TiAl基合金弯曲疲劳的断裂机制

通过对弯曲疲劳断裂宏观试验结果以及相应的卸载表面观察和断口观察分析研究,发现在疲劳加载的过程中,首先在缺口根部产生裂纹,裂纹在应力循环的作用下不断扩展,直至疲劳裂纹的长度达到与疲劳外加力所匹配的临界裂纹长度时,突然发生整体解理断裂.在一定应力下的疲劳弯曲加载试验中,随着循环次数的增加,产生的裂纹变长,即产生的损伤严重,疲劳区域变宽,其断裂机制是疲劳区各裂纹单向扩展,解理区起裂源分散扩展直至断裂.对于循环次数较小的材料,其断裂机制是具有发散扩展路径的起裂源直接产生于缺口根部,然后分散扩展直至断裂,在其扩展的路径上并不因疲劳区与解理区而有任何的不同.     

全层状TiAl基合金断裂机理原位观察

通过对裂纹与晶内片层和晶界的交互作用的原位观察,研究了全层状组织TiAl基合金的断裂机制。结果表明：裂纹萌发和扩展方式不仅依赖于片层与拉伸轴的相对取向,还受晶界取向的制约。当片层与拉伸轴成较大角度时,沿片层裂纹扩展是通过主裂纹与沿片层微裂纹的连接及剪切的过程;而当拉伸轴近乎平行片层时,跨片层裂纹依靠对界面分离和跨片层微裂纹这两种形式的微裂纹的连接进行扩展的,纵向交叉晶界有利于断裂韧性的提高,而横向晶界则不利于材料断裂韧性。     

外加电位对奥氏体不锈钢应力腐蚀与腐蚀疲劳交互作用的影响SCIEI

本文研究了0Cr18Ni9Ti奥氏体不锈钢在42%沸腾MgCl_2中,在低频,高平均应力循环载荷下的环境敏感断裂行为,研究了应力腐蚀疲劳与应力腐蚀在裂纹扩展规律及断口形貌上的差别与联系。从断裂特征上分析了应力腐蚀与腐蚀疲劳的交互作用,并着重研究了外加极化电位对这种交互作用的影响。     

腐蚀疲劳裂纹扩展的断裂模型

将修正的疲劳裂纹扩展静态断裂模型和裂尖腐蚀溶解相结合,提出了腐蚀疲劳裂纹扩展(CFCP)的腐蚀-钝化-断裂模型.根据该模型和断裂力学原理,导出了CFCP速率的定量表达式,它揭示了CFCP速率与力学条件,裂尖表面腐蚀率、加载频率、假设的裂尖材料元临界断裂应力之间的定量关系,并能说明氢脆对CFCP率的影响规律。实验结果表明,应用所提出的模型可很好地描述铝合金在35％NaCI中CFCP的一般规律。     

腐蚀坑导致高压开关导电管结构失效的过程分析

某高压开关设备在电站运行中导电管发生断裂,通过腐蚀坑引起的结构失效的过程分析,结合宏观检验、扫描电镜与能谱分析等方法,结果表明:导电管的失效过程为腐蚀坑形成、腐蚀坑扩展、裂纹形核、裂纹扩展、最终断裂。裂纹扩展造成晶间腐蚀,在晶间腐蚀和内应力的协同作用下导致剥落腐蚀。     

高强度铝合金构件腐蚀疲劳失效分析

在应力作用下对带有涂层的高强度铝合金构件在 3.5%NaCl溶液中腐蚀疲劳断口进行了研究.结果表明:在腐蚀条件下高强度铝合金构件断口上不仅出现疲劳辉纹,还出现准解理、解理、沿晶等断裂特征,腐蚀疲劳过程属于阳极溶解机制控制.失效形式为多裂纹断裂,在各个铆孔处均有裂纹萌生,其中有一处为主裂纹,其位置不固定,主裂纹扩展距离较长,最后与其它裂纹汇合,最终导致疲劳断裂.     

