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Polariscope

The document describes two types of polariscopes - plane and circular. A plane polariscope uses two linear polarizers to produce plane polarized light that passes through a stressed specimen, following the direction of principal stress. This produces a fringe pattern seen through the analyzer consisting of isochromatics and isoclinics. A circular polariscope adds quarter-wave plates to convert the light to circular polarization when passing through the sample, then back to linear, eliminating isoclinics and simplifying the fringe pattern. Both setups allow examination of stress distributions in models through photoelastic birefringence effects.

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Talha Jalil
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283 views16 pages

Polariscope

The document describes two types of polariscopes - plane and circular. A plane polariscope uses two linear polarizers to produce plane polarized light that passes through a stressed specimen, following the direction of principal stress. This produces a fringe pattern seen through the analyzer consisting of isochromatics and isoclinics. A circular polariscope adds quarter-wave plates to convert the light to circular polarization when passing through the sample, then back to linear, eliminating isoclinics and simplifying the fringe pattern. Both setups allow examination of stress distributions in models through photoelastic birefringence effects.

Uploaded by

Talha Jalil
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Polariscope

Plane Polariscope
• The setup consists of two linear polarizers and a light source.
• The light source can either emit monochromatic light or
white light depending upon the experiment.
• First the light is passed through the first polarizer which
converts the light into plane polarized light.
• The apparatus is set up in such a way that this plane polarized
light then passes through the stressed specimen.
• This light then follows, at each point of the specimen, the
direction of principal stress at that point.
• The light is then made to pass through the analyzer and we
finally get the fringe pattern.
• The fringe pattern in a plane polariscope setup consists of
both the isochromatics and the isoclinics.
Analyzer
Circular Polariscope
• In a circular polariscope setup two quarter-wave plates
are added to the experimental setup of the plane
polariscope. .
• The effect of adding the quarter-wave plate after the
source-side polarizer is that we get circularly polarized
light passing through the sample.
• The analyzer-side quarter-wave plate converts the
circular polarization state back to linear before the
light passes through the analyzer.
• The basic advantage of a circular polariscope over a
plane polariscope is that in a circular polariscope setup
we only get the isochromatics and not the isoclinics.
• This eliminates the problem of differentiating between
the isoclinics and the isochromatics.
Quarter Wave Plate Analyzer
Bar with hole
Light source:
 White light from a fluorescent tube,
which is supported by two bulbs to
achieve uniform light diffusion.

 Monochromatic light produced by a


sodium vapour lamp.
Summary
• The photoelastic effect (alternatively called the piezo-optical effect) is the change of
refractive index caused by stress. Applications of photoelasticity involve applying a given
stress state to a model and utilising the induced birefringence of the material to examine
the stress distribution within the model. The magnitude and direction of stresses at any
point can be determined by examination of the fringe pattern, and related to the studied
structure.
• 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). If the source light is monochromatic these appear as dark and light fringes,
whereas with white light illumination coloured fringes are observed. The difference in
principal stresses is related to the birefringence and hence the fringe colour through the
Stress-Optic Law.
• Isoclinic fringes occur whenever either principal stress direction coincides with the axis of
polarisation of the polariser. Isoclinic fringes therefore provide information about the
directions of the principal stresses in the model. When combined with the values of (σP -
σQ) from the photoelectric stress pattern, isoclinic fringes provide the necessary
information for the complete solution of a two-dimensional stress problem.

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