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, hr and Wp) 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, σy 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 (Wp), 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.