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Calculating hoop stress in threaded fasteners

Calculating hoop stress in threaded fasteners

Calculating hoop stress in threaded fasteners

(OP)
Does anyone know of a way to calculate the hoop stress generated by  torquing  fasteners?  I  am working on a design where OD  of my fastener is critical and I would like to make it as small as possible but I don't have a good feel for what the hoop stresses will be like.   

RE: Calculating hoop stress in threaded fasteners

agree, debun...no hoop stress in a bolt.  Shank thickness is a function of the interaction between shear and tension, usually designed for one or the other and then a unity check on the interaction is done.

Torque on a bolt produces tension in the shaft and shear on the threads.

RE: Calculating hoop stress in threaded fasteners

There is also shear stress in the shank due to the torsion applied while tightening the bolt.    

RE: Calculating hoop stress in threaded fasteners

hi loafer09

The shear stresses that Ron and I are refering to are those due to torsion during tightening,

desertfox

RE: Calculating hoop stress in threaded fasteners

so is loafer09, if you read his post properly, he wasn't referring to single or double shear but torsion in the shank.

However this will never be limiting unless it is a custom bolt designed to fail before the threads.

RE: Calculating hoop stress in threaded fasteners

There is a hoop stress unless it is a square thread. Otherwise the the normal force of thread on thread has both vertical and horizontal components, during and after torquing.

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Calculating hoop stress in threaded fasteners

(OP)
Yes this is a regular angled thread.  There is a hoop stress.

RE: Calculating hoop stress in threaded fasteners

I believe the hoop stress would be:
(F*tan(thread angle/2))/(l*(D-d))
where F = fastener load, l = length of internal threaded nut, D = outside diameter of the nut or distance across flats, d = thread pitch diameter.

l*(D-d) is the hoop stress area.

F*tan(thread angle/2) is the radial force at the pitch diameter.

Derived from the geometry of the thread to determine radial force component on the thread causing the nut to dilate.

Ted

RE: Calculating hoop stress in threaded fasteners

hydtools, that is probably a high estimate because it ignores friction.

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Calculating hoop stress in threaded fasteners

True, that would be worst case, fully lubricated threads and nut face.  Accounting for friction will reduce the radial force.  For a thread form angle of 60deg, thread friction and nut face friction both equal to 0.15, the reduced radial force would be L*(.5774 - .15 - .15) = L*.2744.  Without friction the radial force would be L*.5774.

Ted

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