Transient and steady-state deformation at notch root under cyclic loading

Abstract

The transient and steady-state cyclic deformation behaviour at a notch root is studied with a view toward assessing the rate of plastic shakedown of notched components subjected to cyclic loading. The failure of existing local strain approach, which is widely used for fatigue life assessment, to correctly account for the mean stress relaxation under asymmetric loading provides the main motivation of the work. Under localised plastic yielding condition, it is found that both elastic-perfectly-plastic and linear kinematic hardening models predict an immediate plastic shakedown while nonlinear kinematic hardening law predicts a progressive shakedown. At the shakedown state, linear kinematic hardening model predicts a nonzero mean stress whereas a zero mean stress is predicted by the nonlinear kinematic hardening model. To provide an efficient method for assessing the rate of mean stress relaxation under transient condition, an integral approach is presented for the rate of elastic or elastic–plastic shakedown at notch root, which is shown to be in good agreement with finite element results.