Facultatea de Fizică
Universitatea "Al.I.Cuza" Iaşi
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| Titlu: The experimental analysis of mechanical stress Two-dimensional photoelasticity |
| Autori: Ecaterina Angheluta, Alina Rogojanu, Dana Ortansa Dorohoi |
| Afiliere: Faculty of Physics, “Al. I. Cuza” University, 700506 Iasi, Romania |
| Abstract: Photoelasticity [1] is an experimental method to determine stress distribution in a material. Unlike the analytical methods of stress determination, photoelasticity gives a fairly accurate picture of stress distribution even around abrupt discontinuities in a material. The method illustrated here serves as an important tool for determining the critical stress points in a material and is often used for determining stress concentration factors in irregular geometries. The method is based on the property of birefringence, which is exhibited by certain transparent materials. Birefringence is a property by virtue of which a ray of light passing through a birefringent material experiences two refractive indices. The photoelastic materials exhibit the property of birefringence only on the application of stress and the magnitude of the refractive indices at each point in the material is directly related to the state of stress at that point. Thus, the first task is to develop a model made out of such materials. The model has a similar geometry to that of the structure on which stress analysis is to be performed. This ensures that the state of the stress in the model is similar to the state of the stress in the structure. The two waves are brought together in a polariscope. The phenomena of optical interference take place and we get a fringe pattern, which depends on relative retardation. Thus studying the fringe pattern one can determine the state of stress at various points in the material. Isoclinics are the locus of the points in the specimen along which the principal stresses are in the same direction. Isochromatics are the locus of the points along which the difference in the first and second principal stress remains the same. Thus they are the lines which join the points with equal maximum shear stress magnitude.[1] http://en.wikipedia.org/wiki/Photoelasticity |
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