【作者】 翟建明；

【导师】 李晓阳；

【作者基本信息】 北京工业大学 ， 工程力学， 2013， 博士

【摘要】 腐蚀疲劳是指腐蚀性介质与交变应力协同作用所引起的材料破坏的现象，它广泛存在于石油化工、核工业、航空航天以及海洋船舶等工业之中。随着我国工业化水平的高速发展，对安全生产与设备安全性的要求也越来越高，腐蚀疲劳问题在工程领域中也显得愈加重要。在对疲劳问题的研究中，腐蚀疲劳因为腐蚀环境、服役工况的多变性而显得更加复杂，它将会涉及到力学、电化学、材料科学等多个学科。国家2006年²020年中长期发展纲要中也将“材料服役与环境的相互作用、性能演变、失效机制及寿命预测原理等”列为重大战略需求的基础性研究项目，以期望解决材料的环境服役问题。基于以上研究背景，本文对腐蚀疲劳问题展开了一系列的研究。由于腐蚀疲劳包含了腐蚀与疲劳两个不同的问题，对腐蚀疲劳的研究可以通过腐蚀、疲劳分别进行研究后再进行综合研究。因此，为了解决工程中的腐蚀疲劳及其可靠性的问题，本文的研究主要分三个部分，一是疲劳可靠性问题的研究，二是腐蚀程度评定的研究，三是腐蚀疲劳及其可靠性问题的研究。在疲劳可靠性的研究中，本文基于对数疲劳寿命遵循正态分布的假设，通过构造材料对数疲劳寿命、对数疲劳寿命标准差分别与应力水平之间的函数μ（S）与σ（S），建立得到了材料的条件概率密度分布曲面（CPDDS）并对其性质展开了讨论。该CPDDS可以较全面的反映材料的疲劳性质如S-N曲线、p-S-N曲线及理论疲劳极限。材料的理论疲劳极限即材料在规定的服役时间内发生失效的概率为小概率事件时的疲劳强度值，该定义利用CPDDS中的小概率事件突破了传统方法中对疲劳极限的定义。本部分研究提出了一种通过建立材料的CPDDS来研究材料疲劳性能的方法，同时该方法还可以用于随后的腐蚀疲劳及其可靠性的研究中。为了对材料经受H₂S腐蚀后的腐蚀程度进行评定，本文提出了逐层显微硬度试验的方法。通过材料经H₂S腐蚀后的硬度随材料打磨层深的变化，证明了金属材料在不同浓度的H₂S溶液中经过不同时间腐蚀后会产生H₂S腐蚀层、氢脆影响层的分层现象，其中溶液浓度对分层的影响不明显，腐蚀时间对分层有显著性影响。对本文采用的45号钢材料来说，经过48h浸泡腐蚀后材料的氢脆影响层会达到最大值，经过96h浸泡腐蚀后材料的H₂S腐蚀层会达到最大值。通过对金属材料腐蚀评定的研究，本文还提出了材料氢脆影响层中硬度随腐蚀溶液浓度、腐蚀时间与层深变化而变化的力学模型，并对模型中的参数进行了物理定义，该模型的提出为氢损伤的研究提供了研究思路。在腐蚀疲劳及其可靠性的研究中，本文结合材料腐蚀评定与疲劳可靠性研究方法，提出了一种研究工程中腐蚀疲劳问题的新方法，为腐蚀疲劳的机理解释提供了定性的解释。本文以45号钢为例进行了腐蚀疲劳的试验研究，研究发现腐蚀对材料产生的分层现象会对材料的疲劳行为产生重要的影响。H₂S腐蚀层因为点蚀坑的存在极易引发微裂纹的萌生与加速裂纹扩展，导致材料的抗疲劳特性减弱，引起材料理论疲劳极限的降低；氢脆影响层中包含的氢损伤会导致材料失效的随机性增大，导致材料疲劳寿命的分散性增大，引起材料可靠性寿命的降低。以上的研究结果为材料基于疲劳强度的可靠性设计、基于疲劳寿命的可靠性设计提供了理论参考，同时可用于工程中服役设备与材料的检修方案制定提供有效的试验数据。更多还原

