【作者】 冷晓畅；

【导师】 苗张木；

【作者基本信息】 武汉理工大学 ， 海洋工程结构， 2011， 硕士

【摘要】 海洋工程结构不仅结构复杂,而且其工作环境也非常恶劣,当海洋工程结构局部萌生了疲劳裂纹,在一定的疲劳裂纹的扩展速率的情况下,疲劳裂纹扩展会对海洋工程结构造成一定破坏,这就需要研究怎样保证海洋工程的结构安全。因此研究海工用钢的疲劳裂纹扩展速率是很有意义。本文的研究内容分为四部分：(1)关于海工用钢的疲劳裂纹扩展速率试验研究(第二章)；(2)关于海工用钢疲劳裂纹扩展速率与断裂韧性CTOD的关系(第三章)；(3)是关于海工用钢疲劳裂纹扩展速率的有限元分析(第四章)；(4)是关于基于FRANC2D/L的海工用钢疲劳裂纹扩展细观研究。海工用钢具有厚度大,强度高,疲劳性能要求高等特点,本文选取具有代表性的海工用钢EH40钢作为研究对象。首先,本文分析得到确定疲劳裂纹扩展载荷的公式,对海工用钢EH40进行疲劳裂纹扩展速率试验,将规范中的七点递增多项式法修改成五点递增多项式法,并编程对试验数据进行分析,得到疲劳裂纹扩展速率公式。结果表明：EH40钢的疲劳裂纹扩展速率在疲劳裂纹扩展的中速区。其次,本文在疲劳裂纹扩展速率试验中测得裂纹嘴张开位移CMOD,通过转换得到CTOD,并计算了CTOD和疲劳裂纹扩展速率da/dN之间的关系式。同时进行了CTOD低温韧性试验,通过断口分析了预制疲劳裂纹扩展速率与断裂韧性CTOD的关系。结果表明疲劳裂纹扩展速率与断裂韧性成反比关系。然后,本文通过虚拟裂纹闭合法(VCCT)和FRANC2D/L软件两种有限元方法模拟了疲劳裂纹扩展速率,结果表明有限元模拟得到的值与试验值基本吻合,有限元模拟疲劳裂纹扩展速率具有良好的精度。最后,基于耦合内聚力模型(CCZM)理论,本文通过FRANC2D/L软件对两种尺寸的海工用钢EH40钢的多晶体模型,在九种边界条件下分析了晶体界面裂纹的形成和扩展。同时也分析了含有夹杂颗粒多晶体界面和疲劳载荷作用下多晶体界面的疲劳裂纹的形成和扩展。结果表明：宏观疲劳裂纹扩展在某一程度上是细观条件下晶体界面的损伤的积累形成的。研究材料细观条件下多晶体裂纹的萌生与扩展为更深入地了解疲劳裂纹扩展奠定了基础。更多还原

【Abstract】 Not only the Marine engineering structures are complicated, but the working condition is very serious. When there are local cracks exit in the Marine engineering structure, under the certain crack propagation rate, fatigue crack propagation of Marine engineering structure will cause some damage to it. So it needs to study how to keep the Marine engineering structure safe. Therefore, the research of the propagation of the Marine engineering structure rate is a very meaningful work.This study includes four parts:the first part is about experimental studies of the fatigue crack growth rate of steel of marine engineering (Chapter Two); the second part is about relationship between the fatigue crack growth rate and fracture toughness of steel of marine engineering (Chapter three); the third part is about finite-element analysis of the fatigue crack growth rate of steel of marine engineering(Chapter four); the last part is about detail study of the fatigue crack growth rate of steel of marine engineering bases on FRANC2D/L. steel of marine engineering has its own characteristic such as thick, high strength, good fatigue resistance and so on, so steel of marine engineering EH40 was choosed as the object of study in this paper.Firstly, this paper got the formulas of the load which decides the fatigue crack propagation, then made a test of fatigue crack propagation rate about steel EH40.After that,this paper changed the seven point incremental polynomial technique which exited in the standard into five point incremental polynomial technique, programming of the it to analysis the data of the test and getting the formula of fatigue crack propagation rate. The result showed that the fatigue crack propagation rate of steel EH40 locate in the medium-speed area of fatigue crack propagation.Secondly, this paper measured the crack mouth opening displacement (CMOD) through the test of fatigue crack propagation rate, changing it into CTOD, and calculating the equation between the CTOD and the fatigue crack propagation rate da/dN.Simultaneously, this paper tested the crack opening displacement under temperature which below zero, studying the relationship between prefabricated fatigue crack propagation rate and fracture toughness CTOD. The result showed that the fatigue crack propagation had a inverse relation to fracture toughness.Then the fatigue crack growth rate was simulated by two finite element methods which included virtual crack close technique and software of FRANC2D/L respectively. The result showed that the value which got through simulated by finite element methods inosculate to experimental value, and finite element methods has the feature of good precision in simulating fatigue crack growth rate.Finally, based on the theory of couple cohesive zone model(CCZM),this paper study the formation and extension of polycrystal interface on marine used EH40 steel by FRANC2D/L,under nine boundary conditions. Meanwhile, this paper studied the formation and extension of polycrystal interface which contains includes and the polycrystal interface under the fatigue loads. The result showed that the macro fatigue crack propagation revealed the accumulation of damage of polycrystal interface in mesoscopic condition. The study of formation and extension on polycrytal interface in mesoscopic condition laid a foundation to in-depth understanding of fatigue crack propagation in macro condition.更多还原