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

• Published in: 中国机械工程学报 Vol. 33; no. 1; pp. 34 - 49
• Main Authors: Qinxue Pan, Ruipeng Pan, Chang Shao, Meile Chang, Xiaoyu Xu
• Format: Journal Article
• Language: English
• Published: School of Mechanical Engineering, Beijing Institute of Technology, Bei-jing 100081, China 2020; Key Laboratory of Fundamental Science for Advanced Machining, Beijing Institute of Technology, Beijing 100081, China
• Subjects: Axial stress; Coupling techniques; Bolted connections; Ultrasonic waves; Influencing factors
• ISSN: 1000-9345; 2192-8258

Bolts are important fasteners indispensable in the manufacturing field for their advantages, which include conveni-ent 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.