10 Replies Latest reply on Mar 26, 2013 8:07 PM by Radoslaw Koneczny

    Nonlinear materials

    Erik Robbins

      Hello,

      I'm trying to run a nonlinear simulation on a spline that's undergoing torsion. I want to see how it behaves past its yield point so I created a new material with the same properties as before and a stress strain curve seen in the attached images. Yet, each time I run the simulation the response seems to be linear as seen below in the response graph. As you can see, the stress rises well above the yield point of 212000 psi for the ultra high strength inconel. Does anyone have any idea on what I might be doing incorrectly?

      Thanks

        • Re: Nonlinear materials
          Bill McEachern

          you might want to consider a bi-linear NL plasticity model. In either case you need to be careful on what you are plotting: does node 50375 see a non-linear response with respect to "time". Obviously not by the looks of it. did you havethe large dispalcement flag set inthe NL properties? Youneed that set to invoke the equilibrium iterations.

            • Re: Nonlinear materials
              Erik Robbins

              Why would NL plasticity be used? Inconel is a steel and acts in an elastic manner until yield. I would expect a nonlinear response on that node because the stresses go past the yield point of 212000 psi. The stress vs. displacement plot also shows a linear response, which I didn't expect to be the case. Large displacement is set on.

              Response Graph-2.jpg

                • Re: Nonlinear materials
                  Bill McEachern

                  I agree but I doubt Iconel's response is non-linear elastic. I just try to use the model that most closely matches the materials behaviour. If you do change the model to a plasticity model, the first point you enter should be the yield point. There is an issue somewhere. As above 212ksi your materail should turn to mush and that is not occuring. The other material in the areas near the yeild material should be picking up the load as they turn to mush so stresses of 300ksi tell me that the model is not enabled becuase they shoudl be flat lining around 212ksi. What strain is required to get 300ksi? What strains are present?

                • Re: Nonlinear materials
                  Radoslaw Koneczny

                  Yes, where in this model node 50375 is located.

                  Node is node , and element is element, strain is deformation of element. And you plot stress in node.

                  You apply torque . How? Linear ? Maybe try to plot node displacement in time instead node stress.

                • Re: Nonlinear materials
                  Joe Galliera

                  Please upload your complete material data curve.  You can save it as a file in the dialog showing the strain and stress data.  There seems to be something fishy with the results.  What is your source for material properties?  Special Metals, which has the rights to Inconel branded alloys, is the best place for this information.

                   

                  And one note on your material values (which won't change the results): you have a density value of 1020 lb/in^3 but it should be 1020 kg/m^3.  The way you have it makes the density about 28,000 times heavier than intended... making it perhaps the most dense substance known to man.

                  • Re: Nonlinear materials
                    Jared Conway

                    sorry to throw another comment in here, but are you expecting plastic deformation? if so, i don't think you'll want to be using nonlinear elastic material.

                     

                    any chance you've done a simple beam to test the material properties with a simple fix restraint/loading condition to make sure it behaves the way you want? then expand that to torsion before moving to your full model that looks like it includes contact?