| I-II mixed-mode crack is widely spread in engineering application. It often brings fatiguefailure to structures under cyclic loading. This paper focuses on study of elastic-plasticmixed-mode fatigue crack propagation. The main content of the paper is described asfollows:A second-development is carried out with the user element subroutine UEL incommercial finite element code ABAQUS. Based on FORTRAN language, a subroutine forpredicting mixed-mode fatigue crack propagation is developed, in which the extended finiteelement method (XFEM) is coupled successfully with cyclic cohesive zone model (CCZM).In addition, the post-processing program is compiled based on the ABAQUS scriptlanguage PYTHON. The programs above serve as the foundation of numerical simulationabout mixed-mode fatigue crack growth.A compact-tension-shear (CTS) specimen is modeled for the study of I-II mixed-modecrack. CCZM parameters regarding normal direction are determined by fitting theload-opening displacement curves of CTS specimen during crack propagation and the modeI fatigue crack rate curve. Tangential parameters are determined based on isotropicprinciples.The XFEM coupled with CCZM is used to predicting the I-II mixed-mode fatiguecrack propagation. The crack propagation angle is calculated from nonlocal maximumprinciple stress (NMPS) criterion. A modified damage evolution equation is proposedconsidering the effect of load directions on mixed-mode fatigue crack growth.The computations show that by incorporating the effect of loading direction, theXFEM coupled with CCZM has a good ability to predict fatigue crack growth underdifferent loading directions. For the crack propagation direction in CTS specimen, theprediction of NMPS criterion is a little smaller than the analytical solutions of MTScriterion. The plastic zone at the crack tip changes with the loading directions. The loadingdirection not only has an influence on the size, but also the shape of the crack-tip plasticzones. |
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