Bolts can snap due to excessive vibration causing uneven stress or overtightening, often resulting in the top twisting off.
Bolts are designed to hold components together under tension. However, when the forces acting on a bolt exceed its material strength, it can fail, commonly referred to as snapping or breaking. This failure isn't always a clean break; sometimes, the bolt head or a section of the thread twists off.
Causes of Bolt Snapping
Several factors contribute to bolts snapping, as highlighted in the provided reference:
- Vibration and Uneven Stress: According to Thomas, large amounts of vibration can lead to uneven stress on bolts, which can cause breakage. This phenomenon is referred to as “Bolt Locking”. When vibration is significant, the bolt might experience dynamic loading or fatigue, concentrating stress in specific areas rather than distributing it evenly, ultimately leading to failure.
- Overtightening and Improper Tools: The top of the bolt twists off, which is most often the result of tightening the bolt too tightly or using the improper tool for tightening the bolt. Overtightening applies excessive tensile stress to the bolt, potentially stretching it beyond its elastic limit. Using the wrong tool (like an impact wrench on a bolt not designed for it) can apply sudden, high torque, causing shear or torsional stress that the bolt material cannot withstand, resulting in the head shearing off.
Preventing Bolt Snapping
Preventing bolt snapping involves addressing these root causes:
- Use Correct Torque: Always tighten bolts to the specified torque using a torque wrench. This ensures the bolt is sufficiently secured without being overstressed.
- Use Proper Tools: Match the tool to the fastener and the application. Avoid using tools like standard impact wrenches on bolts requiring precise torque control, unless specified.
- Control Vibration: In applications with high vibration, consider using locking nuts, washers, or thread-locking compounds to help maintain bolt tension and prevent loosening or uneven stress caused by movement.
- Ensure Even Loading: Proper joint design and assembly techniques help distribute the load evenly across all bolts in a connection.
By understanding these common causes and taking preventative measures, the risk of bolt failure through snapping can be significantly reduced.
