A Study Of Effects Of Interfacial Friction In The Splite Hopkinson Pressure Bar Tests

The relations between the effect of interfacial friction between the specimen and bars in the split Hopkinson pressure bar(SHPB) technique and the tested material properties are studied experimentally and theoretically in this paper. Five materials in different properties, such as silicon rubber, polyurethane foam, Comp.B explosive, PBX-HMX(97%) polymer bonded explosive and 6061-T6 aluminum alloy, respectively, are investigated.SHPB experiments are carried under three interfacial friction conditions for the tested materials. Three different experimental interface conditions are lubricated interface, dry interface and bonded interface respectively. The experimental results showed that the effects of interfacial friction in the split Hopkinson pressure bar tests are related to the tested material properties. Each material specimen is chosen in reasonable length-to-diameter ratio to satisfy the experimental requests. At the same time, a pulse shaping technique is used in the experiments. It can ensure dynamic stress equilibrium and homogeneous deformation in the soft and brittleness specimens. On the other hand, it can ensure the specimen loaded under the same constant strain rate during the tests. In this way, we can eliminate the influence of strain-rate effects and two-dimensional effects.Based on the isotropic elastic hypothesis, a theoretic analysis of the friction effects of interface between the specimen and bars is made by the energy conservation consideration. A theoretic formulation for the friction effects is reduced which showed that material Poisson's ratio, interfacial friction coefficient, length-to-diameter ratios of specimen and the axial strain during the tests are four influencing factors to the friction effects.The experimental results of the five materials are analyzed by above theories, which result in a conclusion that the material being of viscoelastic feature, large Poisson's ratio, in a little length-to-diameter ratio is particularly sensitive to the friction effects in the SHPB experiment with a large axial strain. By the way, different failure features of the silicon rubber and the two exolosives specimens submitted to different interface conditions are discussed.