9 Replies Latest reply on May 12, 2014 1:50 PM by Shaun Densberger

    Stress Concentrations at a discontinuity

    Phil Perlich

      When you have 2 bodies bonded together with a sharp corner, a discontinuity exists and the stresses computed near the discontinuity are meaningless. My question is, are the free body forces also meaningless near the discontinuity?

      Thanks.

        • Re: Stress Concentrations at a discontinuity
          Shaun Densberger

          No; typically the reaction loads will not be impacted by stress singularties. However, note that convergence on energy norms does not imply convergence on internal forces. If you primary concern are internal loads, then make sure that they converge.

          • Re: Stress Concentrations at a discontinuity
            Jared Conway

            some pictures of what you're working with and an example would be really good here to make sure that you're on the same page as shaun.

             

            in general, i've never seen someone try to converge on free body force.

            • Re: Stress Concentrations at a discontinuity
              Phil Perlich

              I'm attempting to determine weld size using the procedure contained in the attachment "116_Welds.pdf" which references "Determination of Weld Loads & Throat.pdf". I am working on a tank with under-head legs. The legs are W6x15, the lower tank head is 2:1 elliptical shape. Everything is modelled as surface bodies in a single part file.

              Capture1.PNG

              The bottom of the legs are fixed. I applied a remote load (rigid connection) to the top edge of the head. The location of the remote load is at the tank's centroid. The load is primarily a vertical load with a much smaller horizontal load.

              I used split faces on the legs to space the nodes 1/4" apart with an instance of 1/8" node spacing on the end of the beam's flanges. I also used split faces on the head as can be seen above. I used draft quality mesh, with global bonded compatible mesh settings, but the mesh didn't seem to be compatible. I checked all my settings and everything seemed ok, but clearly the mesh is off.

              Capture2.PNG

              So I added more split lines to the head even though I don't think its required.

              Capture3.PNG

              This mesh satisfied me, so I ran the study.

               

              To be continued...

              • Re: Stress Concentrations at a discontinuity
                Shaun Densberger

                Totally forgot about this thread, to which I want to make a correction to my previous statement.

                 

                Whether or not stress singularities will effect your internal force results depends on how the software calculates said forces. If the software is using the stiffness matrix and the displacement field solution to calculate the internal forces, then no, stress singularities will not effect the internal force solution. However, if the software is integrating the stress over the area to calculate the internal forces, then stress singularities will effect your internal force values. I did some digging around and I cannot find out which method SW uses, so you might want to do some testing with a very basic model to gain some insight.