Name of torque actually going into tensioning fastener 1

[CamJPete]

Hello all. I'm trying to get my terminology correct for torque.

I've got a design where a fastener is threaded into a locking insert. I understand that some of the input torque gets "eaten up" by the locking feature, so the running torque must be added to the final desired torque that tensions the fastener. What is the name of this torque that actually goes into pretensioning the fastener? Is it seating torque? Installation torque? Input torque? Final torque? Tensioning torque?

In formula terms: T_that_tensions_fastener + T_running = T_into_wrench. It's the T_that_tensions_fastener that I'm after the correct name for. Thank you.

(While I'm asking, what is the correct name of the T_into_wrench also?)

 

[rb1957]

"effective" torque ? Torque at wrench = effective torque + running torque (to overcome locking feature).

another day in paradise, or is paradise one day closer ?

 

[3DDave]

You forgot the torque that goes into friction under the head of the fastener.

 

[hydtools]

Net fastener torque?

Ted

 

[CamJPete]

Effective torque has a nice ring to it. I'll note it as a possible name. However, what about the application with inserts with no locking feature and thus no running torque present? Effective torque sounds a little confusing. Installation torque sounds more appropriate for the "no running torque" cases. It's only when running torque is present that the term "installation torque" needs to be separated out into the torque into the wrench and the torque going toward preload. Perhaps that's where I'm getting confused. I'd use the term "installation torque" if no running torque were present. But if it is present, it no longer is descriptive enough.

3DDave, I should mention that I will still go through the process of calculating the desired final preload with the equation T = K*D*P, with some appropriate K value included. All other influences other than the deformed thread friction (like head friction) should theoretically be defined by the nice little nut factor K.

 

[Tmoose]

The input torque gets "eaten up" by the locking feature is called "prevailing torque" I believe.

Good old S9086-CJ-STM-010/CH-075R2 has some definitions and descriptions, but none real good for what the final torque value is named

"Prevailing torque is the torque required to rotate one part of an unloaded fastener
relative to the other. This can vary from essentially none for a new, clean fastener held in your hand, to
significant amounts for self-locking fasteners, to large amounts for fasteners with damaged threads. Regardless of
the prevailing torque, the final torque value that you can see on your torque wrench must equal the torque specified
for that particular application, plus the prevailing torque that you measured as you turn the nut on the bolt
in its unloaded state. Otherwise, the actual clamping force that you achieve will be short by the amount of torque
required to overcome the prevailing torque. The torque required to draw two mating surfaces together, such as
that required to draw up cold sprung piping joints, is not prevailing torque. Once the clamping force achieved by
the fastener exceeds the force required to bring the joint together, the threshold of preload has been reached..."

 

[hydtools]

I like "net". It is what is left after subtracting all the parasitic torques from the gross, applied torque.

Ted

 

[CamJPete]

Ah, net! I think I like that even a bit better than effective. I missed your first reply.

Tmoose. Yes, prevailing = running. That is a good description for the layman. Thanks for sharing.

 

[tbuelna]

From NASA-STD-5020:

"Breakaway Torque: For fastening systems incorporating prevailing torque locking features, this is the torque required to initiate relative motion between mating threads when the self-locking mechanism is fully engaged and the fastener is unseated. For the purpose of this Standard, this torque can be measured in either the tightening or loosening direction."

"Effective Torque: A torque in excess of any running torque."

"Locking Torque: See Running Torque.”

"Prevailing Torque: See Running Torque."

"Running Torque: The torque required to overcome kinetic friction of the mating threads plus the torque required to overcome the locking feature when 100 percent of the locking feature is engaged and the fastener is unseated. This torque can be measured in either a loosening or a tightening direction while the mating threads are in relative motion."

"5.8 Installation Torque Specification and Control
The requirements in this section apply when preload is generated by torque control.
a. The engineering documentation shall specify the installation torque range or specify an applicable standard that defines the installation torque range.
b. The engineering documentation shall clearly identify when the installation torque is the torque above running torque.
When engineering documentation does not specify “above running torque,” the specified torque is understood to be the final torque indicated by the torque instrument. Running torque does not generate preload. Specifying torque above a measured running torque provides tighter control of preload."

 

[Artisi]

How about residual torque?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)