A constitutive model in linear thermoviscoelasticity of polymers based on the concept of cooperative relaxation |
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Authors: | Aleksey D Drozdov |
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Institution: | (1) Institute for Industrial Mathematics, 4 Hanachtom Street, Beersheba, 84311 Israel , IL |
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Abstract: | New constitutive relations are derived for amorphous glassy polymers based on the concept of cooperative relaxation. A polymer
is treated as a system of rearranging regions (flow units) embedded into a homogeneous elastic matrix. The viscoelastic (time-dependent)
response of a medium is explained by rearrangements of segments of long chains in relaxing regions which occur at random instants.
The kinetics of rearrangement is described in the framework of the Eyring concept of thermally activated processes, whereas
the energy of any flow unit is assumed to randomly change at the instant of its reformation. Based on experimental data, phenomenological
formulas are proposed for material functions. Adjustable parameters are found by fitting observations for mixtures of nylon
with lithium halides in isothermal tensile relaxation tests. The thermoviscoelastic response in other tests is studied numerically.
It is demonstrated that the material behavior predicted by the constitutive model in non-isothermal tests substantially differs
from that predicted by conventional models whose adjustable parameters are determined by using the same experimental data.
Received September 30, 1998 |
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