27-10-2012, 11:10 AM
Numerical Hopkinson Bar Analysis: Uni-Axial Stress and Planar Bar-Specimen Interface Conditions by Design
ABSTRACT
High strain rate characterization of materials is usually performed using the Split Hopkinson Pressure Bar (SHPB) in the
strain rate range 100 - \h10,000. 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.