Bolt preload measurement based on the acoustoelastic effect using smart piezoelectric bolt

Precise measurement of bolt preload force is particularly important in the assembly process of aviation equipment, which is directly related to the normal working performance and indicators of the equipment. According to the acoustoelastic effect, a model considering theoretical error and measurement error is proposed. The relationship between the change of time-of-flight (CTOF) and the bolt preload is established by the model. With the increase of the preload, the CTOF approximately increases linearly. Therefore, a smart piezoelectric bolt was developed. Piezoceramic transducer is embedded in the bolt head at pre-determined spatial locations. Experimental results show that the relative error of the smart bolt is about 1%. In addition, the influence of contact pressure and contact phase is discussed. The results show that the characteristic of smart piezoelectric bolt eliminates the effect of the couplant and makes the measurement more precise than the measurement performed using the ultrasonic probe. This method provides a promising way to measure the bolt preload.