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1997 Contents


MIA EVALUATION OF MATERIAL DEFECTS DETECTED USING ESPI AND SHEAROGRAPHY (1997)

ABSTRACT

Most manufactured components have to undergo routine maintenance inspections. This paper presents two non-contacting NDE techniques known as Electronic Speckle Pattern Interferometry (ESPI) and Shearography which, through rapid inspection, produce real time qualitative results. A third technique known as Mechanical Impedance Analysis (MIA), which evaluates an object's vibrational response to an audible signal, is also outlined.

The authors show how MIA can be used to supplement ESPI and Shearography by quantifying flaws initially detected by the optical interference techniques. The principles of the optical NDE methods are described as applied using a portable NDT unit. Samples are inspected and defects are located in the fringe patterns obtained. MIA is applied to the samples in the vicinity of the suspected flaws and a clear outline of the boundary of the defect in obtained. Discussion of the advantages and limitations of ESPI and Shearography as well as the benefits of MIA conclude this paper.

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DETECTION AND QUANTIFICATION OF CRACKS IN PRESSURE VESSELS USING ESPI AND FEA MODELLS (1997)

ABSTRACT

Non destructive evaluation tools of the optical kind can reliably detect defects. Electronic speckle pattern interferometry (ESPI) is a fast, non-contacting optical NDE technique which can quantify the location of the flaw but essentially only provide qualitative information regarding the size of the defect. By combining finite element methods to evaluate the results obtained from ESPI, the authors attempt to provide quantitative information about the nature of the defects.

Numerous thumbnail cracks, which vary both in size and orientation, are produced in the side walls of small pressure vessels. Out of plane ESPI is used to detect the surface displacement of the pressure near the defect. Using finite element techniques to model the pressure vessel, thumbnail cracks and loading parameters, a displacement field around the flaw is reproduced. The finite element deflection map is compared to that obtained experimentally using ESPI and areas of correlation are highlighted.

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