共查询到19条相似文献,搜索用时 156 毫秒
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腐蚀疲劳过程中裂尖阳极溶解对裂纹扩展的作用 总被引:7,自引:3,他引:4
在模拟腐蚀疲劳裂尖介质中,分别用铂丝和40CrNiMo钢为辅助电极测定了在不同拉伸速率下中温回火的40CrNiMo钢的腐蚀电流密度i_(a)与应变速率、塑性应变量的关系,其结果为:利用疲劳裂纹尖端应变的弹塑性有限元计算,得到腐蚀疲劳裂尖阳极溶解引起的裂纹扩展与△K的关系,结果表明:中温回火的40CrNiMo钢在3.5%NaCl水容液中裂尖阳极溶解对腐蚀疲劳裂纹扩展的直接贡很小,阳极溶解的主要作用是影响为裂尖断裂区氢致开裂提供氢原子的阴极过程。 相似文献
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FATIGUE CRACK GROWTH FOR Ti-6Al-4V ALLOY IN WATER 总被引:1,自引:0,他引:1
用断裂力学方法研究了Ti-6Al-4V合金退火板材在蒸馏水中的疲劳裂纹扩展,测定了疲劳裂纹扩展速率dα/dN同应力强度因子幅度△K,温度和频率的关系。同时进行了空气中的对比疲劳试验。并用扫描电镜观察了疲劳断口形貌。实验表明,疲劳裂纹的扩展在水中比在空气中快。其扩展速率随温度升高而降低,随频率降低而增加。在10Hz频率下裂纹扩展速率同温度的关系可表示为(dα/dN)=Ae~(Q/RT)(△K)~(2.7),其中Q=6.2kJ/mol。疲劳断裂面上的延性条纹和裂隙条纹同载荷循环有近似一一对应关系;而脆性条纹的间距则比相应的宏观扩展速率大几倍。本文认为,水中疲劳裂纹扩展的加快,是水同钛合金裂纹表面的反应产生的氢所造成的;温度和频率对疲劳裂纹扩展速率的影响,可以用应变感生氢化物机制得到说明;进而提出,应变感生氢化物的形成是裂纹扩展的速率控制过程。 相似文献
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用断裂力学方法研究了Ti-6Al-4V合金退火板材在蒸馏水中的疲劳裂纹扩展,测定了疲劳裂纹扩展速率dα/dN同应力强度因子幅度△K,温度和频率的关系。同时进行了空气中的对比疲劳试验。并用扫描电镜观察了疲劳断口形貌。实验表明,疲劳裂纹的扩展在水中比在空气中快。其扩展速率随温度升高而降低,随频率降低而增加。在10Hz频率下裂纹扩展速率同温度的关系可表示为(dα/dN)=Ae~(Q/RT)(△K)~(2.7),其中Q=6.2kJ/mol。疲劳断裂面上的延性条纹和裂隙条纹同载荷循环有近似一一对应关系;而脆性条纹的间距则比相应的宏观扩展速率大几倍。本文认为,水中疲劳裂纹扩展的加快,是水同钛合金裂纹表面的反应产生的氢所造成的;温度和频率对疲劳裂纹扩展速率的影响,可以用应变感生氢化物机制得到说明;进而提出,应变感生氢化物的形成是裂纹扩展的速率控制过程。 相似文献
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<正> 在模拟压水堆环境中,对SA508 3级压力容器钢进行了腐蚀疲劳试验。试验研究的变量有空气和压水堆环境,频率变化在1~10Hz 范围,纵、横裂纹扩展方向,温度为20℃和50℃,以及R 比值为0. 2与0. 7。发现在压水堆环境中,降低试验频率,增加疲劳裂纹扩展速率,压水堆环境试验会促使裂纹扩展(与空气试验比较)。对纵向裂纹扩展来说,疲劳裂纹扩展速率是较主要的,稍微增加温度会显著加快疲劳裂纹扩展速率,个别的空气试验指出疲劳裂纹扩展速率比ASME 标准预测的大。断口组织的迹象指出疲劳裂纹扩展速率是由氢脆机理 相似文献
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腐蚀疲劳裂纹扩展的机理 总被引:4,自引:0,他引:4
S.A.Shipilov 《中国腐蚀与防护学报》2004,24(6):321-333
针对高强度低合金钢、钛合金和镁合金进行了腐蚀疲劳裂纹的扩展FCG、外加电压对于腐蚀疲劳裂纹扩展速率的影响以及断裂表面的研究。在外加电压对于腐蚀疲劳裂纹扩展速率影响的研究过程中,在一段时间内发生极化,可以根据此期间内的开路电压记录裂纹扩展速率,并测量极化情况下的裂纹增长速率。由于裂纹扩展测量技术的进步,测量的时间很少超过300s,这使观测非独立模式阴极极化对于腐蚀疲劳裂纹扩展速率的影响成为可能。当最大应力强度(Kmax)超过给定材料--溶液组合的特定临界特征值时,阴极极化会加速裂纹的扩展。当Kmax低于临界值,而所有其他条件(试件、溶液、pH值、载荷频率、应力比率、温度等)不变时,同样的阴极极化会妨碍裂纹扩展,或者对于裂纹扩展无影响。断口显微分析结果显示,阴极极化下加速裂纹的扩展是由于氢致腐蚀(HIC)。因此,根据氢致腐蚀机理以及KHIC和△ KHIC的显示,Kmax的临界值,以及应力范围(△ K)是由相应的腐蚀疲劳裂纹扩展的症状所确定的。当Kmax > KHIC(△ K > △ KHIC)时,腐蚀疲劳裂纹扩展的主要机理是HIC。对于大多数的材料--溶液组合的研究表明,当Kmax < KHIC(△ K < KHIC)时,应力协助扩散在腐蚀疲劳裂纹扩展中起决定性作用。 相似文献
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《稀有金属材料与工程》2017,(10)
测定了难变形高温合金GH4720Li在650、700、750及800℃空气环境下的疲劳裂纹扩展速率,并结合断口分析了在纯疲劳及保载90 s下,温度对合金疲劳裂纹扩展速率的影响。结果表明,随着温度升高,合金疲劳裂纹扩展速率的增长幅度变大。800℃时,合金的疲劳裂纹扩展速率急剧增大。温度升高,疲劳裂纹的扩展方式发生了明显变化,650℃时断口为沿晶和穿晶断裂混合型,700~800℃时断口以沿晶断裂为主。保载时间延长,裂纹扩展速率加快,且裂纹扩展速率的温度敏感性增加。 相似文献
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HAN Enhou HAN KYumei ZHENG Yuli KE Wei Corrosion Science Laboratory Institute of Corrosion Protection of Metals Academia Sinica Shenyang China postdoctoral Institute of Corrosion Protection of Metals Academia Sinica Shenyang China 《金属学报(英文版)》1993,6(6):373-378
