Cracking simulation-based fatigue life assessment

A fracture mechanics numerical model is developed to simulate the collective behavior of growing short fatigue cracks originating from the surface of unnotched round specimens made of a two-phase alloy. The specimen surface roughness is considered resembling microcracks of different sizes and locations along the minimum specimen circumference. Material grains of different phases, sizes, and strengths are randomly distributed over that circumference. Variations in mechanical and microstructural features of grains are randomly distributed. Possible activities of surface cracks are predicted against loading cycles till either fracture occurs or all existing cracks become nonpropagating. The material's S-N curve and fatigue limit can, thus, be assessed. Published experimental data on ferritic-pearlitic steel specimens in push-pull constant amplitude loading (CAL) were utilized. Different specimens were randomly configured and virtually tested. Comparison of experimental results and corresponding predictions validates the model, which, further, recognizes the effect of surface roughness, specimen size, and mean stress on lives.