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Wang Yanqun Liu Yinghua Yang Haiyuan,

力学学报 , 1997,
Abstract: A method of finite element modeling of fatigue crack growth and closu re behavior is presented. The cyclic plastic hardening behavior of materials is taken into account. The chosen cyclic plasticity constitutive model has been exa min ed. After a discussion about the influence of finite element mesh on the numerical results, a mesh optimization criterion is suggested. Employing the suggested mumerical method and considering the crack closure effect, we investigate the evolution of the profile of crack surfaces, the stress and strain fields ahead of the crack tip and the forward and reversed plastic zones. The influence of cyclic hardening and stress ratio on the crack opening stress level is discussed as well.
Density Evolution of the Surface Short Fatigue Cracks of 1Cr18Ni9Ti Pipe-Weld Metal
Density Evolution of the Surface Short Fatigue Cracks of 1Cr18Ni9Ni Pipe—Weld Metal

Yongxiang ZHAO,Jinnuo WANG,Qing GAO,

材料科学技术学报 , 2002,
Abstract: The evolutionary density and the scatter of densities of the short fatigue cracks on the surface of 1Cr18Ni9Ti pipe-weld metal were observed by local and overall viewpoints, respectively. The local viewpoint, which is in accordance with a so-called ``effectively short fatigue crack criterion", paid attention to the dominant effective short fatigue crack (DESFC) initiation zone and the zones ahead of the DESFC tips. The overall viewpoint focused on the whole test piece of specimen. The results revealed that the density and scatter evolution exhibited a significant character of microstructural short crack and physical short crack stages. The evolutionary behavior by the local viewpoint was sensitive to the increase of DESFC size and tip location. The mechanism of the short crack growth associated with the general test observations that the DESFC acted gradually as a long crack and the scatter of DESFC growth rates tended gradually to that of a long crack was well revealed. Intrinsic causes of the random cyclic strain-life relations and stress-strain responses are appropriately given. In contrast, the evolutionary behavior by the overall viewpoint was non-sensitive and violated the general test observations. Therefore, the intrinsic localization and randomization of material evolutionary fatigue damage should be more appropriately revealed from the observations by the local viewpoint.
X Y Li,X T Tian,H C ZhuWeldng Division,Beijing Polytechnic University,Beijing,China National ho of Advanced Welding Technology,HIT,Harbin,China,
X. Y. Li
,X. T. Tian and H. C. Zhu

金属学报(英文版) , 2000,
Abstract: Mismatching is one of the basic characteristics of welded joints.Overmatched welded joint with a crack in hard weld is simplified as a cracked body of CCP type SHS (a hard bar sandwiched between two soft material with a crier perallel to the interface ) in this paper.Effects of mechanical heterogeneity on fatigue crack growth and crack closure of this model are studied by experimental and elastic - plastic finite element methods. It is found that, residual plastic deformation remaining in the wake of a growing crack tip, which cases crack closure,is affected the plastic deformation in adjacent soft mate- rial near by the crack tip. Both the shape of crack tip plastic zone and stress distribution ahead of crack tip in heterogeneous cracked body are different from that of homogeneous one. Crack closure (open- ing) loads are estimated by investigating the changes of crack tip opening displacement during fatigue loading, and a new model of crack oening process is presented. Because of the difference in the effect of mechanical heterogeneity on displacement of non - fatigue crack and fatigue crack, conventional CTOD can not reflect the real deformation at crack tip of SHS specimens.
Design fatigue curves based on small crack growth and crack closure  [PDF]
Somnath Chattopadhyay
Journal of Applied Science and Engineering Technology , 2008,
Abstract: The propagation behavior of short cracks cannot be studied by linear elastic methods because of the large plastic region near the crack tip, as well as a break down in correlation of the stress intensity factor with the fatigue crack growth rates. The proposedfatigue design approach incorporates a distanceparameter in conjunction with linear elastic fracture mechanics and effectively integrates long and short crack growth test data. This distance parameter is a material constant, which allows for the effects of (a) large-scale plasticity, (b) crack closure,and (c) fatigue crack threshold. Furthermore, this parameter successfully predicts fatigue crack growth behavior of short cracks. The practical applicationof this method is for studying fatigue crack initiation in pressure vessels and is based on the concept that initiation occurs only when the material ahead of the crack tip is damaged enough by cyclic straining. In this paper, the initiation and growth of small cracks have been investigated along with consideration for crack closure. These results provide the design fatigue curves for some typical structural materials and lead to realistic estimates of fatigue lives for materials used in pressure vessels.The techniques outlined in this paper are equally applicable to materials used in aerospace and automotive industries.