Based on theoretical analysis about local strain,strain rate and dissolving rate at crack tip,the corrosion fatigue crack growth rate of steels ZG20SiMn and SM50B-Zc in fresh waterand 3.5% NaCl solution were measured experimentally,and the PH and electrode potentialwithin crack were also measured continuously along with crack propagating.It showed thatthe increase of crack growth rate,caused by both decreasing frequency and raising stressratio,was mainly accelerated by hydrogen embrittlement. 相似文献
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S690高强钢由于其良好的综合力学性能广泛用于海洋平台中. 海洋平台结构易产生腐蚀疲劳失效,海水腐蚀、循环载荷和结构本身的拘束水平对裂纹扩展有重要的影响. 通过空气中和海水环境中的S690高强钢疲劳裂纹扩展试验,结合显微断口分析,研究了拘束水平对S690高强钢腐蚀疲劳裂纹扩展行为的影响. 结果表明,在阳极溶解和氢致开裂的共同作用下,海水环境对S690高强钢疲劳裂纹扩展具有明显的加速作用. 同时随着裂纹的不断扩展,拘束水平对S690高强钢腐蚀疲劳裂纹的影响不断增加,且裂纹扩展速率与裂纹扩展前后的拘束水平增量和结构本身的拘束水平均密切相关. 相似文献
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In this paper, crack growth behaviour and the crack tip chemistry of X70 pipeline steel in the near-neutral pH environment were investigated using the in-situ measurements. The stress corrosion crack propagated forward under the cyclic load, with a mean crack growth rate (CGR) of 4.28?×?10–3?mm/cycle. The CGR da/dN obeys well with the stress corrosion fatigue mechanism. During the crack propagation, the crack tip environment differed significantly from the bulk solution. An aggressive electrolyte with low pH (about 4.0) and high concentration of Cl– (about 3.8?M) was produced near the crack tip. These results provided the direct evidence for simulating the crack tip solution and investigating the crack tip anodic dissolution. 相似文献
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Results obtained for the corrosion fatigue of the aluminium-zinc-magnesium alloy 7017-T651 in seawater at frequencies from 0.1 to 70 Hz are examined on the basis of existing models for predicting crack growth rates. The enhanced growth rates in seawater, compared with dry air, are not compatible with the simple superposition model that may be applied to 7079-T651, unless some secondary process produces several orders of magnitude increase over the stress corrosion rates observed under static loading. The changes in fracture mode observed at certain critical crack velocities, and their dependence upon the square root of the reciprocal of the frequency of loading, are shown to be consistent with an environment-enhanced crack growth rate involving diffusion of hydrogen ahead of the crack tip during each fatigue cycle. Examination of the reported frequency dependence of crack growth rates during corrosion fatigue in steels and other aluminium alloys indicates a need for further work to identify the rate-determining steps for crack propagation during corrosion fatigue. Theories proposed to date are found to be inadequate. 相似文献
