Enhanced contrast detection of subsurface defects by pulsed infrared thermography based on the fourth order statistic moment, kurtosis

Francisco J Madruga,Olga M Conde,Xavier P Maldague,Clemente Ibarra-Castanedo,José M López-Higuera,Douglas D Burleigh,Ralph B Dinwiddie

doi:10.1117/12.818684

Abstract

The automatic detection of subsurface defects has become a desired goal in the application of non-destructive testing and evaluation techniques. In this paper, an algorithm based on the fourth order standardised statistic moment, i.e. kurtosis, is proposed for detection and/or characterization of subsurface defects having a thermal diffusivity either higher or lower than the host material. The analysis of thermographic data for the detection of defects can be reduced to the temporal statistics of the thermographic sequence. The final result provided by this algorithm is an image showing the different defects without the necessity of establishing other evaluating parameters such as the delayed time of the first image or the acquisition frequency in the analysis, which are required in other processing techniques. All the information is contained in a single image allowing to discriminate between the defect types (high o low thermal diffusivity). Synthetic data from Thermocalc® and experimental works using a PlexiglasTM specimen were performed showing good agreement. Processed results using synthetic and experimental data with other methods used in the field of thermography for defect detection and/or characterization are provided as well for comparison.

Highlights

Thermal inspection is a useful technique for the non-destructive testing and evaluation (NDT&E) of materials and systems
The aim of this paper is to investigate the performance of the fourth order statistic parameter, namely kurtosis, applied to pulsed thermographic inspection
The proposed method based on the kurtosis statistic parameter has demonstrated to be a promising tool for detecting subsurface defect from pulsed thermography data

Summary

Introduction

Thermal inspection is a useful technique for the non-destructive testing and evaluation (NDT&E) of materials and systems. The pulsed thermography technique is capable of detecting defects in large areas in a fast manner (a few seconds or minutes). The technique is based on the detection of surface temperature anomalies that appear in response to the application of a thermal pulse to the specimen surface. Several processing techniques have been proposed in order to improve defect detection and quantification. Thermal contrast-based techniques are very popular since they allow enhancing the defect contrast with simple subtraction operations[1]. The main drawbacks or this kind of algorithms are that they required to establish a non-defective area to calculate the thermal contrast, which is seldom easy or possible to do, and that they are strongly affected by nonuniform heating[2]. There is no reduction on the amount of data to be processed

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