Photoelasticity: Investigating the distribution of strains in mechanically stressed bodies

In the experiment P5.4.2.3, the magnitude and direction of mechanical stresses in transparent plastic models are determined. The plastic models become optically birefringent when subjected to mechanical stress. Thus, the stresses in the models can be revealed using polarization-optical methods. For example, the plastic models are illuminated in a setup consisting of a polarizer and analyzer arranged at right angles. The stressed points in the plastic models polarize the light elliptically. Thus, the stressed points appear as bright spots in the field of view. In another configuration, the plastic models are illuminated with circularly polarized light and observed using a quarter-wavelength plate and an analyzer. Here too, the stressed points appear as bright spots in the field of view.