re: bolt bending
re: bolt bending
(OP)
I usually use the basic minor diameter for computing the section modulus of a bolt in bending. It's the smallest diameter, and thus conservative. But is there perhaps a way to be less conservative?
Has anybody else used the effective diameter that can be back-calculated from the stress area of a bolt in tension, and used that for computing bolt section modulus?
Has anybody else used the effective diameter that can be back-calculated from the stress area of a bolt in tension, and used that for computing bolt section modulus?





RE: re: bolt bending
For a static tensile load I suppose that's not such an issue, but any shear or bending wouldn't it come into play?
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RE: re: bolt bending
If you're bending the threaded part, I wouldn't use the tensile area, because you don't know where the effective section centroid is relative to the centerline, in general, at any point of interest. I.e., the section modulus sort of wobbles along the length of the thread, as the centroid follows a helix, going both above and below the wrapped centerline.
Can you explore uncommon thread forms, e.g. those with large root radii, or just use a larger bolt?
Mike Halloran
Pembroke Pines, FL, USA
RE: re: bolt bending
Thanks for the inputs!
RE: re: bolt bending
Mike Halloran
Pembroke Pines, FL, USA
RE: re: bolt bending
When I do bolted joints in bending, I assume the bolts are infinitely stiff and calculate the bending stresses as increased tensile forces on the bolt see link below and scroll till you see the heading bolts withstanding bending forces:-
http://www.roymech.co.uk/Useful_Tables/Screws/Bolt...
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: re: bolt bending
Bending the threaded section of a bolt is not good design practice. If I were analyzing this, I would use the minor diameter for my bending and stress calculation because it is conservative, as you note. Also, I would consider that the bottom of the thread acts as a stress concentration, making a conservative analysis value that much more important.
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JHG
RE: re: bolt bending
Are you bending the threaded rod to create a hook?
Are you using the threaded rod as a lifting eye?
http://www.e-rigging.com/assets/images/Drawings/Ey...
http://www.e-rigging.com/machinery-eye-bolts
http://i809.photobucket.com/albums/zz11/Bartlomiej...