A frequency‐dependent high‐cycle fatigue damage model and its application in crack nucleation of marine riser from corrosion pits

Abstract

Based on the continuum damage mechanics theory, a frequency-dependent high-cycle fatigue damage evolution model was established. According to the fatigue results of API X80 steel, the frequency-dependent damage evolution parameters were regressed. Using the available riser mechanical model, the user subroutine of high-cycle fatigue damage evolution was compiled, and the accelerating effect of corrosion pits on fatigue crack initiation of the marine riser was analyzed. The results show that a single corrosion pit at the surface can reduce crack nucleation life by more than 80%. In a double corrosion pits' case, the stress interference between pits significantly affects the crack nucleation. Circumferential double pits can produce a fatigue crack earlier than the single pit, but the effect of axial double pits is just the opposite. When the spacing reaches a certain distance, the stress interference disappears, and the crack nucleation life approaches that of a single pit case.

Fatigue evaluation on the effect of impact pits with various impact conditions by a CDM‐based approach

“…Damage evolution equations are derived from the thermodynamic framework and are combined with a damage‐coupled constitutive model. Due to the coupling between the damage field and stress field, the method can reasonably describe the failure process in the material 35–38 …”

“…Due to the coupling between the damage field and stress field, the method can reasonably describe the failure process in the material. [35][36][37][38] In this work, a CDM-based fatigue life prediction approach is established to study the effect of low-velocity impact pit on fatigue behaviors. The JC model is modified to simulate the impact process to obtain residual stresses at the impact zone.…”