| The fracture caused by mixed-mode crack propagation is one of the mainfracture modes of the chemical machinery components. The mixed-mode crackpropagation aroused widespread concern due to its complexity in theory analysis andextensive applications in actual structures. Moreover, it is the interaction betweenmode-I (open mode crack) and mode-II (slide mode crack) which contributes most tofatigue fracture. Therefore, it is of marvelous significance to investigate thegeneration and propagation mechanism of I-II mixed-mode fatigue crack theoreticallyand practically. An emerging numerical analysis method—The Extended FiniteElement Method (XFEM) was introduced in detail in the paper. And the XFEM wasused on ABAQUS to analyze the behavior of I-II mixed-mode fatigue crackpropagation. The Compact Tension Shear specimens (CTS) were adopted in bothsimulation and experiment. Its material was Q345R. The simulation results andexperimental results were compared and analyzed. The principle contents andconclusions are as follows:The theory of XFEM was detailed. The thoughts and contents of using XFEM tosolve the crack problems were illustrated. The expressions of displacement function,governing equation, discrete equation, shape function partial derivative and numericalintegration, etc. were derived. In order to ensure the convergence and enhance theaccuracy, the partition of unity method (PUM) was given. A virtual node method forcoupling the XFEM with ABAQUS to realize the fracture analysis was presented.The level set method (LSM) was utilized to track the crack propagation. At the sametime the update of LSM was calculated to improve the accuracy. The way ofcomputing stress intensity factor (SIF) using direct method theory based on XFEMwas expounded in detail. The SIF was calculated by deriving the expressions ofdiscrete displacement and the control equation of virtual work.Under mixed mode I-II step loading conditions, the mixed mode I-II fatiguecrack propagation experiment was implemented utilizing CTS specimens of differentthickness and load angles. Therefore, the crack propagation path and the crack propagation rate were obtained. The XFEM analysis was conducted with the CTSmodels at the same time. The crack propagation path under the simulation conditionwas acquired. In addition, SIF was calculated in order to obtain the crack propagationrate. The influences of thickness and load angles on the mixed mode I-II fatigue crackpropagation were analyzed. The results showed that the crack propagation path wasmainly affected by the load angles. However, the thickness had little effect on crackpropagation path. The mixed mode I-II fatigue crack propagation path and rate variedwith the change of the load angles.By comparing the experimental results with XFEM simulation results, it wasfound that XFEM was validated in solving the mixed mode I-II fatigue crackpropagation problems. Also it had been proven of higher accuracy and strongercompatibility to adopt XFEM to analyze the mixed mode fatigue crack propagation. |
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