Strain rate concentration factor in comparison with stress concentration factor of a circumferential notch in a round bar specimen

Abstract

High-speed tensile testing is now being recognized as a standard testing method for evaluating the impact strength of engineering materials. The impact speeds of Izod and Charpy tests cannot be controlled and therefore do not correspond to the real failure of real products. The brittle-ductile transition of structural materials is affected by the temperature and loading speed. In the high-speed tensile test, it is necessary to obtain the strain rate at the notch root accurately to understand the effect of impact load. For smooth specimens, the strain rate can be determined from the tensile speed u/t and specimen length l as ε_smooth = u/tl. For notched specimens, however, the strain rate at the notch root ε_notch should be analyzed accurately. In this study, therefore, the strain rate concentration factor defined as K_tε = ε_notch/ε_smooth is studied with varying the notch geometry. To predict the strain rate concentration factor K_tε accurately, the relationship between K_tε and the stress concentration factor K_t^* = σ_max/σ_gross is investigated. Here, σ_gross is the remote tensile stress and P is the tensile load. It is found that the strain concentration factor K_tε can be estimeted from stress concentration factor K_t^* when the relative notch depth 2t/D≦0.5 (t : notch depth, D : the specimen diameter).