Effect of fatigue damage induced by cyclic plasticity on the dynamic tensile behavior of materials

It is often necessary to predict the response of engineering structures when subjected to impact loading conditions such as: automobile and train crash, high speed impact of debris and high speed manufacturing processes. An optimum combination of body structure and material is highly required and thus an exact evaluation of high strain rate properties of materials has been demanded. However in all cases, an initial damage free material is assumed and new structures, without fatigue damage, are tested. It is unknown how the fatigue damage induced during service may affect the dynamic response of materials. In the present paper the dynamic response of fatigue damaged 6061-T6 aluminum alloy and AISI 4140T steel specimens due to cyclic plasticity and subjected to impact loading are investigated. Samples subjected to previous low cycle fatigue are considered. Results show that previous fatigue damage affects the quasi-static behavior of steel more significantly than that of aluminum. Dynamic yield stress of 6061-T6 aluminum samples is more sensitive to fatigue damage than to strain rate. Previous fatigue damage has a detrimental effect on ductility of AISI 4140T steel, mainly on the dynamic tests.