Fatigue of Polycrystalline Copper at Constant and Variable Plastic Strain Amplitudes

Fatigue behavior of polycrystalline copper of two different grain sizes was studied using constant and randomly varying plastic strain amplitude tests. The different regimes in the ess‐curves of large‐grained samples ( d ˜ 2.0 mm) were found to be reflected also in the measured fatigue lives in both test modes. The variable amplitude fatigue lives of the small‐grained samples ( d ˜ 0.03 mm) seemed to follow the Coffin–Manson linear law. The damage accumulation rate in variable amplitude tests was found to be lower than in the corresponding constant amplitude tests, e.g. when expressed as cumulative plastic strains to failure. The fatigue life predictions based on the Palmgren–Miner rule, rain‐flow analysis and the constant amplitude life data measured in this work were also conservative.