ISSN:
1435-1528
Keywords:
Linear viscoelasticity
;
thermorheological simplicity
;
material-specific function
;
nonlinear constitutive equation
;
strain measure
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Abstract In linear viscoelastic investigations the frequency dependence of the phase shift between stress and strain appears to be very characteristic of the molecular structure of the material. This function is also a good approximation of the slope of the double logarithmic plot of the absolute value of the shear modulusG d vs. the angular frequencyω. The product (G d /π) sin 2δ comes very close to the relaxation spectrumH(τ), withτ = 1/ω, in all physical states of the material. The experimentally observed separability of time and strain effects in nonlinear viscoelasticity of highly viscous isotropic polymer fluids imposes restraints to the form of the constitutive equation. A single integral superposition equation of the Boltzmann type containing the product of a time function and a nonlinear strain function gives good results in describing experimental data in shear as well as in elongation. The molecular structure affects both functions in a different way. A universal definition of the nonlinear tensorial strain measure has not yet been developed. There are some indications that a definition on the basis of the principal stretch ratios may be fruitful.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01534297
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