1 Reply Latest reply on Mar 8, 2011 11:06 PM by Anthony Botting

    Equation for Bolt Pre-tension

    Alessandro Tornincasa

      Hi,

      SolidWorks Simulation has bolt connectors, in which you specify Bolt Pre-tension. Behind the curtains, SolidWorks Simulation applies a thermal load to the bolt, in order to make it shrink and exert an axial force on the fastened parts.

       

      I was wondering if there is a formula somewhere that relates thermal load you need to apply and axial force you want to get. I need to simulate a real bolt and I'd like to get my bolt pre-tension right the first time, without trial and error.

       

      I found something here, but it's not convincing:

      http://www.engineersedge.com/thread_strength/thread_tension_heat.htm

       

      Thanks,

       

      Alessandro

        • Re: Equation for Bolt Pre-tension
          Anthony Botting

          It looks correct. I thought of how to do it from a different point of view. You want to shrink the bolt so that the change in length equals the coeff of thermal expansion * change in temperature*original length:

           

          (Delta-L) = (alpha)*(Delta-T)*(L).

           

          Once it is shrunk by that amount, you want to apply a tension force to the bolt to stretch it back to it's original length:

          F = [(Delta)-L]* (AE/L)

           

          Substituting for Delta-L (the change in length):

           

          F = (alpha)*(Delta-T)*(AE)

           

          Where F is in pounds of axial force (not the psi units the article uses).