Defect depth quantification using lock-in thermography

Abstract. The aim of the paper is to study some factors influence on the contrast decreasing of the ampligram and phasegram obtained after optical lock-in thermography. It is analysed the effect of delay between excitation source modulated parameter changing and modulated signal due to thermal inertia of halogen lamp filament. Two software corrections for decreasing the effect of these factors are developed. In order to evaluate the effect of these corrections, lock-in thermography measurement is performed and multiple results processing at different correction parameters values are performed. The contrast dependence from correction parameters is presented in graphical form. Multiple results processing with random correction parameters values using the both corrections are performed for determination of maximum possible contrast An iterative method with less number of results processing for choosing appropriate values of correction parameters using the both corrections is proposed. The effect of this method is presented and compared in tabular and graphic form.

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“…A frequency of 0.2 Hz is chosen. At this frequency the heat wave penetration is approximately the thickness of the board [4].…”

Section: Experiments and Resultsmentioning

confidence: 99%

Specificity in the Optical Excitation Lock-in Thermography Results Processing

Stoynova

Bonev

2017

MATEC Web Conf.

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“…C. Manyong et al [ 44 ] and L. Junyan et al [ 45 ] used LIT to evaluate the FBH defects in steel structure and showed that the phase angle differences between the defective regions and sound regions provide the defect location and size. D. Sharath et al [ 46 ] studied on the blind frequency and phase contrast methods to evaluate the artificial square, rectangular and circular defects in austenitic stainless steel using LIT. It was concluded that blind frequency is dependent on the defect size and shape and could not be applied for depth quantification unless a normalization method is used.…”

Section: Introductionmentioning

confidence: 99%

Thermographic Inspection of Internal Defects in Steel Structures: Analysis of Signal Processing Techniques in Pulsed Thermography

Chung

Shrestha

Lee

et al. 2020

Sensors

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This study performed an experimental investigation on pulsed thermography to detect internal defects, the major degradation phenomena in several structures of the secondary systems in nuclear power plants as well as industrial pipelines. The material losses due to wall thinning were simulated by drilling flat-bottomed holes (FBH) on the steel plate. FBH of different sizes in varying depths were considered to evaluate the detection capability of the proposed technique. A short and high energy light pulse was deposited on a sample surface, and an infrared camera was used to analyze the effect of the applied heat flux. The three most established signal processing techniques of thermography, namely thermal signal reconstruction (TSR), pulsed phase thermography (PPT), and principal component thermography (PCT), have been applied to raw thermal images. Then, the performance of each technique was evaluated concerning enhanced defect detectability and signal to noise ratio (SNR). The results revealed that TSR enhanced the defect detectability, detecting the maximum number of defects, PPT provided the highest SNR, especially for the deeper defects, and PCT provided the highest SNR for the shallower defects.

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“…Pulsed (PT) [7,8,9,10,11,12] and lock-in (LT) [13,14,15,16,17,18,19,20,21,22] thermography are the techniques used in the last years for defect depth, thickness or more in general defect/damage measurement.…”

Section: Introductionmentioning

confidence: 99%

On the Thickness Quantification of Composite Materials by Using Lock-In Thermography

Palumbo

2019

Materials

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Many structural components made of composite materials need an accurate thickness control during fabrication and/or maintenance. In this regard, various non-destructive techniques can be used for the online measuring of thickness of large components such as wings and fuselage in the aerospace industry. In this work, the capabilities of lock-in thermography technique in thickness measurement of glass fiber reinforced plastic material were investigated and a correct procedure has been proposed to ensure the best measurement accuracy. An analytical approach and several tests were carried out on a sample specimen with the aim to study the main test parameters. Finally, the limits of technique have been discussed.

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Defect depth quantification using lock-in thermography

Cited by 32 publications

References 18 publications

Specificity in the Optical Excitation Lock-in Thermography Results Processing

Specificity in the Optical Excitation Lock-in Thermography Results Processing

Thermographic Inspection of Internal Defects in Steel Structures: Analysis of Signal Processing Techniques in Pulsed Thermography

On the Thickness Quantification of Composite Materials by Using Lock-In Thermography

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