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Transient waves were initiated by allowing a thick PMMA disk to strike a periodic stack of ceramic layers bonded by thin weak silicone rubber layers. Pressure at interfaces of ceramic and bond layers was measured by carbon gauges along the centerline of the stack. Comparison of experimental histories with those from a 1-D analysis [J. Acoust. Soc. Am. 94, 172–184 (1993)] and a 2-D axisymmetric analysis [J. Acoust. Soc. Am. 99, 3513–3527 (1996)] reveals that waves propagate two-dimensionally and that flexure of the ceramic layers controls attenuation and shape of compressive wave of first arrival. Viscoelasticity of the bond material sharply reduces tensile stresses.

Abstract. In order to characterize materials with respect to their susceptibility to shear band formation at high strain rates, a modified Hopkinson pressure bar apparatus and hat-shaped steel specimens with a shear zone having a width significantly larger than the typical width of adiabatic bands are used. The sample is directly impacted by the striker. The force acting on the sample is measured with a PVDF-gauge between the sample and the output bar. The displacement is recorded with an electrooptical extensometer. The energy absorbed by the shearing process up to failure can be used as a reference for the susceptibility of materials to shear band formation. The method is demonstrated comparing the shear behavior of two high-strength steels with similar metallic structure and strength. Differences were found in the transition region between quasi-static and fully adiabatic shearing conditions where the energy up to rupture differs by 40 %. For fully adiabatic shear band formation, the deformation process of both materials equals. At extreme rates, shear processes are mainly governed by the thermodynamic properties of the materials. On the other hand, strength and structural properties play a role for low and intermediate rates where global and localized shear mechanisms occur in parallel.

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