Photoelastic Effect
Definition and meaning of Photoelastic Effect in chemistry.
Photoelastic effect is the phenomenon where a transparent material becomes optically birefringent when subjected to mechanical stress, causing the material to change how it transmits polarized light. The degree of induced birefringence is directly proportional to the difference between the principal stresses at each point in the material (the stress-optic law).
In more detail
When stress is applied to an optically isotropic transparent material such as glass or acrylic resin, the material's refractive indices change in different directions according to the stress applied. This induces birefringence: light polarized in different directions travels at different speeds through the stressed region. When linearly polarized light passes through a stressed material and then through a second polarizer (analyzer), interference between the two light components produces colored fringe patterns. The fringe pattern directly maps the stress distribution throughout the material, allowing engineers and materials scientists to visualize and measure internal stresses without damaging the specimen.
Key facts
| Field | Physical Chemistry |
|---|---|
| Phenomenon type | Stress-induced birefringence |
| Common materials | Glass, acrylic, polycarbonate, epoxy resins |
| Governing principle | Stress-optic law (birefringence proportional to principal stress difference) |
A transparent plastic disk compressed between opposing forces displays colored interference fringes when viewed under crossed polarizers. The color and spacing of the fringes indicate stress magnitude and direction at each point in the disk.
Frequently asked questions
Why is the photoelastic effect useful in engineering?
It provides a direct visual method to observe stress distributions inside loaded materials and components without damaging them, enabling engineers to validate designs and identify stress concentrations.
Is the photoelastic effect reversible?
Yes, the birefringence and color fringes disappear when mechanical stress is removed, though some materials may retain permanent deformation at high stress levels.