Proposed fatigue damage measurement parameter for shot-peened carbon steel based on fatigue crack growth behavior

• Effect of residual stress relaxations on fatigue crack growth was investigated.
• Especially, we focused on the crack propagation from edge of initial notch.
• Fatigue crack formation was strongly dependent on remained residual stress level.
• We suggested the new parameter to evaluate damage growth by residual stress state.

A new technique for evaluating fatigue-damage accumulation in shot-peened (SP) carbon steel based on variations in residual stress is proposed. Using findings from previous studies, a fatigue damage parameter for a material treated with SP based on the change in induced compressive residual stress (CRS) is examined. A plastic replica method with the focused ion beam (FIB) technique is used to assess the relationship between the residual stress state and the fatigue crack growth (FCG) behavior of SP specimens over the fatigue lifespan. It is found that the residual stress relaxation phenomenon can be used as an effective parameter for determining the fatigue damage growth, provided the residual stress relaxation rate of each mechanical load and the critical threshold relaxation boundary of each material is known.