Ryan351
Automotive
- Nov 9, 2013
- 10
Coworker and I were discussing this yesterday.
We needed to do a quick 24 study on the clamp force, or rather the holding ability (not sure what term to use, sorry) of a bolt/nut.
We torqued the nut on a pancake load cell and recorded the results over a 24hr period.
The torque applied was 90Nm and the clamp force was 17,663N. After an hour it has relaxed to 17,542N and at 24 hours 17,471N
So-
Initial 17,663N
1 hour 17,542N; Loss of 121N
24 hour 17,471N; Loss of 192N
This was to be expected. An initial higher loss with lower loss over time as the bolt stretched and relaxed.
The discussion then went to this hypothesis, "if the system was left alone forever in a vacuum, assuming no corrosion or outside reactionary forces, the nut and bolt clamp force will relax to 0".
My coworker cited entropy. But I'm under the impression that is relocated for thermal. But I've been wrong many times!
The other hypothesis is that eventually the opposition force of the part being clamped with reach equilibrium with the opposing clamping force of the nut and bolt and stop there. In short, there will always and forever be a clamp force, albeit lower than the initial.
So the question is, if a nut and bolt were torqued and left alone in a vacuum, would it EVENTUALLY reach 0 clamp force.
And I mean indefinite amount of time.
I'm sorry of I didn't use correct terms here, I've read a lot on these forums and there are A LOT of smart people on here!![[bigsmile]](/data/assets/smilies/bigsmile.gif "[bigsmile] [bigsmile]")
Thank you!
Ryan
We needed to do a quick 24 study on the clamp force, or rather the holding ability (not sure what term to use, sorry) of a bolt/nut.
We torqued the nut on a pancake load cell and recorded the results over a 24hr period.
The torque applied was 90Nm and the clamp force was 17,663N. After an hour it has relaxed to 17,542N and at 24 hours 17,471N
So-
Initial 17,663N
1 hour 17,542N; Loss of 121N
24 hour 17,471N; Loss of 192N
This was to be expected. An initial higher loss with lower loss over time as the bolt stretched and relaxed.
The discussion then went to this hypothesis, "if the system was left alone forever in a vacuum, assuming no corrosion or outside reactionary forces, the nut and bolt clamp force will relax to 0".
My coworker cited entropy. But I'm under the impression that is relocated for thermal. But I've been wrong many times!
The other hypothesis is that eventually the opposition force of the part being clamped with reach equilibrium with the opposing clamping force of the nut and bolt and stop there. In short, there will always and forever be a clamp force, albeit lower than the initial.
So the question is, if a nut and bolt were torqued and left alone in a vacuum, would it EVENTUALLY reach 0 clamp force.
And I mean indefinite amount of time.
I'm sorry of I didn't use correct terms here, I've read a lot on these forums and there are A LOT of smart people on here!
Thank you!
Ryan