XU Yongbo,WANG Zongguang,

材料研究学报 , 1988,
Abstract: This review paper presents the important results on dislocation behaviornear the crack tip during in situ deformation.It includes:Experimental ob-servations on dislocations emission from a crack-tip during deformation andthe existance of dislocation-free
Influence of Grain Boundary on Fatigue Behavior of Ni-base Bicrystals
Influence of Grain Bounary on Fatigue Behavior of Ni-base Bicrystals

Jiansong WAN,Zhufeng YUE,Xiaoliang GENG,Zhixian LU,

材料科学技术学报 , 2002,
Abstract: The influence of the grain boundary on the fatigue behavior was studied by two three-point-bending (TPB) specimens. One TPB specimen was named Bicrystal 1, whose pre-crack was along the grain boundary and the applied load paralleled to pre-crack direction, while the other TPB specimen was named Bicrystal 2, whose the pre-crack was perpendicular to the grain boundary and the applied load paralleled also to the pre-crack. It was found that the rate of the fatigue crack growth of Bicrystal 1 was about a tenfold higher than that of Bicrystal 2. The fatigue behavior of Bicrystal 2 specimens was dependent on the distance between the crack tip and grain boundary. The crack growth rate was highest when the crack tip was at a critical distance to the grain boundary, while the rate was the lowest when the crack tip reached grain boundary. After the crack was over the grain boundary, the crack growth rate increased. The crystallographic finite element method was applied to analyze the stress and strain structure ahead of the crack, in order to reveal the above characteristics of the fatigue behavior. It is the grain boundary-induced redistribution of stresses near the crack tip that induces the difference of fatigue behavior.

ZHENG Yesha,WANG Zhongguang,AI Suhua,

金属学报 , 1995,
Abstract: It was observed first in this test that the stabilized dislocation cell and wall structures had been formed on near fatigue threshold of physcial short crack in dual-phase steels. There was a probability of forming dislocation cell on ferrite-martensite interfaces in long crack growth threshold. where the dislocation lines were more dense, there were the dislocation lines of single(R = 0,-1) and cross slip(R=-1) in the second stage of long crack growth ;there were obviously rare and lengthened dislocation lines of single and cross slip in the third stage of long crack growth. It is indicated that the dislocation morphologies of fatigue crack tip were the products of strain history. The dislocation cell and wall structures were substable on near physical short crack threshold. it was constituted into dynamic balance with cyclic stress-strain on threshold, and also was one of microstructural parameters.

HUA Wenjun,WANG Zhirui,ZHANG Jirong,

金属学报 , 1996,
Abstract: The relationships between microstructure, fracture surface and propagation behaviour of fatigue crack in TiB2 particulate reinforced ZA-8 Zn alloy and in the corresponding constitute matrix materials were studied. The present results indicate that the resistance to fatigue crack growth of the employed composite is in general superior to that of constitute matrix materials, especially for the short crack behaviour. This is attributed to (1) the interaction between particle and crack tip decreased the stress intensity ahead of the crack tip,(2) owing to the excellent interface strength,(3) the addition of reinforcement caused the change of matrix microstructure and refined the structure and (4) the bridging function of reinforcement. Finally, the mechanism for the difference in fatigue crack growth behaviour of the two materials was discussed. Correspondent HUA Wenjun, Beijing Institute of Aeronautical Materials, Beijing 100095
Experimental Analysis of Stable Crack Extension based on Crack Tip Opening Angle Criterion

BAI Guo-juan,ZHANG Xiao-jing,XU Wu,WANG Hai,

实验力学 , 2012,
Abstract: ASTM and ISO had published their fracture mechanics test standards on specimens with low constraint. Various methods had been used to determine the crack tip opening angle during stable crack extension to characterize the material fracture resistance. In this paper the ASTM standard is validated by studying the crack stable growth behavior of aluminum alloy sheet with 1mm thickness. The crack tip opening angle is measured by using optical microscopy method. Experimental results have shown that the crack tip opening angle is nearly a constant value of 6 degree after about 2mm of stable tearing. This value is independent on specimen geometry and initial crack length. It is also found that the constant crack tip opening angle and residual strength obtained from saw and fatigue cracked specimens are nearly the same.

SUN Shuming South China University of Technology,Guangzhou,GU Jialin,CHEN Nanping Tsinghua University,Beijing,

金属学报 , 1991,
Abstract: The deformation process and the strain field ahead of crack tip in Ni single crystal have been studied under SEM, and by grid method as well as compu- ter image processing. The presence of hydrogen extends the localized plastic band inhomogeneous further and significantly increases the plasticity in high deep strain area.
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