Glossary

A dynamic load on fasteners is a force that changes in magnitude or direction over time, contrasting with a constant and steady static load. Because these loads fluctuate, they put a different, more complex kind of stress on a fastener than a static load does. Dynamic loads can originate from a variety of sources, including vibrations from machinery, sudden impacts, or repeated cyclic forces. An understanding of dynamic loading is critical for engineers, who must design systems that can endure these forces without failing.

How dynamic loads affect fasteners
The effects of dynamic loads pose significant challenges to fastener integrity. Constant vibration or fluctuating forces can cause a fastener to lose its preload, which is the clamping force that holds a joint together. If this preload decreases, the fastener can gradually loosen. This is particularly problematic in situations with repeated, back-and-forth applications of force, known as fatigue or cyclic loading. Over time, these cyclic stresses can cause micro-cracks to form in the fastener's material, which can eventually lead to a sudden and catastrophic fatigue failure, even at stress levels below the fastener's maximum tensile strength. Dynamic loads can also cause stress concentration in certain areas of a bolted joint, increasing the risk of failure at those specific points due to uneven force distribution.

Methods for mitigating dynamic load effects
Engineers and designers employ several strategies to prevent fastener failure from dynamic loads. To prevent fasteners from vibrating loose, locking mechanisms are used, such as thread lockers, locknuts, or toothed washers. For applications involving high-cycle fatigue, chemical-based adhesive anchors can provide a strong bond capable of handling repeated movement. Another approach is to design the overall joint to be more rigid than the fastener itself, which shifts the burden of dynamic forces onto the joint, thereby reducing the stress placed directly on the fasteners. These methods are crucial for ensuring the reliability and safety of components subjected to fluctuating forces.