Study On Residual Fatigue Life Prediction For Crack Damaged Offshore Platform Structures

Offshore platform serving on the open sea may be exposed to the fatigue failure.Residual fatigue strength evaluation is a key part in life-cycle evaluation of structural safety and it's important in providing guidance for structural maintenance.Recently,Fatigue Crack Growth(FCG)approach is commonly used to simulate the crack growth path and predict the residual fatigue life for cracked structures.However,the traditional computational models of the FCG approach require both very small elements and repeatedly remeshing which makes the approach too time-consuming for the fatigue life prediction of large engineering structures.Therefore,a fast and robust approach is needed for evaluation of residual fatigue strength.In this paper,a reliable approach combined with eXtended Finite Element Method(XFEM)and Direct Cyclic Analysis is presented based on ABAQUS for fatigue life prediction.This approach realized arbitrary crack growth and fatigue life prediction for structures subjected on complicated loads.Based on equivalent region integral method,J integrals for planar elements and three dimension solid elements are programed in Python to validate the XFEM in commercial software ABAQUS.Crack surfaces searching code is also programed utilizing level-set approach to calculate the crack length.On this basis,Direct Cyclic Analysis and energy Paris Law are combined with XFEM.This approach is introduced as an efficient fatigue analysis approach for cracked structures.The fatigue crack growth simulations of edge crack in a rectangular plate and edge crack in a circular opening plate validated this approach.In addition,a crack growth rate checking algorithm is introduced into the original algorithm to check whether the crack growth rate is calculated reasonably in each substep of propagation.This alternative algorithm avoided the energy release rate calculation error by Virtual Crack Closure Technology(VCCT)and improved the robustness.Finally,the fatigue behaviors of cracked stiffened panel and cracked tubular joint are investigated.The rationality and correctness of this improved approach are validated by comparing with the experimental results and traditional results.