A theoretical study on vertical finite cracks detection using pulsed laser spot thermography (PLST)

Bu, Chiwu; Tang, Qingju; Liu, Yuanlin; Jin, Xiangyang; Sun, Ze; Yan, Zugen

doi:10.1016/j.infrared.2015.05.009

Cited by 9 publications

(6 citation statements)

References 10 publications

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“…Figure 18 The distances d are deduced for each crack selected pixels once the heated area pixels have been located from amplitude images. The gradient of the product of the amplitude and phase images is calculated via a program running under Matlab according to the procedure described in the former section in order to obtain Ι from the polynomial fits of G 2 (µ 2 ) and then Ι d from Equation (4). The crack depth is evaluated from Equation (6).…”

Section: Experimental Set-up and Methodologymentioning

confidence: 99%

“…The active infrared thermography is a non-contact and non-destructive promising technique for perpend icular crack detection. It uses a local heating solicitation which can be continuous [1][2][3], pulsed [4][5][6][7][8] or modulated [9,10]. The disturbances of the heat diffusion produced by a crack which acts as a thermal barrier are then analyzed.…”

Section: Introductionmentioning

confidence: 99%

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Open crack depth sizing by multi-speed continuous laser stimulated lock-in thermography

Boué¹,

Holé²

2017

Meas. Sci. Technol.

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A crack located in the thermal diffusion zone of a heat source behaves like a thermal barrier modifying the heat diffusion. For a moving continuous source, the sample surface is heated on a little area near the crack for a duration which depends on the speed of the thermal source. A lock-in process synchronized by the displacement of the continuous heat source along the crack is studied. The thermal signature of the crack is extracted via a space operator applied to the amplitude and the phase of surface temperature images for various speeds of the thermal source. With the technical solution presented in this article, the thermal signature images are analysed according to a length representative of the thermal diffusion length to give a local evaluation of the crack depth (around 3 mm at the maximum) for crack lengths of about few centimetres long. The multi-speed lock-in thermography approach is initially studied with Finite Element Method (FEM) simulations. Experimental tests using an infra-red camera validate the method in a second part. The results do not depend on the heating source if its power is sufficient to produce a temperature rise detectable by an infra-red camera. The depth estimations are obtained independently of the crack width and heat source trajectory. The multispeed lock-in thermography is a method without contact, without sample preparation, non-polluting, non-destructive and with simple optical adjustments.

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Section: Experimental Set-up and Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Open crack depth sizing by multi-speed continuous laser stimulated lock-in thermography

Boué¹,

Holé²

2017

Meas. Sci. Technol.

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“…There are two main types of thermography: passive and active. Based on the sources and nature of energy for active thermography, there are six different types: pulse [188], lock-in/modulated [131], pulse phase [72], vibrothermography/thermosonics [43], eddy current [199] and laser spot thermography [17]. Thermography is mostly used in studying thermal behaviour of manufacturing operations.…”

Section: Non-destructive Evaluation For Automated Degradation Assessmentmentioning

confidence: 99%

Continuous maintenance and the future – Foundations and technological challenges

et al. 2016

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“…If the depth of the crack is finite, the temperature distribution in the material cannot be written analytically and the solution has to be sought numerically. Several research groups have applied finite element methods (FEM) to solve the heat diffusion equation to simulate the surface temperature of a sample containing a finite crack when it is illuminated by a focused laser beam [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. However, in these works, only cracks wider than 40 µm were studied because in classical continuous FEM, the cracked sample is divided into two domains: the bulk and the air filling the crack [ 33 ].…”

Section: Introductionmentioning

confidence: 99%

Sizing the Depth and Width of Narrow Cracks in Real Parts by Laser-Spot Lock-In Thermography

Colom

Rodríguez‐Aseguinolaza

Mendioroz

et al. 2021

Materials

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We present a complete characterization of the width and depth of a very narrow fatigue crack developed in an Al-alloy dog bone plate using laser-spot lock-in thermography. Unlike visible micrographs, which show many surface scratches, the thermographic image clearly identifies the presence of a single crack about 1.5 mm long. Once detected, we focus a modulated laser beam close to the crack and we record the temperature amplitude. By fitting the numerical model to the temperature profile across the crack, we obtain both the width and depth simultaneously, at the location of the laser spot. Repeating the process for different positions of the laser spot along the crack length, we obtain the distribution of the crack width and depth. We show that the crack has an almost constant depth (0.7 mm) and width (1.5 μm) along 0.7 mm and features a fast reduction in both quantities until the crack vanishes. The results prove the ability of laser-spot lock-in thermography to fully characterize quantitatively narrow cracks, even below 1 μm.

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A theoretical study on vertical finite cracks detection using pulsed laser spot thermography (PLST)

Cited by 9 publications

References 10 publications

Open crack depth sizing by multi-speed continuous laser stimulated lock-in thermography

Open crack depth sizing by multi-speed continuous laser stimulated lock-in thermography

Continuous maintenance and the future – Foundations and technological challenges

Sizing the Depth and Width of Narrow Cracks in Real Parts by Laser-Spot Lock-In Thermography

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