Stress tensor measurement using birefringence in oblique transmission

Abstract

A method for measuring the full sterss tensor of liquids obeying the stress-optical rule is presented. This technique is an extension of the procedure recently described by Burghardt and coworkers 4) wherein light is sent obliquely through a sample sheared between transparent plates. However, in the present development, the light is transmitted in the plane containing the velocity gradient and neutral directions, thereby reducing the necessary optical measurements by one. A polystyrene-tricresyl phosphate (TCP) solution is used as the test sample. The first and second normal stress differences in steady shear flow measured by this method show good agreement with the mechanical results measured by Magda et al.1) using a modified cone and plate rheometer. The transient behavior of the first and second normal stress differences following the start-up of shear flow is also presented.