氯化物溶液中不锈钢腐蚀疲劳裂纹初始萌生的过程机理

研究了动应力（往复弯曲疲劳应力）对氯化物溶液中不锈钢点蚀敏感性的促进作用。 在固溶态３１６Ｌ不锈钢表面点蚀孔中产生了明显的非敏化态晶间腐蚀。在点蚀孔内受腐蚀晶界处孕育 产生了初态腐蚀疲劳裂纹,裂纹由沿晶转变为穿晶扩展,形成主裂纹并继续扩展直至材料失稳断裂。阐 述了在动应力和侵蚀性介质联合信息作用下ＣＦ裂纹萌生的过程机理。论述了动应力－环境介质－材料 特性在多种腐蚀类型交互作用中的贡献和相关性。     

腐蚀疲劳裂纹扩展的机理

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。     

光学材料的磨削损伤控制试验研究

基于K9玻璃不同的磨削工艺参数确定其磨削损伤层深度随工艺参数变化的规律，并通过工件磨削损伤层深度的动态检测研究其裂纹扩展规律。结果表明:工件磨削过程中的裂纹损伤是动态扩展过程。固定工艺参数下，裂纹稳态扩展，损伤层深度不变；采用损伤更小的工艺参数磨削，裂纹的扩展速度小于材料的去除速度，其损伤层深度逐渐减小，损伤的去除速度逐渐减慢直至二者间达到稳态平衡。同时，为了去除前道工序的损伤层，后道工序的材料去除量需达到前道工序损伤层深度的2～3倍。      

低碳钢的组织对腐蚀疲劳的影响

本文研究了两种低碳钢不同显微组织在盐水和空气中的疲劳裂纹扩展行为,发现显微组织对钢的腐蚀疲劳抗力有重要影响。还讨论了钢的腐蚀疲劳机制及断裂机制图。     

腐蚀疲劳过程中裂尖阳极溶解对裂纹扩展的作用

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。     

应力腐蚀机理和基于FEM的应力腐蚀裂纹扩展模拟技术的研究进展

本研究总结了应力腐蚀研究的5个经典理论:活性通路理论、钝化膜破坏理论、氢脆理论、腐蚀产物楔入模型和环境破裂三阶段理论。详细介绍了最为广泛接受的钝化膜破坏理论,在此基础上,从单一参数计算和应力腐蚀裂纹扩展模拟两个方面着重介绍了基于有限元方法对应力腐蚀裂纹扩展的研究方法和技术,单一参数计算可以满足获取应力腐蚀裂纹扩展预测模型关键参数,但是将裂纹尖端认为是一个点的假设存在不合理,应力腐蚀裂纹扩展模拟可以将载荷和环境因素综合考虑在内,但还仍然不能仿真出裂纹微观扩展现象。研究结合实践总结提出了应力腐蚀裂纹扩展模拟的工程技术方法,讨论了有限元技术在应力腐蚀研究方面不能实现微观物理过程、时间相关性等存在的问题,指出了基于应力腐蚀时间相关性的应力腐蚀裂纹扩展模拟研究是应力腐蚀破坏预防及预测研究工作的重点。     

The influence of crack tip morphology on crack propagation rates in corrosive environments

It is shown that, under conditions where corrosion processes are dominant, stress corrosion and corrosion fatigue crack propagation rates are reduced by micro-branching, and blunting, of the crack tip. A quantitative analysis is presented based on transition effects observed following “step” load changes during stress corrosion tests. Although a precise numerical model is difficult to obtain, it provides an insight into some aspects of environmental crack growth behaviour.     

Beitrag zum Spannungsrißkorrosions-Verhalten der AlZnMg-Legierungen

The stress corrosion cracking behaviour of aluminium-zinc-magnesium alloys The stress corrosion cracking of AlZnMg3 is a two-phase process where the preparation period may also take place without tensile stress. With decreasing pH, the service life is reduced, the reduction being confined to the preparation period. The same applies to anodic connection associated with heavy pitting corrosion where the fracture consists of stress corrosion cracking zones and transcrystalline force fracture. Even with cathodic connection, stress corrosion cracking is encountered. Since, in this case, the current density does not decrease prior to fracture, it must be assumed that the propagation of the crack may have nothing to do with the electro-chemical dissolution at the tip of the crack. Even minor quantities of water — e.g. in carbon tetrachloride — are sufficient to cause stress corrosion cracking, probably through adsorption of atomic hydrogen which has the effect of reducing the surface energy.     

