How does photoelastic stress analysis work?

In photoelastic stress analysis, a reflective coating is applied to the surface of the object under investigation, and a tool such as a digital polariscope splits coherent, monochromatic light into two beams and shines them on the object through a system of polarizers.

What is the photoelastic method?

Photoelasticity is a whole-field technique for measuring and visualizing stresses and strains in structures. The method utilizes a birefringent model of the actual structure to view the stress contours due to external loading or residual birefringence.

What is photoelastic coefficient?

Photoelastic coefficient for a uniaxial crystal where “Δϵij is the change in the dielectric constant parallel and perpendicular to the direction of stress X.” In this definition they are using the dielectric constant (aka the permittivity) instead of the index of refraction.

What are photoelastic model materials?

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.

Where is photoelastic method used for?

The method is used primarily for analyzing two- dimensional plane problems, which is the emphasis in these notes. A method called stress freezing allows the method to be extended to three- dimensional problems. Photoelastic coatings are used to analyze surface stresses in bodies of complex geometry.

What are Isoclinic and Isochromatic?

Isoclinic fringes are lines of constant stress difference; isochromatic fringes are obtained when the principal stress direction coincides with the polarisation of the polariser.

How does a photoelastic modulator work?

The photoelastic modulator (PEM) is a resonant polarization modulator. It operates at the resonant frequency of a desired mechanical vibration mode of its optical element. The PEM is made of isotropic optical materials, in contrast to the birefringent materials used in electro-optic modulators.

What is the maximum stress concentration factor?

A stress concentration factor is the ratio of the highest stress (smax)) to a reference stress (s) of the gross cross-section. As the radius of curvature approaches zero, the maximum stress approaches infinity. Note that the stress concentration factor is a function of the geometry of a crack, and not of its size.

What is isochromatic fringe pattern?

[¦ī·sō·krə′mad·ik ′frinj ‚pad·ərn] (optics) A pattern of bands, each of uniform color, observed when a plate is placed in a polariscope and subjected to stress, making it birefringent.

What is PEM device?

A photoelastic modulator (PEM) is an optical device used to modulate the polarization of a light source. The photoelastic effect is used to change the birefringence of the optical element in the photoelastic modulator.

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.

How do you calculate birefringence?

Birefringence can be determined as it is the difference in the optical path (OPD) between the O- and E-rays, also known as the retardation, divided by the thickness t of the polymer part.

How do you test for birefringence?

Measurement. Birefringence and other polarization-based optical effects (such as optical rotation and linear or circular dichroism) can be observed by measuring any change in the polarization of light passing through the material. These measurements are known as polarimetry.

What is stress concentration chart?

A stress concentration factor (Kt) is a dimensionless factor that is used to quantify how concentrated the stress is in a mechanical part. It is defined as the ratio of the highest stress in the part compared to a reference stress.

What is a good stress concentration factor?

If the material is flawless with no discontinuities, then the stress concentration factor is 1. If there is a discontinuity, then the stress concentration factor is greater than 1.

How do you find KT?

kT = RT/N.