A TESTING METHOD TO INVESTIGATE LOW CYCLE FATIGUE BEHAVIOR OF SLICE MATERIALS BASED ON CYCLING PLASTICITY CORRECTION

A series of constant amplitude low cycle fatigue tests for thin funnel-like plates of N18 zircaloy and SAPH440 steel were carried out. Based on the principle of fatigue damage equivalent on local stress and strain, Manson-Coffin model of strain fatigue life prediction and the equation of cyclic stress-strain relationship for the two materials were established. A new method to obtain cyclic constitutive relationship for a material obeying Masing law was proposed, and experiments on low cycle fatigue of a turbine rotor steel B65A-S at 300℃ were employed to verify the validity of this method. According to the finite element analysis on the basis of calibrated cyclic constitutive relationship, two types of transforming models from mean stress of a thin funnel-like plate to local axial stress at the root of the funnel and from measuring strain to local axial strain at the root of the funnel for the two materials were set up. Finally, low cycle fatigue tests for straight round bars of SAPH440 steel were completed, and the accuracy of the new test method for low cycle fatigue of thin funnel-like plates was completely certificated.