The large diameter split pressure Hopkinson bar (SHPB) is an important tool to obtain the dynamic mechanical properties of brittle materials such as rocks. There are at least three disadvantages when it is used for testing rocks. These are: (1) strong oscillation and dispersion of the incident wave will result in serious oscillations of resultant test curves, (2) conventional loading method will cause serious non-uniformity of the stress or strain in the rock specimen, (3) variation of strain rates during loading regime is extremely unstable. The present work introduces the design of an impactor, which overcomes the above disadvantages and can initiate a half-sine loading wave in a 75mm diameter SHPB. The proposed impactor has been designed and fabricated by using an impact discrete inverse method based on wave mechanics and characteristic line theory. The impactor has been successfully applied for measuring dynamic constitutive relations of rocks. The numerical result of the shape of the loading wave is in a good agreement with the shape of the measured wave.
The conventional split Hopkinson bar (CSHB) is the most widely used experimental technique for investigating the dynamic behaviors of high-strength materials. Attempts to apply the split Hopkinson pressure bar (SHPB) in measurement on more brittle materials, such as rocks, concretes and granites, always are researched [2,4].