Bolt Fatigue Life
Bolt Fatigue Life
(OP)
Juvinall and Marshek (1991 text) and Shigley and Mischke (1989 text) use a similar approach for estimating S-N curves of notched metals, based on tests conducted in smooth rotating members. The test result numbers are then adjusted for certain various factors such as: load type, member size, surface finish, notch type, etc... The texts include surface finish factors for notches (threads) that are machined, ground, hot-rolled or polished, but neither include a surface finish factor for a notch (thread) that is cold rolled. Anyone have a good reference to recommend?
Andy





RE: Bolt Fatigue Life
The general description is that the root will have a flaw free and smooth surface and the root should blend in smoothly at the point of tangency on the flank. It is understood that any defect below the pitch line is detrimental to the fatigue life.
I have seen a call out of a 32 micro inch finish on the shank of high strength > 200,000 PSI fasteners.
On our H11 fasteners we use a binocular microscope (40X) to examine the roots.
You might check out SPS as they have done considerable work on fastener fatigue.
www.spstech.com
RE: Bolt Fatigue Life
In ASTM STP 1236 Structural Integrity of Fasteners, a comparison was made between machined threads and rolled threads in the low cycle fatigue range. At 105 cycles, rolled threads could withstand 1.56 times the stress that machined threads could.
I recommend both ASTM STP 1236 & STP 1391, available at:
http://www.astm.org
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Bolt Fatigue Life
RE: Bolt Fatigue Life