Abstract
The present paper investigates monitoring of fatigue cracks of a metal structure using an eddy current micro sensor. Fatigue cracks tend to occur at bolt-jointed structures on an aircraft. In order to detect the damage quantitatively, a kind of change-prone micro eddy current sensor is designed and fabricated with flexible printed circuit board (FPCB) technology. A forward semi-analytical model is built by extracting a material’s conductivity as the damage feature parameter, and characteristics analysis is conducted based on the model. The research focuses on setting up and utilizing the eddy current fields to analyze interaction of adjoining coils when the damage occurs, and investigating optimization on the working parameters of the sensor. In the experimental section, several common connection structures are applied to explore the sensor’s monitoring ability both in air and in a corrosive environment. The result shows that the optimal working frequency is about 1 MHz. The eddy current micro sensor is capable of monitoring the crack growth with an accuracy of 1 mm, the average error being 4.6 % compared to fracture analysis. The sensor keeps high resolution of damage in aqueous corrosion. Due to the fretting fatigue, wear appears on the polyimide foil, leading to the decreases of the monitoring signal.
Highlights
Structure health monitoring (SHM) is the process of implementing a damage-identification strategy for civil infrastructures and mechanical parts [1]
Condition-based maintenance (CBM) is proposed as a promising philosophy for the application of accurate structural maintenance, instead of traditional scheduled maintenance based on various non-destructive technologies (NDT) [2]
To monitor cracks in the metal structure of an aircraft, a kind of change-prone embedded grating eddy current array sensor is proposed, and a crack extension experiment aiming at verifying the performance of the sensor is carried out
Summary
Structure health monitoring (SHM) is the process of implementing a damage-identification strategy for civil infrastructures and mechanical parts [1]. Structural damage of an aircraft directly affects the safe reliability, mission availability, and service life of a military aircraft. Structure health monitoring could provide reliable information about the damage to a part that should be repaired or be replaced. Extensive investigations have been presented and various sensors have been applied to monitor the state of structures in real time. Fiber Bragg grating (FBG) sensors have been extensively used as a powerful and highly effective method for structural health monitor [3,4,5], including soil nail system [6], slopes [7], piles [8, 9], and so
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