Evaluation of Ceramic Specimen Geometries Used in a Split Hopkinson Pressure Bar

Various ceramic specimen geometry and insert configurations being used for dynamic compression testing in a split Hopkinson pressure bar are analyzed numerically using DYNA2D. The objective of the analysis is to study the magnitude and locations of stress concentrations in the specimen, the degree to which the hard ceramic indents into the bar, the stress distribution with the specimen, and the effect of specimen size relative to the bar diameter. It is found that a "dog-bone" shaped specimen with end diameter matching the bar diameter is an ideal geometry which yields a uniform stress distribution with the gage length of the specimen. A cylindrical specimen with impedance matched tungsten carbide inserts is also found to be a sound combination for obtaining reliable experimental data on the failure strength of ceramics. A cylindrical specimen with diameter matched conical alumina inserts performs equally well but has the disadvantage of additional machining costs in making the conical ceramic inserts