Numerical and Experimental Investigations of Curved Fatigue Crack Growth under Proportional Cyclic Loading

Abstract

The present paper demonstrates that the common computer‐aided two‐dimensional crack path prediction can be considerably improved in accuracy by using a new predictor‐corrector procedure in combination with the modified virtual crack closure integral (MVCCI) method. The numerical crack growth simulation is still based on a step‐by‐step technique, but uses a piecewise curved approximation of the crack path. By this method, both the new locus of the crack tip and the slope of the crack path at the crack tip can be computed simultaneously by the mode I and II stress intensity factors for only one virtual tangential crack extension with respect to the previous step. Furthermore, the paper presents a new finite element technique of calculating stress intensity factors of mixed mode problems by MVCCI Method. The procedure is devised to calculate the separated strain energy release rates by using the convergence of two separate calculations with different element sizes in the neighbourhood of the crack. The method provides robust calculation ability, even in the case of very coarse meshes. In order to evaluate the validity and efficiency of the proposed higher order crack path simulation method in relation to the well‐established basic strategies, experiments of curved fatigue crack growth are carried out with a specially designed specimen under proportional lateral force bending. In all investigated cases the computationally predicted crack trajectories show an excellent agreement with the different types of curved cracks that are obtained in the experiments as a function of the position of crack initiation.