Modeling of I + II mixed mode crack initiation and growth from the notch

Abstract

The fatigue crack initiation and growth from the notches under combined loading are modeled by the finite element method. The compact tension shear (CTS) specimens of Q345R steel are used to study the I+II mixed mode crack growth behavior. To consider the effect of the residual stress and loading history induced by fatigue crack growth, the dynamic crack propagation model is employed in the finite element simulation. A multiaxial fatigue damage criterion is employed and an Armstrong–Frederick type cyclic plasticity model was inputted as a UMAT to describe the material behavior. The fatigue crack initiation and growth from the notch root of the CTS specimen is determined by the stabilized stress–strain responses of the material points near the notch root and the fatigue damage of different material planes. The material point with maximum fatigue damage corresponds to the fatigue initiation position, and the crack growth orientation from the initiation position is identical to the material plane on which maximum fatigue damage arises. The fatigue crack propagates on the material plane with maximum crack growth rate. The results of prediction are in excellent agreement with the experimental observations in terms of crack initiation orientation, crack growth rate and crack growth path.