R. Fulchiron et al., DETERMINATION OF THE ELONGATIONAL BEHAVIOR OF POLYPROPYLENE MELTS FROM TRANSIENT SHEAR EXPERIMENTS USING WAGNER MODEL, Journal of non-Newtonian fluid mechanics, 48(1-2), 1993, pp. 49-61
This work deals with the nonlinear viscoelastic behavior of commercial
polypropylenes on the basis of Wagner's constitutive equation. First,
shear dynamic experiments are performed to determine the relaxation s
pectrum assuming a log-normal law which is in agreement with the theor
y of linear viscoelasticity. Secondly, shear and elongation experiment
s are performed at constant strain rates to obtain the damping functio
n, while checking the separability assumption of the memory function i
nto a time-dependent linear function and a strain-dependent nonlinear
part. The damping function is described by a single law, partially ind
ependent of molecular parameters and which can be used either for shea
r or elongation flows through a general invariant of the relative Fing
er strain tensor.