3 Replies Latest reply on Feb 23, 2018 8:10 PM by Siavash Khajehhasani

    Too small von Mises stress? (locking lever)

    Yun Man Poon

      Hi I'm a starter on simulation and I'm sorry if my question may be repeated in other posts.

      I was working on an analysis for a lever, having major thickness of 4.92mm, with fillets of 0.3mm radius on all edges, and:

      1 - a hinge on one end

      1 hinge.png

       

       

      2 - a flat support at the bottom face

       

       

      3 - a roller support on the tip at the other end

       

       

       

      4 - a 206 N load (by pressing a smaller metal cylinder against the arc) along an edge on the inner arc, with specified applying angle

       

       

       

      So I ran the static analysis to generate the von Mises stress distribution, which gave a maximum of 8e+7 N/m2. The material was the default alloy steel from solidworks library (Elastic modulus 2.1e+11, Poisson's ratio 0.28). I was on Solidworks Premium 2015.

      While a quick math done on the load 206 N, divided by an assumed contact area of 4.32mm*0.1mm, should give more than 4e+8 N/m2. What was the input going wrong to deviate the result? I am happy to provide more information if needed, thanks!

        • Re: Too small von Mises stress? (locking lever)
          Siavash Khajehhasani

          Not getting into the last paragraph and taking about expectations, I'd like to grab your attention to some other points:

          1) suppress all fillets, they have minor effect on your structure and their only job is wasting your mesh.

          2) How's your mesh resolution? Are these results independent of mesh resolution?

          3) The stress pick is concentrated at a specific area...

            • Re: Too small von Mises stress? (locking lever)
              Yun Man Poon

              Contact Stress Roller on Concave Surface Equation and Calculator

              Thank you Siavash !!

              The last paragraph was about the case when two cylinders are pressing against each other, since they are not perfectly rigid bodies, there should be an contact area with a width and a length. And with the higher rigidity of both solids, the smaller the contact area. The length L is the thickness of my lever = 4.32mm excluding the fillets. The width b was assumed to be very small for both metal, i.e. 0.1mm.

              Thus the expected stress is the applied force 206N / (4.32mm*0.1mm) = 4e+8 N/m2.

               

              1. But my actual piece does have the fillets, shall I remove them for the simulation ?

               

              2. That study was performed with the default mesh solution, that is the middle resolution. Choosing finest mesh and halving the mesh size did increased the stress for about four times...!! But what resolution should be the appropriate one for correct result?

               

              3. Do you mean the stresses are reasonably distributed in the part? I observed that, but the stress value was not as expected.