Lamping force and Fastner Torque 2

[GrzegorzD]

Hello,
I have a problem with solving the clamping force (compressed tube between two plates and a screw M14) after 172Nm fastner torque + 90 deg. It's easy to find the clamping force before twisting 90deg. After 172Nm achive we control only lenght instead fo torque (1/4 of pitch thread if it is normal M14 it is .25x2=0.5). I have no idea how much kN it will be.
Thanks for help
Greg

 

[CoryPad]

You need to know the stiffness of the joint. You can measure this experimentally, calculate it with mechanical simulation software, or you can estimate it as a cylinder with diameter slightly larger than the bolt/nut contact diameter and length equal to the clamped length. When you know the stiffness and the displacement, then you can solve for force.

Regards,

Cory

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

 

[MintJulep]

Or, if you know the stiffness of the bolt and are already measuring the elongation you can simply solve directly for tension in the bolt.

 

[desertfox]

Hi GrzegorzD

Expanding on the above posts if you know the Modulus of Elasticity for the bolt and joint materials and there area's then the force can be calculated from the following:-

(FL/(Eb*Ab))+ (FL/(Ej*Aj))= 1/4 pitch of thread


Where F = unknown force
L = Is the length of the bolted components ie the
distance between the underside of the nut to the
underside of the bolt head and also the
effective length bolt over which the force acts.
Eb,Ej = Modulus of Elasticity for bolt and joint material
respectively.

Ab,Aj = Area of bolt and joint respectively

regards desertfox

 

[GrzegorzD]

Thanks all for replay.
Unfortunately I can't measure it experimentaly (because for now on I haven't steel sleeve - I have to find the proper one which after test reduce lenght 0,15 mm permanent (plastic). The lenght of the sleeve is 75/-0.2 mm.
I solve that when I use torque 172Nm - the clamping force will be about 120.7kN - it's very high I think, because if I add 1/4 pitch additionally so that the bolt will demage. I think about M14x1.5 10.9 bolt now.