Bolt design against fatigue
Bolt design against fatigue
(OP)
In BS4604 it refers to calculating the torque applied to a bolt based upon 0.6 of the proof load, or UTS as I read it. For fatigue applications, however, it says that only 0.5 of the proof load should be used. This appears contradictory to the advice usually given to torque the bolt to almost yield stress to reduce the load variation in the bolt and failure from fatigue. Is there any reason why the design standard should recommend reducing the bolt torque for fatigue load applications?
corus






RE: Bolt design against fatigue
HTH
VOD
RE: Bolt design against fatigue
i might select a torque so that the maximum preload (the upper range of the scatter for the method used to measure torque, PLIs, torque wrench, ...) was fty (maybe 95%fty). a consideration should also be how much tension is expected in service ? (lower tension loads, i'd reduce the preload slightly).
RE: Bolt design against fatigue
From the theory if the maximum preload can be achieved then the stress range on the bolt should be less and as such the chance of fatigue failure reduced. I can only presume that a higher preload increases the mean stress in the bolt and thus hastens failure even though the tress range has been reduced, as Voyagethingy implies. I wondered if there was any reference to this to satisfy other's arguments.
corus
RE: Bolt design against fatigue
h
Furthermore, in a book by the Allianz mention is made of a fatigue limit of approximately 50 MPA, more or less regardless of quality (assuming proper manufaturing).