A Digital System For Real-Time Holographic Stress Analysis

P. Hariharan; B. F. Oreb; N. Brown

doi:10.1117/12.934901

13 December 1983 A Digital System For Real-Time Holographic Stress Analysis

P. Hariharan, B. F. Oreb, N. Brown

Proceedings Volume 0370, Holographic Data Nondestructive Testing; (1983) https://doi.org/10.1117/12.934901
Event: Holographic Data Nondestructive Testing, 1982, Dubrovnik, Croatia

Abstract

In holographic interferometry, measurements on the fringe pattern using at least three different directions of illumination or viewing permit evaluating the displacement vector at any point. However, the use of holographic interferometry in stress analysis has been limited so far by the fact that interpolation between the fringe maxima and minima to determine the phase at a particular point is tedious and not very accurate. Accurate measurements are possible by heterodyne holographic interferometry, but there are problems in applying it to real-time measurements at a large number of points. This paper describes an improved system for real-time holographic stress-analysis, which uses a diode-array tele-vision camera to view the interference pattern and digital electronics to measure and store the irradiance levels at a 100 x 100 grid of points. The phase at each point is calculated from the irradiance values obtained from three successive scans of the array, made with the phase of the reference beam shifted in steps of 120° by means of a piezoelectric translator. The optical system permits four holograms to be recorded in quick succession, using a photothermoplastic camera, with the object illuminated from four different directions. Data from these holograms are stored on a floppy disc; they can then be transferred to a fast computer for further processing to determine the displacement vector at each point and, hence, the stress distribution.

Citation Download Citation

P. Hariharan, B. F. Oreb, and N. Brown "A Digital System For Real-Time Holographic Stress Analysis", Proc. SPIE 0370, Holographic Data Nondestructive Testing, (13 December 1983); https://doi.org/10.1117/12.934901

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