基于模式转换的电磁超声螺栓轴力测量

Electromagnetic ultrasonic measurement of bolt axial force based on mode conversion

针对传统的螺栓轴向应力测量的不足和压电超声在无损检测的缺陷,提出一种利用电磁超声换能器(EMAT)测量紧固螺栓轴向应力的方法,通过EMAT在螺栓趋肤层产生横波,由于波形转换在螺栓端面的反射而产生纵波,分析纵波和横波的射线路径,得出螺栓轴向应力与两种模态波飞行时间的比值关系。实验结果表明:所提方法可以成功地接收模态转换纵波,并且得出横波与模态转换纵波的声速比与螺栓的轴力变化成线性关系,从而以此关系测量螺栓的轴力。

In view of the deficiency of traditional bolt axial stress measurement and the defect of piezoelectric ultrasonic in nondestructive testing, a method of measuring bolt axial stress by using electromagnetic ultrasonic transducer(EMAT)is proposed.Transverse wave is generated in bolt skin layer by EMAT,and longitudinal wave is generated due to the reflection of wave transformation on bolt end face.The ray paths of longitudinal wave and transverse wave are analyzed, and the relationship of ratio between bolt axial stress and the time-of-flight of two modal waves is obtained.The experimental results show that the method can successfully receive the mode converted P-wave, and the sound velocity ratio of S-wave and mode converted P-wave has a linear relationship with the axial force of the bolt, so as to measure the axial force of the bolt.