Calculation of Dynamic Stress Intensity Factors for Pipes During Crack Propagation by Dynamic Finite Element Analysis

A dynamic finite element analysis method was proposed for calculating the dynamic stress intensity factors for pipes during crack propagation. The proposed method can directly calculate the stress intensity factors without the simplification used in theoretical analyses, and it can consider the effects of the crack velocity and gas decompression. It was found that the stress intensity factors of long propagating cracks in pipes saturated at a certain value in the case of a high crack velocity. However, the stress intensity factors for pipes were in good agreement with those of band plates in the case of a high crack velocity, the stress intensity factors for pipes were different from those of band plates in the case of a low crack velocity. This result could be explained by the effect of bulging on the stress distribution around a crack tip. The effect of bulging was more prominent for pipes with smaller diameters. In contrast, the dynamic stress intensity factors for band plates were in good agreement with the theoretical values that consider the dynamic effects and tended to decrease monotonically with increasing crack velocity. Additionally, the effects of gas decompression, caused by leakage from opened cracks, on the stress intensity factors for pipes were investigated. An explanation of the change in crack direction, reflecting a change from an axial crack to a circumferential crack, which is observed in actual pipeline fractures, was given by analyzing the ratio of the longitudinal stress to lateral stress.