Research on the Effect of Mean Stress and Dwell Position on the Fatigue Properties of Powder Superalloy (FGH95)
Abstract
Fatigue tests were conducted on powder superalloy (FGH95) at a temperature of 650 oC considering the effects of mean stress and stress dwell time. Standard specimens and two distinct geometric forms of notched specimens were utilized in the study. It is observed that the fatigue lives of the standard specimens followed a consistent S-shaped pattern with increasing the mean stress. In stress dwell tests, both types of notched specimens exhibited nearly identical fatigue lives for the maximum and minimum stress dwells (MAX-D, MIN-D). The experimental findings were analyzed using a damage-coupled unified creep-plasticity (D-UCP) constitutive model. For MAX-D, a notable accumulation of cumulative damage was observed within the initial cycles, with the rate of damage evolution rapidly saturating in subsequent cycles. Conversely, for MIN-D, although the cumulative damage in the initial cycles was relatively modest, the rate of damage evolution was significantly higher compared to the MAX-D condition. These factors collectively contribute to the gradual convergence of cumulative damage under both MAX-D and MIN-D conditions, providing an explanation for the approximately equal lifespan between the two loading conditions.