Refined control of loading rate in SHPB tests on rock-like materials

The split Hopkinson pressure bar (SHPB) test is widely used for the characterisation of materials through dynamic stress measurement. A persistent problem with this technology is a lack of refined projectile loading rate control, for which an effective method is proposed here. Based on the gas adiabatic equation of state and full consideration of the projectile's force state when driven by high-pressure gas, the relationships between launch gas pressure, specific location of projectile in the launch barrel and loading rate of the projectile were obtained. The accurate control of projectile loading rate in the SHPB test was achieved by controlling the launch gas pressure and the exact location of the projectile in the launch barrel. To aid locating the projectile exactly, a calibrated-position ramrod is designed, for which a detailed practical operation is herein reported. By using the described method, unguided trial-and-error loss of material and equipment are avoided, experimental error is reduced, and experimental efficiency is improved. As well, the proposed control method for projectile loading rate control is very simple and easily implemented. According to results, the deviation between the measured and designed projectile loading rate is effectively controlled within ±2% by this method.