Predicting plastic energy dissipation (PED) using phenomenological constitutive equations for glassy and semi-crystalline polymer solids

It has been experimentally demonstrated that Plastic Energy Dissipation (PED) is a dominant melting mechanism in twin-rotor co- and counter-rotating processing equipment. Such devices force compacted polymer particulates to undergo repeated compressive, volume-wise, large compressive deformations, resulting in massive dissipative heating of the solid particulates and rapid melting. The large magnitude of PED has two important consequences: it results in very rapid end efficient volume-wise melting, enabling very fast processing rates and produces a very narrow "age distribution" melt, important for reactive processing. To date the experimental evaluation of PED, during large unconfined compressive cylindrical sample deformations, at appreciable strain rates, can be used to arrive at reasonable engineering estimates of the melting lengths for given polymers in specific processing equipment operating under given processing conditions. But this task involves a large number of PED-evaluation experiments, because of the lack of constitutive equations which are capable of describing the compressive stress-strain behavior of solid polymers at "engineering" strains and strain rates. The object of this presentation is to evaluate and modify existing constitutive relations for amorphous polymers using the large experimental date that have been generated in our laboratories. An acceptable constitutive relation will not only reduce the number of experiments necessary to evaluate PED and estimate melting lengths, but a needed element in the development of PED melting simulation models.