High-strain, high-strain-rate flow and failure in PTFE/Al/W granular composites

Dynamic compression experiments were performed on a pressed PTFE/Al/W mixture to understand the composite behavior at high-strain and high-strain rate. The high-strain-rate tests were carried out in a drop-weight apparatus at impact velocities of 3.5 and 5 m/s, providing strain rates of approximately 4 x 10(2) s(-1). Aluminum jackets of varying thickness were used to ensure that specimens underwent confined deformation but did not separate into fragments. Failure was preceded by extensive plastic deformation concentrated primarily in the PTFE component. W particle-PTFE interface separation provided initiation and propagation of cracks. In extensively deformed specimens (strains of up to -0.875), PTFE nanofibers formed along cracks as a result of shear localization and significant softening caused by plastic deformation. The Zerilli-Armstrong constitutive equation for polymeric solids was used to simulate the response of the composite. Its use is justified by the fact that the majority of plastic strain is concentrated in the PTFE polymer. (c) 2007 Elsevier B.V. All rights reserved.