共查询到18条相似文献,搜索用时 62 毫秒
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AISI321不锈钢单周过载疲劳裂纹扩展的延迟效应 总被引:2,自引:0,他引:2
在恒△K控制条件下研究了AISI321不锈钢在空气中不同过载比下的单周过载疲劳裂纹扩展延迟效应。结果表明:过载比越大,延迟效应越显著,延迟效应作用距离远大过载塑性区尺寸。讨论了裂纹过载延迟效应机理,认为AISI321不锈钢过载后的疲劳裂纹扩展延迟行为主由塑性诱发裂纹闭合引起,并对其进行了定量描术。 相似文献
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环境对AISI321不锈钢疲劳裂纹扩展过载效应的影响 总被引:5,自引:0,他引:5
研究了3.5%NaCl溶液对恒应力强度因子范围△K控制下AISI321不锈钢疲劳裂纹扩展过载行为的影响.与在空气中的结果比较表明,两种条件下存在相似的过载延缓效应,但是环境极大地削弱了过载对疲劳裂纹扩展的延缓效应,削弱程度随过载比不同而变化,以“损失循环数”表征约为40%-70%,以“过载影响区尺寸”表征则为30%-40%.分析表明,用“损失循环数”表征过载对裂纹扩展的延缓效应不够充分,无法区分环境对裂纹闭合的削弱和增强作用,“过载影响区尺寸”可以区分环境对过载塑性形变增强裂纹闭合的综合影响.对断口的SEM分析发现,过载造成的塑性形变在溶液中比在空气中受到更多的磨损,表明环境对过载延缓效应的削弱除了对裂尖的影响外,还包括对过载导致的塑性诱发裂纹闭合的影响. 相似文献
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本文选用18Cr2Ni4WA低碳高强钢研究晶粒度对近门槛疲劳裂纹扩展行为的影响。研究表明:随着晶粒尺寸从58μm粗化到207μm,断口表面粗糙度增加三倍以上。但在所研究的条件下,裂纹扩展速率和门槛值几乎不变。对近门槛断口的SEM观察表明,它们的断裂机理基本相同,均以穿晶断裂为主。根据断口粗糙度模型,提出了粗糙度并不改变裂纹闭合效应的观点,并解释了晶粒度与近门槛裂纹扩展行为无关的现象。 相似文献
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不同温度下Ti40合金的疲劳裂纹扩展行为 总被引:3,自引:0,他引:3
研究了Ti40合金在室温、300、500和600℃下的疲劳裂纹扩展行为,计算了Ti40合金在300、500、600℃下当△K为20 MPa m1/2时与裂纹扩展密切相关的表观激活能.结果表明:随温度升高,Ti40合金疲劳裂纹扩展速率增加;不同温度下的疲劳裂纹扩展曲线在△K为45.50MPam1/2处相交于一点.表观激活能值随温度升高先增加后减小,在500℃时达到最大,由此可见,500℃是Ti40合金热力学等性质发生变化的转折点. 相似文献
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本文开展热处理后工业纯钛TA2不同载荷水平下疲劳裂纹扩展实验,考虑裂尖塑性变形程度,研究疲劳裂纹扩展规律以及热处理状态对疲劳裂纹扩展不同阶段的适应性。结果表明,不同疲劳载荷下热处理对疲劳扩展速率产生不同的影响。A类加载热处理后的疲劳裂纹扩展速率下降是由于近门槛区有效载荷的降低,以及近门槛值的提高。B类加载下热处理对有效载荷以及裂尖塑性变形几乎没有什么影响。C类与D类加载下热处理后裂尖塑性变形受到限制,而导致疲劳裂纹扩展速率下降。 相似文献
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DENG Rongying ZHOU Aihua JIANG Huaiqing LI Chunxiu Institute of Mechanics Academia Sinica Beijing ChinaZHANG Liqing SUN Yutian Beijing Institute of Engineering Beijing China Originally published in ACTA METALL SIN 《金属学报(英文版)》1989,2(6):439-443
The effect of pearlite interlamellar spacing(d)from 0.31 to 0.77 μm of T8 steel on fatiguecrack propagation near threshold has been investigated at different stress ratios(R).Theclosure stress intensity factor(K_(cl)),the threshold value(ΔK_(th))and crack tip opening dis-placement range(ΔCOD)were measured.The results show that pearlite interlamellar spac-ing in this range has no effect on K_(cl),but has effect on the threshold value in low stress ratio.The threshold value is higher for materials with larger interlamellar spacing.No matter whatthe stress ratio is,during the propagation near threshold,the propagation rate will be thesame,provieded the crack tip opening displacement range is the same.Metallurgical examinations were also carried out to show that the crack propagationpath is sensitive to mierostructure.The crack always propagates along either boundary ofpearlite colony or ferrite lamellar in pearlite. 相似文献
