stress at which the short fatigue crack initiates and becomes a non-propagating crack.. The length of non-propagating crack is related to grain sizes and stress level. The coaxing effects disappear when the following stress level is greater than the critical value.

关键词: : fatigue damage , null , null

Laboratory of Fatigue and Fracture for Materials(LFFM)

WA NG Zhongguang Professor , Director of the LFFM , Shenyang , 110015 , China.

材料科学技术（英文）

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INFLUENCE OF TEMPERATURE ON FATIGUE CREEP INTERACTION FRACTURE MAP

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 , null , null , null

The Morphology of Rolling Contact Fatigue Fracture of Hardened Steels

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 , null , null , null , null , null

MECHANISM MAP OF TORSIONAL FATIGUE FRACTURE

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 , null , null

Key R&D activities for development of new types of wrought magnesium alloys in China

Transactions of Nonferrous Metals Society of China

Many researchers in China are actively engaged in the development of new types of wrought magnesium alloys with low cost or with high-performances and novel plastic processing technologies. The research activities are funded primarily through four government-supported programs: the Key Technologies R&D Program of China, the National Basic Research Program of China, the National High-tech R&D Program of China, and the National Natural Science Foundation of China. The key R&D activities for the development of new wrought magnesium alloys in China are reviewed, and typical properties of some new alloys are summarized. More attentions are paid to high-strength wrought magnesium alloys and high-plasticity wrought magnesium alloys. Some novel plastic processing technologies, emerging in recent years, which aim to control deformation texture and to improve plasticity and formability especially at room temperature, are also introduced.

关键词: wrought magnesium alloy;microstructure;properties;alloy designing;plastic deformation;research projects;y-zr alloys;mechanical-properties;mg-4y-4sm-0.5zr alloy;grain-refinement;rare-earth;microstructure;gd;phase;temperature;evolution

Quantitative study of correlation between fracture surface roughness and fatigue properties of SiC/Al composites

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

Development of rapidly quenched soft magnetic materials in China

Shaoxiong ZHOU

材料科学技术（英文）

The discovery of the first Fe-based ferromagnetic amorphous alloy in 1966 had made an impact on conventional magnetic materials because of its unique properties. Since then, a number of amorphous magnetic materials have been successfully developed and used in a wide variety of applications. A brief review of R & D activities on amorphous soft magnetic materials in China is given from the beginning to the present in a somewhat chronological order, followed by a brief introduction to their applications on electric and electronic industries. An analysis and a prospect of Chinese market of such amorphous materials are also presented.

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Fracture mechanisms in bulk metallic glassy materials

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

THERMAL FATIGUE AND FRACTURE MECHANICS ANALYSIS OF GREY CAST IRON

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 , null , null