The effect of inlet angles of a tapered channel on viscoelastic flows in a Maxwell model was numerically investigated by the perturbation method using oblique coordinates. These results have shown that the characteristic flow pattern of viscoelastic liquids such as a shape of a wine glass is produced by the sudden contraction into the slit rather than by turning round the corner, and, in addition, that the inlet angle of a tapered channel has little effect on the shape of the main flow.

View full abstract

In order to establish the relationship between the distribution function F_τ(τ) of relaxation time τ and the shape and the characteristic parameters of dynamic loss tangent (tanΔ)-temperature (T) curves, theoretical equations representing tanΔ-T curves are derived; seven functions given by F_τ(τ)=k_n'τⁿ' and three functions given by triangles. WLF and Arrhenius types are assumed for temperature dependence of τ. On the basis of these theoretical equations, tanΔ-T curves are numerically calculated. In the case of n'_??_0, the peak value of tanΔ-T curve, (tanΔ)_max, peak temperature T_max and the ratio of half value width ΔT_1/2/ΔT_{1/2 (s)} (the suffix s indicates the system composing of a single relaxation time) depend on those factors as the average relaxation time τ, F_τ, the total number of Maxwell elements in a system N, the ratio of elastic modulus before and after relaxation α, and the minimum relaxation time τ_l in F_τ(τ). In the case of n'_??_-0.5, a significant shoulder is observed on tanΔ-T curves in the lower temperature region than T_max. The necessary condition to have this shoulder is (tanΔ)_max_??_3.5/(n'+3)⁴ and N_??_√<10>, The tanΔ-T curve (especially, ΔT_1/2/ΔT_{1/2 (s)} ), measured in the temperature range in which appears the dynamic absorption arising from microbrownian movement of polymer segments in amorphous region of semi-crystalline polymers (α_a), is remarkably different from that calculated by using the above mentioned functions for F_τ(τ). Contrary to this, tanΔ-T curves determined experimentally in the temperature range of α_a absorption of amorphous polymers are in good agreement with those calculated by using n'=-2-0. In the actual experiment, no shoulder, is observed on tanΔ-T curves for both amorphous and semi-crystalline polymers.

View full abstract

This paper outlines the way to measure the bending length of comparatively stiff fabrics by the Clark method, and presents the theoretical basis of this method. We derived the relation theoretically between the bending length and the hanging length of the specimen at the critical angle at which swing back occurs on the assumption that the test specimen is completely elastic. This theory is applicable to measure the bending length by the Clark Stiffness Tester, which correlates well to the 41.5° cantilever method. But the Clark method gives approximately 10% smaller values than the 41.5° cantilever method.

View full abstract