7 Replies Latest reply on Apr 5, 2017 12:52 PM by Ryan Dark

    curve S-N by simulation fatigue

    Imane Amarir

      hi

      Please, how we can get the curve S-N by simulation fatigue ? and i want to change the thikness of structure and compare the curve S-N

        • Re: curve S-N by simulation fatigue
          Ryan Dark

          Hi Imane,

          You would typically obtain an S-N curve from the material supplier you are sourcing your material from or have a laboratory run testing to obtain a precise S-N curve for that material.  Otherwise, if the material is specifically a steel the program can approximate an S-N curve as you apply the material in the fatigue study (see below).

           

            • Re: curve S-N by simulation fatigue
              Imane Amarir

              thank for your answer, but my teacher wants me to work only with simulation fatigue without experimental test and he want me to change the thikness of structure and to see the difference in the curve SN

              but always i get the same curve even if i change the thikness

                • Re: curve S-N by simulation fatigue
                  Ryan Dark

                  Hi Imane,

                  The S-N curve is an intrinsic material property.  It should not change when you change the geometry of an object.  What will change is the stresses experienced in the object that will put it in a different region of the S-N curve.  This is what would change the lifespan of an object.

                   

                  From what you describe, you are just looking at running two different static studies followed by two corresponding fatigue studies using the same fatigue S-N curve.  From that you would be able to see what the difference in lifespan is for your designs.  With that in mind, you might be able to use an arbitrary S-N curve for your assignment just to illustrate this difference in fatigue life.

                    • Re: curve S-N by simulation fatigue
                      Imane Amarir

                      im working on welded structure and my aim to prouve that the durability decreases as the thickness of the fillet weld and with the reduction of the thickness of the structure by simulation fatigue but i don't know how.

                      Please give me more detail to prove it

                      before running always i have this message

                       

                        • Re: curve S-N by simulation fatigue
                          Ryan Dark

                          Hi Imane,

                          You have described a very simple comparison study.  First, model your structure with the thickness and fillet sizes you wish to use as a baseline in your comparison.  You will then setup the model with a specific static loading/fixtures (in a "static" type study) that the model will undergo in cycles.  Once you have setup and run that "Static" baseline study you would then run the baseline "Fatigue" study for an arbitrary number of cycles.  This is all just to set your baseline data.

                           

                          Now comes the fun part.  If you make a good parametric model you will be able to configure the sizes of both the thickness and fillet sizes of the model to change the model to thickness and fillet sizes you want to test.  Once you have created the new configuration of your model you would again create a "Static" study with the same loading/fixtures as the baseline and run it.  Following that you would run a new "Fatigue" study with the same number of cycles as the baseline study.  Now you have two sets of static data and fatigue data to compare.

                           

                          You can keep creating new configurations of your model with various wall thicknesses and fillet sizes and keep iterating the "Static" loading and "Fatigue" cycling to see how your changes are changing the lifespan of your model.