Low-cycle fatigue life prediction of circumferentially notched component based on elastic-plastic stress-strain analyses.

Abstract

The circumferentially notched medium carbon steel specimens of root radii of 2, 3 and 5 mm were low-cycle fatigued. Meanwhile the stress-strain response was calculated at the notch root by means of the F. E. M. and the Neuber's rule. The crack initiation lives of the notched specimens were controlled well by the equivalent stress, the equivalent plastic strain and the axial plastic strain produced at the notch roots. The axial plastic strain versus crack initiation life curve estimated through Neuber's rule predicts the shorter and the longer lives in the higher and the lower plastic strain regions, respectively. The applicability of Neuber's rule to the estimation of the crack initiation life extends much more in the notched specimen of the smaller root radius. The above three quantities are also the dominant factors for the failure life of the notched specimen, nevertheless the stress and strain gradients develop in the cross section of the notched specimen. The necessity of the fracture mechanics approach to the surface crack produced at the notch root was suggested.