Author(s)

H. Sakamoto, Y. Ohbuchi & Y. Nakamura

Abstract

The change of mechanical properties under cyclic loading was measured and the cyclic hardening/softening phenomena at the early stage of fatigue around the crack tip were made clear by the Micro-Indentation Method. The effects of the stress concentration, the strain amplitudes and the number of cycles on the dynamic micro hardness of the material surface were examined in detail. The cyclic local plastic behaviours agree well with the change of surface micro dynamic hardness and it is shown that this Micro-Indentation Method is effective as the evaluation method of mechanical properties under cyclic loading. Keywords: plastic behaviour, micro-indentation, cyclic loading, plastic hardening, low cycle fatigue. 1 Introduction Recently, as the evaluation method of the mechanical properties of surface treatment material and thin film, the Micro-Indentation Tester has received attention from micro-electron manufacturing industries [1–4]. The change of material properties under cyclic loading plays an important role in the fatigue process. In this study, the change of material properties, that is, the cyclic hardening/softening phenomenon at the early stage of fatigue around the crack tip, was measured by a Micro Indentation Tester [5]. The effects of the stress concentration, the strain amplitudes and the number of cycles on the surface micro hardness were examined. The conventional method of micro Vickers hardness demands the measurement of the diagonal length of indentation and a lot of time is required for this measurement.

Keywords

plastic behaviour, micro-indentation, cyclic loading, plastic hardening, low cycle fatigue