Experimental study of the compression properties of Al/W/PTFE granular composites under elevated strain rates

Granular composites consisting of aluminium (Al), tungsten (W) and polytetraflouroethylene (PTFE) are typical energetic materials, which possess high density and strength along with other advantageous properties. To investigate the mechanical behaviour of Al/W/PTFE granular composites, compression tests of three Al/W/PTFE mixtures under quasi-static loading and high strain rate conditions were conducted on a CSS-44100 Materials Testing System and a Split-Hopkinson Pressure Bar (SHPB), respectively. By employing Al bars, the amplitude of the transmitted signal was significantly enhanced and a high signal-to-noise ratio was obtained. This enhancement was due to the decreased Young's modulus of the bars, which led to increased signal amplitude from the strain gauges. The Al/W/PTFE granular composites were processed using a cold isostatic pressing and vacuum sintering approach. In this work, the fracture modes and stress-strain relationships of Al/W/PTFE composites with mass ratios of Al:W:PTFE of 24:0:76, 12:50:38 and 5.5:77:17.5 were studied. A detailed discussion is provided to cover the effect that tungsten addition, strain rate and mass ratio have on the deformation behaviour of the composites. The results show that the mass ratio plays a significant role in determining the dynamic behaviour and failure modes of the composites. Both the Al/W/PTFE (24:0:76) and the Al/W/PTFE (12:50:38) composites are strain rate dependent, elasto-plastic materials characterised by increased yield stress with increased strain rate. However, the Al/W/PTFE (5.5:77:17.5) composite is a brittle material, which shows brittle fracture at a relatively low strain.