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Lamping force and Fastner Torque
2

Lamping force and Fastner Torque

Lamping force and Fastner Torque

(OP)
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

RE: Lamping force and Fastner Torque

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

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RE: Lamping force and Fastner Torque

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.

RE: Lamping force and Fastner Torque

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
 
          
  

RE: Lamping force and Fastner Torque

(OP)
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.

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