Study of EMI-Based Damage Type Identification in a Cracked Metallic Specimen Repaired by a Composite Patch
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LECTROMAGNETIC METHODS
Study of EMI-Based Damage Type Identification in a Cracked Metallic Specimen Repaired by a Composite Patch Amir Hossein Keshvari Farda, *, Roohallah Ghasemib, and Bijan Mohammadic a
School of Aerospace Engineering, Sharif University of Technology, Tehran, Iran b School of Mechanical Engineering, Tehran University, Tehran, Iran c School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran *e-mail: [email protected] Received May 9, 2019; revised August 11, 2019; accepted August 23, 2019
Abstract—Using adhesively bonded composite patch repairs has been increased in various industries to improve the structural integrity of cracked metallic structures in recent decades. Monitoring of crack propagation and composite patch debonding, as two dominant failure mechanisms in this repair technique, plays a significant role in the integrity assessment of the component. This research conducts an experimental investigation on the simultaneous monitoring of these two failure mechanisms in a cracked metallic specimen repaired by a composite patch. For this purpose, the electromechanical impedance method was used to evaluate the feasibility of recognizing the type of damage at any phase of total damage propagation process. Two piezoelectric sensors were implemented, one mounted on the metal and the other on the composite patch. Investigation of impedance spectrums and damage index trends showed that debonding and crack propagation produce different effects on the measurements made by sensors. These differences were used as a basis of identifying the type of damage. As a result, some features were introduced to classify the type of damage in each step of damage propagation. Keywords: crack, debonding, electromechanical impedance, piezoelectric, structural health monitoring, composite patch, damage index DOI: 10.1134/S1061830920060054
1. INTRODUCTION During recent decades, composite patches have been widely used to repair cracked and corroded metallic components in various industries [1]. This method is an efficient approach to extend the life of structures as well as maintaining their efficiency [2]. Adhesively bonded composite patches have many advantages such as improving fatigue behavior, maintaining strength and stiffness, reducing corrosion effects, and easy implementation on complex surfaces [1]. However, the two significant sources of damage in this kind of repair are debonding of the patch from the structure and propagation of cracks in the damaged structure under the patch. Obtaining information about the state of crack propagation and debonding is the most critical factor in determining the health of repair and its efficiency. Since the damage of metallic components is not visible after the repairing process, it is a challenging task to acquire a proper perception about the repair efficiency in critical parts of a structure, particularly on inaccessible components and where conducting non-destructive tests are not easily feasible. To solve this problem, it seems
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