Numerical simulation of the Split Hopkinson Pressure Bar test technique for concrete under compression

The Split Hopkinson Pressure Bar [SHPB] technique has been commonly used to investigate concrete compressive response under high strain rate. However, there appears to be a lack of agreement in the literature about a number of critical issues pertaining to this test method. In this paper, computational simulation models are employed to critique the technique and obtain a better understanding of it. Influential parameters are identified and attempts are made to shed light on some controversial issues surrounding the interpretation of high strain rate test data. The results show that significantly different strain rates can be obtained from the same SHPB test depending on the method used to estimate the strain rate value. Furthermore, comparing the results of simulations with pressure-independent and pressure-dependent constitutive material models show that strength increases associated with strain rate are strongly, but not totally, reliant upon the confinement introduced by lateral inertial effects and the frictional condition at the interface between the pressure bars and the specimen. Based on these observations, it is argued that the so-called ‘rate-enhanced’ models that explicitly account for strength increases as a function of strain rate should not be used in numerical simulations that already account for the effects of lateral confinement, since such models would tend to double-count the strain rate effect.