Abstract
A photographic method is described which gives, upon the superposition of ordinary light- and darkfield isochromatic fringe patterns, a new fringe pattern (mixed field). This mixed-field pattern has fringes at the (N/4 and 3N/4 positions. Use of the mixed-field fringe pattern coupled with the oridinary light- and dark-field patterns permit fringes to be read at theN/4,N/2, 3N/4 andN positions, and thus represents a factor of 2 increase in the number of countable fringes. The method is illustrated on two plane-stress examples, a three-dimensional example, and a case employing birefringent coatings.
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Dally, J.W., Ahimaz, F.J. Photographic method to sharpen and double isochromatic fringes. Experimental Mechanics 2, 170–175 (1962). https://doi.org/10.1007/BF02325785
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DOI: https://doi.org/10.1007/BF02325785