About the dynamic strength enhancement of concrete-like materials in a split Hopkinson pressure bar test

Split Hopkinson pressure bar (SHPB) technique has been used widely to measure the dynamic strength enhancement of concrete-like materials at high strain-rate between 101 and 10^3 s^?1. Although SHPB technique has been verified for metallic materials, the validity and accuracy of SHPB results for non-metallic materials have not been thoroughly studied. The present paper examines the application of SHPB to determine the dynamic strength of concrete-like materials whose compressive strength is hydrostatic-stress-dependent. It shows that the apparent dynamic strength enhancement beyond the strain-rate of 10^2 s^?1 is strongly influenced by the hydrostatic stress effect due to the lateral inertia confinement in a SHPB test. This apparent dynamic strength enhancement has been wrongly interpreted as strain-rate effect and has been adopted in both dynamic structural design and concrete-like material models for analytical and numerical simulations, which may lead to overprediction on the dynamic strength of concrete-like materials. The SHPB test is simulated in the present paper using FE method and Drucker–Prager model to investigate how the hydrostatic stress affects the SHPB test results of concrete-like materials. A rate-insensitive material model is used in order to examine this pseudo-strain-rate sensitive phenomenon. A collection of SHPB test results of concrete-like materials are compared with simulation results, which confirms quantitatively that the apparent dynamic strength enhancement of concrete-like materials in a SHPB test is caused by the lateral inertia confinement instead of the strain-rate sensitivity of the tested material.