적외선 열화상 기법을 이용한 알루미늄 표면 직하 결함 크기의 정량적 평가에 관한 연구

Abstract

Non-destructive testing is the key testing technique for improving reliability, diagnosing facility safety and maintaining the equipment in places such as industrial sites. Among non-destructive testing technologies, infrared thermography (IRT), which monitors an object by detecting the infrared energy released from it, is getting a lot of attention. IRT has many advantages including rapidity of testing and the visibility of the results. Until now, infrared thermography was used in industrial sites in a limited form that detected abnormalities over extensive areas. However, the use of non-destructive testing by infrared thermography has now been expanded and applied for more precise non-destructive testing in a narrow range of areas such as finding defects of machine parts or metallic materials. It is no longer just for detecting an abnormality in an extensive area. However, with actual industrial equipment and structures it is difficult to perform quantitative evaluations and standardizations because the equipment is composed of various metals and materials in different forms. Also, in addition to the state monitoring and safety diagnosis, accurate base data information regarding form, size, location and direction in the actual defects for various materials has not been established. Therefore, it is necessary to compile comparative data and develop a quantification method to easily evaluate them quantitatively. In this paper, the goal was to be a preliminary study to establish the quantified standardization. Therefore, the study was performed to deduce the quantitative testing technique and improve the reliability for sub-surface defects using infrared thermography and image processing. Aluminum, which is widely used in the industrial world, was used as a study subject. The defect test pieces were produced in various sizes and depths. The results were compared and analyzed through infrared thermography experiments and finite element analysis. The quantitative evaluation of defects was performed through image processing with the obtained images after validating the experiments and analysis. With the suggested image processing algorithm, it was possible to measure the defect size by minimizing the image errors, slant correction, noise removal and binarization that could occur during the infrared testing. Thus the quantitative evaluation and comparative analysis for surface and sub-surface were performed. In addition, in order to enhance the efficiency and reliability of the quantitative testing method, the infrared thermography experiments were conducted by using the measured distance as the experiment variable. The quantitative evaluation and comparative analysis were performed according to the measured distance variables. It was confirmed that the measured distance was affected by the quantitative evaluation results of the sub-surface defect. Additionally, ultrasonic tests were conducted to verify if the C-Scan image could be evaluated. With C-Scan image evaluation results, the possibility of quantitative evaluation for the C-Scan image was confirmed and the reliability of the suggested quantitative testing technique was enhanced.