LOOSENING OF THREADED FASTENINGS BY VIBRATIONS

Loosening of threaded fastenings by vibrations was divided into two processes: an increasing bolt load process and a decreasing bolt load process. There were two parts of calculation manipulated in each process.;The second part was to calculate the angle of nut loosening by using the results obtained from two torque equilibrium equations, one for a bolt and the other for a nut.;The conclusions of this thesis were: (1) Increasing the thread friction will decrease the speed of nut loosening. (2) Increasing the base friction will decrease the speed of nut loosening. (3) Increasing the helix angle will increase the speed of nut loosening. (4) According to an investigation of the effect of thread angles of 40, 50, and 60 degrees on nut loosening, increasing the thread angle will increase the speed of nut loosening. (5) Increasing the nut wall thickness will decrease the speed of nut loosening. (6) Increasing the nut height will decrease the speed of nut loosening. (7) According to an investigation of the effect of the bearing pressure distribution with m = 0.5, 1.0, and 1.5 (m is the ratio of pressure at the outermost radius to the average pressure) on nut loosening, the loosening is maximum at m = 0.5. (8) Increasing the bolt length will decrease the speed of nut loosening. (9) Increasing the bolt preload will increase the speed of nut loosening. (10) Increasing the dynamic-static load ratio will increase the speed of nut loosening.;The first part was to calculate the load distribution in the engaged threads by modifying Sopwith's model. This thread load was used to compute stress, strain, and displacement in a bolt and a nut.