Determination of the radial inertia-induced transition strain-rate in split Hopkinson pressure bar tests †

The transition strain-rate represents the start of significant contributions from radial inertia-induced lateral confinement to the axial compressive strength of the tested materials. However, it has been misinterpreted for decades by many studies as the start of significant strain-rate effect on the dynamic uniaxial compressive strength of the tested materials. Based on the dimensional analysis and numerical and experimental data, a semi-empirical formula to determine the transition strain-rates for various engineering materials is proposed. Errors in SHPB tests due to the contribution of the lateral confinement effect are estimated. It is found that, except for metals, transition strain-rates of concrete-like, rock-like and polymeric materials are unfortunately located in the valid range of SHPB tests that has been commonly accepted by research communities. Thus SHPB tests cannot be treated as valid measurements under uniaxial stress state when strain-rates are greater than the transition strain-rate.