(1) The fundamental principle behind using friction is to prevent relative rotation between the threaded components. This can be achieved through various methods such as elastic washers (including flat spring washers and corrugated spring washers), double nuts, and nylon locking rings. These solutions rely on the frictional force generated between the threads to maintain the connection's integrity under vibration or dynamic loads.
(2) Another approach is to break the relationship between the thread pair by converting it into a non-moving joint, which eliminates the possibility of rotation. Common techniques include welding, spot welding, and the use of metal bonding agents. Additionally, thread-locking sealants function as a form of metallic bond. Once heated to a specified temperature, these sealants lose their effectiveness, allowing for easy removal without damaging the fastener.
Improving the fatigue strength of bolted connections is crucial, as the failure of tensioned bolts often results from fatigue rather than static loading. To enhance this, several key measures can be taken:
(1) It is essential to apply the correct pre-tension force during installation. When the rigidity of the joint remains constant, increasing the pre-tension can significantly improve the bolt’s fatigue resistance and help eliminate harmful gaps in the assembly.
(2) Enhancing the load distribution along the threads is also important. In most cases, the force applied to each thread is uneven, with the first thread bearing the highest stress and the load decreasing toward the end of the nut. After about the eighth thread, the remaining threads experience minimal stress.
To address this, methods such as using a slotted nut, an internal conical nut, or a ring groove nut can be employed. Another effective solution is the use of a wire screw sleeve. The main goal is to reduce additional stresses and stress concentrations by ensuring that the bolt axis remains perpendicular to the contact surface of the joined parts. This helps the bolt only experience tensile forces instead of bending moments. Practical solutions include adding a spherical washer, using a wedge washer to match an inclined surface, or incorporating features like bosses or recessed seats.
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