Fourier-transform vibrothermography with frequency sweep excitation utilizing local defect resonances. (March 2017)

• Record Type: Journal Article
• Authors: Rahammer, Markus; Kreutzbruck, Marc
• Is Part Of: NDT & E international. Volume 86(2017)
• Page Start: 83
• Page End: 88
• Publication Date: 2017-03
• Subjects: Vibrothermography -- Frequency sweep -- DFT -- Local defect resonance; Nondestructive testing -- Periodicals; Contrôle non destructif -- Périodiques; Electronic journals; 620.1127
• DOI: 10.1016/j.ndteint.2016.11.012
• Languages: English
• ISSNs: 0963-8695

Abstract

Abstract: The defect activation and detection efficiency of low-energy vibrothermography can be further improved by periodically sweeping the ultrasonic excitation frequency and Fourier-transforming the temperature data at the modulation frequency. This is due to the resulting periodic heat production. While typical local defect resonance investigations make use of known resonance frequencies, this technique instead employs a wideband ultrasonic excitation signal. It can therefore be used to detect defects quickly without knowing the LDR frequency in advance, while still keeping the efficient defect activation effects provided by LDR. Otherwise undetectably low thermal defect signals are enhanced by means of Fourier filtering and the defects' resonance frequencies are characterized by their phase values. Highlights: Wideband ultrasonic excitation for vibrothermography of unknown defect resonances. Frequency sweep excitation and Fourier-transform evaluation. Phase angles provide information about local defect resonance frequencies.