Experimental Mechanics @ Michigan State University
EM Basics: Spectral Contents Analysis in PEA
		Earlier developments were by Redner^1 and by Sanford and Igenyar^2. Essentially, for the point of interest the light intensity is collected over a range of wavelengths to form a spectrum. A theoretical model of the spectral contents of the point in a fringe pattern is fitted to the experimental data using the fringe order as the fitting parameter. The maximum fringe order that can be recognised is approximately equal to the number of wavelengths at which intensity information is collected ^3,4. Hence an RGB camera can be used to obtain fringe orders up to about three^5. No information about isoclinic angle is available. Recent work has produced significantly faster algorithms which do not need any a priori knowledge of the range of fringe order being measured6. The University of Sheffield has implemented the technology in a number of novel instruments.
Spectra for fringe orders of 0.5, 2.25, & 5.75
Obliquerscope for measuring individual principal stresses in reflection coatings using spectral contents analysis.		1. Redner, A.S., 1984, ‘Photoelastic measurements by means of computer assisted spectral contents analysis’ Proc. 5th Int. Conf. Experimental Mechanics, Montreal, pp.421-7. 2. Sanford, R.J., Igenyar, V., 1985, ‘The measurement of the complete photoelastic fringe order using a spectral scanner, Proc. SEM Spring Conf. Experimental Mechanics, pp. 160-8. 3. Carazo-Alvarez, J., Haake, S.J., Patterson, E.A., 1994, 'Completely automated photoelastic fringe analysis', Optics & Lasers in Engineering, 21:133-149 4. Bhat, G.K., Redner, A.S., 1999, ‘Minimizing number of images required in photoelastic multi-wavelength and phase-shifting analysis’, Proc. SEM Spring Conf. Theor. Exptl. & Comp. Mech., pp. 541-3. 5. Petrucci etc 6. Pacey, M.N., Wang, X.Z., Haake, S.J., Patterson, E.A., 1999,‘The application of evolutionary and maximum entropy algorithms to photoelastic spectral analysis’, Experimental Mechanics, 38(4): 265-273.
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