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工业纯铁在3.5%NaCl水溶液中裂尖材料溶解速率与裂纹扩展速率的关系 总被引:1,自引:0,他引:1
利用形变金属的溶解模拟裂纹尖端的溶解行为,研究工业纯铁在3.5%NaCl水溶液中溶解速率与裂纹扩展速串的关系.研究表明由于腐蚀因素引起的裂纹扩展速率远大于裂纹尖端材料的溶解速率.在阳极溶解机制下,腐蚀疲劳裂纹扩展速率不能用纯机械因素引起的裂纹扩展速率和裂尖材料溶解速率的叠加来表示. 相似文献
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腐蚀疲劳波形效应的裂尖析氢、输氢模型与试验验证 总被引:1,自引:1,他引:1
把裂尖表面形变动力学和裂尖表面氢反应电化学动力学相结合,对裂尖表面析氢反应的波形效应进行了定量分析,把裂尖形变动力学与位错运动力学相结合,提出了氢的接力式位错输送概念,并建立了波形效应的位错输氢模型,用上述定量模型与理论对正据齿波、三角波和负锯齿波三种波形的腐蚀疲劳裂纹扩展速率的相对大小进行了预测。为验证上述模型,还用疲劳测试和断口分析和研究了三种波形对GC-4(40CrMnSiMoVA)钢在3.5%NaCI溶液中的腐蚀疲劳裂纹扩展特性的影响。试验结果与模型预测结果十分吻合。 相似文献
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B.P. Somerday P. Sofronis K.A. Nibur C. San Marchi R. Kirchheim 《Acta Materialia》2013,61(16):6153-6170
The objective of this study was to quantify the effects of mechanical and environmental variables on oxygen-modified accelerated fatigue crack growth of steels in hydrogen gas. Experimental results show that in hydrogen gas containing up to 1000 v.p.p.m. oxygen fatigue crack growth rates for X52 line pipe steel are initially coincident with those measured in air or inert gas, but these rates abruptly accelerate above a critical ΔK level that depends on the oxygen concentration. In addition to the bulk gas oxygen concentration, the onset of hydrogen-accelerated crack growth is affected by the load cycle frequency and load ratio R. Hydrogen-accelerated fatigue crack growth is actuated when threshold levels of both the inert environment crack growth rate and Kmax are exceeded. The inert environment crack growth rate dictates the creation of new crack tip surface area, which in turn determines the extent of crack tip oxygen coverage and associated hydrogen uptake, while Kmax governs the activation of hydrogen-assisted fracture modes through its relationship to the crack tip stress field. The relationship between the inert environment crack growth rate and crack tip hydrogen uptake is established through the development of an analytical model, which is formulated based on the assumption that oxygen coverage can be quantified from the balance between the rates of new crack tip surface creation and diffusion-limited oxygen transport through the crack channel to this surface. Provided Kmax exceeds the threshold value for stress-driven hydrogen embrittlement activation, this model shows that stimulation of hydrogen-accelerated crack growth depends on the interplay between the inert environment crack growth increment per cycle, load cycle frequency, R ratio and bulk gas oxygen concentration. 相似文献