TM 175 considers the mechanisms involved in the phenomenon of bolt self-loosening which may take place during repeated applications of shear loads on the bolted joint, including the relative motion in bolt threads, slackening and unscrewing of the bolt. The torque/tension relationship in prevailing torque nuts is also examined. Examples of bolt self-loosening data are presented describing the effects of pre-loading, bolt clamped length and shear displacement during the loss of bolt clamping force. Good joint design which prevents relative movement of the members is always the best method to prevent bolt self-loosening. However, if vibration or the repetitive application of shear loading is unavoidable and the required pre load cannot be maintained, this Item gives guidance to minimize the loss of clamping force and reduce any damage due to bolt self-loosening.
