Calculating hoop stress in threaded fasteners

[debun]

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.

 

[desertfox]

hi debun

Not sure from your post whether you really need hoop stress, normally during tightening of a bolt you get tension and shear stresses.
Have a look at this site:-

http://www.roymech.co.uk/Useful_Tables/Screws/Preloading.html

desertfox

 

[Ron]

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.

 

[loafer09]

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

 

[desertfox]

hi loafer09

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

desertfox

 

[EngAddict]

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.

 

[paddingtongreen]

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.

 

[debun]

Yes this is a regular angled thread. There is a hoop stress.

 

[hydtools]

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

 

[paddingtongreen]

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.

 

[hydtools]

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