Fatigue crack propagation direction under different loading conditions using MTS and MSS criteria

Abstract

Fatigue Crack Growth plays a major role on structural integrity. When mixed mode fatigue crack propagation is introduced by complex geometry or loading conditions, numerical methods are essential for fatigue life determination. This paper explores the differences between two crack propagation models. Using an automatic fatigue crack growth algorithm and the finite element method, crack propagation on CTS and four-point bending specimens was simulated. Both specimens allow for pure mode I, mixed mode and pure mode II loading conditions. According to the maximum tangential stress criteria, fatigue crack propagation occurs along the direction where tangential stress is maximized. Comparing crack propagation results with literature, it was possible to conclude that this criterion can be used under pure mode I or mixed mode loading conditions. The maximum tangential stress criterion was also compared to the maximum shear stress criterion, where crack propagation occurs along the direction that maximizes shear stress. Crack propagation directions between these criteria were compared and it was possible to conclude that the maximum shear stress criterion should be used for pure mode II loading conditions. Overall, this methodology allows for fatigue crack growth simulations under complex loading conditions.