426 ISSN 1061-8309, Russian Journal of Nondestructive Testing, 2020, Vol. 56, No. 5, pp. 426–434. © Pleiades Publishing, Ltd., 2020. Eddy Current Characterization of 3D Crack by Analyzing Probe Signal and Using a Fast Algorithm Search Abderrahmane Abbassi a, *, Tarik Bouchala a, b, ** , ***, Abdelhak Abdou b, c, ****, and Bachir Abdelhadi c, ***** a Faculté e des Sciences Appliqué es, Laboratoire LAGE, Univ Ouargla, Ouargla, 30000 Algérie b Electrical Engineering Department, Med boudiaf University, bp 166 M’sila, Algeria c Laboratory of Electric Traction Systems—(LSTE—Batna 2), Electrical Engineering Department, Faculty of Technology, Batna 2 University, Batna, Algeria *e-mail: abbassi.abderrahmane@univ-ouargla.dz **e-mail: bouchala.tarek@univ-ouargla.dz ***e-mail: tarik.bouchala@univ-msila.dz ****e-mail: abdelhak.abdou.0005@gmail.com *****e-mail: abdelhadi3b@yahoo.com Received March 29, 2019; revised July 24, 2019; accepted August 16, 2019 Abstract—The study of 3D eddy current non destructive testing system for cracks characterization using finite element method requires a great amount of computing time and memory space. In this article, we have validated the developed model and then determined directly the crack length by ana- lyzing the complete signal. Afterwards, we have extracted from the complete sensor sweep signal the maximal amplitude that we have exploited to estimate the crack depth. Keyword: eddy current sensor, crack characterization, 3D finite elements, simplified signal DOI: 10.1134/S1061830920050022 1. INTRODUCTION Any fracture of equipment in operation is a disaster that can have considerable consequences. The frac- ture of a piece in a given structure can cause a succession of catastrophic events that will destroy other parts or equipment in good condition, in need of refurbishment and much longer costly downtime [1]. In less severe cases, these fractures can cause the retirement of machinery and systems stopping the production. In the industrial applications, several objectives are aimed by eddy current nondestructive testing (EC-NDT), [1, 2]. In our case, the objective is to identify the crack length L d and depth D d ; while the crack with is about 0.2 mm [3, 4]. As a first step, in this article, we determine firstly and directly the crack length L d by analyzing the complete signal obtained by displacing the sensor along the defect axis. In fact, we extract by this procedure the defect length L d and sensor resistance R mes that we use as an input in an algorithm com- posed of 3D-FEM implemented in Comsol multiphysics and deterministic algorithm search [5]. So, after convergence the defect depth is obtained. Finally, the crack size and shape can be easily reconstructed. 2. STUDIED DEVICE Eddy current NDT system is composed of an absolute probe inspecting a plate presenting a paral- lelepiped crack as shown in Fig. 1. The simulation of any electromagnetic system needs the knowledge of all physical and geometrical characteristics in different regions. The physical and geometrical parameters of the studied system are given by Table 1 [4]. 3. MESH GENERATION A better resolution requires very fine mesh of the studied domain. However, using a very fine mesh induce an increase in the simulation time. For this reason, the refinement concerns only the sensitive zones such as coil and neighboring space of crack. The mesh depicted in Fig. 2. ELECTROMAGNETIC METHODS