Stress-optical analysis of fluids

Summary Recent advances in Rheology have emphasized the necessity of measuring the stress distribution in flowing viscoelastic fluids which is qualitatively different from the one in Newtonian liquids. The use of flow-birefringence for this purpose has advantages. The concept of the stress-optical coefficient, well known in the stress optical analysis of solids, can be also applied to fluid flow. The extinction angle determines the recoverable shear strain,s a parameter in the flow of viscoelastic fluids. This would mean that mechanical and optical flow phenomena are caused primarily by stresses, not by the rate of shear. Experimental results presented confirm this postulate.