A Brief Review and Advances of Thermographic Image - Processing Methods for IRT Inspection: a Case of Study on GFRP Plat
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REVIEW PAPER
A Brief Review and Advances of Thermographic Image - Processing Methods for IRT Inspection: a Case of Study on GFRP Plate F.W. Panella 1 & A. Pirinu 1 & V. Dattoma 1 Received: 12 August 2019 / Accepted: 2 November 2020 # The Author(s) 2020
Abstract The present work introduces a different data processing strategy, proposed in order to improve sub-surface defect detection on industrial composites; in addition, a resume of thermal data processing with most common algorithms in literature is presented and applied with new data. A deep comparison between the common absolute contrast, DAC, PCT, TSR and derivative methods and a new proposed contrast mapping procedure is implemented. Thermographic inspection was done in reflection mode on a Glass Fiber Reinforced Plastic plate, with flat bottom hole defects. Thermal data computation method is found to be critical for simultaneous defect detection and automatic mapping, optimized to identify defect boundaries at specific depth, with help of accurate image processing, implemented in a Matlab GUI for a reliable and rapid characterization of internal damage. The new processing approach, the Local Boundary Contrast method, elaborates different contrast maps and facilitates recognition of damage extension. Tanimoto criterion and the signal-to-noise ratio method were applied as a criterion to assess defect detectability of various processing methods. Keywords Composite material . Differential absolute contrast . Image-processing . Principal component thermography . Pulsed thermography . Thermal signal reconstruction
Nomenclature DAC Differential Absolute Contrast DIC Digital Image Correlation EOF Empirical Orthogonal Function FPA Focal-Plane Array GFRP Glass-Fibre Reinforced Plastic IDAC Interpolated Differential Absolute Contrast IRT Infrared thermography (IRT) NAN Not a number NDT Non-Destructive Testing NETD Noise Equivalent Temperature Differences PCT Principal Component Thermography PPT Pulsed phase thermography PT Pulsed Thermography SNR Signal to noise TSR Thermal Signal Reconstruction
* F.W. Panella [email protected] 1
Department of Engineering for Innovation, University of Salento, 73100 Lecce, Italy
Introduction Non-destructive testing with active thermography involves verification of mechanical properties and material integrity [1, 2], investigating discontinuities and internal defects present in analyzed component [3]. The main advantages of IRT enhanced international interest for thermal inspection systems in several applications, i.e. the industrial, military defense, archaeological or medical fields [4–7]. IRT procedures provide accurate analyses that established these techniques as effective tools for real time monitoring of different structures, particularly in case of composite laminates [8–10]. Manufacturing, repair processes and in service load history could induce several flaw typologies in composite components, as delamination, diffused porosity, or fiber-matrix cracking [11–13]; interest on active thermographic methods is pr
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