Corrosion effects on fatigue crack propagation of stainless steel and its heat affected zone in pH buffer solutions

A corrosion fatigue crack propagation test for 430 stainless steel and its heat affected zone was conducted in pH buffer solutions, and the results were compared with model predictions. The bare corrosion effect on fatigue crack propagation, particularly in corrosive environments was evaluated by means of a modified Forman equation. As shown in the results, the average corrosion rate determined from the ratio of corrosion induced crack length to the entire crack length under a cycle load was 0.11 and 0.37 for the base metal and heat affected zone, respectively, with a load ratio of 0.5, frequency of 0.5, and a pH 10.0 environment. The modeling and experimental processes demonstrate a step towards a methodology enabling the corrosion effects on fatigue crack propagation behavior to be determined.     

管线钢应力腐蚀破裂的机理与寿命预测

阐述了管线钢在高pH和近中性pH环境中的应力腐蚀破裂（SCC）机理，高pH SCC为阳极溶解，而近中性pH环境较复杂，主要观点是阳极溶解和（或）氢致开裂。分析了SCC裂纹萌生和扩展过程。介绍了相关的SCC寿命预测方法，重点讨论了Weibull分布和Monte Carlo模拟。     

腐蚀环境对飞机梁结构连接件疲劳寿命和裂纹扩展的影响

借助腐蚀环境谱与疲劳载荷谱交替作用来模拟沿海飞机停放-飞行-停放过程。以飞机梁结构连接件的下壁板为主要研究对象,采用标记载荷法和详细目视检测法监测其裂纹的扩展状况,并采用GE5显微镜观测断口形貌。分析了腐蚀环境对梁结构连接件疲劳寿命与裂纹扩展的影响。试验结果表明:在形成穿透裂纹的初始阶段,试验件受到表面的防护漆以及连接处的密封胶保护,腐蚀环境在该阶段对梁结构连接件的疲劳寿命影响不明显,与非腐蚀试验相比, 该阶段的寿命仅缩短了5.5％;在穿透裂纹的扩展阶段,腐蚀环境加速了穿透裂纹的扩展过程,同时还加剧了穿透裂纹扩展过程的分散性,与非腐蚀试验相比,穿透裂纹的扩展寿命缩短了23.1％。     

某离心压缩机叶轮断裂失效原因分析

针对某型号离心压缩机叶轮的断裂失效问题,采用金相检测手段检测了失效叶轮的焊接接头,并利用商用软件AN-SYS从焊接的角度对叶轮结构受力进行了模拟计算与分析。结果发现,叶片和轮盘焊接角接头存在应力集中,进一步计算表明,在存在焊接缺陷的情况下,较小的作用力就能促使应力达到很大峰值,应力集中加速了裂纹的扩展及失稳,从而造成产品的结构失效。     

某石化电厂脱硫装置导流罩失效分析

分析了某石化电厂高效脱硫装置导流罩破坏的原因。结果表明：由于混用了不合适的材料,该材料在硫酸环境中的交变应力下发生了开裂,其主要失效表现为点蚀、晶间腐蚀、应力腐蚀和腐蚀疲劳,失效的主要原因是腐蚀疲劳断裂和延迟断裂;晶间腐蚀和点蚀及其在应力作用下的发展是产生裂纹的重要原因。     

组装式离心压缩机腐蚀积垢原因分析及处理措施

针对组装式离心空气压缩机积垢、腐蚀、叶轮变形断裂等问题分别进行了分析阐述,首先对叶轮积垢、蜗壳积垢及流道的腐蚀现象做了说明,之后对其形成的原因进行了分析,最终提出相关问题的解决措施。改进的结果使机组运行周期由1500h延长至8000h,提高了机组运行的可靠性,延长了压缩机的使用寿命。     

