Light Intensity in 3‐D Photoelastic Analysis

Abstract

Normalized minimum light intensity of a three‐dimensional photoelastic medium, measured in a direct illumination polariscope by crossed arrangement of filters, is explored as a reliable characteristic quantity. The variation of the light intensity, for a given wavelength, resulting from superimposing noncoinciding coplanar bending and membrane stresses is studied as a function of their ratio. The graphical representation of this relation yields interesting novel information. This relation has been formulated in a mathematical model that might be used to determine the ratio for measured values of the light intensity. An additional independent experimental set of data can be obtained by varying the wavelength of the light source. It is shown that the quality and interpretation of the data so obtained is affected significantly by the selected wavelength. Furthermore, it appears that the discrete representation of photoelastic medium as a pile of birefringent plates is applicable only for low values of the stress ratio.