The Society of Rheology: 69th Annual Meeting (Oct 1997) Abstract of Paper

Title	THE USE OF GENERALIZED STRAIN MEASURES IN A THERMOVISCOELASTIC CONSTITUTIVE EQUATION FOR AMORPHOUS POLYMERS
Authors	P. Shirkhande, M.R. Hooker, and J.M. Caruthers
Address	School of Chemical Engineering, Purdue University, West Lafayette, IN 47907-1283

Using the framework of Rational Mechanics as developed by Coleman (Arch. Rat. Mechan. Anal., 1964), thermoviscoelastic constitutive equations for amorphous fluids and solids have recently been developed (Lustig, et al, J. Rheol., 1996), where relaxation occurs on a material timescale t*. During the development of these constitutive equations, the nonequilibrium Helmholtz free energy was expanded in a Frechet series in terms of the temperature and deformation histories, where the deformation was given in terms of right Cauchy-Green deformation tensor C for solids and the relative reight Cauchy-Green deformation tensor Ct for fluids. Objectivity and material symmetry only require that the constitutive functionals depend upon C or Ct; however, the constitutive functionals could just as well depend upon any functon of C or Ct. We have introduced generalized deformation tensors, which are arbitrary functions of C or Ct respectively, and then rederived the relevant constitutive equations. For situations where there is no rotation of the principal axes of defromation, the resulting constitutive equations are structurally similar, where there is only a change in the strain measure; however, for deformations that include rotation of the axes there are additional couplings between the various components in the stress constitutive equation. The predictions of the new constitutive equations have been compared with nonlinear viscoelastic data for an epoxy resin system, whre predictions using the generalized deformations are better able to describe the experimental data. We believe that the constitutive equations reproted in this communication using the generalized deformation tensors are the most general formulation consistent with the principles of Rational Thermodynamics for a rheologically simple material, where the vicoelastic relaxation occurs on a material timescale.

Session	Rheology of Solids
Date	Monday, October 20, 1997
Time	1:55
Room	Senate

Name	E-mail
Shirkhande, P	No Entry
Hooker, M R	No Entry
Caruthers, James M	Caruther@ecn.purdue.edu

69th Annual Meeting (Oct 1997)

Abstract of Paper SL7

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Abstract