【Abstract】 Corrosion fatigue of the material is caused by the synergy of corrosive media andalternating stress, it is widely present in the engineering such as petrochemicalindustry, nuclear industry, aerospace and marine vessels. With the rapid developmentof the industry, production safety and equipment security requirements are alsoincreasing, and the corrosion fatigue problem is increasingly important in engineering.Corrosion fatigue, which is related to mechanics, electrochemistry, materials scienceand other disciplines, is very complex because of the variability of the corrosiveenvironment and the service conditions. Thus the long-term development frameworkfrom2006to2020of our Country has put the "Interaction of material service and theenvironment, Performance evolution, Failure mechanisms and Life predictionprinciple" as a major strategic need of basic research projects, expect to solve thematerial environment service problems.Based on the above background, studies on the corrosion fatigue issues aredeveloped in this paper. For the corrosion fatigue contains two different problems,corrosion and fatigue respectively. Thus the corrosion fatigue study can be firstdivided into two independent studies, corrosion study and fatigue study, and thencarry out a comprehensive study. In order to solve the problem of corrosion fatigueand its reliability in engineering, there are three parts of the research, the first is thestudy of the fatigue reliability, the second is the study of the corrosion assessment,and the third is the study of the corrosion fatigue and its reliability.In fatigue reliability studies, based on the assumption that the logarithmic fatiguelife follow the normal distribution, a conditional probability density distributionsurface （CPDDS） of material is established by constructing the functions μ（S） andσ（S）. Where μ（S） is the function between the logarithm of fatigue life and the stresslevel, σ（S） is the function between the standard deviation of logarithmic fatigue lifeand the stress level. The CPDDS can reflect the fatigue properties of the materialmore comprehensively, such as the S-N curve, p-S-N curve and the theoretical fatiguelimit. The theoretical fatigue limit is the stress level at which the material failure is asmall probability event within the required service time. The definition of thetheoretical fatigue limit broke the conventional definition of the fatigue limit. A newmethod for researching the performances of the material fatigue is proposed in thisstudy, while the method can also be used in the study of the corrosion fatigue and itsreliability. In order to assess the corrosion degree of the material after the H₂S corrosion, thelayer by layer micro-hardness test method is proposed. By monitoring the hardnesschanging with the thickness of the polished layers after the H₂S corrosion, thestratification phenomenon is proved. The material will induce the corrosion layer andthe hydrogen embrittlement affected layer after the H₂S corrosion, wherein thesolution concentration plays little role on these stratifications, the etching time playsan important role on these stratifications. For the C45steel used in this paper, thethickness of the hydrogen embrittlement affected layer will reach the maximum after48h immersion, the thickness of the corrosion layer will reach the maximum after96himmersion. The mechanical model which expresses the hardness changing with thesolution concentration, etching time and the layer thickness is proposed in this part,and the physical definition of the model parameters is also given. The proposed modelprovides a new research method for the hydrogen damage study.In studies of the corrosion fatigue and its reliability, a new research method ofthe corrosion fatigue in engineering is proposed by the combination of the corrosionassessment and the fatigue reliability research, and the qualitative explanation of thecorrosion fatigue mechanism is given. The corrosion fatigue test of C45steel isresearched in this part, the study found the material stratifications after the corrosionhave an important impact on the fatigue behavior. The corrosion layer can easily leadto the micro-crack initiation and accelerate the crack propagation because of thepresence of pitting, resulting in the weakening of anti-fatigue properties, causing thereduction of the theoretical fatigue limit; the hydrogen embrittlement affected layerbecause of the hydrogen damage will lead to the increase of the material failurerandomness, resulting in the material fatigue life dispersibility increases, causing areduction in material‘s reliability life. The above findings provide a theoreticalreference for the fatigue strength based reliability design or the fatigue life basedreliability design, and the valid test data for life maintenance program development ofthe serving equipment and materials in engineering.更多还原