3 Replies Latest reply on Aug 12, 2011 5:14 PM by Adam Fain

    pin shear stress

    Adam Fain

      Hello,

       

      I am trying to find the stress on a pin caused by a reaction force.  The pin holds a jaw arm for a gear/bearing puller.  I've attached pictures of what the Jaw arm + pin would look like, and also just the pin itself with fixtures and a load applied.  Before I ran the simulation I did a simple shear calculation on the pin:

       

      shear = V/A = 4V/pi*d^2

      'V' in this case is going to be a load of 10/3 Tons, so about 6667 lbf.  The diameter of the pin is 0.375 in.  The shear stress is about 60,000 psi using that calculation.

      So I set up the pin as shown, figuring the jaw arm only contacts a portion of that surface causing the reaction.  Once I get done with the simulation I get a max shear stress of over 100,000 psi as shown.  Am I missing something here?  Maybe I oversimplified my hand calculation, I'm not sure...

        • Re: pin shear stress
          Anthony Botting

          Hi Adam:
          The hand calculation looks correct but I recall that it represents the average shear stress over the entire pin cross section. You might try plotting the TXY or TXZ (or whichever shear component is appropriate). Nevertheless the stress exactly at the boundary between the fixture and the load would be very high because of the singularity (the super-rigidity of the fixture right at the boundary). You might try a contact analysis with a bearing holding the pin (as opposed to fixing the pin ends), which would help mitigate the stresses due to the elasticity of the bearing. Still,  I believe the stress at the contact junction would be very high, but perhaps not that high. Hope this helps a little. -Tony

          • Re: pin shear stress
            Loren Sackett

            In pin.jpg, you applied the load on the portion of the pin that would be in contact with the jaw, but the restraints on the pin go all the they around the pin.  You will get better results if you only apply the restraints on the portions of the pin that will be in contact (in other words the restraints should be only on the side of the pin opposite to the applied force).

             

            Doing an FEA with contact elements (as Anthody suggested) will give even better results.

             

            On another note, FEA results are usually not very accurate in the immediate vicinity of boundary conditions (especially fixed restraints).  I usually validate pins using hand calculations only in order to avoid the problems you are seeing.

            • Re: pin shear stress
              Adam Fain

              Thank you both for the responses.  I plotted the stress as TXY and it gave me very close results to what I had calculated, which makes sense.  I ended up modeling the Jawhead and inserting the pin into that then running the simulation.