管线钢表面裂纹体的三维断裂特性和断裂判据研究

3-D FRACTURE MECHANICS CHARACTERISTICS AND CRITERION FOR PIPELINE STEEL WITH SURFACE CRACK

采用中心表面裂纹试样的三点弯曲试验,研究X70管线钢表面裂纹体的断裂特性。结果表明,二维断裂力学参量KⅠ已不能客观描述和表征表面裂纹体断裂现象和裂端应力场强度。采用三维断裂力学参量KZ,能很好描述和表征表面裂纹体的试验现象和裂纹尖端应力场强度,三维断裂韧度KZC与表面裂纹的几何尺寸和裂纹形态无关,是管线钢表面裂纹体的客观韧性指标。建立穿透裂纹和表面裂纹的统一断裂准则,即三维断裂力学准则,KZ=K(F(TZ))～(1/2)≤KZC,将该准则和失效评估图(failure assessment diagram,FAD)技术相结合,可以进行含表面裂纹管道的安全性评定。

Fracture characteristics of X70 pipeline steel with surface crack were investigated by three point bending tests of center surface crack specimens. The experiment results indicate that two dimension fracture mechanics parameters KI can not characterized factually for experiment phenomenon and crack tip stress intension of surface crack. Three-dimensional fracture mechanics parameter KZ was proposed to characterize the crack tip stress intension of surface crack. Three-dimensional fracture toughness KZC does not regard geometry size and shape of surface crack, and it is a objective toughness of pipeline steel with surface crack. The unified fracture criterion of through thickness crack and surface crack, KZ=K√F（TZ）≤KZC was constructed. Combining with failure assessment diagram （FAD） technology, this 3-D fracture mechanics criterion can be used to evaluate the safety of pipeline containing surface crack or surface crack-like flaw.