Fatigue of OFHC pure copper and 316L stainless steel subjected to prior tensile and cyclic prestrains

Strong plastic deformations are often endured by industrial metallic parts along their shaping process. Understanding the effect of such prestrain on the subsequent fatigue properties is thus an important matter. To this aim, this work compares the effect of monotonic and cyclic axial preloadings (at room temperature) on the subsequent cyclic behavior. Two Face Centered Cubic (FCC) materials were used: OFHC pure copper and AISI 316L stainless steel. For comparison sake, monotonic and cyclic prestrains conducting to similar maximal flow stress were applied. The internal stress states and the microstructures were characterized after the prestrains. Strain controlled fatigue tests on prestrained specimens are known to shorten the fatigue life as confirmed by the experiments of this paper. The softening of the different internal stress components (back stresses and effective stresses) in fatigue as well as the modification of the fatigue life induced by the prestrains are discussed in relation with the surface roughness, the mean stress and the microstructure of each sample. Finally, the preponderant role of the microstructure on life reduction is highlighted.