전단간섭계를 이용한 압력용기의 결함 및 비결함부의 변형 동시계측

Abstract

In general, methods to measure deformation are largely divided into a contact style and a non-contact style. Representative contact style deformation measure methods include a strain gauge and a accelerometer, a non-contact method is Laser Doppler Vibrometry(LDV) using the doppler principle, and a representative non-contact method electronic speckle pattern interferometer is ESPI, which can measure and analysis precisely and in a real-time the deformation applied to the whole fields of the objects but is so sensitive to external disturbances that the applicability is so low in the industries without a optical table. Another method using speckles is Shearography, which composes the interferometer appropriately enough to detect derivative components of deformation. Like a strain gauge, Shearography can directly acquire information on the strain. Stress concentration will occur when external forces are applied to an object with a defect, and the deformation of rigid bodies will not change the strain. In this regard, Shearography is very efficient to measure the defects of an object and very endurable against external disturbances, and so it is frequently employed as a nondestructive inspection technique on industrial sites. Shearography, which easily composes interferometer and can measure laser what coherence length of laser is relatively short, has been more widely employed and it is used to vibrations analysis of objects and hired as an efficient method in the nondestructive inspection sector including the quantification of defects and the analysis of composite material structures. Until recently, researchers used Shearography so as to measure just the slope of deformation, to quantify defect lengths by measuring the distance between the inflection points of deformation slope taking place on defected regions of pressure vessels to know defect lengths, and use Shearography in order to compare ESPI to vibration modes applied to a certain object. Currently, ESPI is mainly used to measure the deformation of objects and Shearography is used to measure only the defects of objects only. This thesis uses Shearography and numerical integration to quantitatively measure various types of out-plane deformation applied to objects, with a view to overcome the limits of the other methods and Shearography. In the past, a researcher arbitrarily applied shearing amount where the most important variable of Shearography according to the sensitivity of detecting the defects. In contrast, this thesis proposes an idea that considering Shearography is basically an image processing method, shearing amount can be converted into the number of pixels in the surface, and applied to the results of measurement by Shearography, and then numerically integrated in order to quantitatively measure the deformation of objects. To verify that, it experimented on a circular plate to which out-of-plane deformation is appled, pressure vessel with internal defects, and determined the correlation between ESPI and Shearography. It also has been confirmed that shearing amount on the surface can be substituted by the number of pixels and that Shearography can measure out-plane deformation. Furthermore, an experiment to measure the deformation of a circular plate has an error rate of about 1.43%~1.87%; it is very precise in comparison to ESPI. In an experiment to measure the defects of defective pressure vessel, the rate is about 5.4%~14.4%. Therefore, a new measurement technique that measures quantitatively deformation on the non-defect part by the pressure changes through the experiments for measuring deformation of the cylindrical pipes using the variation of shearing amount of shearography was proposed. The maximum deformation decreases linearly when the shearing amount increases through the comparison with the maximum deformations by changing the shearing. Based on the results of experiments, the quantitative value of maximum deformation could be inferred when the shearing amount is "0". In other words, the deformation when the hearing amount is "0" can be equal to adding a deformation on defect part and a deformation on non-defect part. The possibility for improving the degree of precision for the out-of-plane deformation measurement of shearography through this study.