Fotoelastsus

Fotoelastsus is a phenomenon where certain materials exhibit a change in their optical properties, specifically their refractive index, when subjected to mechanical stress. This means that when a transparent material is deformed, it can become birefringent, meaning it splits a beam of light into two components that travel at different speeds and are polarized perpendicular to each other. This induced birefringence is directly proportional to the applied stress or strain.

The effect was first observed by Sir David Brewster in 1816. Fotoelastsus is a consequence of the interaction between light and the atomic structure of the material. When stress is applied, the material's internal structure is distorted, leading to changes in the arrangement and spacing of its atoms and molecules. These alterations affect how light propagates through the material, causing the refractive index to vary depending on the direction of light polarization relative to the stress.

This photoelastic effect has significant practical applications. It is widely used in photoelastic stress analysis, a non-destructive testing method to determine stress distribution within a material. By observing the patterns of color or light intensity that appear when a stressed photoelastic material is viewed between two polarizing filters (a polariscope), engineers can visualize and quantify stress concentrations, which are crucial for designing safe and efficient structures and components. The colors observed are interference patterns that depend on the magnitude of the stress. Fotoelastsus is also utilized in optical devices and sensors.