抄録
Theories on normal force effect have been proposed by several workers since Weissenberg's first investigation. In experiments, however, data on this effect are not enough to verify these theories in generality.
Two kinds of silicon oil were taken up as samples, one 104 centi stokes, the other 105 centi stokes. These samples were irradiated with a variety in radiation dose by γ ray from Co60. Normal force (σ11-σ22), steady flow viscosity over a range of shear rate from 10-2 to 102sec-1 and dynamic modulus and viscosity over a range of angular frequency between 5×10-2 and 3×10sec-1 were measured by a Weissenberg Rheogoniometer at 20°C. The variation of dynamic modulus and viscosity with the shear rate of superposed steady flow was also measured.
Silicon oils with more radiation dose have larger viscosity and normal force. It is found that the normal force of more irradiated specimen was larger than that of less irradiated ones though their viscosities were in the same magnitude. This is considered to be due to cross linkages in the materials.
Two kinds of molecular weight were determined: one according to the relation between molecular weight and viscosity which was treated as a linear molecule, the other according to the relation between molecular weight and radiation dose treated as cross linked materials.
The recoverable shear s was calculated from the values of shearing stress σ12 and normal force σ11-σ22 in steady flow. It was found that these silicon oils follow “Hooke's low in shear” from the linearity of plots in s against σ12.
The comparison of curves of dynamic viscosity against angular frequency and the steady flow viscosity against shear rate was made, and approximate equality of shear rate and angular frequency was seen.
The elastic modulus G and relaxation time τ in the sense of Maxwell model were calculated from both steady flow and dynamic experiments, making use of the equality of shear rate and angular frequency. The values of G and τ agreed in the order of magnitude in the range where normal force experiments were done.
