Ultrasound excited thermography: an efficient tool for the characterization of vertical cracks

Abstract

Ultrasound excited thermography has gained a renewed interest in the last two decades as a nondestructive testing technique aimed at detecting and characterizing surface breaking and shallow subsurface discontinuities. It is based on measurement of the IR radiation emitted by the specimen surface to detect temperature rises produced by the heating of defects under high amplitude ultrasound excitation and is primarily addressed to flaws with contacting faces, such as kissing cracks or tight delaminations. The simplicity of application and the ability to detect small cracks in challenging media makes it an attractive emerging technology, which is still in a development stage. However, it has proven to provide an opportunity for the quantitative characterization of defects, mainly of vertical cracks. In this review, we present the principles of the technique and the different experimental implementations, we put it in context with other nondestructive tests and we summarize the work done in order to improve defect detectability and test reliability, with the final goal of determining the probability of detection. Then we review the contributions aimed at characterizing vertical cracks, i.e. retrieving the geometry and location of the crack from surface temperature data, generated by ultrasonic excitation.

Matched-Filter Thermography

“…Specifically, detection of dental caries at very early stages of formation has proven to be a key application of thermography in biomedicine by providing diagnostic contrast based on enhanced absorption of light at caries [7][8][9], as opposed to other emerging technologies such as Raman spectroscopy [13] and optical coherence tomography (OCT) [14,15], which rely on changes in scattering of light at caries. Appealing, if not unique, characteristics of thermography include: being no-contact, having the ability to inspect opaque [4,[16][17][18][19][20] and turbid materials [7][8][9], and being scalable [3,4]. Moreover, depending on the application, different types of external excitation, such as optical [7], magnetic [17], mechanical waves [19], electrical [4,16] or even cyclic stress/strain [18], can be utilized to induce the thermal wave field inside the sample.…”

“…Appealing, if not unique, characteristics of thermography include: being no-contact, having the ability to inspect opaque [4,[16][17][18][19][20] and turbid materials [7][8][9], and being scalable [3,4]. Moreover, depending on the application, different types of external excitation, such as optical [7], magnetic [17], mechanical waves [19], electrical [4,16] or even cyclic stress/strain [18], can be utilized to induce the thermal wave field inside the sample. A comprehensive review of conventional thermography techniques such as PT and LIT can be found in another paper of this special issue on "Novel Ideas for Infrared Thermography also Applied in Integrated Approaches".…”

In-plane local defect resonances for efficient vibrothermography of impacted carbon fiber-reinforced polymers (CFRP)

“…As such, the defects behave like localized heat sources and can be detected with a thermographic system [1]. This makes vibrothermography a promising technique for detection of tightly closed cracks and kissing bonds in composites, especially if the defect interfaces are aligned normal to the inspection surface which is hard to detect using other NDT techniques [2].…”

Lock-in thermography using a cellphone attachment infrared camera

“…1 LIT, compared to most other NDT techniques, has the advantages of being non-contact, having the ability to inspect opaque [1][2][3][4][5][6] and turbid materials, [7][8][9] and being scalable (e.g., microscopic LIT of leakages in integrated circuits 2 vs. inspection of airplane parts 6 ). Moreover, depending on the application, different types of external excitation, such as optical, 8 electrical, 1,2,10 magnetic, 3 mechanical waves (ultrasound) 5 or even cyclic stress/strain, 4 can be utilized to induce the thermal wave field inside the sample. Due to these promising abilities, LIT has been successfully implemented in research for defect detection and evaluation of broad range of materials, spanning from composite materials, 10 to semiconductor, 11 to biological hard tissues.…”