School of Mechanical Science & Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
Ultrasonics. 2014 Mar;54(3):914-20. doi: 10.1016/j.ultras.2013.11.003. Epub 2013 Nov 20.
A method is proposed to measure the stress on a tightened bolt using an electromagnetic acoustic transducer (EMAT). A shear wave is generated by the EMAT, and a longitudinal wave is obtained from the reflection of the shear wave due to the mode conversion. The ray paths of the longitudinal and the shear wave are analyzed, and the relationship between the bolt axial stress and the ratio of time of flight between two mode waves is then formulated. Based on the above outcomes, an EMAT is developed to measure the bolt axial stress without loosening the bolt, which is required in the conventional EMAT test method. The experimental results from the measurement of the bolt tension show that the shear and the mode-converted longitudinal waves can be received successfully, and the ratio of the times of flight of the shear and the mode-converted longitudinal waves is linearly proportional to the bolt axial tension. The non-contact characteristic of EMAT eliminates the effect of the couplant and also makes the measurement more convenient than the measurement performed using the piezoelectric transducer. This method provides a promising way to measure the stress on tightened bolts.
提出了一种利用电磁超声换能器（EMAT）测量拧紧螺栓的应力的方法。EMAT 产生剪切波，由于模式转换，剪切波的反射产生纵波。分析了纵波和剪切波的射线路径，然后建立了螺栓轴向应力与两种模式波的飞行时间比之间的关系。基于上述结果，开发了一种 EMAT 来测量螺栓的轴向应力，而无需松开螺栓，这是传统 EMAT 测试方法所需要的。螺栓张力测量的实验结果表明，可以成功接收剪切波和模式转换的纵波，并且剪切波和模式转换的纵波的飞行时间比与螺栓轴向张力呈线性比例关系。EMAT 的非接触特性消除了偶联剂的影响，并且使测量比使用压电换能器进行的测量更方便。该方法为测量拧紧螺栓的应力提供了一种很有前途的方法。
