ABSTRACT
The test results show that bolt loosening is a function of both oscillatory torque amplitude and bolt initial shank stress. A representative plot of cycles to loosening versus oscillatory torque amplitude curves for a 1/2-13 standard cap screw at different initial preloads is shown in Figure 7. Examination of these bolt loosening curves shows that in some respects they are similar to fatigue curves. As the amplitude of the applied oscillatory torque is reduced, a larger number of cycles is required for bolt loosening, until eventually the bolt will apparently withstand a certain level of fluctuating torque indefinitely. This finding led Clark and Cook (1966) to the conclusion that accidental overloads contribute more to bolt loosening than do continuous repetitive oscillatory torques of small amplitude.
