| Summary: | Austenitic stainless steel with a bimodal harmonic structure (HS) is a recently developed material that consists of a periodic arrangement of coarse-grained (CG) structures surrounded by a network of ultra-fine grains (UFG). This material is characterised by high strength and good ductility. In this study, we analysed the fatigue performance of HS materials by modifying our previous multiscale model to extend its applicability from only homogeneous materials to HS materials. A novel method was proposed to characterise the microstructural features of HS materials considering the distributions of CG and UFG. A microstructure model was developed to reproduce grain maps using these characterised microstructures. The multiscale model was successfully validated by experimental results for two types of austenitic stainless steels. The model was used to elucidate the governing microstructural factors of fatigue performance in HS materials through systematic simulations. Consequently, a higher UFG area fraction was confirmed to improve fatigue life, and a UFG area fraction of approximately 40% is suggested for optimal microstructural design to balance fatigue performance and fabricating costs. This study presents the first step in the qualitative design of the fatigue performance of HS materials to replace the expensive and inefficient experimental analyses used in previous studies.
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