A novel method for measuring the stress distribution of polymeric melts in flow fields by flow-induced birefringence

In order to calculate the stress distribution of the polymer melts in flow field, the conventional equipment of birefringence measurement is improved by reasonably rearrange the optical components in this paper, and a novel method to calculate the stress distribution of polymer melt in flow fields by measuring the flow-induced birefringence is proposed. The image obtained from this method contains both the information of the birefringence and the orientation angle, the orientation angle of the image is 45° where the light intensity gets maximum or minimum, so the shear stress alone the isoclinic line of an angle of 45° can be calculated, the deficiency of the conventional equipment that only used to measure the tensile stress along the axis of symmetry is overcome. In the last, the flow field of LDPE1810D in a self-made visualization die in extrusion condition was measured by using this equipment; the distribution of stress, along the isoclinic lines of an angle of 45°, was calculated. It is proved that this method is capable of the measurement of the birefringence of the flow fields, thus the stress distribution.