The uniaxial compression stress-strain curves of the loading and unloading cycle and the corresponding maximum points of yield for poly(methyl methacrylate) in the temperature range, T= 233-343 K and engineering strain range, ~t= 10-4-10 -1 s -1 are measured. A micromechanics model for the thermally activated plastic deformation of glassy polymer is suggested and the exact theoretical expression for plastic strain rate, ~p, is obtained. The thermodynamic parameters characterizing the plastic deformation process, including activation volume, V~, activation enthalpy, AH, and activation entropy, AS, and their curved profiles changing with condition variables T and ~t are provided. The number of structural repeat units in a V~ for various T and ~t values are calculated. The changing trends of parameters AH and AS with V~ and the relationships between AH and AS for various T and ~t are presented and compared with that between AHm and ASm for viscous flow in the molten state of the same polymer. The results show that the plastic deformation of glassy polymer can be regarded thermodynamically as the non-Newtonian viscous flow of overcooled melt.
Посилання на статтю:
Analysis of thermally activated plastic deformation for glassy polymer poly(methyl methacrylate) / X. X. Zhu and G. R. Zhu // Polymer. – 1992. – Vol 33. – P. 4968-4976.