Depth-sensing indentation-based studies of surface mechanical behavior and fatigue damage evolution of an austenitic stainless steel subjected to cyclic straining

Abstract In this paper the depth-sensing indentation (DSI) testing was used to study the elasto-plastic behavior and damage evolution in the surface layers of 304 stainless steel subjected to low-cycle fatigue loadings. For this purpose, the load–penetration depth ( P − h ) curves on the surface layers of cyclically deformed specimens corresponding to various stages of fatigue process were measured, from which the indentation characteristic parameters ( HV , S , h r and W p ) were extracted to evaluate the surface elasto-plastic behavior of the stainless steel during cyclic deformation. Based on the indentation characteristic parameters, the basic mechanical properties ( E , σ y and n ) were estimated using Dao et al.’s analysis algorithm to establish the constitutive descriptions of the fatigued surface layers. In terms of the continuum damage mechanics, a new damage indicator parameter, the indentation plastic work ( W p ), was proposed to characterize the fatigue crack-initiation damage for the stainless steel, and its evolution character during fatigue cycling was analyzed. In this study the deformation microstructures formed in near-surface regions of fatigued specimens were also examined using OM and TEM techniques to provide the micro-mechanisms for the surface mechanical behavior and fatigue damage evolution. It is finally suggested that the DSI testing could provide a potential nondestructive evaluation method for the early detection of fatigue damage of engineering components and structures in alternating service conditions.