Sensors and Actuators A 309 (2020) 111999 Contents lists available at ScienceDirect Sensors and Actuators A: Physical j ourna l h o mepage: www.elsevier.com/locate/sna A one-dimensional approach towards edge crack detection and mapping using eddy current thermography Natali Barakat a , Jafar Mortadha a , Ali Khan a , Bassam A. Abu-Nabah a,∗ , Mohammad O. Hamdan a , Samer M. Al-Said b a Department of Mechanical Engineering, American University of Sharjah, United Arab Emirates b Department of Mechanical Engineering, Jordan University of Science and Technology, Jordan a r t i c l e i n f o Article history: Received 20 January 2020 Received in revised form 1 April 2020 Accepted 2 April 2020 Available online 6 May 2020 Keywords: Crack detection Eddy current thermography Heat diffusion a b s t r a c t Eddy current thermography (ECT) is an emerging nondestructive evaluation (NDE) technique, which is used to detect defects in metallic components. In this study, a one-dimensional (1D) heat transfer approximation is delivered to detect, locate and size surface edge cracks in bar samples using a low- power ECT experimental setup. The induction of eddy current heat generation function on one side of the sample delivers a quasi-one-dimensional heat transfer model where heat only propagates along the sample. The presented model takes into consideration convection heat transfer losses along the sample. It is demonstrated that convection heat transfer losses are considered negligible as heat propagates along a relatively high thermal conductivity metallic material such as aluminum alloys. This leads to an approximately uniform temperature gradient in a quasi-steady-state heat transfer condition along a crack-free sample. The presence of an edge crack alters the heat propagation near the crack. Accordingly, estimating the temperature gradient along a sample at a quasi-steady-state condition allows the detection and sizing of edge cracks far from the ECT excitation coil. Applying the proposed ECT inspection technique to detect edge cracks in aluminum alloys delivered an accuracy of 13 % in crack depth estimation. © 2020 Elsevier B.V. All rights reserved. 1. Introduction Eddy current thermography (ECT) is an active thermography nondestructive evaluation (NDE) technique, which is used to detect and characterize surface defects in conductive materials and struc- tures [1–3]. Its experimental setup mainly consists of an induction heating system, an excitation coil with an optional water cooling system and a computer-integrated infrared (IR) camera [4–6]. The coil is placed at a small lift-off distance away from the sample’s sur- face where ECT can be applied in one of two modes of operations, namely reflection or transmission modes. In the reflection mode, the IR camera and the coil are placed on the same side relative to the surface of interest, whereas in the transmission mode, the IR cam- era and the coil are placed on opposite sides of the specimen [7,8]. The ECT setup can also be classified as either stationary when there is no relative motion between the specimen and the excitation coil, or moving when relative motion exists [5,9]. The induction heat- ing system generates a high frequency alternating current between ∗ Corresponding author. E-mail address: babunabah@aus.edu (B.A. Abu-Nabah). 10 to 400 kHz in the coil, which then generates an electromag- netic field that interacts with a conductive specimen and induces eddy currents in the material [6,10–13]. Alternatively, eddy current pulsed thermography (ECPT) can be used where induction heating is achieved by generating a short pulse (100−200 ms) of high fre- quency current with a relatively high current amplitude ranging between 100 and 400 A [4,6,7,9,12]. A comparative analysis between ECPT and long-pulse ther- mography (LPT) for the detection of flat-bottom holes (FBHs) demonstrated ECPT’s capabilities in detecting FBHs in materials of higher electric and thermal conductivities such as aluminum alloys [14]. Previous studies have looked into different ECPT con- figurations to characterize rolling contact fatigue (RCF) cracks and proposed designs such as the ferrite-yoke-based structure [12], which was recently modified to L-shaped ferrite magnetic open sensing structure to improve the thermal contrast of omnidirec- tional fatigue cracks [15]. The depth below the specimen’s surface to which eddy current penetrates is called the skin depth or eddy current standard pen- etration depth. As eddy current flows in the material, it generates heat (Joule heat), which diffuses across the specimen [5,13,16,17]. If a specimen contains a defect such as a crack, the eddy current flow https://doi.org/10.1016/j.sna.2020.111999 0924-4247/© 2020 Elsevier B.V. All rights reserved.