Alumina-filled epoxies are composites having constituents with highly dissimilar mechanical properties. Complex behavior during shock compression and release can result, particularly at higher alumina loadings. In the current study, a particular material containing 43% alumina by volume was examined in planar-impact experiments. Laser interferometry was used to measure particle velocity histories in both reverse-impact and transmitted-wave configurations. Hugoniot states and release-wave velocities were obtained at shock stresses up to , and represented smooth extensions of previous data at lower stresses. Surprisingly high release-wave velocities continued to be the most notable feature. Measured profiles of transmitted waves show a gradual transition from viscoelastic behavior at high shock stresses to a more complex behavior at lower stresses in which viscous mechanisms produce a broadened wave structure. This wave structure was examined in some detail for peak stress dependence, evolution towards steady-wave conditions, and initial temperature effects.
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The steady-shock velocity, or Hugoniot shock velocity, is defined by the conservation relation for a steady shock wave: , where and identify a stress-velocity point on the Hugoniot curve and is initial density. Although unsteady evolution occurs in ALOX wave profiles, the motion of the half-maximum point on wave profiles appears to be nearly steady and accurately represented by the Hugoniot shock velocity (Sec. III). The rise time to the half-maximum point becomes very small at higher shock pressures (Fig. 6).
