Low-Cycle Fatigue Behavior of a Nickel-Based Alloy Under Combined Bending/Tension Loading

Abstract

In this paper, the effect of a combined bending/tension loading on the fatigue resistance and on the fatigue crack growth characteristics of a nickel-based alloy at room temperature is studied. For this purpose, a device was specifically designed so that it can be mounted onto a servohydraulic push-pull testing machine. With the device, a simultaneous displacement and rotation of the specimen extremities generate a combined bending/axial stress; the ratio between the bending stress and the axial stress may be specified by adjusting the eccentricity between the specimen axis and the load axis. Stress-controlled fatigue tests were carried out on plate specimens under bending/tension loading with a surface stress ratio of −0.52 (ratio between the maximum cyclic stress on the back face and that on the front face of the specimen). During each test, the fatigue crack length was monitored using two traveling video-cameras. The experimental results obtained under bending/tension loading have been analyzed in connection with the data obtained under pure tension loading. In particular, the fatigue crack propagation rate expressed in terms of the stress intensity factor of a crack under combined loading was examined.