James J. Lee

Testing low-impedance materials such as polymeric foams under dynamic compression presents challenges for traditional Hopkinson-type methods, which often fail to maintain stress equilibrium or transmit sufficient force. This study introduces a modified Direct Impact Hopkinson Pressure Bar (mDIHPB) system with an intermediate loading stage, addressing some of these limitations. Closed-cell Rohacell IG-71 foam was tested at strain rates of 100-1000/s, demonstrating improved resolution and reliability in material characterisation, supported by a numerical model. A rate-dependent foam model was developed and calibrated using low-rate experimental data, and subsequently implemented in the Abaqus/Explicit solver to validate the experimental method and provide insight into stress wave interactions and deformation mechanisms. This numerical framework complements the experimental setup, offering predictive capability and a foundation for future dynamic testing of low-impedance materials. Compared with conventional SHPB and DIHPB techniques, the mDIHPB enables longer pulse durations, enhanced force sensitivity, and effective observation of foam deformation through densification, providing a compact and versatile solution for low-impedance material testing at medium-to-high strain rates.