Abstract
Active infrared thermography is an attractive and reliable technique used for the non-destructive evaluation of various materials and structures, because it enables non-contact, large area, high-speed, quantitative, and qualitative inspection. However, the defect detectability is significantly deteriorated due to the excitation of a non-uniform heat source and surrounding environmental noise, requiring additional signal processing and image characterization. The lock-in infrared thermography technique has been proven to be an effective method for quantitative evaluation by extracting amplitude and phase images from a 2D thermal sequence, but it still involves a lot of noise, providing difficulties in detection. Therefore, this study explored the possibility of improving the signal-to-noise ratio by applying filtering to a stainless-steel plate with circular defects. Thereafter, automated defect detection was performed based on the threshold value through the binary images. In addition, a comparative analysis was performed to evaluate the detectability according to the presence or absence of a filtering application.
Highlights
The importance of non-destructive testing (NDT) in industry occupies a large part of the inspection of machines or structures in various fields such as shipbuilding, automobiles, construction, civil engineering, and nuclear power [1,2,3]
The automatic defect detection of backside of STS304 plate based on lock-in infrared thermography was performed
signal-to-noise ratio (SNR) evaluation was performed after applying median filtering to remove noise from the signal processing image: the amplitude image improved by 2.67%, and the phase image improved by 18.22%
Summary
The importance of non-destructive testing (NDT) in industry occupies a large part of the inspection of machines or structures in various fields such as shipbuilding, automobiles, construction, civil engineering, and nuclear power [1,2,3]. Austenitic stainless steel has high mechanical properties and corrosion resistance; it can be applied in a wide temperature range and various operating conditions, from cryogenic to high temperature [6,7,8]. It is used in various fields such as interior and exterior materials for construction, automobile parts, aircraft fuselages, and medical devices. Lock-in infrared thermography, one of the active IRT techniques, was applied to automatically detect defects on the backside of STS304 metal plates.
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