PSI - Issue 58

M.R.A. Rahim et al. / Procedia Structural Integrity 58 (2024) 9–16 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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primarily focused on a variety of grain sizes, revealed that the geometry of the microstructure, specifically the comparison between homogeneous and inhomogeneous microstructure morphologies, plays a critical role in fatigue resistance. The homogeneous microstructure morphology showed higher fatigue crack initiation resistance than the inhomogeneous grain size morphology of the microstructure, with the same average grain size for both at different stress amplitudes. Fatigue testing at stress amplitude 200 MPa indicates a higher number of cycles for the both microstructure morphology in which crack retardation happens, typically known as run-out. The S-N curve shows that the homogeneous microstructure required more cycles to nucleate a first crack due to the microstructural geometry. The endurance limit fatigue crack initiation of the S - N curve, as established by the TMM and experimental data, is identified at a stress amplitude of 300 MPa with all microstructures exceeding fatigue crack initiation life of 1×10 6 cycles. The homogeneous microstructure morphology has a hexagonal structure that can distribute the stress equally within the grains, thus reducing the stress concentrations. In contrast, the inhomogeneous microstructure morphology contains high stress concentrations due to its uneven grain structure requiring fewer cycles to nucleate the first crack. In view of a different microstructure morphology, the stress concentration factor is the best way to determine the geometry influence on fatigue crack initiation life. Contrary to the homogeneous microstructure, where crack initiation was found to be oriented in only one, the inhomogeneous microstructure takes a scattered pattern of directions of nucleated cracks across the model. In reality, the P91 microstructure morphology is similar to the inhomogeneous microstructures M1 to M3. The discoveries of different cyclic behavior depending on microstructure morphology have practical implications for material selection and design optimization for applications where fatigue crack initiation is critical in heavy industries, especially power plant equipment. Consequently, understanding the significance of microstructure morphology in enhanced fatigue crack initiation life enables the precise scheduling of preventive maintenance, extending their operating intervals and reducing downtime for critical components in industrial applications. Acknowledgements The authors would like to express their gratitude to staff members of the Institute for Materials Testing, Materials Science and Strength of Materials (IMWF) at the University of Stuttgart, Germany, the Smart Manufacturing Research Institute (SMRI) at School of Mechanical Engineering, Universiti Teknologi MARA (UiTM), Malaysia, the Institute of Material Research of SAS, Watsonova, Košice , Slovakia, the Department of Mechanical and Manufacturing Engineering at Faculty of Engineering and Built Environment, University Kebangsaan Malaysia (UKM), Malaysia, the Department of Occupational Safety and Health (DOSH), Malaysia. The Public Service Department of Malaysia financially supports this research with reference number JPA(I)870614145415. Ján Dusza gratefully acknowledges the support of the Alexander von Humboldt Foundation. References Bassi, F., Beretta, S., Conte, A. Lo, Cristea, M., 2017. 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