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Research Papers: Heat and Mass Transfer

Quantitative Three-Dimensional Imaging of Heterogeneous Materials by Thermal Tomography

[+] Author and Article Information
J. G. Sun

Nuclear Engineering Division,
Argonne National Laboratory,
Argonne, IL 60439
e-mail: sun@anl.gov

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received March 5, 2012; final manuscript received June 17, 2016; published online July 19, 2016. Assoc. Editor: Ali Khounsary.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Heat Transfer 138(11), 112004 (Jul 19, 2016) (10 pages) Paper No: HT-12-1083; doi: 10.1115/1.4033998 History: Received March 05, 2012; Revised June 17, 2016

Infrared thermal imaging based on active thermal excitations has been widely used for nondestructive evaluation (NDE) of materials. While the experimental systems have remained essentially the same during the last few decades, development of advanced data-processing methods has significantly improved the capabilities of this technology. However, many limitations still exist. One fundamental limitation is the requirement, either explicitly or implicitly, of the tested material to be homogeneous such that detected thermal contrasts may be used to determine an average material property or attributed to flaws. In this paper, a new thermal tomography (TT) method is introduced, which for the first time can evaluate heterogeneous materials by directly imaging their thermal-property variations with space. It utilizes one-sided flash thermal-imaging data to construct the three-dimensional (3D) distribution of thermal effusivity in the entire volume of a test sample. Theoretical analyses for single and multilayer material systems were conducted to validate its formulation and to demonstrate its performance. Experimental results for a ceramic composite plate and a thermal barrier coating (TBC) sample are also presented. It was shown that thermal diffusion is the primary factor that degrades the spatial resolution with depth for TT; the spatial resolutions in the lateral and axial directions were quantitatively evaluated.

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Figures

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Fig. 1

Schematic of pulsed thermal-imaging test setup

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Fig. 2

Predicted and exact material effusivity (a) profiles and (b) cross section images as a function of depth for a single-layer system

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Fig. 3

Predicted and exact material effusivity (a) profiles and (b) cross section images as a function of depth for a two-layer system

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Fig. 4

Predicted and exact material effusivity (a) profiles and (b) cross section images as a function of depth for a three-layer system

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Fig. 5

Predicted thermal effusivity e(z) profiles for two- and three-layer material systems (e.g., 1 and 2 indicate that the first- and second-layer materials are Nos. 1 and 2, respectively) and a time t1/2 profile for a three-layer system

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Fig. 6

Diagram and hole dimensions of a flat-bottom-hole plate (dimensions of 5 cm × 5 cm with thickness between 2.3 and 2.7 mm)

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Fig. 7

Thermal images taken at t = 0.01 and 0.6 s after thermal flash from front surface of a CMC plate with machined flat-bottom holes at back surface

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Fig. 8

Plane thermal effusivity images at various depths below the front surface of a CMC plate with machined flat-bottom holes at back surface

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Fig. 9

(a) Cross-sectional thermal effusivity images and (b) corresponding diagrams along the horizontal lines of the flat-bottom-hole plate as illustrated in Fig. 5

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Fig. 10

(a) Cross section effusivity image and (b) effusivity depth profile for TBC sample

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Fig. 11

Plane effusivity images at various depths of TBC sample

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Fig. 12

Effusivity derivative curve as a function of depth for a one-layer material with a material effusivity of 2000 J/(m2 K s1/2) and a thickness of 10 mm

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Fig. 13

Temperature distributions within a semi-infinite material at various times after a thermal flash is applied on z = 0 at t = 0

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