The Simulation of Extremely Low Cycle Fatigue Fracture Behavior for Pipeline Steel (X70) Based on Continuum Damage Model

Natural gas transmission pipelines installed in seismic and permafrost regions are vulnerable to cyclic loads with a large strain amplitude. Under these conditions, the pipe may fail extremely low cycles, situation which is also known as cycle fatigue (ELCF) failure. The fracture mechanism of ELCF shows significant difference that fatigue, life usually deviates from Coffin–Manson law. Thus, it essential develop an effective model predict failure pipeline. In this study, series tests performed on pipeline steel (X70). A damage coupled mixed hardening developed simulate behaviors. Continuum law under monotonic load extended by introducing equivalent plastic strain. By assuming softening induced accumulation, parameters fitted directly peak stress each cycle. Then, input into commercial software ABAQUS user material subroutine behaviors specimens. simulation results show good agreements test both load, verifies reliability model.