Photoelasticity

As photoelasticity a branch of optics or the design theory is referred to, in the polarized by the use of light, the stress distribution is investigated in translucent bodies. At transparent, two-dimensional workpiece models particularly high stress are visible under mechanical stress points.

Basis is the property of many of optically isotropic materials, to be birefringent under mechanical stresses. Wherein the polarization plane of the incident light is rotated or it is formed elliptical or circularly polarized light. This can be visualized using a polarimeter.

By using monochromatic light results in a system of dark and light stripes, the arrangement allows reliable conclusions on the distribution and abundance of the mechanical stress on all parts of the body.

In the image produced at a loaded by forces specimens two types of dark bands: the isochromats are lines with constant principal stress difference, the isoclines the direction of a main voltage coincides with the polarization direction of the incident light, they thus represent the stress trajectories of the body of the given load.

To distinguish between isochromatic and isoclinic, the loaded sample ( or the polarization direction of the light ) are rotated - in the photoelastic image change by the isoclines, but not the isochromates. Another possibility is the use of circularly polarized light, - in this case, no visible isoclines (lower two images ).

If white light is used, created for each color different light-dark pattern - this gives the color pattern, as shown on the left. Only in the case of the 0 order of the stripes fall all the colors together. This results in black bars on the unloaded sites in the sample ( lower corner of the angle ).

In the quantitative analysis, one starts from a plane stress. The two principal strains in the sample plane of the material influence the refractive index, the third principal stress in the thickness direction has no effect.

This method is still occasionally used in the testing of materials by transparent resin models (with optical activity ) were examined for the stresses which can occur in practical applications. The voltage distribution in the model is consistent with that in the real component, even if the deformation is different.

The improved method of calculation using the finite element method, these studies are mainly carried out on the computer today.