Modes of Joint Failure
The main function of a bolt is to clamp two or more joint members together. The objective of
the assembly functio n/process is to introduce tension in the bolt that produces clamping force.
A joint is considered to have failed when there is loss of claming force in the bolt.
There are a number of ways that bolts can lose the clamping force and the joint fail.
a. Mechanical Failure of the bolt
- too much tension during installation (excessive torque applied). (This should never
happen if the joint is designed* right)
- Mechanical failure due to elevated temperature
- Corrosion destroyed the bolt
- Stress corrosion cracking failure
- Fatigue failure
*Design refers to proper material, quality, dimension,
heat treatment, application specs. Etc.
· Poor heat treatment in low cost bolt – head may be pulled off.
· Bolt head welded to threaded rod –
· Bolt designed without proper fillet radii-.