How does bolt size effect fatigue?

[nashjp]

It has come to my attention that we have been using fatigue data obtained from 1/2" bolts (grade 8). A recent test showed that larger bolts (same class/grade) can have a much reduced fatigue limit. I have been unable to find much information on how to account for size but have heard Eurocode 3 and some other codes provide recommendations. I am looking for good sources of information and recommendations to account for size for bolt fatigue.

 

[Bluexcell]

Some pointers:

Eurocode 3 Design of steel structures

Part 1-1 General rules and rules for building
Part 1-1/A1 General rules and rules for building Annexes D and K revised
Part 1-1/A2 General rules and rules for building Annexes G,H,J revised, N and Z
Part 1-2 Structural fire design
Part 1-3 Cold formed thin gauge members and sheeting
Part 1-4 The use of stainless steels
Part 2 Bridges and plated structures
Part 3-1 Towers, masts
Part 3-2 Chimneys
Part 4 Tanks, silos and pipelines
Part 5 Piling
Part 6 Crane structures
Part 7 Marine and maritime structures
Part 8 Agricultural structures


Eurocode 3 links:

http://www.conformance.co.uk/CE_MARKING/ce_cpd.html

http://www.setra.fr/euronormes/Anglais/Telechargements/EurocodesGb.PDF

Design software based on Eurocode 3:

http://www.sharewareconnection.com/play/k3718.html

Bolt selection / analysis software:

http://www.industrialtechnology.co.uk/1999/apr/boltscience.html

Fatigue analysis ( all types ):

http://www.mech.uwa.edu.au/DANotes/intro/contents.html.

http://www.mech.uwa.edu.au/DANotes/threads/home.html

http://www.mech.uwa.edu.au/DANotes/threads/fatigue/fatigue.html.

regards

Bluexcell
# . # Up all night again ....
~

 

[PriamEngineering]

mmm.... How did you conduct your fatigue tests? If you treated the bolt as a rotating beam specimen I'm not suprised you get confusing answers. The analysis of bolted joints is in relaity quite a complex problem. There are several good texts which expalin in fine detail the physics of them (bickord id the best IMHO). However we engineers work in the real world and use standards to design bolted joints. In general if the alternating axial stress in the bolts is less than 6% of the UTS of the bolt (with the UTS no greater than 785 MPa) then there will be no fatigue failure of the bolt. This of course assumes the bolted joint has been assembled correctly.


Good luck

Deeko