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JING Xiaotian LOU Bingzhe GU Chenqing SHEN Fusan Shanxi Institute of Mechanical Engineering Xi''''an China Dept.of Materials Shanxi Institute of Mechanical Engineering Xi''''an China 《金属学报(英文版)》1990,3(4):268-275
The morphology of the retained austenite in the carburized case of 20CrNiMo steel and itstransformation during fatigue crack propagation through the case were investigated by usingX-ray and TEM analysis.In the carburized case both film and block shaped retainedaustenite were found.Due to the crystallographic orientation relationship at the interface,thefatigue crack is inclined to pass through the block shaped retained austenite and thereby stim-ulates its strain-induced martensitie transformation.During the process of the fatigue frac-ture,most of the retained austenite structures on the crack path are transformed into themartensite,and the untranaformed parts on the fracture surface remain less than 6%.Thetransformation of the retained austenite,which is restrieted mainly within the plastic zone,oc-curs only during the proeess of fracture,and is independent of the magnitudes of the externalstress,stress ratio and cyclic number.The volume expansion accompanying the transforma-tion creates an additional residual displacement of about 0.44μm on fracture surfaces,whichis equivalent to the magnitude of the plasticity-induced residual displacement.The phasetransformation induced fatigue crack closure is believed to be an important factor affectingthe fatigue crack behaviors in the high carbon laver of the carburized case. 相似文献
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PEI Hongxun Institute of Corrosion Protection of Metals Academia Sinica Shenyang China Institute of Corrosion Protection of Metals Academia Sinica Shenyang China 《金属学报(英文版)》1989,2(4):284-292
Based on the experimental study of complex biaxial mode Ⅰ fatigue crack growth and thediscussion on Von Mises'theory,a new approach is proposed for correlating crack propaga-tion rate under both in-phase and out-of-phase biaxial stress cycling.The results emphasizethe contribution of plasticity to fatigue crack growth. 相似文献
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在双轴加载条件下对Ⅰ型疲劳裂纹扩展进行了研究。载荷范围从0.08σ_s到0.71σ_3,包括比例加载和非比例加载。基于对Von Mises理论的讨论,提出一个新的力学参数。双轴加载条件下的弹塑性参数P成功地描述了双轴比例加载和非比例加载下的疲劳裂纹扩展。 相似文献
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SHORT FATIGUE CRACK BEHAVIOUR IN ISO-STRESS SPECIMENS 总被引:1,自引:0,他引:1
HOGN Youshi LU Yonghua ZHENG Zhemin Institute of Mechanics Academia Sinica Beijing China Institute of Mechanics Academia Sinica Beijing China 《金属学报(英文版)》1990,3(4):276-281
Fatigue tests were made on a vibration machine using specially designed specimens to investi-gate the initiation and propagation features of short fatigue cracks in a weld metal.The spec-imens were triangular in shape so that when loaded as a cantilever beam the surface tensilestress is constant.Test results show that short fatigue cracks mainly originate from slip bandswithin ferrite grains.The development of short fatigue cracks is marked by a gradual increasein crack density with fatigue cycles.Coalescence of short cracks leads to crack propagationand the crack path is predominantly transgranular. 相似文献
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Z.X. Wu X. C. Wu Engineering College Yangzhou University Yangzhou China 《金属学报(英文版)》2001,14(4):235-240
1. Introduction The initiation and propagation behavior of short cracks occupies a significant fraction of the fatigue life of unflawed material[13]. For this reason an understanding of the basic characteristics of short cracks in a smooth specimen is very important. There have been some studies concerned with the multiplication of cracks during fatigue in carbon steels[3~1 and a stainless steel1~J. In particular Goto reported that there is a continuous formation of microcracks during the en… 相似文献
