Stress tensor measurement using birefringence in oblique transmission |
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Authors: | T Takahashi Prof G G Fuller |
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Institution: | (1) Mechanical Engineering, Nagaoka University of Technology, Nagaoka, Niigata, Japan;(2) Chemical Engineering, Stanford University, 94305-5025 Stanford, California, USA |
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Abstract: | A method for measuring the stress tensor of liquids obeying the stress-optical rule is presented. In particular, the procedure makes it possible to determine the shear stress, and the first and second normal stress differences for rheometric flows. This technique is an extension of the procedure recently described by Burghardt and coworkers (Brown et al., 1995) 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 Madga et al. (1993) 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. |
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Keywords: | Birefringence stress tensor rotational rheometer first normal stress difference second normal stress difference |
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