Research Review of Principles and Methods for Ultrasonic Measurement of Axial Stress in Bolts

Qinxue Pan,Chang Shao,Xiaoyu Xu,Meile Chang,Ruipeng Pan

doi:10.1186/s10033-020-0431-x

Qinxue Pan, Chang Shao + Show 3 more

Open Access

https://doi.org/10.1186/s10033-020-0431-x

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Abstract

Bolts are important fasteners indispensable in the manufacturing field for their advantages, which include convenient assembly and disassembly, easy maintenance, refastenability to prevent looseness, and the avoidance of a phase change in the connected material composition. The precise control of the tightening force in bolts is closely related to the safety and reliability of the connected equipment or structure. Although there are many methods for estimating the tightening force applied to a bolt during assembly, poor accuracy in controlling the preload during the tightening process and a lack of monitoring to determine the residual axial force in service remain issues in evaluating the safety of bolted assemblies. As a nondestructive testing technology, ultrasonic measurement can be applied to successfully address these issues. In order to help researchers understand the theoretical basis and technological development in this field and to equip them to conduct further in-depth research, in this review, the basic knowledge describing the state of stress and deformation of bolts, as well as conventional testing methods are summarized and analyzed. Then, through a review of recent research of the ultrasonic measurement of the axial stress in bolts, the influence of the effective stressed length and temperature are analyzed and proposed methods of calibration and compensation are reviewed. In order to avoid coupling errors caused by traditional piezoelectric transducers, two newly proposed ultrasonic coupling technologies, the electromagnetic acoustic transducer (EMAT) and the permanent mounted transducer system (PMTS), are reviewed. Finally, the new direction of research of the detection of residual axial stress in in-service bolts that have been assembled to yield is discussed.

Highlights

Bolts are indispensable fasteners in the manufacturing and national defense industries and are critical components of important infrastructure, such as aerospace, vehicle, ship, railway, bridge, and building facilities
As a nondestructive and high-precision testing technology, the ultrasonic method can eliminate the influence of the friction coefficient on the measurement of torque and provide both online preload measurement during the assembly process and real-time monitoring of the change in residual axial force during service
It has been observed that this method provides sufficient resolution to estimate an axial stress less than 10% of the yield stress of the material with a maximum error of 5%

Summary

Introduction

Bolts are indispensable fasteners in the manufacturing and national defense industries and are critical components of important infrastructure, such as aerospace, vehicle, ship, railway, bridge, and building facilities. The change in the resistance of the strain gauge from before to after tightening is measured by the resistance strain gage to indirectly obtain the axial stress in the bolt The accuracy of this method is higher than that of the torque method, but it is necessary to attach a strain gauge to the surface of every bolt, which can be time consuming, difficult to do, and provides poor stability in application. As a nondestructive and high-precision testing technology, the ultrasonic method can eliminate the influence of the friction coefficient on the measurement of torque and provide both online preload measurement during the assembly process and real-time monitoring of the change in residual axial force during service.

Ultrasonic Measurement Methods Based on Acoustoelasticity Theory

Analysis of Influencing Factors

Findings

Discussion of Development Prospects

Conclusions and Outlook