Torsional Wind-Up in Studs

[swall]

This somewhat pertains to my Helicoil thread. Am I correct in my thinking that when a long stud is tightened to obtain proper clampload of the joint, there will be some residual torsion stress in the stud? This would be for a long stud, such as a 10mm stud, 250mm long. Rolled threads at both end, so that the shank of the stud is smaller diameter than the threads.

 

[CoryPad]

Regardless of length, a threaded stud (or the threaded shank of a screw) has a torsional stress from the combination of the pitch torque and thread friction torque. After assembly, the head friction torque counteracts the shank torques so that there is a residual torsional stress. However, this is reduced during use of the joint. VDI 2230 states the following:

"The torsional stress always becomes smaller in the working state than in the assembly state. In joints preloaded beyond the elastic limit, a complete reduction of the torsional stress has often been observed. In elastically preloaded joints, the torsional stresses in many cases decreased to 50 % under static loading and are also completely reduced in the long term under alternating loading."

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SnTMan]

Handbooks often state the the torsional stress is relieved in a short period of time with the joint at rest, however the presence of torsional stress in addition to tensile is why bolts or studs break when being tightened.

Regards,

Mike