Multiscale fatigue assessment of wire arc additively manufactured aluminium alloys with experimental and simulation approach

Abstract

This study investigates the fatigue behaviour of wire arc additively manufactured (WAAM) aluminium alloys, emphasizing the role of pore in fatigue life assessment. Using a multiscale experimental and simulation approach, it was found that fatigue life is highly sensitive to pore size, with larger pores significantly reducing durability. However, an ultra-fine and uniform pore distribution was observed to enhance fatigue resistance despite increased porosity levels. X-ray synchrotron micro-computed tomography (micro-CT) revealed that WAAM specimens contained a higher number of micropores compared to cold-rolled counterparts, with a 3-µm average pore diameter. Fatigue life is sensitive to pore size; however, ultra-fine distribution of pores can generate a favourable fatigue life, irrespective of the number of pores. Residual tensile stresses were identified as a key factor reducing fatigue strength, while material grain refinement contributed to an improved fatigue notch factor (Kf approaching unity). The study further demonstrated that fatigue strength decreases with increasing pore size, in accordance with fracture mechanics principles. The S–N curve estimation, incorporating the fatigue notch factor, successfully predicted the fatigue life of WAAM components, validating the applicability of this method. Given the variability in WAAM microstructure, defect-free fatigue strength should be reassessed whenever process parameters change. These findings highlight the need for standardized S–N curves for additively manufactured metals and emphasize the importance of high-resolution defect characterization in fatigue assessment. The insights gained will aid in optimizing WAAM process parameters to enhance structural reliability in aerospace, automotive, and maritime applications.