An experimental study on residual stress relaxation in low‐cycle fatigue of Inconel 718Plus

Residual stress relaxation induced by the application of mechanical loads is determined by the nature of residual stress, the elasto-plastic material properties, and the type of applied load. Despite the importance of the first load cycle, analytical models available in the literature generally assumed residual stress relaxation as a continuous process. Residual stress induced by machining on Inconel 718Plus superalloy cylindrical specimens was measured before and after the application of load cycles under strain control. Low-cycle fatigue tests were carried out at room temperature for different strain amplitudes, and X-ray diffraction measurements were performed before and after 10 and 100 cycles. A comprehensive analytical model was derived to describe the relaxation process associated with the initial cycles and that associated with the continuous application of load cycle, which is based on the plastic strain energy per cycle W and requires the evaluation of parameters that are only dependent on the material and not on the strain amplitude.