Particle size effect on strength, failure and shock behavior in Polytetrafluoroethylene-Al-W granular composites

TL;DR

This study investigates how particle size and porosity influence the mechanical and shock response of PTFE-Al-W granular composites, revealing size-dependent strength and energy absorption behaviors through experiments and simulations.

Contribution

It demonstrates the impact of tungsten particle size on strength, failure modes, and energy deposition in PTFE-Al-W composites, highlighting mesoscale force chains and dynamic behavior.

Findings

Smaller W particles increase compressive strength in porous samples.

Porosity and particle size affect energy distribution during shock loading.

Mesoscale force chains explain strength variations observed in simulations.

Abstract

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.