Effect of preloading on corrosion fatigue of 70/30 brass

The effects of a single tensile overload and precycling load in air on subsequent corrosion fatigue cracking in 70/30 brass exposed to 1 M sodium nitrite solution were studied. A single tensile overload caused a decrease in subsequent corrosion fatigue crack propagation rate. Precycling load also showed retardation effects, depending on the load conditions for precycling and corrosion fatigue. A transsition from a higher mean stress for precycling to a lower mean stress for corrosion fatigue decreased corrosion fatigue crack growth rate, while an opposite transition did not appreciably change the corrosion fatigue crack propagations. The responses of bulk mechanical properties to a presingle overload and precycling load in air were measured, showing hardening which may probably be responsible for the observed retardation.     

疲劳损伤对核电汽轮机焊接转子接头应力腐蚀开裂敏感性的影响

采用慢应变速率拉伸试验(SSRT)研究了不同程度疲劳损伤对核电汽轮机焊接转子接头应力腐蚀开裂敏感性的影响，利用扫描电子显微镜等观察手段讨论了疲劳损伤对汽轮机焊接接头应力腐蚀开裂敏感性和二次裂纹的作用机理. 结果表明，疲劳损伤增强了核电汽轮机焊接转子接头应力腐蚀开裂敏感性. 此外，疲劳损伤的作用使空气中试样的塑性提高而在腐蚀溶液中塑性降低，也影响了试样内部二次裂纹的产生和扩展.     

A quantified concept of the hydrogen permeability of passivating films at a crack tip during stress corrosion cracking of structural materials

A general theoretical and methodological approach to local dissolution and hydrogen embrittlement contributions to stress corrosion cracking in various structural materials is discussed. According to this approach a quantified determination of the hydrogen embrittlement contribution to stress corrosion cracking in high-strength steels, titanium, aluminium, and zirconium, and zirconium alloys appears to be possible. On the basis of a few postulates, a quantitative concept of hydrogen permeability of the passivating film at the tip of a crack in the metal is developed; this concept allows for the first time a quantified determination of the relationship between critical hydrogen concentration and stress intensity factor in steels, titanium, and aluminium, and aluminium alloys under hydrogen embrittlement. Two new methods for studying adsorption processes at the tip of a growing crack during stress corrosion cracking are an additional outflow of this concept.     

循环载荷下裂尖形变规律的实验研究

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。     

奥氏体不锈钢在MgCl2介质中的应力腐蚀疲劳特征

本文研究了力学因素对0Cr18Ni9Ti奥氏体不锈钢在MgCl_2水溶液中应力腐蚀(SCC)和腐蚀疲劳(CF)交互作用的影响。研究了应力腐蚀疲劳(SCF)在裂纹扩展规律及断口形貌上的特征。结果表明:任何促使裂尖应变速率提高的力学变量,都有可能使SCF断口形貌发生穿晶型向沿晶型的转化。     

The characteristics of hydrogen diffusion and concentration around a crack tip concerned with hydrogen embrittlement

Previously, we proposed a physical model for hydrogen diffusion and accumulation around the crack tip and performed accurate numerical analysis which takes account of the effects of both hydrogen diffusion and accumulation due to the stress gradient. Based on this analysis, the characteristics of hydrogen accumulation around the crack tip were clarified.Since the characteristics of stress corrosion cracking and corrosion fatigue are dominated by chemical anodic reaction, hydrogen embrittlement and dislocation mechanism, to perform the analysis on the competitive phenomenon by these mechanism and to relate the sensitivity of hydrogen embrittlement to the characteristics of corrosion fatigue, it is necessary to construct a exact physical law on the characteristics of hydrogen diffusion and concentration and to formulate the characteristics as a simple function such as diffusion constant, D, yield stress σ_ys, and stress intensity factor, K. The effect of stress field such as plane strain and plane stress on the hydrogen embrittlement is necessary to be clarified as the effect of specimen thickness on the hydrogen embrittlement.In this paper, based on this view point, the effect of D, σ_ys, and K on hydrogen embrittlement were investigated and formulated. A quantitative parameter which characterize hydrogen embrittlement was proposed for both cases of plane strain and plane stress conditions as the effect of specimen thickness on the hydrogen embrittlement.