轧机油膜轴承锥套接触疲劳损伤的机理分析

研究了油膜轴承锥套与辊颈接触表面在轧制载荷作用下发生微动疲劳损伤的力学机理。在分析油膜轴承油膜压力分布特征的基础上,采用有限元法给出了锥套与辊颈接触区边缘产生接触应力集中和微滑移的分布规律,阐明了弹性结合连接的锥套与辊颈接触表面产生微动疲劳损伤的原因。利用断裂力学裂纹尖端应力场与接触边缘区域应力局部渐近场的等效原则,给出了疲劳裂纹自点蚀处萌生与扩展的力学条件。上述结果为锥套和辊颈的实际损伤状态及模拟试验所验证。     

Assessment of fatigue life of remanufactured impeller based on FEA

Predicting the fatigue life of remanufactured centrifugal compressor impellers is a critical problem. In this paper, the S-N curve data were obtained by combining experimentation and theory deduction. The load spectrum was compiled by the rain-flow counting method based on the comprehensive consideration of the centrifugal force, residual stress, and aerodynamic loads in the repair region. A fatigue life simulation model was built, and fatigue life was analyzed based on the fatigue cumulative damage rule. Although incapable of providing a high-precision prediction, the simulation results were useful for the analysis of fatigue life impact factors and fatigue fracture areas. Results showed that the load amplitude greatly affected fatigue life, the impeller was protected from running at over-speed, and the predicted fatigue life was satisfied within the next service cycle safely at the rated speed.     

X80管线钢焊接接头的硫化氢应力腐蚀试验研究

采用X80管线钢焊接接头制作楔形张开加载（WOL）试样，在硫化氢介质中进行恒位移应力腐蚀试验，分别测得母材、焊缝和热影响区的临界应力强度因子KISCC和裂纹扩展速率da／dt。试验结果表明，热影响区的‰最小，裂纹扩展速率最大，具有较差的抗应力腐蚀开裂的能力，是应力腐蚀开裂的薄弱环节。且通过对X80管线钢焊接接头的显微组织观察和基本力学性能研究，对影响X80钢应力腐蚀影响因素提供了试验依据，并对试验结果予以验证。     

SPV490Q钢焊接接头在不同浓度硫化氢溶液中的应力腐蚀开裂行为

对SPV490Q钢焊接接头的楔形张开加载(WOL)预裂纹试样在不同浓度硫化氢溶液中进行了应力腐蚀试验,测定了焊缝的应力腐蚀临界应力强度因子KISCC和应力腐蚀裂纹扩展速率da/dt。结果表明:随着H2S浓度的升高,SPV490Q钢焊缝的应力腐蚀临界应力强度因子KISCC下降,应力腐蚀裂纹扩展速率da/dt增大,焊接接头的应力腐蚀抗力降低。     

在役压力容器含缺陷结构腐蚀疲劳剩余寿命预测的随机分析

本文根据OCr18Ni9钢在1000ppm NaCl溶液中的腐蚀疲劳裂纹扩展速率计算公式，采用概率方法，考虑裂纹尺寸、载荷、材料等参数的随机性，给出腐蚀疲劳剩余寿命随机计算方法。最后，通过工程案例说明方法的可行和有效。     

离心压缩机2级叶轮断裂失效分析

采用宏观、微观及SEM等分析方法,对离心压缩机2级叶轮断裂失效原因进行分析。结果表明,离心压缩机叶轮断裂原因是由于断裂源处表面脱碳,存在大量铁素体,使叶轮在该处硬度、强度及耐疲劳性能明显下降,难以承受压缩机工作状态对其产生的应力作用,形成疲劳方式开裂。     

制氧压缩机组中间冷却器不锈钢封头的开裂分析

通过无损检测、常规力学性能试验以及金相分析等手段对制氧压缩机组中间冷却器不锈钢封头的开裂失效进行分析。分析结果表明：该失效属于304不锈钢的应力腐蚀开裂。由于1级冷却器管的开裂泄漏而造成的高温氧气 含氯离子冷却水介质环境，封头一筒体对接环焊缝区域的残余应力以及封头一侧热影响区中的晶界碳化物析出是诱发应力腐蚀开裂的三个主要因素。     

