改良したワイセンベルグ・レオゴニオメーターによる非定常法線応力差の測定

抄録

It has been pointed out by many investigators that the servo system of the Weissenberg Rheogoniometer may not be suitable for the measurement of transient normal stress in polymer solutions and melts. In the present study, transient normal stress was measured by a modified Weissenberg Rheogoniometer with cantilevers of different stiffnesses for polymer solution. Experimental results were compared with those taken by the original servo system. Conclusions obtained in this study are as follows:
(1) Steady value of normal stress can be measured within experimental error of 5%, when the gap change induced by the stress between cone and plate is less than 9 μ in steady state.
(2) The time when the normal stress reaches its maximum at the start of steady shear flow depends on stiffness of the cantilever. For obtaining a correct normal stress development curve, maximum gap change should be less than 2.5 μ.
(3) Apparent relaxation time for normal stress relaxation after cessation of steady shear flow depends markedly on stiffness of the cantilever.
(4) The servo system of the Weissenberg Rheogoniometer does not give correct values of normal stress for either stress development or stress relaxation experiment. However, the error is evaluated to be less than 10% for experimental conditions employed in this study.
(5) Both steady and transient shear stresses are little affected by the normal stress measurement system when the torsion rod used is stiff enough.