An Eddy Current-Based Structural Health Monitoring Technique for Tracking Bolt Cracking.

Hu Sun,Dawei Lin,Xinlin Qing,Tao Wang,Yishou Wang

doi:10.3390/s20236843

Abstract

Bolted joints are the primary structures for the load transfer of large-scale structures. It is vital to monitor the process of bolt cracking for enduring structural safety. In this paper, a structural health monitoring technique based on the embedding eddy current sensing film has been proposed to quantify the crack parameters of bolt cracking. Two configurations of the sensing film containing one-dimensional circumferential coil array and two-dimensional coil array are designed and verified to have the ability to identify three crack parameters: the crack angle, the crack depth, and the crack location in the axial direction of the bolt. The finite element method has been employed not only to verify the capacity of the sensing film, but also to investigate the interaction between the crack and the eddy current/magnetic field. It has been demonstrated that as the crack propagates, the variations of the induced voltage of the sensing coils are influenced by both eddy current effect and magnetic flux leakage, which play different roles in the different periods of the crack propagation. Experiments have been performed to verify the effectiveness and feasibility of the sensing film to quantify three crack parameters in the process of the bolt cracking.

Highlights

Bolted joint is one of the most critical processes of assembly connection for large-scale structures, such as aircraft, civil engineering, train, marine structures, etc., because it plays a vital role in transferring the main load and ensuring the structural safety
There are two classical methods used to detect cracks at the bolt: longitudinal wave method and shear wave method. Because of their different principles, the noticeable difference between the two methods is that the transducer of longitudinal wave is located at the top of the bolt, while that of the shear wave is located at the cylinder side of the bolt
The purpose of this paper is to develop an eddy current array sensing film that can quantitatively monitor the process of bolt cracking

Summary

Introduction

Bolted joint is one of the most critical processes of assembly connection for large-scale structures, such as aircraft, civil engineering, train, marine structures, etc., because it plays a vital role in transferring the main load and ensuring the structural safety. The bolt cracking often occurs due to the electrochemical corrosion, stress corrosion, hydrogen embrittlement, fatigue, etc., which causes structural failure and has been a severe threat to the structural security [1,2,3]. The bolt is often used in the harsh environment such as complex stress, high temperature and high pressure, periodic vibration, etc., and is affected by temperature, stress, and vibration fatigue for a long time, which causes the initiation and progress of fatigue cracks. If the bolt crack cannot be detected in time, it can cause bolt fracture and more severe accidents. Some nondestructive testing (NDT) methods are used to detect cracks in bolts. There are two classical methods used to detect cracks at the bolt: longitudinal wave method and shear wave method. Ultrasonic phased array technology is used to visually scan and image the cracks at the bolt

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Methods

Conclusion