15 Replies Latest reply on Jan 9, 2014 1:02 AM by Mikael Martinsson

    Elastic modulus vs SS curve

    Mikael Martinsson

      Hi.

      Say that I use a non-linear material model, like plasticity von mises, and then define a SS curve.

      Normally I would start my SS curve at or directly above the yield strength of the material.

      Below this point the elastic modulus handle the response

       

      What happens if I add data for stress and strain below the yield strength in my SS curve?

      Will the solver still use this data instead of the elastic modulus, or will it ignore this information and use E modulus until yield?

       

      I can't try it because I don't have premium/non-linear, but I'm curious how this works.

      Thank you in advance for your response.

        • Re: Elastic modulus vs SS curve
          Jared Conway

          If you don't have sim prem, why is this important?

           

          I'm not exactly sure how it will behave. Most likely you'll get an error because you've given an incorrect input. If anything it will ignore everything below yield.

          • Re: Elastic modulus vs SS curve
            Kevin De Smet

            As long as the SS curve doesn't invade other countries, I'm cool with it.

             

            Sorry, sorry I know... lame joke

            • Re: Elastic modulus vs SS curve
              Mikael Martinsson

              Jared:

              My world is dynamic, not static, so I hope that we will upgrade to premium/non linear in the near future. Anyway, knowledge about how the software works is important to me, so I understand the assumptions that I do (or that the software does). This is something that I often miss in the educations from SW resellers. They tell which buttons to press, but not always why.

               

              Anyway, I will follow up this question with an example and additional question as soon as I'm back home again.

              In the mean time have a Happy New Year.

               

              Mvh Mikael

              • Re: Elastic modulus vs SS curve
                Bill McEachern

                The first point you enter is the yield point for plasticity models. Are you saying you have a non-linear leastic region before a plastic region? I would suspect that if this was a common situation a material model would exist for such a circumstance. I am not aware of one. Anybody else?

                • Re: Elastic modulus vs SS curve
                  Mikael Martinsson

                  Hi.

                  Sorry for the confusion.

                   

                  Well, I have a cast Aluminium material similar to 333,0.

                  Specification for the material is:

                   

                  Elastic modulus: 73GPa

                  Poissons ratio: 0,33

                  Yield strenght: 140 MPa (Rp0,2 min)

                  UTS: 240 MPa (min)

                   

                   

                  I also have SS curves on two sample rods from the actual part (see below)

                  It is a non-linear material, and it's brittle (about 1% strain)

                   

                  How should I define this material as non linear in SW?

                  AB46000.JPG

                    • Re: Elastic modulus vs SS curve
                      Jared Conway

                      "How should I define this material as non linear in SW?"

                       

                      >how do you want it to behave?

                       

                      your options are really to pick a point where it is yielding and enter the rest of the curve as ss to get a von mises elasticity

                      or enter the full curve and have it act elastically

                        • Re: Elastic modulus vs SS curve
                          Mikael Martinsson

                          Thanks for your answer Jared.

                           

                          In the latter solution, I would then use a non linear material model, and this doesn't require any elasticity modulus, only ss curve I pressume?

                          (As mentioned before I don't have this option today so I can't look for myself)

                           

                          How do I enter the ss curve if I go for the first solution? 0,2% strain meets the curve at about 112 MPa not 140 as in specificiation. Or because of the elasticity I should draw a line from 140MPa back to 0,2% and then move this angled line to find the corresponding stress at 0,4%, 0,6%, 0,8% ?

                           

                          I probably learned this at school, but it was 20 years ago so I hope that somebody can refresh my memory.

                          Thank you in advance.

                            • Re: Elastic modulus vs SS curve
                              Jared Conway

                              "In the latter solution, I would then use a non linear material model, and this doesn't require any elasticity modulus, only ss curve I pressume?

                              (As mentioned before I don't have this option today so I can't look for myself)"

                               

                              yes, it would be nonlinear elastic: http://help.solidworks.com/2014/English/SolidWorks/cworks/c_Nonlinear_Elastic_Model.htm

                               

                              "How do I enter the ss curve if I go for the first solution? 0,2% strain meets the curve at about 112 MPa not 140 as in specificiation. Or because of the elasticity I should draw a line from 140MPa back to 0,2% and then move this angled line to find the corresponding stress at 0,4%, 0,6%, 0,8% ?"

                               

                              0.2% method is standard and you'll have to accept the discrepancy, that is part of the assumptions in this case.

                               

                              or go with 140 and accept the discrepancy on the other side of the curve.

                               

                              as bill mentioned, there is no way to get both in this situation. i guess potentially you could run a sim with nonlinear elastic to see the behavior up to the yield point and the vonmisses afterwards. unfortuantely therei s no model that combines both.

                               

                              maybe a more general question but where do you see the stresses in this part ending up? are you designing something that you want to see plastic deformation?

                                • Re: Elastic modulus vs SS curve
                                  Mikael Martinsson

                                  "maybe a more general question but where do you see the stresses in this part ending up? are you designing something that you want to see plastic deformation?"

                                   

                                  No, I wouldn't design anything above yield with this kind of brittle material. But we had a customer part that failed on the field a couple of years ago. They claimed it was due to porosity (HPDC) but we set up a real test and showed that the part was overloaded. It broke every time at the specified max load. (we didn't have simulation at the time).

                                   

                                  I recently did a linear elastic simulation on the part and it showed stress above yield for a large part of the section where the part broke.

                                  I then found the SS curve for the material and found that only a very small part of the curve could be considered linear elastic.

                                  All this made me interested in the non linear part of SW simulation.

                                   

                                  But anyway, thanks again for your answer.



                                   



                                   


                                  • Re: Elastic modulus vs SS curve
                                    Mikael Martinsson

                                    I have one more question.

                                     

                                    In the online help for the plasticity von mises model it states:

                                     

                                    "When you define a stress-strain curve, the first point on the curve should be the yield point of the material. Material properties like elastic modulus, Yield strength, etc will be taken from the stress-strain curve when it is available and not from the material properties table in the Material dialog box. Only Poisson's ratio (NUXY) will be taken from the table."

                                     

                                    http://help.solidworks.com/2014/English/SolidWorks/cworks/c_Plasticity_von_Mises_Model.htm

                                     

                                    How does this work if the first point on my curve is the yield strength and the solver doesn't consider elastic modulus from material properties before this point?

                                    The linear line from the first point to the second point in my ss curve perhaps has a lot lower angle/elasticity module compared to the one entered in the properties. I assume that this would be the case with my curve above.