Modelling of the mechanical behaviour of two pure PTFE powders during their compaction at room temperature

Since PolyTetraFluoroEthylene (PTFE) is not melt processible because of its very high melt viscosity, parts made of this material are generally manufactured by cold compaction of powder material followed by sintering of the green compact. The aim of this study is to identify 3-D constitutive equations suitable for the finite element analysis of PTFE powder compaction. To exhibit the influence of their geometrical aspect on their mechanical behaviour, two pure PTFE resins were tested, viz. a free flowing pelletized resin and a granular fine cut resin. To study the behaviour of these powders during their compaction along different loading paths, a novel triaxial device has been designed and installed on a six-actuator triaxial testing machine. The results obtained for hydrostatic loading were favourably compared with results obtained by isostatic pressing. Various complex loading paths were also investigated. Full 3D elasto-viscoplastic non-associated constitutive equations, viz. a non-linear Drucker-Prager/cap type model, could be identified.