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Colour Adaptation in Three Fringe Photoelasticity


Three fringe photoelasticity (TFP) can give the total fringe order from a single colour isochromatic fringe field by suitably comparing the colour with a calibration specimen. The fringe order evaluation can be erroneous when the materials for the calibration specimen and the application specimen are different. This is because of the colour variation between the two materials. This is conventionally handled by preparing individual calibration tables for each application. A new methodology to tune the calibration table obtained for a single material to accommodate the tint variation in TFP is proposed for the use of different specimen materials. Discontinuities in fringe order variation are smoothed using the refined TFP (RTFP) procedure. The elegance of the new methodology for solving a multi-material system is bought out by solving the problem of a bi-material Brazilian disc. The results obtained are compared with the phase shifting technique.

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Correspondence to K. Ramesh.



Representation of Fringe Order Data as an Image

In order to visually appreciate the performance of TFP, it is desirable that the result is represented as an image. The value of fringe order is a real number whereas the digital image has to be an array of integer values. This requires some processing and approximation of the fringe order data. The fringe order obtained by TFP for all points on the specimen image is saved as an array of floating point values in a file for further processing. The fringe order data are converted into a set of grey level values using the equation

$$ g{\left( {x,y} \right)} = {\text{INT}}{\left[ {\frac{{255}} {B} \times f{\left( {x,y} \right)}} \right]} = {\text{INT}}{\left[ R \right]} $$

where f(x, y) is the fringe order at point (x, y), B is the maximum fringe order of the calibration table (three in most cases), g(x, y) is the grey level value at the point (x, y) and INT [R] is the nearest integer of R.

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Madhu, K.R., Prasath, R.G.R. & Ramesh, K. Colour Adaptation in Three Fringe Photoelasticity. Exp Mech 47, 271 (2007).

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  • Digital photoelasticity
  • Refined TFP
  • Colour adaptation