HARDNESS-FLOW STRESS RELATIONS OF FATIGUED AND TENSILE STRAINED MATERIALS

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 FeC at high flow stresses and for CuZn 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 FeC at low flow stresses, CuZn at high flow stresses and AlSi and AlMg 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. © 1979.