Fringe patterns in integrated photoelasticity

In integrated photoelasticity the measurement data may be strongly influenced by the rotation of the principal stress axes. By pointwise measurements, usually the characteristic directions and optical retardation are determined and on their basis conclusions about the stress distribution along the light beam are made. However, often the integrated fringe pattern, obtained in a circular polariscope, can be recorded. This fringe pattern is determined by the integrals of the principal stresses as well as by the rotation of the principal stress directions. We consider the effect of rotation of the principal stress axes in the general form. It is shown that the rotation diminishes the distance between interference fringes and the contrast of the fringe pattern is also diminished.