Time and frequency behaviour in TSR and PPT evaluation for flash thermography

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Abstract

Subsurface defects can be detected by flash thermography evaluating the temperature response at the surface. Many techniques have been developed in the past to localise defects and also to estimate their depth and size. Two of the most established methods are TSR and PPT, whereby TSR analyses the data in the time domain, and PPT evaluates the signal in the frequency domain. In order to get the data in the frequency domain, Fourier transformation, especially FFT is used to calculate the phase shift for the different frequencies. The usage of FFT assumes a periodic signal or a temporal signal limited in time. As this is not the case for the temperature signal after a short pulse heating, the transformation to the frequency domain generates some errors. Therefore parameters as e.g. sampling frequency or time duration of evaluation have to be selected carefully. Even if many publications have been already dealing with this topic, in this paper a new approach is attempted by comparing the temporal behaviour as it is handled by the TSR technique with the frequency behaviour calculated by PPT. The results are interpreted with the help of simulation and measurements for flat bottom hole samples are also presented.

Details

Original languageEnglish
Pages (from-to)164-184
Number of pages21
JournalQuantitative infra red thermography (QIRT Journal)
Volume14.2017
Issue number2
Early online date1 Feb 2017
DOIs
Publication statusPublished - 2017
EventThermosense: Thermal Infrared Applications XXXIX 2017 - Anaheim, United States
Duration: 10 Apr 201713 Apr 2017