Oscillation elimination in the Hopkinson bar apparatus and resultant complete dynamic stress-strain curves for rocks

This paper highlights an improved experimental approach for eliminating oscillation that exists in the dynamic stress-strain response of rocks and other brittle materials obtained from tests using a split Hopkinson pressure bar (SHPB). Both analytical and experimental results for a number of rock types are presented to verify the idea. Results from the investigation indicate that oscillation in the dynamic stress-strain response of these materials originates from the Pochhammer-Chree dispersion of the loading incident wave, and more evidently from the relatively low strength and elastic modulus of the samples compared with metallic materials. In order to control the oscillation effectively, it is proposed that a half-sine loading waveform should be used instead of the conventional rectangular loading waveform in SHPB tests. Experimental results obtained from both the conventional and the improved methods are presented, including dynamic complete stress-strain curves for granite, sandstone and limestone. The improved method eliminates oscillation in the tests, provides better stability of strain rate and more representative results than those obtained from the conventional rectangular loading waveform shape. (C) 2000 Elsevier Science Ltd. All rights reserved.