Hardness-flow stress relations of fatigued and tensile strained materials

Abstract

Hardness-flow stress relations have been determined for aluminium, Al-1%Si, Al-5%Mg, copper, Cu-36%Zn and Fe-0.16%C during strain-controlled bending fatigue in the high cycle region and during monotonic straining. The hardness after both types of deformation was found to be approximately equal for copper and FeC at high flow stresses and for CuZn at low flow stresses. The fatigued specimens were markedly harder than the tensile strained specimens at the same values of flow stress for copper and FeC at low flow stresses, CuZn at high flow stresses and AlSi and AlMg at all flow stresses. The situation is unclear for aluminum minimum owing to the smallness of the hardeness change. The relations, especially the non-uniform variation of hardness in fatigued copper, are discussed with respect to dislocation structures. The possibility of evaluating the stress amplitude even after fatigue failure is emphasized.