Research on the Numerical Calculation Method for Antiloosening Performance of Screwed Joints under Complex Working Conditions

Table 2

Procedures for measuring critical residual preload of loosening by rotation.

Step	Procedure
1	Before the actual working condition test, attaching the ultrasonic transducers to the bolt head (Figure 11).
2	Calibrating the preloads on the bolts to ensure satisfactory accuracy for the preload measurement (Figure 12).
3	For each test of one cycle under actual working conditions, monitoring the residual preload FVR and rotation angle of the marking line (Figure 13).
4	If loosening by rotation occurs in the first monitoring, increasing and remonitoring the assembly preload FM.
5	If loosening by rotation does not occur after multiple observations and the residual preload FVR slowly decreases, reducing and remonitoring the assembly preload.
6	The residual preload FVR is obtained until loosening by rotation occurs after the first monitoring, and the calculation of the critical residual preload of loosening by rotation is calculated using equation (20).