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Bolt Looseness Detection Based on Piezoelectric Impedance Frequency Shift
Open AccessArticle

A Smart Washer for Bolt Looseness Monitoring Based on Piezoelectric Active Sensing Method

Key Laboratory of Metallurgical Equipment and Control of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, China
Author to whom correspondence should be addressed.
Academic Editor: Gangbing Song
Appl. Sci. 2016, 6(11), 320;
Received: 21 September 2016 / Revised: 14 October 2016 / Accepted: 20 October 2016 / Published: 26 October 2016
(This article belongs to the Special Issue Structural Health Monitoring (SHM) of Civil Structures)
Piezoceramic based active sensing methods have been researched to monitor preload on bolt connections. However, there is a saturation problem involved with this type of method. The transmitted energy is sometimes saturated before the maximum preload which is due to it coming into contact with flat surfaces. When it comes to flat contact surfaces, the true contact area will easily saturate with the preload. The design of a new type of bolt looseness monitoring sensor, a smart washer, is to mitigate the saturation problem. The smart washer is composed of two annular disks with contact surfaces that are machined into convex and concave respectively, to eliminate the complete flat contact surfaces and to reduce the saturation effect. One piezoelectric patch is bonded on the non-contact surface of each annular disk. These two mating annular disks form a smart washer. One of the two piezoelectric patches serves as an actuator to generate an ultrasonic wave that propagates through the contact surface; the other one serves as a sensor to detect the propagated waves. The wave energy propagated through the contact surface is proportional to the true contact area which is determined by the bolt preload. The time reversal method is used to extract the peak of the focused signal as the index of the transmission wave energy; then, the relationship between the signal peak and bolt preload is obtained. Experimental results show that the focused signal peak value changes with the bolt preload and presents an approximate linear relationship when the saturation problem is experienced. The proposed smart washer can monitor the full range of the rated preload. View Full-Text
Keywords: bolt loosen; active sensing; smart washer; non-destructive monitoring bolt loosen; active sensing; smart washer; non-destructive monitoring
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MDPI and ACS Style

Yin, H.; Wang, T.; Yang, D.; Liu, S.; Shao, J.; Li, Y. A Smart Washer for Bolt Looseness Monitoring Based on Piezoelectric Active Sensing Method. Appl. Sci. 2016, 6, 320.

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