Dual-beam shearography와 Digital image correlation 기법을 이용한 압력용기의 감육결함 및 변형측정

Abstract

These days, non-destructive inspection technology used in industrial field has been widely used the field of safety diagnostic tests such as industrial machinery, nuclear power plants, heavy and power plants, ports, car etc. The absence defect of industrial facilities through the test results quickly and accurately detect the defects, are responsible an important role in the industry by gaining the reputation of the product, such as the health, economy and reliability. Therefore, one of nondestructive testing, optical measurement inspection methods largely measure the deformation of whole area and are 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. shearography technique can measure the first derivative of surface displacement and detect object defect of whole field as non-contact. Thess technique has applied to the aerospace, nuclear industry and heavy chemistry plant etc for non-destructive testing. Recently the advantage of shearography that is remarkably insensitive to external vibration had applied to measure the deformation and strain of object defect. This paper proposes new modified shearography called dual-beam shearography, which can measure simultaneous the out-of-plane deformation and the in-plane deformation by using another illuminated laser and simple image processing method. Digital image correlation method in non-destructive technique similar as non-contact inspection also can measure to deformation according to external changes. This principle of principle record irregular patterns that exist in the two images as a combination of a digital signal and each pixel in the transformed image before find out whether mapping any point within the image after the transformation and use gray values fringe within a certain area around each pixel. All pixel have the minimum error and find the corresponding pixel in the opposing images that is associated. Therefore digital image correlation method has the advantage that it can be interpreted as a three-dimensional the deformation of object by using the mapping technology to match the two images based on image of specific points coming from two CCD cameras and the necessary equipment include two cameras, white light by using light resource and pixel size have to a high resolution of up to 1/100. Furthermore, an experiment to measure the deformation of a circular plate has an error rate of about 3.2%~5.4%; it is very precise in comparison to ESPI. In an experiment to measure the defects of defective pressure vessel, the rate is about 0.1%~0.2%. 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. As well as showing the possibility for improving the degree of precision for the out-of-plane deformation measurement of dual-beam shearography through this study, digital image correlation in the comparison experiment method is thought to affect many areas of the various measurements.