Residual Stress in a Bent U-Bolt
Residual Stress in a Bent U-Bolt
(OP)
I'm looking at a U-bolt that has been bent from A36 rod. It will be loaded in such a way as to produce both tension in the legs and moment in the bend. Does anyone know of a reference that would help me estimate the residual stress in the bend? I plan to stay in the elastic range with a healthy factor of safety, but I would still like some idea of the stesses already in the bolt. I know I could heat each piece to relieve the stress, but I would like to avoid this if possible. Thanks for your help.






RE: Residual Stress in a Bent U-Bolt
Cheers
Greg Locock
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RE: Residual Stress in a Bent U-Bolt
In my mind this is no different from a welded I beam or a rolled section, which everybody knows have residual stresses, sometimes beyond elastic limit and everybody just choose to ignore.
We do de same with A320 bolts that can be re-used after tensioning, even if that tensioning took them over the elastic limit, which it does.
I do not see why the approach would not work with a U-bolt although I would like to hear what other engineers have to say.
Incidentally, I would assume that all U-bolts commercially available have been formed by bending straight rods, I doubt they are cast that way.
RE: Residual Stress in a Bent U-Bolt
To achieve the desires shape it has to go plastic, and apart from going through the heat treatment to relieve the stresses you will have residual effects. But if you get some bloke on the shop floor bending a but of plate sheet in to an angle the same thing occurs. If memory serves correct then wouldn't the stress/strain will follow a hysteresis loop back down to zero stress with an associated permanent strain? Havnt had a coffee yet so I might be confused.
RE: Residual Stress in a Bent U-Bolt
Thanks all for your help.
RE: Residual Stress in a Bent U-Bolt
Page 62 talks about reuse of bolts. It might help.
I still think that the bolt goes plastic, deforms, and when tension drops to zero, the deformation stays, but when loading the bolt again it loads elastically. 40818 put it quite nicely.
RE: Residual Stress in a Bent U-Bolt
AS4100 is based on plastic analysis for compact sections.
AS4100 also, if I recall correctly, stretching the memory a bit, states that a bolt can be reused / retightened, once only, in its original location, then must be replaced with a new version.
Would suggest you investigate specify a "u bolt" "off the shelf" - less risk, hopefully the OEM will specify a rated capacity and should be cheaper (and quicker) then having a contractor complete the deed, in unknown circumstances (doesn’t matter what you tell them, unless you watch and enforce the required procedure).
As stated earlier, suspect some form of stress relieving process may retrieve some of the original properties, subject to details by others. Maybe you could do the modifications with the material at an appropriate temperature (hot work, rather than cold) again, details by others.
Regards,
Lyle