基于子模型与网格随移技术的叶轮三维裂纹应力强度因子分析

基于断裂力学理论和有限元数值分析方法,针对压气机叶轮由于铸造缺陷和疲劳引起的三维裂纹,应用子模型技术和ParaMesh网格随移技术,给出了压气机叶轮轴孔三维裂纹前沿应力强度因子的求解方法及途径,并对压气机叶轮轴孔三维裂纹的扩展方向和扩展速率进行了分析.压气机叶轮轴孔三维裂纹应力强度因子求解结果表明,叶轮轴孔三维裂纹前沿...     

16MnR钢在硝酸盐环境下应力腐蚀性能试验研究

用楔形张开加载(WOL)预裂纹试样研究了16MnR钢在硝酸盐环境中的抗应力腐蚀性能。测定了16MnR钢母材及焊接接头在硝酸盐环境下的临界应力强度因子KISCC和应力腐蚀裂纹扩展速率；同时研究了缓蚀剂、材质、溶液温度对16MnR钢应力腐蚀开裂的影响，结果表明，缓蚀剂谈明显的降低应力腐蚀敏感性，增加裂纹的孕育时间；焊接接头与母材相比，由于没有元素Ni的不良作用，具有较高的应力腐蚀抗力；16MnR钢的硝酸盐应力腐蚀敏感性随温度升高而降低。     

不同腐蚀环境下高强铝合金腐蚀行为

针对航空铝合金材料在服役过程中因恶劣环境而导致材料腐蚀的问题,通过分析腐蚀形貌、腐蚀坑开口面积、腐蚀深度、点腐蚀坑数量、pH值、腐蚀产物等变化,研究2xxx航空铝合金在不同腐蚀环境(3.5%NaCl水溶液、模拟油箱积水溶液和潮湿空气)中的腐蚀行为和机理。结果表明,在3.5%NaCl水溶液中,铝合金试样表面腐蚀坑的产生主要发生在前24h内,其最大腐蚀坑深约为45μm,而在72~120h, 随预腐蚀时间的延长,腐蚀坑深度、个数的增加并不明显;铝合金试样在模拟油箱积水环境中的腐蚀规律与在3.5%NaCl水溶液中的相似,但腐蚀坑最大开口面积和腐蚀坑的个数明显减少;与前两种环境相比,试样在潮湿空气环境中的腐蚀程度明显减小,腐蚀坑总体个数最少,最大腐蚀坑深约在20μm以内,最大开口面积约在5000μm²左右,且随着腐蚀时间的增长,腐蚀坑之间的深度差距越来越小。     

Corrosion fatigue of steel under cavitation erosion generated intermittently in 3% salt water (results of two-stage tests with and without cavitation erosion)

Two-stage fatigue tests with and without cavitation erosion were performed in 3% salt water. When corrosion fatigue with cavitation erosion (erosion fatigue) is changed to corrosion fatigue during a test, the fatigue life decreases remarkably and the total number of stress cycles to failure becomes smaller than that for tests involving erosion fatigue only. In the reverse case, when corrosion fatigue conditions are changed to erosion fatigue conditions, the fatigue life increases slightly compared with the life expected from the linear damage law (Miner's law). The variation in fatigue strength can be explained by the characteristics of crack propagation in each environment. From these results, it is presumed that the corrosion fatigue strength of the material exposed intermittently to cavitation erosion decreases remarkably.     

