X80管线钢动态断裂分析的落锤撕裂实验与有限元模拟

Investigation of dynamic fracture of X80 pipeline steel based on drop weight tear test and finite element simulation

已有的不同类型落锤撕裂实验数据表明,高钢级管线钢的单位断裂能和裂尖张开角依赖于断裂速度。本文进一步确定了其依赖关系是由断裂韧性而非试件几何差异所引起,并且定量分析了基于断裂准则所定义的断裂韧性与断裂速度之间的关系。利用所提出的黏结本构法则分别对X80管线钢标准试件和修正试件的落锤撕裂实验进行了三维有限元模拟,并将有限元结果与实验结果进行了对比。结果表明:有限元计算的加载曲线、断裂速度、裂尖张开角与对应的实验结果吻合较好,故本文提出的黏结本构法则能较好地应用于X80管线钢的动态断裂分析;标准试件的断裂韧性高于修正试件的断裂韧性,而标准试件的断裂速度则低于修正试件的断裂速度;七次有限元计算结果都表明断裂韧性随稳态断裂速度的增大而减小,且二者的关系可以由本文提出的自然指数函数进行描述。

Recent tests based on different types of drop weight tear tests show that fracture energy per fracture area and crack tip opening angle of high grade pipeline steel dependent on fracture speed. In order to investigate if this dependence is induced by the difference of fracture toughness and geometric property of specimens, and quantitatively to investigate the dependence of dynamic fracture toughness on fracture speed, the standard and modified drop weight tear tests of X80 pipeline steel are simulated by three dimensional finite element analysis(FEA) which is based on a properly designed constitutive law of cohesive zone model. The comparison between FEA results and test results shows that the loading curve, fracture speed and crack tip opening angle in finite element simulation agree well with the corresponding experimental results, respectively. The presented constitutive law of cohesive zone model describes the dynamic fracture of X80 pipeline steel well. The fracture toughness of standard specimen is higher than that in modified specimen, while the fracture speed of standard specimen is smaller than that in modified specimen. The FEA results show that the dependence of fracture energy per fracture area and crack-tip opening angle on fracture speed is mainly induced by fracture toughness, not by geometric property. Making use of standard and modified specimens, seven simulations of drop weight tear test are conducted, respectively. The FEA results of both the standard and modified specimens show that the fracture toughness decreases with steady-state fracture speed, and their relation can be described by the suggested empirical relation.