<title>Crack detection by TV holography: continuous and pulsed techniques</title>

Abstract

Two TV-Holographic techniques to detect cracks in mechanical elements are demonstrated. One of them employs continuous illumination and is based in the modal analysis of the part. The other one consists in the study by pulsed TV-Holography of transient waves induced in the part.

<title>Transient bending wave analysis by Fourier evaluation of single-pulsed TV holography fringe patterns</title>

“…by means of a 2-D FFT algorithm yields&(7 where F is the symbol of two-dimensional Fourier transform, capital letters denote Fourier spectra, u and v are horizontal and vertical spatial frequencies respectively, C* represents the complex conjugate of C and j = -1Provided that variations of background, modulation and phase of interest are slow compared with the spatial carrier frequency ug, the Fourier spectrum of a single-pulsed TVH correlation fringe pattern consist of three separated regions.A(u,v) is centered on the origin of the Fourier plane, and contains the background and low-frequency information. The other two lobes, C(u-uC,v) and C*(…”