Accession Number : AD0866371

Title :   Electro-Optical Noncontacting Techniques for Sonic Fatigue Tests.

Descriptive Note : Final technical rept. 1 Apr 68-1 Apr 69,

Corporate Author : BENDIX RESEARCH LABS SOUTHFIELD MI

Personal Author(s) : Marom, E.

Report Date : DEC 1969

Pagination or Media Count : 83

Abstract : Coherent light reflected from specimens has been used to detect surface structure variations as a function of time. By processing this reflected light to allow the display of optical correlation functions, one can detect fatigue or strain in the material being examined. It has been established that lensless correlators are quite adequate for this type of measurement, and that the measurements can be made from relatively large distances (a few feet), as well as through intermediate glass panels and in the presence of ambient light. However, it was found that temperature variations, vibrations, and the mechanical stability of all the components have to be well controlled to obtain accurate measurements. Correlation signals are affected by so many factors that no significance can be meaningfully attached to their absolute value. Their relative and subsequent variations are, however, of large significance. This property indeed is very useful in detecting the outset of fatigue, but does not allow calibration of strain measurements. Nonetheless, strain has been measured up to an accuracy of 20 microstrains by detecting the displacement of two regions as indicated by the position (rather than intensity) of the correlation peak signal. In the detection of vibrations, holographic techniques were used to display vibrational modes, whereas time-dependent interferometric displays were used to determine the amplitude of vibrations up to a few thousand wavelengths. (Author)

Descriptors :   *COHERENT RADIATION), (*NONDESTRUCTIVE TESTING, (*SONIC FATIGUE, DETECTION), ELECTROOPTICS, OPTICAL INSTRUMENTS, VISUAL INSPECTION, CORRELATION TECHNIQUES, METAL PLATES, MICROSTRUCTURE, FATIGUE(MECHANICS), STRAIN(MECHANICS).

Subject Categories : Test Facilities, Equipment and Methods

Distribution Statement : APPROVED FOR PUBLIC RELEASE