【作者】 余立；

【导师】 苗张木；

【作者基本信息】 武汉理工大学 ， 海洋工程结构， 2010， 硕士

【摘要】 疲劳破坏和脆性断裂是海洋工程结构中最常见的两种破坏形式。随着海洋结构物逐渐迈入深海,用于海洋结构物上的钢板厚度越来越大,强度越来越高,所以海工用钢的疲劳性能和韧性对保障结构安全起着更加重要的作用。如果钢板的抗疲劳性能好,那么结构不会产生疲劳裂纹或者裂纹扩展的速度很慢；如果钢板的韧性好,那么即使结构产生了疲劳裂纹也可以有效地将裂纹止住,不会发生危害极大的脆性断裂。因此对海工用钢进行疲劳性能和韧度的评价是一项很有意义的工作。本文的研究内容分为三个部分：第一部分是关于海工用钢韧度评定的研究(第二章)；第二部分是关于海工用钢疲劳性能测试的研究(第三、四章)：第三部分是关于海工用钢疲劳寿命和CTOD值关系的研究(第五章)。海工用钢具有厚度大,强度高,韧性要求高等特点,本文选取了具有代表性的海工用钢EQ70作为研究对象。首先本文结合海工用钢的特点分析了现有的测定材料韧度的方法,证明CTOD试验是评定海工用钢韧度最适宜的方法,并用该方法对EQ70钢的韧度进行评定,结果表明EQ70具有良好的低温韧性。然后本文比较了目前测试材料疲劳性能的方法,结合海工用钢的特点选取一套合适的方法测试了EQ70钢的疲劳寿命,得出材料S-N曲线,进而得出P-S-N曲线。结果显示,EQ70钢具有良好抵抗裂纹萌生的能力。同时,本文还对疲劳数据的分布规律进行了分析,证明EQ70钢的对数疲劳寿命满足正态分布规律。接着本文在P-S-N曲线基础上,提出了P-S-N曲面法。该方法可以统计材料在不同可靠度下的S-N曲线。经过验证,该方法具有良好的精度,能够帮助设计人员更加方便快捷地得出目标可靠度下的S-N曲线。最后本文将疲劳试验数据和CTOD试验数据进行了分析,得出了EQ70钢对数疲劳寿命1gN和韧度CTOD值δ具有正相关线性关系。利用这种关系,本文提出了两种方法和一个模型方程。两种方法分别为概率分布法和P-δ直线法,前者可以用于评价CTOD值满足允许值的概率大小以及用于比较两种材料的韧性值的优劣,后者用于确定目标可靠度下CTOD特征值。CTOD-寿命模型方程为预测同种材料疲劳性能和韧度值奠定了基础。更多还原

【Abstract】 Fatigue failure and brittle fracture are the most common failure modes in the ocean engineering structures. With the tendency of application of ocean structures into deep-sea, the thickness and strength of steel plate used in the ocean structures is increasing. The fatigue performance and the toughness of the steel play more important role for the safety of the ocean structures. If the fatigue performance is good, the fatigue crack initiation will not happen or the speed of the crack propagation is very low. Further more, if the toughness of steel is good enough, the crack propagation will stop even if there have been fatigue cracks in the structures. It will not cause the brittle fracture which is very dangerous for safety of the structures. Therefore, it is a very significant work to evaluate the fatigue performance and toughness of the marine steel.The main contents of this dissertation can be divided into three parts:the first part is study about assessment of the toughness of the marine steel(chapterⅡ); the second part is study about assessment of the fatigue performance of the marine steel(chapterⅢandⅣ);the third part is study on relationship between CTOD and fatigue life of marine steel(chapterⅤ). The steel for ocean structures has the advantages of high strength, heavy thickness and so on, this dissertation selects EQ70 steel as study object which is representative.Firstly, taking the characteristics of the marine steel into account, the dissertation analyzed the current methods of determination of the toughness of material and it is concluded that the CTOD test is the best method to evaluate the toughness of marine steel, then evaluated the toughness of EQ70 steel by this method. The test results showed that EQ70 steel has good performance of low temperature toughness.Secondly, compared the current methods of fatigue testing, the dissertation designed a fatigue testing which is applicable to marine steel and got S-N curve by the method. The testing results showed that EQ70 steel has good fatigue performance. Then further analysis of the experimental data is made to obtain the P-S-N curve which is based on different probability. At the same time, the dissertation has analyzed the distribution of the fatigue data and it proved that the logarithm of fatigue life follows normal distribution.Since to get S-N curve in different reliability is very complicated, P-S-N surface method which can reflect the S-N curve in nearly all reliability is developed. It is proven that the P-S-N surface method has good accuracy and it will help the designers obtain the S-N curve in prescriptive reliability.Finally, the linear relationship between the logarithm of fatigue life and CTOD is got and also the explanation from microscopic aspect is given. The dissertation presents two methods and one model equation. The two methods are called respectively Probability Distribution Method and P-δCurve Method, while the former can give the probability of CTOD of the material meeting the criterion and can compare the toughness of two kinds of steel plate. The model equation has established a foundation of the relationship between toughness and fatigue performance of the marine steel.更多还原