Abstract Under alternating axial external forces, threaded fasteners are prone to fatigue failure. At present, the main focus is on improving material strength to optimize fatigue resistance; most of these methods have greatly increased the cost. Plastic strengthening is a traditional method that does not increase the cost, is easy to operate and can effectively improve the fatigue resistance. Without changing the fastener, the fatigue resistance can be enhanced to a certain extent by simply pre-tightening it beyond the target clamping force and then untighten it to the target clamping force. However, currently there is no clear specification for the maximum pre-tightening force that exceeds the target clamping force. Too strong or too weak maximum pre-tightening force may cause micro-cracks in the fastener or fail to be effectively strengthened. In addition, the strengthening mechanism of the threaded structure has not been clearly explained. This study, the relationship between the strengthening level and the using conditions is clarified through experiments and finite element stress analysis, and the plastic strengthening mechanism is revealed, which is also of guiding significance for the plastic strengthening of other structures.
Hou et al. (Thu,) studied this question.