D. Penumadu, J. A. Yamamuro, A. E. Abrantes, G. A. Campbell
June 21, 2013
A series of experiments were performed on an assembly of four commercially available polymer pellets at room temperature. An automated deformation controlled triaxial testing system was used for the entire testing program. Lubricated end platens were used to assure uniform strain conditions during the application of compressive loading on the confined cylindrical specimen of a given polymer pellet type at a target bulk density. The test results in terms of the deviator stress-strain and volume change characteristics of polymer pellets were obtained for use in the modeling and analysis of solids conveying in plasticating screw extruders. Testing procedures are described that can be used routinely to obtain the strength and deformation behavior of an assemblage polymer pellets. The deviator stress-axial strain and volumetric strain-axial strain curves are presented for four confining stress levels (l00, 200, 300 and 400 k Pa) for these materials using both dry and saturated specimens. The water saturated specimens were used in parallel for obtaining reliable measurements of the volumetric strain variation during the application of deviator stress. The effect of using water as the pore fluid on the mechanical behavior was also discussed. The angles of internal friction of these four polymeric materials were determined and the use of Mohr-Coulomb failure criteria was evaluated. These confining pressure dependent friction angles are compared with the angle of repose measurements. The stress transfer coefficients as a function of wall friction for the potential states of confinement of these polymer pellets in the solids conveying portion of an extruder are also summarized.