腐蚀对新型高强度铝合金疲劳裂纹萌生机制及扩展行为的作用

根据编制的某机场环境加速试验谱,通过腐蚀试验模拟飞机服役过程中遭受的潮湿空气、盐雾、二氧化硫、酸雨和干/湿交变等严酷条件的侵蚀作用,采用飞机主承力结构新型高强度铝合金7B04-T74,制备单边缺口拉伸(Single edge notch tension, SENT)试样进行预腐蚀和疲劳试验,分析不同程度腐蚀损伤对疲劳裂纹萌生、裂纹扩展行为和疲劳寿命的影响,揭示腐蚀对裂纹萌生及扩展行为的作用机理。结果表明,在腐蚀初期,疲劳裂纹萌生源主要为单个蚀孔,裂纹扩展路径较为平直;随着腐蚀程度的加重,在多个蚀孔处同时萌生多条小疲劳裂纹,萌生疲劳裂纹的蚀孔具有隧道效应,扩展路径不规则,形成“之”字形裂纹;疲劳裂纹萌生机制是材料第二相与腐蚀损伤之间相互竞争的结果;腐蚀导致疲劳寿命显著降低,尤其是裂纹萌生寿命,腐蚀12年试验件裂纹萌生寿命仅为未腐蚀试验件裂纹萌生寿命的2.2%。     

Numerical Calculation and Experimental Research on Residual Stresses in Precipitation-hardening Layer of NAK80 Steel for Shot Peening

Shot peening can improve fatigue strength of materials by creating compressive residual stress field in their surface layers,and offers a protection against crack initiation and propagation,corrosion,etc.And fatigue fracture and stress corrosion cracking of NAK80 steel parts are improved effectively.Currently there lacks in-depth research in which the beneficial effect of the residual stress may be offset by the surface damage associated with shot peening,especially in terms of the research on the effective control of shot peening intensity.In order to obtain the surface residual stress field of NAK80 steel after shot peening,the samples are shot peened by pneumatic shot peening machine with different rules.The residual stress in the precipitation-hardening layer of NAK80 steel is measured before and after a shot peening treatment by X-ray diffraction method.In order to obtain true residual stress field,integral compensation method is used to correct results.By setting up analytical model of the residual stress in the process of shot peening,the surface residual stress is calculated after shot peening,and mentioning the reason of errors occurred between calculated and experimental residual stresses,which is mainly caused by the measurement error of the shoot arc height.At the same time,micro hardness,microstructure and roughness in the precipitation-hardening layer of NAK80 steel before and after shot peening were measured and surveyed in order to obtain the relation between shot peening strength and surface quality in the precipitation-hardening layer.The results show that the surface quality of NAK80 steel is significantly improved by shot peening process.The over peening effect is produced when the shot peening intensity is too high,it is disadvantageous to improve sample’s surface integrity,and leading to reduce the fatigue life.When arc high value of optimal shot peening is 0.40 mm,the surface quality is the best,and the depth of residual stress in the precipitation-hardening layer reaches to about 450 μm.Numerical calculation is very useful to define the process parameters when a specific residual stress profile is intended,either to quantify the benefits on a specific property like fatigue life or to help on modeling a forming process like shot peen forming.In particular,the proposed parameter optimization in the progress of shot peening and effective control of the surface texture provide new rules for the quantitative evaluations of shot peening surface modification of NAK80 steel.     

疲劳门槛值统一理论模型的比较及验证

针对应力比对疲劳裂纹扩展及门槛值的影响,依据裂纹闭合与裂纹扩展驱动力机制的统一思想,阐述了Zhu-Xuan模型与Kwofie-Zhu模型的建立过程,并基于25Cr2Ni2MoV转子钢焊接接头的疲劳裂纹扩展试验数据对模型进行验证。结果表明,两种模型在近门槛值区和Paris区均有良好的预测效果,其中Zhu-Xuan模型形式简单,对CrMoV钢具有普适性,预测门槛值的误差在10%以内,而Kwofie-Zhu模型预测结果更准确,但应用过程涉及参数求解,过程较复杂。研究认为,裂纹闭合与扩展驱动力机制的统一模型描述疲劳裂纹扩展行为的应力比相关性是合理可行的,且具有较好精度。