三维断裂理论在管线钢安全评定中的应用

引入三维应力约束Tz理论和等效厚度概念 ,对三维裂纹的应力强度因子和断裂韧性的计算进行了改进 ,并通过含表面裂纹、单边和双边角裂纹的断裂试验验证了三维断裂理论用于油气输送管线钢剩余强度评定的可行性。试验结果表明 ,此管线钢中的裂纹起裂韧性Ki值随裂纹形态和方位的不同有较大差别 ,且都低于穿透裂纹的起裂值。经三维断裂理论分析后发现 ,所有三维裂纹形态的三维起裂韧性Kzimax都与穿透裂纹的三维起裂韧性Kzithrough值很接近。这说明三维起裂韧性Kzi基本与裂纹形态和几何尺寸无关 ,管线钢的断裂韧性得到统一。

The application of three-dimensional fracture theory on pipeline steel residual strength assessment

A three-dimensional stress constraint factor Tz was introduced. The calculation of stress intensity factor of part-through crack in the petroleum and gas pipeline steel was modified by an equivalent thickness conception. The fracture experiments of part-through crack with wide and narrow center surface cracked panels, single and double corner cracked panels of a sort of high strength pipeline steel were carried out, and the feasibility of three-dimensional fracture theory on pipeline steel residual strength assessment was verified. The test results show that the initial toughness Ki of part-through crack vary greatly with crack geometry and orientation, and are lower than that of through-thickness crack. By the three-dimensional fracture theory, the influence of crack geometry on three-dimensional stress strength factor Kz is disappeared. The maximum three-dimensional initial toughness Kzimax of all sorts of part-through crack is very close to that of through-thickness crack. So the three-dimensional initial toughness Kzi can be regard as a material constant. The residual strength of part-through crack will be predicted by use of fracture data from through cracks of arbitrary thickness, this may be very useful in pipeline safety assessment.