Bolt tension monitoring with reusable fiber Bragg-grating sensors

Abstract

Bolted/mechanical fastening is one of the oldest and most widely used joining techniques. While it has many advantages such as ease of assembly and repair, it also has some important limitations. One such concern is bolt clamping load control and monitoring during and after joint assembly. Conventionally used torque wrenches can provide only an approximation of the clamping load and cannot be used for load monitoring. Clamping force transducers are bulky, expensive, and cannot usually be incorporated into the bolted joint for continuous load monitoring in the field. In this work, a novel implementation of a transducer device, called here for convenience the ''bolt tension monitor,'' is described and tested. It utilizes removable and reusable fiber Bragg-grating sensor(s) embedded in a bolt shaft for preload and retained clamping force measurements. While the inherent small size of the fiber Bragg-grating provides precise monitoring without significant effect on the intrinsic properties of the bolt, the embedding of an fiber Bragg-grating sensor with temporary adhesives allows quick assembly, disassembly, and reassembly of the sensor. Furthermore, these instrumented bolts can be used for structural health monitoring and defect detection in joints and structures. The technique shows great potential in simple adaptation to conventional manufacturing practices, precise clamping load measurement, and structural health monitoring of bolts and resulting joints.

Approach to feed drive load measurements in heavy turning

“…For the sensor to function properly it must be preloaded by means of a screw. An interesting solution is screw stress measurement by a built-in fibre-optic Bragg sensor [16]. This could make possible transmission of force on the same principle as in the designed system, but without the use of ring sensors.…”

Axial Load Measurement of Bolts with Different Clamping Lengths Based on High-Frequency Ultrasonic ZnO Film Sensor

“…The torque and turn-of-the-nut methods are always used for pre-tightening, and their axial load measurement error is up to 25% [ 3 ]. The FBG method generally encapsulates the FBG sensor on the outer surface of the screw or inserts it inside the bolt to measure the unevenly distributed strain [ 4 ]. However, the bolt structure needs to be destroyed to measure the axial load of the bolt [ 5 ].…”

Full-range bolt preload monitoring with multi-resolution using the time shifts of the direct wave and coda waves

“…Some traditional methods, including the strain gauge-based methods, 21 vibration-based methods, [22][23][24][25] ultrasonic-based methods, 26,27 and impedance-based methods, [28][29][30][31][32] need to bond sensors to the structures, and therefore they belong to the contact approaches. In recent years, novel contact measuring approaches, for example, the fiber Bragg gratings (FBG)-based approaches 33,34 and the vibro-acoustic modulation-based methods, [35][36][37] were developed. With the rapid development of smart materials and systems, intelligent components, 38 such as smart bolts or smart nuts, were proposed.…”