1 Reply Latest reply on May 3, 2012 8:32 PM by Jerry Steiger

    Applying preload to balance external load

    Alessandro Tornincasa

      Hi all,

      I have this model which is an extreme simplification of a press.

      1.png

       

      I've atatched the model to this forum thread.

      The two colums are threaded, and there are four nuts fastening them.

       

      If you apply esternal load this is the deformed shape you'll get:

      2.png

      The press works in a way that load is cyclical (up and down movement), and I don't want my threaded colums to be subject to fatigue.

      I want to therefore preload them.

       

      My questions are:

      - what would be the best way to create a pre-load ?

      - Would a preload that equals the external load be enough to prevent the threaded colums from being subject to fatigue ?

       

      Thanks,

       

      Alex

        • Re: Applying preload to balance external load
          Jerry Steiger

          Alex,

           

          I may be way off base here, but it seems to me that there is no way to stop the columns from seeing a cyclic load, and therefore no way to stop them from fatigue. With no preload, the load goes from 100,000 N to -100, 000 N. Suppose you preload them with a 100,000 N load. The load will go 200, 000 N to 0. You have shifted the mean stress, but the alternating stress hasn't changed. I believe you would get the best fatigue life with no preload, since the stress can go as high as the fatigue strength of the material.

           

          Jerry Steiger