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QIAN Yourong HE Xiangdong Beijing University of Aeronautics Astronautics Beijing China QIAN Yourong Dept.of Materials Science Engineering Beijing University of Aeronautics Astronautics Beijing China 《金属学报(英文版)》1990,3(3):204-207
The fatigue crack growth rate (CGR) of ultra high strength steel 30CrMnSiNi2A in distilledwater at 18,35 and 55℃ were measured.It was confirmed that the temperature is strongly af-fected on the corrosion fatigue CGR of ultra high strength steel.An expression concerning theeffects of Δ K and temperature on the CGR was proposed.The fact that the apparentactivation energy (36.6 kJ/mol) resulted from regressive analysis of CGR data was similarto the activation energy of hydrogen diffusion in γ-Fe,strongly supporting the theory ofhydrogen-assisted crack growth.The overload retardation effect was greatly reduced in cor-rosion fatigue crack growth,especially at lower frequency,e.g.,0.1 Hz.This phenomenonmight be due to the increase of the SCC component of CGR after an overload. 相似文献
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高强度钢腐蚀疲劳裂纹扩展的温度效应和过载迟滞效应 总被引:2,自引:0,他引:2
通过在18,35和55℃蒸馏水中疲劳裂纹扩展试验,证明了超高强度钢30CrMnSiNi2A腐蚀疲劳具有强烈的温度效应,得到了ΔK值和温度对裂纹扩展速率影响的复合表达式。由于扩展速率数据拟合得到的表观激活能值(36.7kJ/mol)十分接近于氢在γ-Fe中的扩散激活能值,支持了氢助裂纹扩展的观点。对大气中疲劳裂纹扩展具有重要价值的过载迟滞效应,在腐蚀疲劳时显著地减小,在0.1Hz的低频率下尤其明显。 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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通过考察碳素工具钢的表面滑移、疲劳破坏及表面裂纹的扩展条件,以统一的局部应力讨论了光滑试样和裂纹试样的疲劳特征。分析和实验结果表明,在裂纹试样的名义应力小于光滑试样表面滑移门槛应力的范围内,线弹性断裂力学是有效的,对应裂纹扩展门槛值的裂尖性区为一常数。 相似文献
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ZHENG Yesha WANG Zhongguang AI Suhua State Key Laboratory of Fatigue Fracture for Materials Institute of Metal Research Academia Sinica Shenyang China 《金属学报(英文版)》1992,5(5):385-389
SEM microfractography of near-threshold fatigue crack propagation were carried out in thedual-phase steels of 3 martensite morphologies and 6 volume fractions of martensite (V_m).All of them are featured by cyclic cleavage characteristics in near-threshold region,i.e.,main-ly controlled by mode Ⅱ stress.In the higher ΔK regions,the fracture surfaces are character-ized by mixed modes including cyclic cleavage facets,two types of secondary cracks andstriations,etc..The roughness-induced crack closure of fracture surface is attributedprimarily to extreme high fatigue crack growth threshold values. 相似文献