Toughness characterization of a metal filled PolyTetraFluoroEthylene using the J-integral

Abstract

PolyTetraFluoroEthylene (PTFE) is a semi-crystalline polymer that demonstrates a range of fracture properties when tested at various temperatures and loading rates. The addition of a powdered aluminum filler to obtain enhanced mechanical properties results in a multiphase material containing crystalline, amorphous and filler phases. In this work fracture toughness is measured for the aluminum filled PTFE material over a range of test temperatures and loading rates using a version of the ASTM E1820 normalization method and the non-linear elastic J-integral. The normalization method works exceptionally well for this material to define both the initiation fracture toughness and the J-integral resistance curves over a wide range of test conditions. When this material is loaded at modest rates, at or above ambient temperature it demonstrates a high toughness behavior, but if the test rate is elevated to 25 mm/s or above the fracture toughness rapidly falls. On the other hand, if elevated temperatures or slow loading rates are used, time-dependent crack growth is observed, and the fracture toughness in this instance is also very low. Scanning electron microscope observations show that very different micromechanical mechanisms exist under these different loading conditions resulting in the dramatic changes in material toughness observed.