A Fully Non-Contact Ultrasonic Propagation Imaging System for Closed Surface Crack Evaluation |
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Authors: | D Dhital J R Lee |
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Institution: | 1.Department of Aerospace Engineering and LANL-CBNU Engineering Institute Korea,Chonbuk National University,Jeonju,Republic of Korea |
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Abstract: | Cracks are one of the most common types of damage occurring in engineering structures. A reliable nondestructive evaluation
technique is essential to detect any possible damage at the initiation phase. Real fatigue closed-surface cracks are difficult
to detect through visual inspection. Ultrasound has been widely used, but conventional contact ultrasonic inspection techniques
are not suitable for couplant-sensitive structures. In addition, these techniques are generally laborious for large field
structures and the inspection speed is relatively slow. We present a novel fully non-contact hybrid ultrasonic propagation
imaging (UPI) system that uses laser ultrasonic scanning excitation and piezoelectric air-coupled sensing. Ultrasonic frequency
tomography and wavelet-transformed ultrasonic propagation imaging algorithms are used to extract damage features. These features
are used to perform a thorough diagnosis of damage. The system enables remote and fully non-contact automatic one-sided inspection
for temporal reference-free damage evaluation, and is also applicable to in-field structures. Optimization provides improved
performance of air-coupled transducers (ACTs) used as receivers for the hybrid UPI system, as shown by our experimental results.
Surface crack evaluation results were analyzed on the basis of ease of damage visualization, accuracy of crack size estimation,
and sensitivity. The proposed hybrid UPI system is sensitive enough to detect a real fatigue closed-surface micro-crack with
size detection accuracy as high as 96%. We also show that the relation between the scanning interval and crack width affects
damage visualization performance, and the accuracy and sensitivity of damage size estimation. |
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