Abstract
In this article, optical excitation thermographic techniques, including pulsed thermography and lock-in thermography, were used to detect foreign object defect (FOD) and delamination in CFRP. Then, vibrothermography as an ultrasonic excitation technique was used to detect these defects for the comparative purposes. Different image processing methods, including cold image subtraction (CIS), principal component thermography (PCT), thermographic signal reconstruction (TSR) and Fourier transform (FT), were performed. Finally, a comparison of optical excitation thermography and vibrothermography was conducted, and a thermographic probability of detection was given.
Highlights
Carbon fiber-reinforced polymer composite (CFRP) is being increasingly utilized in aircraft, vehicles, ships, and sports equipment, etc
Principal component thermography (PCT), originally proposed by Rajic [6] in 2002, extracts the image features and reduces undesirable signals. It relies on singular value decomposition (SVD), which is a tool to extract spatial and temporal data from a matrix in a compact manner by projecting original data onto a system of orthogonal components, known as empirical orthogonal functions (EOF)
Light is transformed into heat, and energy is transferred to the specimen surface
Summary
Carbon fiber-reinforced polymer composite (CFRP) is being increasingly utilized in aircraft, vehicles, ships, and sports equipment, etc. Compared to ultrasonic c-scan [2], magnetic flux leakage [3] and X-ray computed tomography [4], infrared thermography (IRT) is increasingly used as a NDT technique due to its fast inspection rate, being contactless, having high spatial resolution, improved acquisition rate and the development of infrared image processing. Vibrothermography as an ultrasonic excitation thermography is becoming increasing popular in the inspection of CFRP; for example, it was used to detect cracks by the authors and provided positive results [5]. Optical excitation thermography techniques including pulsed thermography and lock-in thermography, were used to detect foreign object defect (FOD) and delamination in a CFRP specimen. Vibrothermography as an ultrasonic excitation thermography technique stimulated at different positions was used to detect these defects for comparative purposes. A comparison of optical excitation thermography and vibrothermography was conducted
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