5 Replies Latest reply on Aug 26, 2009 5:11 AM by Derek Bishop

    Need urgent advice for a pipe wrench FEA

      Hi all

       

      I'm doing a stress analysis on a new design solid grip wrench. As you can see in the pic attached, this wrench is made of a handle and 3 jaws that are connected together with three pins. The wrench has four Tungsten inserts which grip the pipe and are soldered to the jaws. The load is applied to the handle.

      I've made a few assumptions before doing the analysis and I want to know if these assumptions are valid.

      1. Because the inserts are made of Tungsten I'm considering them as rigid bodies in my study.

      2. I've fixed the inner surface of tungsten inserts where they grip the pipe.

      3. Bonded contact sets were defined between inserts and jaws.

       

      I should say that I can't run a non-linear study here (we don't have the product). By increasing the load in some stages the program asks me to turn the "large displacement flag" on. However, by doing this the program fails to calculate the results. The average resulting stresses are still below yield point but I can't go any further. I have also a hot spot on one edge next to one of the inserts with a fairly large stress.

       

      Could you please let me know if I'm on the right path?

       

      Regards,

       

      Reza

        • Re: Need urgent advice for a pipe wrench FEA
          Derek Bishop

          I wouldn't make the inserts rigid. You could have the tungsten inserts as a separate part in the assembly with relevant properties. Are all of the materials used the same on other parts. I'd expect the pins to be made of a different material to the handle.

           

          Consider using pin joints in the study or using no penetration contacts at the pins. It would be inaccurate to have bonded contacts at these locations.

           

          Try running the model in  both the normal and large displacement mode and see what variation occurs.

           

          Looks like you are under the yield stress in most regions. I like to do a FOS plot when you are using different materials. Also do an exploded view of the FEA analysis and have a look out for high stess areas around the pins.

           

          You may also want to consider introducing some moment into the system. The operator may lean down on the handle as well as creating the tangential force on the handle.

           

          And finally, be sceptical of any advice given on this forum. You are the designer and must take responsibility for your designs and analysis work.

            • Re: Need urgent advice for a pipe wrench FEA

              Derek

               

              Thanks for your reply.

              Pins, handle and jaws all have different material. I have already created "No penetration" contacts between pins and other parts.

              My problem is that I can't run the analysis in large displacement mode, the solver fails when I turn this option on.

              Last night I tried another solution, I separated the handle from the rest of the assembly. By applying action, reaction forces on both side of the assembly I can run the model in large displacement mode so I can increase the load until over yield strength. Do you think it is a good approach? I compared the results and they are almost identical with the results of assembly as a whole.

               

              Regards,

               

              Reza