What is the theory of Photoelasticity?
Photoelasticity describes changes in the optical properties of a material under mechanical deformation. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a material, where it gives a picture of stress distributions around discontinuities in materials.
What does Photoelasticity measure?
Photoelasticity is a whole-field technique for measuring and visualizing stresses and strains in structures. When white light is used for illumination, a colourful fringe pattern reveals the stress/strain distribution in the part. Qualitative analysis such as strain concentration points, uniform stress regions etc.
How is polarization used in stress analysis?
Polarized light reveals stress patterns in clear plastic. When certain plastics are placed between two pieces of polarizing material, their stress patterns become dramatically visible in a brightly colored display. A stressed plastic object can be used to illustrate stresses found in bones.
What are fringes in photoelasticity?
The photoelastic effect (alternatively called the piezo-optical effect) is the change of refractive index caused by stress. Two different types of fringes can be observed in photoelasticity: isochromatic and isoclinic fringes. Isochromatic fringes are lines of constant principal stress difference, (σP – σQ).
What are the requirements in selection of photoelastic materials?
1.0 Method of Plastic Application. Photoelastic coatings are available in two basic forms:
What are isochromatic and Isoclinic fringes?
a. Isochromatic fringes are obtained using monochromatic light, whereas isoclinic fringes are obtained using white light. b. Isoclinic fringes are obtained when the principal stress direction coincides with the polarisation of the polariser; isochromatic fringes are lines of constant stress difference.
What is Fringe Photoelasticity?
What is a photoelastic material?
A photoelastic material is one that has a stress dependent refractive index. When placed between crossed polarizers, the rotation of the polarized light by the stress field in the material generates a fringe pattern displaying contours of equal stress.
What is isochromatic fringe pattern?
Isochromatic fringes are lines of constant principal stress difference, (σP – σQ). If the source light is monochromatic these appear as dark and light fringes, whereas with white light illumination coloured fringes are observed.
What is the unit of material stress fringe value?
A quantity used in photoelastic work, equal to the stress which must be applied to a material, in pounds per square inch (1 pound per square inch equals approximately 6.89476 kilopascals), to produce a relative retardation of 1 wavelength between the components of a linearly polarized light beam when the light passes …
What are fringes in Photoelasticity?
Is it possible to express photoelasticity in terms of mechanical stress?
Although the symmetric photoelastic tensor is most commonly defined with respect to mechanical strain, it is also possible to express photoelasticity in terms of the mechanical stress . The experimental procedure relies on the property of birefringence, as exhibited by certain transparent materials.
What is the history of photoelasticity in industry?
The treatise by Coker and Filon (3.1) and the works of M.M. Frocht (3.2) were pioneering in exploring the various aspects and applications of Photoelasticity. Since then the method has been widely used in industry as a means of two and three dimensional stress analysis (3.3 − 3.11).
Can photoelasticity be applied to three-dimensional systems?
Photoelasticity can describe both three-dimensional and two-dimensional states of stress. However, examining photoelasticity in three-dimensional systems is more involved than two-dimensional or plane-stress system.
Is photoelasticity optically isotropic?
Wei-Chih Wang Department of Mechancial Engineering University of Washington W.Wang 1 Photoelasticity Wei-Chih Wang Department of Mechancial Engineering University of Washington W.Wang 2 Photoelasticity Many transparent noncrystalline materials that are optically isotropic when free of stress become optically anisotropic and