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用光学显微镜,扫描电镜和透射电镜观察了Nb单晶在循环变形后的表面形貌和饱和时的错组态。发现疲劳裂纹的萌生和表面形变带有关,当滑移线和形变带方向平行时,在双形变带的公共皱折处很容易萌生疲劳裂纹,已萌生裂纹呈交滑移特征,在裂纹萌生处附近,有很多由交滑移引起的滑移台阶,根据我们的实验结果,从理论上对Mott的疲劳裂纹萌生模型进行修正,也为Mott模型提供了实验依据, 相似文献
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HE Jiawen HU Naisai ZHANG Dingquan Xi''''an Jiaotong University Xi''''an China Professor Research Institute for Strength of Metals Xi''''an Jiaotong University Xi''''an China 《金属学报(英文版)》1993,6(2):96-100
Residual stress concentration at a notch depends on both notch geometry and yield strength ofthe material.It varies through the depth,and its magnitude may be higher than the theoreticalone.Compressive residual.stress concentration at the notch of shot-peened specimen of softmaterial is easily to he relaxed,with the surface damage during shot-peening results in a mi-nor contribution to the fatigue limit.Compressive residual stress increases the crack closureeffect at the notch and may lead to a non-propagating crack. 相似文献
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采用微电极体系和试样背后打孔技术,对300M超高强度钢在3.5%NaCl水溶液中腐蚀疲劳裂纹尖端微区溶液电化学行为进行研究,在极化和无极化条件下分别测试裂化溶液的电位△E和pH值的变化,结果发现,无极化条件下,裂尖pH下降,电位上升,裂尖前沿电位和pH值随裂化分布不均匀,在极化条件下,裂尖电化学特征随极化电位变化而表现不同,基于裂尖电化学行为规律,对腐蚀疲劳裂放展规律进行解释。 相似文献
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FATIGUE CRACK PROPAGATION OF Ni-BASE SUPERALLOYS 总被引:1,自引:0,他引:1
X.B.Liu L.Z.Ma K.M.Chang E.Barbero 《金属学报(英文版)》2005,18(1):55-64
Time-dependent Fatigue Crack Propagation (FCP) behaviors of five Ni-base superalloys were investigated at various temperatures under fatigue with various holding times and sustained loading conditions. The new concept of damage zone is defined and employed to evaluate the alloys‘ resistance to hold-time FCP. A special testing procedure is designed to get the maximum damage zone of the alloys. Udimet 720 and Waspaloy show shorter damage zones than alloys 706 and 718. The fractographieal analyses show that the fracture surfaces of the specimens under hold-time fatigue conditions are mixtures with intergranular and transgranular modes. As the extension of holding time per cycle, the portion of intergranular fracture increases, The effects of loading stress intensity, temperature, holding time, alloy chemisty, and alloy microstructure on damage zone and the crack growth behaviors are studied. Hold-time usually increases the alloy‘s FCP rate, but there are few exemptions. For instance, the steady, state hold-time FCP rate of Waspaloy at 760℃ is lower than that without hold-time. The beneficial effect of hold-time was attributed to the creep caused stress relaxation during the hold-time. 相似文献
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循环载荷下裂尖形变规律的实验研究 总被引:2,自引:0,他引:2
应用散斑干涉技术,在常幅载荷下对疲劳裂纹扩展过程中的一个循环周期内,不同加载阶段的裂尖应变、裂纹张开位移进行了原位测量,给出了裂纹闭合对裂纹张开位移及裂尖形变的影响规律。结果表明:由于裂纹闭合和残余压应力的存在,疲劳裂尖应变与外加载荷的平方并不成正比,在加载初期,裂纹处于闭合状态,裂尖应变无明显变化,随着载荷的增加,裂纹逐渐由远离裂尖处张开并向裂尖发展,一旦裂纹完全张开,裂尖应变迅速增加,对裂尖应力-应变状态的分析表明,裂尖材料的应力-应变关系类似于光滑试样低周拉压疲劳应力-应变滞后关系。 相似文献
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C—Si—Mn—B贝氏体钢的疲劳裂纹扩展特性 总被引:2,自引:0,他引:2
本文研究了C-Si-Mn-B贝氏体钢的疲劳裂纹扩展特性。结果表明,在强度相近的情况下,含1.8%Si钢的门槛值△Kth较0.6%Si钢的低,而且钢中的残余奥氏体对提高△Kth值并非有利。1.8%Si钢的△Kth值随钢的屈服强度降低而提高,然而450℃回火后,虽然△Kt提高,但裂纹扩展速率也显著提高,这表明450℃回火贝氏体脆性促进了疲劳裂纹的扩展。在应力强度因子较高的范围内,疲劳裂纹扩展速率受钢的断裂韧性影响,断裂韧性高,裂纹扩展速率低。 相似文献
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本文研究了8090Al-Li合金穿透疲劳短裂纹的门槛值,测定了不同长度短裂纹的门槛值和裂纹闭合效应,探讨了该合金疲劳短裂纹门槛值、裂纹尾迹和裂尖屏蔽之间的关系,给出了该合金穿透疲劳短裂纹的上界值和理论最低门槛值。 相似文献