Numerical simulation of fatigue crack propagation in friction stir welded joint made of Al 2024-T351 alloy

• We model fatigue crack propagation in thin-walled aluminium alloy friction stir welded structure.
• We use the eXtended FEM to calculate number of cycles for given crack propagation steps.
• Unstable crack propagation is estimated using data for number of cycles vs. crack propagation.
• Experimental verification is on the way to check the validity of numerical simulation.

In this work, fatigue crack propagation in thin-walled aluminium alloy structure with two friction stir welded T joints has been simulated numerically. Crack propagation in stiffened part of the structure between two friction stir welded T joints is analysed by using the eXtended Finite Element Method (XFEM), including software ABAQUS, as well as MORFEO, for modelling and results display. Tensile fatigue loading is applied, with stress ratio R = 0, and maximum stress σmax = 10 MPa. Material properties (Al 2024-T351, as used in aeronautical industry) in different welded joints zones are adopted from available literature data. Following results are obtained by numerical analysis: stress–strain and displacement state in the structure, position of the crack tip and value of stress intensity factor for every crack propagation step, as well as the structural life estimation, i.e. number of load cycles, N, also for each crack propagation step. Using these results the number of cycles at which the crack starts to propagate in an unstable manner is predicted.