# Inductive Thermography as Non-Destructive Testing for Railway Rails
## 8 Discussion and Conclusions  
Inductive thermography is an excellent non-destructive testing method for localizing surface defects in metallic materials in a contact-free and quick way. Especially in the case of ferro-magnetic materials, inductive heating is very efficient and a short heating pulse of 0.1-0.3 s is enough to achieve 1-2 \({}^{\circ}\)C of temperature increase at the surface during the heating, which allows the detection of irregularities with an IR camera. A further advantage of the method is that it not only shows the cracks at the surface, but it also gives an impression of how the cracks lie below the surface. The recorded IR sequence is evaluated in one phase image, reducing the negative effects of inhomogeneous heating and inhomogeneous surface properties, and resulting in an image with very good quality.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Average Surface** & **Average Distance** & **Average Length** \\  & **Angle (a)** & **(c) [mm]** & **(0) [mm]** \\ \hline
**RP02** & \(-40^{\circ}\) & 2.54 & 17.1 \\
**RP03** & \(-42^{\circ}\) & 5.27 & 21.8 \\
**RP04** & \(36^{\circ}\) & 1.7 & 9.2 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The results from the three different pieces of rail.  
Figure 21: (a): Phase image of squat defects measured with inductive thermography; (b): close-up photo of the right squat.  
Head checks on railway rails can cause catastrophic events if they are not detected in time. Nowadays, eddy current testing and ultrasound testing are usually used to inspect the rails. Inductive thermography has great potential as non-destructive testing method to inspect the rails, but the technique is not yet used in the field, only in the laboratory. We have inspected several different railway rails and developed an image processing tool for characterizing head checks. Two different kinds of measurement method were used to inspect long tracks:'stop-and-go' and the scanning technique. The first one gives better results with higher contrast, but the second one is more practicable. Therefore, further research work is planned to improve the quality of the scanning technique to obtain the same image quality as the'stop-and-go' method.  
The following are available online at [[https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)]([https://www.mdpi.com/2076-341](https://www.mdpi.com/2076-341)) 7/11/3/1003/s1, Video S1: Panorama View.  
[PERSON] has performed the experiments, evaluated the images, calculated the rectification and the scanning technique. [PERSON][PERSON] has done the finite element simulations, developed the theory behind the software and written the main part of the software, and she supervised [PERSON] by his work. [PERSON] has provided the rail test specimens, organized the artificial crack arrangements and contributed to the text via the section on head check development and proof reading. All authors have read and agreed to the published version of the manuscript.  
The authors gratefully acknowledge the financial support under the scope of the COMET program within the K2 Center \"Integrated Computational Material, Process and Product Engineering (IC-MPPE)\" (Project No 859480). This program is supported by the Austrian Federal Ministries for Climate Action, Environment, Energy, Mobility, Innovation and Technology (BMK) and for Digital and Economic Affairs (BMDW), represented by the Austrian research funding association (FFG), and the federal states of Styria, Upper Austria and Tyrol.  
Not applicable.  
The authors gratefully acknowledge the support from voestalpine Rail Technology GmbH, especially [PERSON] and [PERSON]. Furthermore.  
The authors declare no conflict of interest.