  A Brazilian disk geometry of an alumina layered composite with alternating
dense and porous layers was dynamically loaded using a Split-Hopkinson Pressure
Bar (SHPB)apparatus under compression. High-speed imaging and transmitted force
measurements were used to gain an insight into stress wave propagation and
mitigation through such a layered system. Uniformly distributed porosities of
20 and 50 vol % were introduced into the interlayers by the addition of fine
graphite particles which volatilized during heat treatment. Brazilian disk
samples were cut from the cylinders which were drilled out of the sintered
laminated sample. The disks were subjected to dynamic impact loading in
perpendicular and parallel orientations to the layers in order to investigate
the influence of the direction of impact. The dynamic failure process of the
layered ceramic consisted of the initiation and propagation of the cracks
mainly along the interphases of the layers. Upon impact, the impact energy was
dissipated through fracture in parallel orientation (0 deg) but transmitted in
perpendicular (90 deg) orientations. The high degree of correlation between the
transmitted force, microstructure and orientation in which the layered systems
were impacted is discussed.
