A theoretical analysis about the influence of interfacial friction in SHPB tests

• Friction effects are investigated in SHPB tests.
• The friction effects are associated with multiple factors.
• Local stress analysis and energy conservation analysis are carried out.
• A theoretical model is constructed to correct the friction effects.

The split Hopkinson pressure bars (SHPB) have been widely used to measure the deformation behavior of materials at high strain rates (103 ∼ 104 s−1). In order to obtain accurate material parameters, the influences of some effects such as friction, inertia, punching and elastic wave dispersion etc. should be considered in the SHPB tests. The present paper focuses on the interfacial friction effects, in which four different materials (silicone rubber, polyurethane foam, PBX-HMX, 6061-T6 aluminium alloy) are tested by the SHPB under three different conditions of interfacial friction (lubricated, dry and bonded). The experimental results show that the interfacial friction can produce a significant increase in the flow stress for some materials. A theoretical analysis based on the conservation of energy is conducted to establish a relation of friction effects to the Poisson ratio, interfacial friction coefficient, length/diameter ratio of the specimen and the longitudinal strain. The deduced relations of friction effects are in accord with the experimental results. Furthermore, the applicability of the theoretical formula is discussed, and interfacial friction coefficient profile under dynamic loading is investigated with a modified split Hopkinson pressure bar. The results indicate that the friction coefficient changes during the loading process. This can help further explain the experimental phenomena.