Ultrasound excited thermography using frequency modulated elastic waves

Zweschper, Th.; Dillenz, Alexander; Riegert, G.; Scherling, Dieter; Busse, G.

doi:10.1784/insi.45.3.178.53162

Cited by 68 publications

(19 citation statements)

References 17 publications

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“…Some works obtained phase angle information and phase images on composite and polymer materials thermograms achieving good results but using very sophisticated methods and equipments [5][6][7][8][9][10] that could not fit field inspections in industrial environments.…”

Section: Using Air Blower Excitation: (A) Non-defective Region (B) Rementioning

confidence: 99%

Defect detection in fiberglass reinforced epoxy composite pipes reproducing field inspection conditions

Souza¹,

Rebello²,

Soares³

et al. 2008

Proceedings of the 2008 International Conference on Quantitative InfraRed Thermography

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Many works that adopt active thermography as a non-destructive inspection method use very sophisticated equipment for test piece thermal excitation and data acquisition, which demand highly prepared operators, causing their application in industrial environments very costly. This paper aims at detecting defects in adhesive joints of fiberglass reinforced epoxi pipes by means of the Fourier transform phase angle analysis of the time evolution pixel amplitude, using simple and low-cost equipment. Results show that is possible to detect defects in adhesive joints, studying the phase angle behavior, even in regions, where the thermograms show no defects. IntroductionInfrared thermography is a well known technique that provides the capability to see the unseen. As a nondestructive method of inspection, it can reveal surface, subsurface and internal structural defects over a wide variety of materials. The technique is based on the reflectiveness of thermal waves by the surface of the materials [1,2].The thermographic technique is showing a good performance on the inspection of composite materials, including adhesive layers [3,4] and has been used by numerous sectors of the industry reaching exciting levels of detection and characterization of a large variety of materials and devices, justifying the great number of studies that have been made recently [4].The active thermography is the kind of infrared inspection that uses the heat of external sources as excitation that can be analysed on permanent or transient state of heat flow. The lockin thermography uses the information of a unique frequency to analyse the amplitude and phase angles relating these data to location and size of the defects. The pulsed thermography analyses the decay on time of a pulse heat excitation without selecting a specific frequency [1,2].The Pulsed Phase Thermography is an active method that allows the analysis of a wide band of frequencies of heat excitation giving information about the magnitude and phase angles of the temperature decay of the objects inspectioned. The behavior of the phase angle can indicate the presence of defects even inside the material´s structure [1,2], not detectable by conventional termography. Pulsed Phase ThermographyPulsed phase thermography allows the analysis of a series of frequencies by means of a single excitation, and it can be performed in a fast way [2]. However, the equipment used in all active techniques still represents some difficulty for a fast and reliable application in the industry environment, because of the high level of qualification necessary for the operators to set and use the equipment, as well as the high costs involved.The information that can be extracted from the pulsed thermography pass through math algorithms to be analyzed on a frequency basis less affected by the noise of the thermal excitation allowing the observation of phase angles over a wide spectrum of frequencies and can be used to compose the phase images to visualize defects non-detectable on the original thermogram...

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Section: Using Air Blower Excitation: (A) Non-defective Region (B) Rementioning

confidence: 99%

Defect detection in fiberglass reinforced epoxy composite pipes reproducing field inspection conditions

Souza¹,

Rebello²,

Soares³

et al. 2008

Proceedings of the 2008 International Conference on Quantitative InfraRed Thermography

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“…In this case, a strong ultrasonic standing wave pattern which might appear as a superposed temperature pattern could hide the real defect. An ultrasound source which has a frequency modulation in addition to the amplitude modulation can solve this problem [13]. The frequencies causing the standing wave pattern are reduced, patterns related to various frequencies are averaged, and finally a more homogeneous phase image with an improved signal-to-noise ratio is achieved.…”

Section: Ultrasound Activated Lockin-thermography With Additional Frementioning

confidence: 99%

Advanced ultrasound activated lockin-thermography for defect selective depth-resolved imaging

et al. 2006

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Ultrasound activated Lockin-Thermography ("ultrasound attenuation mapping") is a defect selective NDT-technique. Its main advantage is a high probability of defect detection ("POD") since only defects produce a signal while all other features are suppressed. The mechanism involved is local sound absorption which turns a variably loaded defect into a heat source. Thermographic monitoring of elastic wave attenuation in defects was reported for the first time in 1979 by Henneke and colleagues for continuous and pulsed ultrasound injection. Later, amplitude modulated ultrasound was used to derive frequency coded phase angle images combining defect-selectivity with robustness of measurement. With mono-frequent ultrasound excitation a standing wave pattern might hide defects. With additional modulation of the ultrasound frequency such a misleading pattern can be minimized. Applications related to quality maintenance (aerospace, automotive industry) will be presented in order to illustrate the potential of frequency modulated ultrasound excitation and its applications.

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“…An improved ULT-version uses frequency modulated ultrasound in addition to the amplitude modulation by the lockin-frequency [6]. In particular, heating outside a defect area increases considerably if the carrier frequency is close to a resonance frequency of the sample.…”

Section: Ultrasound Activated Lockin-thermographymentioning

confidence: 99%

Acoustic Lockin-Thermography of Imperfect Solids for Advanced Defect Selective NDE

Riegert¹,

Zweschper²,

Gleiter³

et al. 2006

AIP Conference Proceedings

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A propagation of an intense acoustic wave in imperfect solids results in a local temperature increase in a defect area. To raise a sensitivity of detection of such faint heat sources, the lock-in approach was applied by using a low-frequency amplitude modulation of acoustic excitation (Ultrasound-Lockin-Thermography). However, for a single carrier frequency, the temperature distribution is often affected by standing wave pattern in the specimen that impedes acoustic thermography of defects. Alternatively, a wide-band time varying modulation enables to avoid resonances of the specimen and minimize the standing wave impact. A burst-phase acoustic thermography uses short acoustic bursts to derive phase angle images from a temperature image sequence at various frequencies. It, therefore, combines a high sensitivity of the lockin counterpart with a wide bandwidth of Burst-Phase-Thermography. A number of case studies concerned with various flaws (delaminations, cracks, voids, non-bonds, etc.) in a wide range of materials are reported and demonstrate a high reliability of defect recognition. A striking similarity found between the results of acoustic lockin-thermography and higher harmonic acoustic nonlinear NDE suggests nonlinear acoustic contribution into the mechanism of acoustic thermography.

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Ultrasound excited thermography using frequency modulated elastic waves

Cited by 68 publications

References 17 publications

Defect detection in fiberglass reinforced epoxy composite pipes reproducing field inspection conditions

Defect detection in fiberglass reinforced epoxy composite pipes reproducing field inspection conditions

Advanced ultrasound activated lockin-thermography for defect selective depth-resolved imaging

Acoustic Lockin-Thermography of Imperfect Solids for Advanced Defect Selective NDE

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