In this article, the theoretical and experimental aspects of three active thermography approaches: pulsed thermography (PT), lock-in thermography (LT), and vibrothermography (VT), are discussed in relation to the nondestructive evaluation (NDE) of honeycomb sandwich structures. For this purpose, two standard specimens with simulated defects (delaminations, core unbonds, excessive adhesive, and crushed core) were tested, and results were processed, examined, and compared. As will be pointed out, the similarities and differences between these active approaches allow conclusions to be made about the most suitable approach for a particular application. In addition, results from NDE inspection by X-rays and c-scan ultrasounds are provided and discussed for reference.

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Comparative Study of Active Thermography Techniques for the Nondestructive Evaluation of Honeycomb Structures

Thermal imaging (TI) is an emerging, non-invasive process analytical technique suitable for the food industry. While TI was originally developed for military applications, it has recently emerged as a powerful non-destructive measurement technique in other industries. This paper provides an overview of TI theory, equipment, and image processing. Recent advances and potential applications of TI for food safety and quality assessment such as temperature validation, bruise and foreign body detection and grain quality evaluation are reviewed.

Applications of thermal imaging in food quality and safety assessment

Eddy current pulsed thermography (ECPT) is an emerging nondestructive testing and evaluation (NDT&E) technique and has been applied for a wide range of conductive materials. In this paper, a single-channel blind source separation is proposed to process the ECPT image sequences. The proposed method enables: 1) automatically extract valuable spatial and time patterns according to the whole transient response behavior without any training knowledge, 2) automatically identify defect patterns and quantify the defects, and 3) to provide guidelines of choosing the optimal contrast functions that can improve the separation results. In this paper, both mathematical and physical models are discussed and linked. The basis of the selection of separated spatial and time patterns is also presented. In addition, an artificial slot and a thermal fatigue natural crack are applied to validate the proposed method.

Automatic Defect Identification of Eddy Current Pulsed Thermography Using Single Channel Blind Source Separation

Pulsed thermography for non-destructive evaluation and damage growth monitoring of bonded repairs

An overview of corrosion defect characterization using active infrared thermography

http://muscle.ercim.eu/images/DocumentPDF/MP_333_A0-15-2004.pdf

Statistical analysis of IR thermographic sequences by PCA

An image processing procedure is proposed aiming at detecting porosity defects in materials used in the aerospace industry by means of the analysis of C-scan images obtained by ultrasound inspection techniques. An image is described through a number of features, which are then analyzed in order to evaluate the similarity of an unknown examined image with respect to a set of reference ones. The procedure is performed by firstly applying a 2D wavelet transform of the input image and then a feature extraction process based on statistics of the detail images produced by the transform itself. A data reduction process is then applied using the principal component analysis technique. Finally, a decision ruler performs the image classification by considering the distance among points in the principal component plane. An application of this procedure is presented for the analysis of single images, giving a localization of defects. Preliminary results, obtained by processing both simulation images and real C-scan maps, showed the efficacy of the proposed method.

E. Bozzi

Papers

Statistical analysis of IR thermographic sequences by PCA

Defect detection in C-scan maps