RESEARCH PAPERS: Experimental Techniques

Analysis of Pulsed Thermography Methods for Defect Depth Prediction

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

 Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439

J. Heat Transfer 128(4), 329-338 (Oct 24, 2005) (10 pages) doi:10.1115/1.2165211 History: Received May 23, 2005; Revised October 24, 2005

Pulsed thermography is an effective technique for quantitative prediction of defect depth within a specimen. Several methods have been reported in the literature. In this paper, using an analysis based on a theoretical one-dimensional solution of pulsed thermography, we analyzed four representative methods. We show that all of the methods are accurate and converge to the theoretical solution under ideal conditions. Three methods can be directly used to predict defect depth. However, because defect features that appear on the surface during a pulsed thermography test are always affected by three-dimensional heat conduction within the test specimen, the performance and accuracy of these methods differs for defects of various sizes and depths. This difference is demonstrated and evaluated from a set of pulsed thermography data obtained from a specimen with several flat-bottom holes as simulated defects.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Schematic diagram of pulsed thermography setup and heat conduction through and around lateral crack within test sample

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Figure 2

Surface temperature decay curves T and Tr at points 1 and 2, respectively, as illustrated in Fig. 1

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Figure 3

Temperature contrast ΔV as a function of dimensionless time ωr for thickness ratio y=0.2, 0.5, and 0.8

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Figure 4

Slope of temperature contrast d(ΔV)∕dωr as a function of ωr for y=0.2, 0.5, and 0.8

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Figure 5

Dimensionless peak-slope time ωs and peak slope d(ΔVs)∕dωr as functions of thickness ratio y

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Figure 6

Temperature and its first and second derivatives as functions of nondimensional time ω in log-log scale

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Figure 7

Schematic illustration of ceramic sample with machined flat-bottom holes

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Figure 8

Thermal images on front surface of ceramic specimen taken at t=0.007 and 0.67s after thermal flash

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Figure 9

Predicted depth image of ceramic sample with flat-bottom holes as illustrated in Fig. 7

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Figure 10

(a) Temperature and (b) first derivative of temperature as a function of time in log-log scale for flat-bottom holes A–F

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Figure 11

Dimensionless temperature-contrast slope as a function of time for flat-bottom holes A–F

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Figure 12

Second derivative of temperature as a function of time in log-log scale for flat-bottom holes A–F

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Figure 13

Measured and fitted first derivatives of temperature in log-log scale for flat-bottom holes A, B, and F

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Figure 14

(a) Comparison of predicted and measured depths and (b) prediction error as function of depth for three thermography methods




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