Infrared thermography based defect detection in ferromagnetic specimens using a low frequency alternating magnetic field |
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| Affiliation: | 1. Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu 603102, India;2. Department of Optoelectronics, University of Kerala, Thiruvananthapuram 695581, India;1. State Key Laboratory for Strength and Vibration of Mechanical Structures, Shaanxi Engineering Research Center of Nondestructive Testing and Structural Integrity Evaluation, School of Aerospace Engineering, Xi’an Jiaotong University, Xi’an 710049, China;2. School of Aerospace, Transport and Manufacturing, Cranfield University, Bedfordshire MK43 0AL, UK;3. Institute of Fluid Science, Tohoku University, Aoba-ku, Sendai, Miyagi 980-8577, Japan;1. Fraunhofer IIS/EZRT, Flugplatzstrasse 75, 90768 Fuerth, Germany;2. Institute of Photonic Technologies (LPT), Friedrich-Alexander-Universität Erlangen-Nürnberg, Konrad-Zuse-Straße 3-5, 91052 Erlangen, Germany |
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| Abstract: | A new active infrared thermography based technique is proposed for defect detection in ferromagnetic specimens using a low frequency alternating magnetic field induced heating. The test specimens (four mild steel specimens with artificial rectangular slots of 8.0, 5.0, 3.3 and 3.0 mm depths) are magnetized using a low frequency alternating magnetic field and by using an infrared camera, the surface temperature is remotely monitored in real time. An alternating magnetic field induces an eddy current in the specimen which increases the specimen temperature due to the Joule’s heating. The experimental results show a thermal contrast in the defective region that decays exponentially with the defect depth. The observed thermal contrast is attributed to the reduction in induction heating due to the leakage of magnetic flux caused by magnetic permeability gradient in the defective region. The proposed technique is suitable for rapid non-contact wide area inspection of ferromagnetic materials and offers several advantages over the conventional active thermography techniques like fast direct heating, no frequency optimization, no dependence on the surface absorption coefficient and penetration depth. |
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| Keywords: | Infrared thermography Magnetic induction thermography Magnetic flux leakage Eddy current thermography Mild steel Ferromagnetic materials |
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