Numerical Investigation on the Necessity of a Constant Strain Rate Condition According to Material’s Dynamic Response Behavior in the SHPB Test

The split Hopkinson pressure bar (SHPB) apparatus is frequently used to investigate the dynamic compression properties of various materials at strain rates from 10² to 10⁴ s⁻¹. Keeping the strain rate constant during loading is an important condition for obtaining accurate experimental results. However, we do not always need to take additional measures to control the constant strain rate loading conditions for materials with different dynamic response behaviors. To investigate the necessity of a constant strain rate condition in the SHPB test according to the different dynamic mechanical response behaviors of materials, a comprehensive numerical analysis scheme combined with the Cowper-Symonds plastic kinematic model was designed to perform the simulation tests. There are two factors primarily resulting in the errors in the calculated stress-strain response for the representative material model. One of them is the dynamic scale factor, which represents the strain rate sensitivity and controls the variation amplitude of flow stress with the change in strain rate. The other factor is the work-hardening rate, which affects the results by expanding the decrease in strain rate. This paper quantitatively describes the effects of strain rate sensitivity and the strain-hardening modulus on the accuracy of the reconstructed stress-strain behavior of a sample under a constant incident pulse. The conclusion presents several reference guides for the necessity of a constant strain rate condition for different dynamic response behaviors of materials based on the representative constitutive model.