Mixed-mode-I/II fracture of polytetrafluoroethylene

The current work deals with mixed-mode-I/II fracture in polytetrafluoroethylene (PTFE). Mode-I fracture in PTFE 7C has previously been shown to exhibit strong phase dependence with a brittle-to-ductile transition associated with the room temperature phase transitions. Increases in fracture toughness around room temperature and above result from the onset of stable fibril formation bridging the crack plane and increased plastic energy dissipation. Mixed-mode-I/II loading conditions are achieved using a modified compact tension specimen with Arcan type fixtures. The fracture toughness (delta)VC of PTFE 7C exhibits a 42% decrease from pure mode-I to near mode-II loading due to a marked decrease in fibril formation.