6 Replies Latest reply on Aug 24, 2015 7:28 AM by Bilounga Engolo Arthur Germain

    Stress concentration on hook

    John Munroe
    John Munroe Aug 24, 2015 2:31 AM

      Hi all

       

      Similar to my other post, I'm trying to simulate a hoop pulling down on a hook with a 50N force.

       

      This is what I've tried to emulate that a hoop sits on those top surfaces.

       

      Capture2.PNG

       

       

      However, it appears that stress concentrates at the edge of a fillet The magnitude of the stress is up to 200MPa, which exceeds the yield strength of 159MPa.

       

      Capture.PNG

       

      Any idea to why might that be the case? There should be more material in the fillet, so shouldn't it be a stronger area instead?

       

      Thank you

       

      John    

        • Re: Stress concentration on hook
          Janko Stellaard
          Janko Stellaard Aug 24, 2015 3:37 AM (in response to John Munroe)

          Hi John,

           

          Did you refine the mesh in the critical area untill you got a constant stress value?

           

          If yes, you can conclude that your model will yield. Solutions for that:

          • Lower the load (per unit surface)
          • Alter the geometry
          • Change the material

           

          Janko Stellaard

          Cadmes BV

          The Netherlands

            • Re: Stress concentration on hook
              John Munroe
              John Munroe Aug 24, 2015 3:45 AM (in response to Janko Stellaard)

              Hi Janko,

               

              Yes, I'm using a curvature-based mesh with max. 0.3mm. The hook has a diameter of 1.5mm.

               

              Perhaps the geometry will need to be changed. Do you know why stress is concentrated at the edge of the fillet? I've tried adding a gusset on the bottom, but that doesn't seem to help. Usually what kind of geometry change is needed to overcome stress concentration?

               

              Thanks

               

              John

                • Re: Stress concentration on hook
                  Janko Stellaard
                  Janko Stellaard Aug 24, 2015 4:00 AM (in response to John Munroe)

                  The absolute size of the mesh is ofcourse not relevant, it is about the relative size. Stress convergence is critical if you check the maximum stress.

                   

                  The stress is concentrated in the middle of the loaded area, because these mesh elements capture most energy from compression. The elements on the side of the loaded area also capture energy, but the energy there is partly transferred to the elements outside of the loaded area.

                   

                  Look at it ass a glas of water that is heated. The inside will warm up quicker than the outside where energy can be dissipated.

                   

                  Janko Stellaard

                  Cadmes BV

                  The Netherlands

                    • Re: Stress concentration on hook
                      John Munroe
                      John Munroe Aug 24, 2015 5:06 AM (in response to Janko Stellaard)

                      I see. I've now added mesh control (0.1mm) to the critical area and this is the result I get.

                       

                      Capture2.PNG

                      Capture.PNG

                       

                       

                      It seems like the stress is concentrated at the ends of the curve for some reason. I'm hoping to have the part die-cast in aluminium, so there aren't many options for another material. Is a change to geometry the only solution?

                       

                      Thanks

                       

                      John

                • Re: Stress concentration on hook
                  Bilounga Engolo Arthur Germain
                  Bilounga Engolo Arthur Germain Aug 24, 2015 7:28 AM (in response to John Munroe)

                  hello , what you want to show in this modelisation

                  explain clearly you idea .

                  you just want to study stress concentration or you want to design

                   

                  explain clearly please