Mixed-Mode Crack Propagation Direction Under Multiaxial Fatigue Loading

Abstract The problem of mixed-mode fatigue crack growth has been a persistent research challenge. The determination of fatigue crack propagation direction directly impacts the components and structures’ safety and integrity, making it crucial in various industrial applications, including welded drilling pipes, aerospace, and automotive engineering. Unlike the uniaxial loading problem, mixed-mode cracks tend to change their direction frequently (kink), and having a cyclic loading adds to the complexity of the problem. This research aims to estimate the crack propagation direction of linear elastic materials subjected to mixed-mode (I+II) loading conditions, proportional or non-proportional cyclic loading. Numerical software was developed based on the approach of Maximum Energy Release Rate (MERR), which has many advantages over other crack propagation criteria. The crack propagation path in a thin-walled cylinder subjected to axial and torsion fatigue loading is investigated. The loading phase difference ranged from 0 degrees (proportional) to different nonproportional phase angles up to 90°. The model simulates the crack propagating a small increment at different angles ranging from 0° to 360°, and the energy released at each angle is calculated. The angle at which the crack releases the maximum energy is taken to be the direction of the crack. Results obtained from the numerical simulations were validated using experimental data from the literature and were also compared to results from other numerical LEFM approaches, demonstrating good agreement with both.