AdvancedTopic 91 of 106Engineering Mechanics
Fasteners and bolted joints
Preload clamps parts together; fatigue and tightening torque are critical.
In depth
Tightening a bolt creates preload that clamps joint members; external load adds only a small fraction to bolt tension. Torque T=K·F·d relates tightening torque to preload. Fatigue is reduced by high preload. Threads, grades and locking devices matter.
Key points
- Preload about 75% of proof strength
- Joint stiffness vs bolt stiffness
- Shear vs tension joints
ExampleWheel nuts are torqued to a specified value.
What is Fasteners and bolted joints?
Preload clamps parts together; fatigue and tightening torque are critical.
Why is it important to understand fasteners and bolted joints?
Bolted joints clamp parts together and carry load through friction and preload, so the bolt size and tightening torque are critical for safety.
Why is preload so important?
Preload keeps the joint clamped, so the bolt sees only a small part of the external load. Loss of preload can let the joint loosen and fatigue the bolt.
How do I find the right torque?
Use the torque-tension relation with the friction coefficient and the required preload, or follow the manufacturer or code value.
How is Fasteners and bolted joints used in practice?
Typical applications include sizing the bolts on a flange connecting two pipes, setting the torque on a wheel nut after changing a tyre and designing a bolt for a bracket that sees fluctuating loads.
What should I learn before Fasteners and bolted joints?
Study "Springs" first (topic 90 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
What are the key points of Fasteners and bolted joints?
Preload about 75% of proof strength. Joint stiffness vs bolt stiffness. Shear vs tension joints.
Can you give an example of Fasteners and bolted joints?
Wheel nuts are torqued to a specified value.
What comes after Fasteners and bolted joints?
The next topic is "Welded joints", which builds directly on this one.
How difficult is Fasteners and bolted joints?
It is classed as Advanced in Engineering Mechanics (topic 91 of 106). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Engineering Mechanics.