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Photoelastic Experiments

Photoelastic Experiments. Andrew Pskowski Arif Patel Alex Sheppard Andrew Christie. Elliptical Polarization. E-electric vector however can also be regarded as light vector =phase increase =variable part of phase factor Curve which is described by end point of light vector

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Photoelastic Experiments

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  1. Photoelastic Experiments Andrew Pskowski Arif Patel Alex Sheppard Andrew Christie

  2. Elliptical Polarization • E-electric vector however can also be regarded as light vector • =phase increase • =variable part of phase factor • Curve which is described by end point of light vector where and are coordinates

  3. Elliptical Polarization • Want to eliminate • After some algebra

  4. Elliptical Polarization • Squaring and adding • a1 and a2 are half the sides of a rectangle which the ellipse is circumscribes in

  5. Circular Polarization a1=a2=a (rectangle now square) , Quarter plate causes this change

  6. Right Handed Right Handed-viewing from source light waves travel clockwise

  7. Left Handed Left Handed-viewing from source light waves travel counter-clockwise

  8. Photoelasticity • It an experimental method used to study the stress distribution in a model. • It involves inducing birefringence on the material being studied. • Our experiment uses 2D photoelasticity.

  9. Birefringence • It is the splitting of a ray of light into two rays when it passes through a material. • It is a property of certain transparent materials. • It occurs when the material is stressed. • It creates fringes or stress patterns.

  10. Birefringence • Each point of interest has a principal stress direction. This is where the only stresses present are normal stresses. • Polarized light transmitted through a birefringent material splits into two light rays, each traveling at different velocities parallel to one of the two principal stress directions. 2nd principal stress direction 1st principal stress direction 1st principal stress direction

  11. Polariscope Light Source Specimen observer First Polarizer Second Polarizer

  12. Picture of our setup Top view Front view

  13. No Polarized Filter Polarized Filter Experimental Pictures

  14. Image Processing • Can be low or high level • Our task is fairly low level because it requires very rigidly defined input • Low level processing typically uses filtering or morphological operations • Filtering can be in spatial or frequency domain

  15. Filtering • Edge detection is a common filtering task • Sobel operator is commonly used here • Based on central difference approximation • Template matching is also based on filters

  16. No Polarized Filter Polarized Filter Processing Images Determine Centers, Diameters Extract Forces

  17. Method Used • Create an Ideal Particle Image D = 12; w = 1.05

  18. Finding Position and Diameter • Search for minimum difference between ideal particle and real particle • Use least squares fitting and convolution

  19. Coloring Particles Based on Force • Use the location of particles from the non-polarized images • Average the ‘intensity’ inside of each particle from the polarized image • Create a new image with • Color the each particle with the average intensity

  20. Processed Image

  21. References • Born,Max and Emil Wolf. Principles of Optics. Cambridge: Cambridge University Press, 1999. • http://www.doitpoms.ac.uk/tlplib/photoelasticity/history.php • http://en.wikipedia.org/wiki/Photoelasticity • http://gibbs.engr.ccny.cuny.edu/technical/Tracking/ChiTrack.php

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