Low-cycle fatigue behavior of a nickel-based alloy under combined blending/tension loading

In this paper, the effect of a combined bending/tension loading on the fati gue resistance and on the fatigue crack,growth characteristics of a nickel- based alloy at room temperature is studied For this purpose, a device was s pecifically designed so that it can be mounted onto a servohydraulic push-p ull testing machine. With the device, a simultaneous displacement and rotat ion of the specimen extremities generate a combined bending/axial stress; t he ratio between the bending stress and the axial stress may be specified b y adjusting the eccentricity between the specimen axis and the load axis. S tress-controlled fatigue tests were carried out on plate specimens under be nding/tension loading with a surface stress ratio of -0.52 (ratio between t he 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 videocameras. The Experimental results obtained under bending /tension loading have been analyzed in connection with the data obtained un der pure tension loading. In particular, the fatigue crack propagation rate expressed in terms of the stress intensity factor of a crack under combine d loading was examined.