阳极溶解型应力腐蚀的有限元模拟

发布时间：2018-02-04 02:20

本文关键词： 应力腐蚀阳极溶解腐蚀产物膜氢有限元模拟　出处：《北京科技大学》2015年博士论文　论文类型：学位论文

【摘要】：应力腐蚀是一种低应力、无征兆的脆断过程,往往会导致灾难性的恶性事故,造成巨大的经济损失和人员伤亡。据统计,应力腐蚀造成的安全事故在腐蚀事故中所占的比例高达35%。因此,一个多世纪以来,应力腐蚀一直是一个重要的研究领域。对于大多数阳极溶解型应力腐蚀(SCC),应力腐蚀过程中会在金属表面或裂纹尖端形成一层腐蚀产物膜,腐蚀产物膜在SCC中起着重要的作用。尽管人们开展了大量的研究,但是还存在争议。本论文利用有限元模拟研究了腐蚀产物膜力学性质和生长规律对阳极溶解性应力腐蚀的影响规律,重点研究了腐蚀产物膜应力的分布,以及对应力腐蚀裂纹尖端应力场的影响规律；同时,也建立了阳极溶解型应力腐蚀的内聚力模型,研究了腐蚀产物膜破裂和应力腐蚀裂纹扩展的动态过程,以及腐蚀产物膜的力学性能(杨氏模量、破裂强度)和腐蚀产物膜导致的应力与应力腐蚀敏感性和门槛应力强度因子的关系。本论文还以310奥氏体不锈钢在42%沸腾氯化镁溶液中阳极溶解型应力腐蚀为例,研究了阴极过程为析氢反应的阳极溶解型应力腐蚀,氢在应力腐蚀中的作用,提出了定量鉴别氢在阳极溶解中作用的方法。获得如下结论： 1)腐蚀产物膜中的残余应力若为压应力,根据力平衡则在金属基体中产生拉应力。有限元模拟研究发现,腐蚀产物膜在金属基体中产生的拉应力非均匀分布,最大应力出现在膜与基体的界面；对于U型单边缺口试样中,最大拉应力出现在试样表面距界面一定距离处,其大小和腐蚀产物膜厚度,膜杨氏模量,缺口的宽度和深度有关。存在两种可能的膜破裂的机制：一是腐蚀产物膜内的大拉应力使膜破裂。二是膜致应力叠加外加应力提高分切应力,促进裂尖前端局部塑性变形,使膜发生破裂。 2)建立了阳极溶解型应力腐蚀的内聚力模型,通过模拟研究发现：对于光滑试样,随着腐蚀产物膜厚度,膜杨氏模量的增加和膜破裂强度的降低,应力腐蚀敏感性增加。膜致拉应力的存在使得试样提前达到屈服阶段,促进应力腐蚀的发生；对于U型单边缺口试样,归一化门槛应力强度因子随腐蚀产物膜厚度和缺口深度的增加而降低。无论是光滑试样还是U型单边缺口试样,裂纹都起源于腐蚀产物膜内。膜致拉应力产生的应力强度因子会叠加在外加应力强度因子上。因此,阳极溶解型的应力腐蚀裂纹在外加应力保持恒定的情况下也可以形核扩展。 3)运川慢应变速率拉仲、电化学以及阴阳极极化的方法研究氢在阳极溶解型应力腐蚀中的行为,获得如下研究成果：310s奥氏体不锈钢在浓度为42%沸腾氯化镁溶液中的应力腐蚀,阴极极化阻碍了应力腐蚀,阳极极化促进了应力腐蚀。开路电位下Iscc(H)/IscC=0.035,应力腐蚀断口形貌和大电流动态充氢下断口形貌完全不同。310s奥氏体不锈钢在浓度为42%沸腾氯化镁溶液中开路电位下的应力腐蚀是由阳极过程控制,氢在其中所占的分量可以忽略不计。
[Abstract]:Stress corrosion is a low stress brittle fracture process, without warning, often lead to disastrous accidents, causing huge economic losses and casualties. According to statistics, accidents caused by stress corrosion should be accounted for in Corrosion Accident in the proportion as high as 35%. therefore, more than a century that stress corrosion has been an important research field.
For most of the anodic dissolution of stress corrosion, stress corrosion cracking (SCC) process will form a layer of corrosion product film on the metal surface or the crack tip, the corrosion product film plays an important role in SCC. Although people carry out a lot of research, but also controversial. Study on mechanical properties and corrosion product film the growth law of stress corrosion on the anodic dissolution of finite element simulation in this paper, the distribution of corrosion product film stress, and stress corrosion crack tip stress field; at the same time, also established the anodic dissolution should be cohesive zone model of stress corrosion, the corrosion product film the dynamic process of stress corrosion rupture and crack propagation, and the corrosion product film mechanical properties (Young's modulus and fracture strength) and corrosion product film caused by stress and stress corrosion sensitivity and threshold stress intensity The relationship between the factors. This thesis also takes 310 austenitic stainless steel in boiling 42% anodic dissolution of magnesium chloride solution stress corrosion for example, anodic dissolution of the cathode process for hydrogen evolution reaction to stress corrosion, stress corrosion of hydrogen in the role, and puts forward the method of quantitative identification of hydrogen in the anode dissolution the conclusion was as follows:
1) the residual stress in the corrosion film if the compressive stress is generated according to the force balance of tensile stress in the metal matrix. The finite element simulation results show that the corrosion product film on the metal matrix tensile stress in non uniform distribution, the maximum stress appears in the film and the substrate on the interface; U type single notched specimen, the maximum tensile stress occurs at the surface of the sample at a certain distance from the interface, the size and thickness of corrosion product film, the young's modulus, gap width and depth. There are two possible mechanisms of rupture of membranes: one is the corrosion product in the film tension stress to rupture. The two film is caused by the stress superposition stress increase the shear stress and the crack tip front, promote local plastic deformation, the membrane was broken.
2) anodic dissolution should be cohesive zone model of stress corrosion is established, the simulation results indicate that: for the smooth sample, with the thickness of corrosion product film, and increase of Young's modulus of rupture strength decrease, increase of stress corrosion sensitivity. The membrane induced by tensile stress due to the existence of the sample in advance to yield stage, promote stress corrosion; for U type of single edge notched specimen, the normalized threshold stress intensity factor increases with the thickness of corrosion product film and the notch depth decreased. Both the smooth specimen or U type single notched specimen, cracks originate in the corrosion product film. The film caused by the tensile stress produced by stress intensity factor will be superimposed on the applied stress intensity factor. Therefore, anodic dissolution of stress corrosion crack when the stress is kept constant under the condition of nucleation can be extended.
3) the slow strain rate tensile, electrochemical method and anode polarization studies of hydrogen in the anodic dissolution of stress corrosion behavior in the obtained results are as follows: 310S concentration of 42% austenitic stainless steel in boiling magnesium chloride solution stress corrosion, cathodic polarization hinder stress corrosion, anodic polarization promoted the stress corrosion. The open circuit potential Iscc (H) /IscC=0.035, stress corrosion fracture and large current dynamic hydrogen charging under completely different fracture morphologies of.310s austenitic stainless steel in a concentration of 42% boiling magnesium chloride solution under open circuit potential stress corrosion is controlled by the anodic process of hydrogen, in which the share of components negligible.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG172.9

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