1990 Volume 18 Issue 4 Pages 180-189
Applicability of the Leonov constitutive model was investigated based on reliable experimental data on steady shear flow and stress relaxation after cessation of the flow for several concentrated polymer solutions and polymer melts. The following conclusions were obtained :
(1) Analytical solutions for stress components in steady shear flow and stress relaxation after cessation of the flow were derived from basic equations of the Leonov model in different ways from those of Leonov et al.
(2) Discrete relaxation time spectra were determined based on the dynamic viscoelastic data, assuming constant ratio τn/τn+1 for adjacent relaxation times and variable relaxation strength Gn.
(3) When the discrete relaxation time spectra were determined properly in wide range of time scales, the Leonov model could predict quantitatively the shear stress and the first normal stress difference in steady shear flow for all samples investigated.
(4) When the steady shear rate was high, the Leonov model gave much smaller stresses than experimental data at long time end of the stress relaxation. Since the first normal stress difference is underestimated in stress relaxation process, evaluation of flow birefringence and molecular orientation should be very careful when it is made based on the predicted stresses.
