Quote:
Originally Posted by bcredliner
... They are regular M10 - 1.5 x 55mm, class 10.9, hex head with captive flat washer, and a 10.9 hex nut with flange ... nuts and bolts. Some bolts are specially designed to be used in a torque to yield application, for example with a long unthreaded reduced diameter neck, so all the yield happens there rather than in the threaded section. These are not. They are regular bolts.
Never heard they are standard bolts before. Where did you find documentation? Great! Anybody have a link to the exact bolt?
BMW specifies that they be torqued using an initial torque plus an angle. TTA. They also specify that they be replaced when removed, which suggests that they are TTY, or torque-to-yield (that following the TTA spec will cause plastic deformation). But it is not 100% certain that they yield when following the TTA specs. To be careful, I assume they do.
Didn't you just write that you assume there is plastic deformation (stretched to point they won't return to original specs)? That means they are not reusable. Standard or otherwise. If there is plastic deformation they should not be used again as the clamping power will be less than spec. We can't be 100% sure but oh well?
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Here are a couple of links to the actual BMW bolt:
https://parts.bmwofsouthatlanta.com/...lt-31101096987
https://www.ecstuning.com/b-genuine-...r/31101096987/
If you google on the part number, you'll find the exact same bolt used in many applications other than for the reinforcement plate on the X5. That, along with everything else about it, suggests that it is a regular bolt. (well, a regular Class 10.9 ...)
The spec is TTA. Whether it actually yields or not is not certain, as far as I know. I've seen signs of deformation on some of my own bolts, but maybe that was from someone overtorquing at some point. I expect that the TTA takes it close to yield, if not into yield. So to be conservative, BMW specifies replacement, and I act as if yield occurs, whether or not it does. Yes, the fact that BMW specifies replacement, I take to mean that they think it might be yielding.
And no, yield (plastic deformation) of a bolt, in general, does not definitively mean it is not reusable. Not at all. Plastic deformation in a steel bolt will cause work hardening that strengthens it, so it should be able to return to the same amount of stretch with no further plastic deformation (all elastic now).
Quote:
Originally Posted by bcredliner
So in short, there are regular bolts that may be used in a TTY application.
So BMW states the torquing process of a TTY bolt just for grins, so forums can debate this forever?
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It's not a TTY bolt, as I tried to say. It's a regular bolt, used in an application with a TTA tightening spec, that may or may not result in yield (if yes, then TTA becomes TTY), probably causing BMW to conservatively suggest replacement, which almost everyone ignores with no ill effects.
BTW, TTA is a very accurate way to torque fasteners, regardless of yield or not. So if yield is known not to occur, a TTA spec will result in more predictable clamping force than just a torque spec.
As I mentioned in probably another thread on this general topic (search on this site, there are probably only a hundred or so to look through), the important thing to avoid is doing the TTA repeatedly. If yield is occuring, you can't keep doing the same angle, since each time, you will pushing further into the yield region, eventually causing fracture.