photoelasticitymenetelmissä

Photoelasticity methods, also known as photoelasticity, refer to a family of experimental stress analysis techniques based on the birefringence property of certain transparent materials. When such materials are subjected to mechanical loading, the stress distribution induces a variation in refractive indices, leading to the formation of interference fringe patterns under polarized light. These fringe patterns provide qualitative and quantitative information about the stress field inside the specimen. The basic principle, first described by Gustav Anton von Arens in the late 19th century, relies on the Hooke’s law relationships between stress and refractive index change, expressed through the stress-optic coefficient of the material.

The most common modes of photoelasticity include the conventional or static method, time‑dependent (dynamic) photoelasticity, and the continuity‑based method. In the static method, a static load is applied and the fringe pattern is recorded, typically using a recording system such as a photographic camera. For dynamic loading conditions, high‑speed cameras and stroboscopic illumination allow the capture of fringe evolution over time. The continuity‑based method further refines the analysis by using known stress boundary conditions to invert the fringe data, often through numerical techniques or least‑squares fitting, enabling the extraction of precise stress values.

Applications of photoelasticity span structural engineering, aerospace, automotive, and civil engineering, where complex geometries and load paths make analytical solutions difficult. The technique excels in providing full‑field stress distribution, assisting in verification of finite element models, and diagnosing stress concentrations around notches, holes, and welds. Despite the advent of digital image analysis, photoelasticity remains valuable because it offers direct, visual evidence of stress behavior and can be performed on scaled physical models. The method requires careful preparation of model specimens, precise alignment of polarizing filters, and accurate calibration of the stress‑optic coefficient to ensure reliable results.