Depth Retrieval Procedures in Pulsed Thermography: Remarks in Time and Frequency Domain Analyses

Panagiotis Theodorakeas,Maria Koui

doi:10.3390/app8030409

Panagiotis Theodorakeas, Maria Koui

Open Access

https://doi.org/10.3390/app8030409

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Journal: Applied sciences	Publication Date: Mar 9, 2018
Citations: 16	License type: CC BY 4.0

Affiliation: National Technical University of Athens

Abstract

In the present study, a Carbon Fibre Reinforced Polymer (CFRP) sample of trapezoid shape, consisting of internal artificial delaminations of various sizes and depth locations, is investigated by means of optical pulsed thermography for the retrieval of quantitative depth information. The main objectives of this work are to evaluate the produced depth estimation accuracy from two contrast-based depth inversion procedures as well as to correlate the acquired results with characteristics such as the location and size of the detected features and with analysis parameters such as the selection of the sound area. Quantitative analysis is performed in both the temporal and frequency domains, utilising, respectively, the informative parameters of thermal contrast peak slope time and blind frequency. The two depth retrieval procedures are applied for the depth estimation of features ranging in size from 3 mm to 15 mm and in depth from 0.2 mm to 1 mm. The results of the present study showed that the two different analyses provided efficient depth estimations, with frequency domain analysis presenting a greater accuracy. Nevertheless, predicting errors were observed in both cases and the factors responsible for these errors are defined and discussed.

Highlights

Pulsed Thermography (PT) is a widely used technique for the Non-Destructive Testing and Evaluation (NDT&E) of advanced materials and structures [1,2,3,4,5]
A Carbon Fibre Reinforced Polymer (CFRP) specimen with internal simulated delaminations of various sizes and and depth locations was investigated by means of PT for the retrieval of quantitative depth depth locations was investigated by means of PT for the retrieval of quantitative depth information
Hidden features located in a depth range from 0.2 mm to 1 mm and varying in size from 3 mm from 3 mm to 15 mm were quantitatively characterised using two different analysis procedures to 15 mm were quantitatively characterised using two different analysis procedures through which through which the impact of different analysis parameters was assessed

Summary

Introduction

Pulsed Thermography (PT) is a widely used technique for the Non-Destructive Testing and Evaluation (NDT&E) of advanced materials and structures [1,2,3,4,5]. Compared with other NDT&E technologies, this thermographic configuration presents remarkable benefits such as its rapid and simple implementation, its suitability for large-scale inspections and complex surface monitoring, as well as its contactless application requiring no physical contact to the material being inspected. The application of the thermal stimulus is followed by the recording of the resultant surface temperature response through the aid of an IR camera, aiming to detect changes in the surface temperature distribution. These changes are normally owned to the presence of internal defects and/or discontinuities which are altering the heat diffusion rate into the inspected component.

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