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2 results on '"Schmitt, Nicolas"'

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

Author

Frédy, Carole, Canto, Rodrigo B., Schmitt, Nicolas, Roux, Stéphane, and Billardon, René

Subjects
*POLYTEF, *POWDERS, *MECHANICAL behavior of materials, *VISCOSITY, *SINTERING, *MATHEMATICAL models, *FINITE element method, *HYDROSTATIC pressure
Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2013
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2. On the formation of defects induced by air trapping during cold pressing of PTFE powder.

Author

Gamboni, Otávio C., Riul, Cassius, Billardon, René, Bose Filho, Waldek W., Schmitt, Nicolas, and Canto, Rodrigo B.

Subjects
*POLYTEF, *FLUOROCARBONS, *POLYMERIZATION, *POLYMER colloids, *POLYMERS, *HYDROGELS, *COLLOIDAL gels, *BIOMACROMOLECULES
Abstract

The manufacturing of polytetrafluoroethylene products is usually carried out by cold isostatic and/or uniaxial pressing of the powdered polymer, followed by sintering of the “green” parts. During pressing, the air initially present in the loose powder leads to the formation of defects in the material, but the mechanisms involved are not entirely understood. The aim of this study was to better understand the role played by the entrapped air during the cold pressing of polytetrafluoroethylene powder. Observation of the microstructure and determination of some mechanical properties of green and sintered samples, manufactured with different quantities of entrapped air by the cold isostatic pressing process, were carried out. The analysis indicated that defects are formed when the entrapped air pressure in the pressed part leads to internal stresses exceeding the intergranular cohesion resistance of the green part. These defects remain in the microstructure even after sintering, considerably reducing the mechanical strength. [ABSTRACT FROM AUTHOR]

Published
2016
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