Method and apparatus for viewing a shearographic image

Optics: measuring and testing – Material strain analysis – By light interference detector

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356347, 356348, 356353, G01B 902

Patent

active

054145120

ABSTRACT:
A shearogram representing an object and including a fringe pattern arising from a change in local surface strain brought about by an applied stress during the making of the shearogram is reconstructed by a special viewer. The viewer holds the shearogram transparency adjacent to a focusing lens having an optical axis, and projects off-axis white light through the lens and transparency to a focal plane where the resulting diffraction pattern is viewed directly on a screen or by a video camera and display monitor. By projecting the light from different positions around the axis a first position can be found which tunes the diffraction efficiency to an optimum for the best view of fringe patterns and a second position can be found which eliminates the fringe patterns and shows only a photographic image of the object. The light source is a rotatable disk with two apertures containing light diffusing elements which are illuminated by a lamp. The disk is rotated to change the projection angle.

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"Measuring The Quality Through the Use of Holographic and Shearographic (L-Ray.RTM.) Nondestructive Tire Testing", Ralph Grant, Oct. 3, 1991, American Chemical Society.

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