Strains in a flexed plate are directly related to the second derivatives of plate deflection. Shearography[1] measures the first derivative of deflections. Therefore, it still requires one more differentiation to obtain the flexural strains. Furthermore, a fringe pattern by shearography is a contour derivative fringe pattern. Automatic fringe analysis is, therefore. required since differentiation or the analysis of the fringe pattern for whole-field is not only laborious but also causes a majore source of error. In order to carry out automatic fringe processing. a "fictious fringe carrier" is introduced to shearography[2]. A fictious frige carrier processes linear fringes of equal spacing in the shearing direction. A perturbed linear fringe carrier is obtained when a flexed plate is deformed. The local perturbation depends on the local deflection gradients. This paper describes the fringe analysis of shearography by making use of spatial phase detection[3]. A deformed carrier fringe pattern is regarded as the phase modulated pattern with a constant spatial carrier. To retrieve phase modulation, the aquired data by TV systems are sinusoidally fitted by using a phase detection algorithm.

Date Published: 1 January 1987
PDF: 2 pages
Proc. SPIE 0813, Optics and the Information Age, (1 January 1987); doi: 10.1117/12.967143

Published in SPIE Proceedings Vol. 0813:
Optics and the Information Age
Henri H. Arsenault, Editor(s)