Numerical Hopkinson Bar Analysis: Uni-Axial Stress and Planar Bar-Specimen Interface Conditions by Design

Report No. ARL-CR-553
Authors: Bazle A. Gama and John W. Gillespie, Jr.
Date/Pages: September 2004; 58 pages
Abstract: High strain rate characterization of materials is usually performed using the Split Hopkinson Pressure Bar (SHPB) in the strain rate range, 102 - 104 . In the one-dimensional analysis of Hopkinson bar experiment, it is assumed that the specimen deforms under uni-axial stress, the bar-specimen interfaces remain planar at all-time, and the stress equilibrium in the specimen is achieved in travel times. The first two assumptions are in general not true for acoustically hard specimens with diameter smaller than the bars. Explicit dynamic finite element analyses are used to investigate these assumptions. A new specimen design is suggested which satisfies the uni-axial stress condition in the specimen under the linear-elastic deformation phase of the specimen. A new Hopkinson bar experimental technique is presented to ensure that the bar-specimen interfaces remain planar at all time. Extensive numerical analyses are performed to quantify the accuracy of the proposed configurations.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2004