A Quantitative Comparison among Different Algorithms for Defects Detection on Aluminum with the Pulsed Thermography Technique

Ester D’Accardi,Davide Palumbo,Umberto Galietti,Rosanna Tamborrino

doi:10.3390/met8100859

Ester D’Accardi, Davide Palumbo + Show 2 more

Open Access

https://doi.org/10.3390/met8100859

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Journal: Metals	Publication Date: Oct 20, 2018
Citations: 36	License type: CC BY 4.0

Affiliation: Polytechnic University of Bari

Abstract

Pulsed thermography is commonly used as a non-destructive technique for evaluating defects within materials and components. In the last few years, many algorithms have been developed with the aim to detect defects and different methods have been used for detecting their size and depth. However, only few works in the literature reported a comparison among the different algorithms in terms of the number of detected defects, the time spent in testing and analysis, and the quantitative evaluation of size and depth. In this work, starting from a pulsed thermographic test carried out on an aluminum specimen with twenty flat bottom holes of known nominal size and depth, different algorithms have been used with the aim to obtain a comparison among them in terms of signal to background contrast (SBC) and number of detected defects by analyzing different time intervals. Moreover, the correlation between SBC and the aspect ratio of the defects has been investigated. The algorithms used have been: Pulsed Phase Thermography (PPT), Slope, Correlation Coefficient (R2), Thermal Signal Reconstruction (TSR) and Principal Component Thermography (PCT). The results showed the advantages, disadvantages, and sensitivity of the various thermographic algorithms.

Highlights

Aluminum alloys, thanks to their low density and ability to resist corrosion, are widely used for manufacturing mechanical components and large structures and, in this regard, many examples can be found in different engineering fields from building to automotive and aerospace.During the manufacturing processes or in-service conditions, several defects may appear in materials that can affect the structure and its mechanical properties
Number of signal to background contrast (SBC); detected defects; maximum maximum SBC; The defect detection has been assessed by imposing a threshold value equal to two times the SDS, The defect detection has chosen been assessed by imposing a threshold value equalif: to two times the for each of the seven intervals for analysis
The different algorithms are investigated under different points of view: number of detected defects, maximum SBC, and correlation between the SBC value and the aspect ratio

Summary

Introduction

Thanks to their low density and ability to resist corrosion, are widely used for manufacturing mechanical components and large structures and, in this regard, many examples can be found in different engineering fields from building to automotive and aerospace.During the manufacturing processes or in-service conditions, several defects may appear in materials that can affect the structure and its mechanical properties. Several non-destructive techniques (NDT) can be used to detect such defects such as X-ray, ultrasound [1], eddy current [2], magnetic method [3] and penetrant test. Wilczek et al [1] performed a comparison among different NDT techniques such as: X-ray, ultrasonic, eddy current and thermography to detect flaws in aluminum pressure die casting. Regarding the porosity detection in aluminum pressure die casting, the radiographic method allows for analyzing raw casting without surface preparation while eddy current and thermography are not suitable for the detection of fine porosity.

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