  The variation of metallic particle size and sample porosity significantly
alters the dynamic mechanical properties of high density granular composites
processed using a cold isostatically pressed mixture of polytetrafluoroethylene
(PTFE), aluminum (Al) and tungsten (W) powders. Quasi-static and dynamic
experiments are performed with identical constituent mass fractions with
variations in the size of the W particles and pressing conditions. The
relatively weak polymer matrix allows the strength and fracture modes of this
material to be governed by the granular type behavior of agglomerated metal
particles. A higher ultimate compressive strength was observed in relatively
high porosity samples with small W particles compared to those with coarse W
particles in all experiments. Mesoscale granular force chains comprised of the
metallic particles explain this unusual phenomenon as observed in a hydrocode
simulation of a drop-weight test. Macrocracks forming below the critical
failure strain for the matrix and unusual behavior due to a competition between
densification and fracture in dynamic tests of porous samples were also
observed. Shock loading of this granular composite resulted in higher fraction
of total internal energy deposition in the soft PTFE matrix, specifically
thermal energy, which can be tailored by the W particle size distribution.
