Simple principle of ultrasonic measurement of bolt preload

The role of the bolt is to tighten, and it is conceivable that the preload (clamping force) is the most important measurement parameter. However, the pre-tightening force can not be directly measured like torque. It can only be measured by indirect method. The measuring method is also varied. The traditional method includes strain gauge method and washer sensor method, while ultrasonic wave is used to measure the pre-tightening force compared with other methods. The method does have many advantages, and can achieve non-destructive measurement, real measurement, information preservation, and cost saving.