油气输送管道疲劳裂纹起裂特性与影响因素

为了研究油气输送管道中疲劳裂纹的扩展特性,在疲劳载荷的作用下在试件中导入了倾斜疲劳裂纹,以此模拟油气管道中存在的实际裂纹.实验采用疲劳载荷的应力比为0和-1,疲劳裂纹的倾斜角度为45°.通过测量沿着裂纹开口方向和滑移方向的不连续位移量,计算管道中用作裂纹起裂判据的Ⅰ型应力强度因子(KⅠ)mes,和Ⅱ型应力强度因子(KⅡ)mes,以及抑制裂纹开口和滑移方向位移的应力强度因子(KⅠ)s和(KⅡ)s;讨论了疲劳裂纹的应力强度因子(KⅠ)s和(KⅡ)s的影响因素.其结果是:对于应力比0和-1的疲劳裂纹,(KⅠ)s和(KⅡ)s都小于零;而回火后的裂纹的(KⅠ)s和(KⅡ)s都接近于零,即压缩残余应力将对裂纹起裂(初始扩展)起到限制和阻碍的作用.

Initial fracture behavior and influencing factors of fatigue cracks in an oil-gas pipeline

In order to study bent fatigue crack behavior within an oil-gas pipeline,slant fatigue cracks were created in a specimen to simulate actual cracks in the pipelines.The stress ratio of the loading was 0 and-1 in this test.The angle of the fatigue crack was 45°.ModeⅠstress intensity factor(KⅠ)mes and mode Ⅱ stress intensity factors(KⅡ)mes,which were regarded as the initial fracture criteria of a crack,were calculated by measuring opening/sliding discontinuous displacement along the cracks.Furthermore,suppressing stress intensity factors of mode Ⅰand modeⅡ(KⅠ)s and(KⅡ)s were obtained,and then the influencing factors were discussed.As a result,(KⅠ)s and(KⅡ)s are smaller than zero for both fatigue cracks made under stress ratios of 0 and-1,because of compressive residual stress around the cracks which caused the crack surface contact.On the other hand,(KⅠ)s and(KⅡ)s equal nearly zero for annealed cracks with both stress ratios of 0 and-1.Therefore,it can be considered that the compressive residual stress will restrain the crack to expand at the initial fracture stage.