Al-PTFE (Al-polytetrafluoroethene) is an important kind of Reactive Material (RM), however only limited importance was placed to the effect of crystallinity of PTFE on the mechanical and reactive behavior. This paper investigated the influence of crystallinity on the compression behavior of Al-PTFE at strain rates range from 10 −2 to 3 × 10 3 s −1 . Two kinds of samples were prepared by different sintering procedures to acquire different crystallinity. The samples' crystallinity was characterized by the density method and X-ray diffraction method. The samples were tested using an electro-hydraulic press for quasi-static loading, and split Hopkinson pressure bars (SHPBs) for high strain rates. Low crystalline samples have consistently higher strength and toughness than the high crystalline samples. The phenomenon was explained by an "elastic-plastic network" model combined with the effect of chain entanglement density. A bilinear dependence of true stress on logε was observed, and Johnson-Cook models were fitted separately according to the different strain rate sensitivity. Finally, a close connection between fracture and initiation of Al-PTFE was confirmed in quasi-static tests, SHPB tests, and drop weight tests. It was hypothesized that the high temperature at the crack tips of PTFE is an important promoting factor of initiation.
Conventionally, the Al-PTFE is thought to be inert under quasi-static or static loads. However, here we reported an initiation phenomenon of Al-PTFE under quasi-static compression. Quasi-static tests suggest that reacted Al-PTFE samples had much higher toughness than unreacted samples. Dynamic test showed that the energy level needed to initiate the material was similar for quasi-static compression (88–100 J) and dynamic impact (77–91 J). The difference in density indicates that unreacted Al-PTFE has a higher crystallinity, which leads to the lower toughness. SEM images show numerous PTFE fibrils in unreacted composites which made the sample harder to crack and initiate.
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