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首页> 外文期刊>Physical mesomechanics >Crack Tip Opening Angle as a Fracture Resistance Parameter to Describe Ductile Crack Extension and Arrest in Steel Pipes under Service Pressure
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Crack Tip Opening Angle as a Fracture Resistance Parameter to Describe Ductile Crack Extension and Arrest in Steel Pipes under Service Pressure

机译：裂纹尖端张开角作为抗裂参数的描述在工作压力下钢管的延性裂纹扩展和逮捕

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摘要

The angle between two element sides representing the crack tip is defined as the crack tip opening angle (CTOA). Its critical value is used as a criterion of fracture resistance for characterizing stable tearing in thin metallic materials. Various methods are used for determination of the CTOA. Optical microscopy is one of the most common methods as well as fitting of experimental load-displacement diagrams by the finite element method (DIC). Additionally, analytical analysis using the experimental load-displacement curve method (SSM) derived from the plastic hinge model of deflection in three-point bending of a ductile specimen is applied. This approach assumes a constant rotation centre distance. Values of CTOA for API 5L X65 pipe steel found by three methods-DIC, CNM, and SSM-are given. Values of CTOA given by these three methods are similar and close to 20A degrees. A discussion on the different parameters used to characterize the fracture resistance of running cracks in a pipe under service pressure is presented. The energy of fracture at impact determined by Charpy or drop-weight tear test (DWTT) tests and the critical J energy parameter are considered as well as the yield locus after damage, cohesive zone energy, and CTOA is another approach. One notes that CTOA is assumed to be constant during stable crack extension and decreases linearly with crack length during the instable and primary phase. A numerical technique to describe a ductile running crack using the node release technique and using CTOA as the fracture resistance criterion is presented. This method is compared with three different two-curve methods (TCMs): the Battelle, high strength line pipe (HLP), and HLP-Sumitomo methods. The Batelle TCM, as the oldest method, based on Charpy energy, gives a strongly conservative prediction. Predictions by the CTOA method are close to those obtained by the HLP-Sumitomo one.
机译：表示裂纹尖端的两个元素侧之间的角度定义为裂纹尖端张开角（CTOA）。它的临界值用作抗断裂的判据，以表征薄金属材料中的稳定撕裂。使用多种方法确定CTOA。光学显微镜是最常用的方法之一，也是通过有限元方法（DIC）拟合实验载荷-位移图的方法。此外，应用了从塑性铰链模型在延性试样三点弯曲变形中导出的实验载荷－位移曲线法（SSM）进行分析。该方法假设旋转中心距离恒定。给出了通过DIC，CNM和SSM三种方法得出的API 5L X65管钢的CTOA值。这三种方法给出的CTOA值相似，接近20A度。讨论了用于表征工作压力下管道中运行裂纹的抗断裂性能的不同参数。通过夏比或落锤撕裂试验（DWTT）测试确定的冲击断裂能，临界J能量参数以及损伤后的屈服轨迹，内聚区能量和CTOA是另一种方法。有人指出，CTOA被认为在稳定的裂纹扩展期间是恒定的，并且在不稳定和初生阶段随裂纹长度线性减小。提出了一种使用节点释放技术并以CTOA作为抗断裂准则描述延性运行裂纹的数值技术。将该方法与三种不同的两曲线方法（TCM）进行了比较：Battelle，高强度管线管（HLP）和HLP-Sumitomo方法。 Batelle TCM作为最古老的方法，基于Charpy能量，给出了非常保守的预测。 CTOA方法的预测与HLP-Sumitomo一种方法的预测相近。

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