Experimental and numerical study on mixed mode I/II fatigue crack growth in planar specimens

This paper focuses on the evaluation of predictive methods for the analysis of fatigue crack growth (FCG) under mixed mode I/II loading. The experimental part of the study consists of a series of fatigue crack growth tests performed on bend and tension specimens with geometries similar to the standard SE(B) and SE(T) ones. For the above specimen types, both mode I and mixed mode FCG tests are first performed. To facilitate an accurate evaluation of the mixed mode test results, finite element analyses of stress intensity factors for crack geometries following the experimentally measured trajectories are carried out. Additionally, the XFEM based algorithm available in the finite element code ABAQUS is explored with respect to its performance in predicting crack growth paths. The subsequent test evaluation focuses on examining a correlation between FCG rates for mixed mode loading conditions with the mode I baseline curve. The results suggest that, using mode I experimental data along with a mode I specimen analysis, both conservative and non-conser vative prediction of mixed mode fatigue crack growth is possible. In this context recommendations of failure assessment procedures regarding the flaw re-characterisation and projection onto principal stress planes, as well rules for the transferability of mode I FCG curves to mixed mode conditions are discussed.