7 Replies Latest reply on Aug 12, 2014 2:41 PM by bill campbell

    Thermal expansion of beam

    Chan Alex

      Hi, seems there are so many professional solidworks users! I am a new one and looking for some help.

      I am doing a simulation about a beam in thermal expansion and have found a strange result.

       

      study : static

      material : alloy steel

      fixtures: one end and all supports

      temperature change : +30K

      mesh: default

       

      Model 1: a 500mm beam with five supports

      The max. displacement is1.395e-001mm

      ther2.jpg

      Model 2: a 1000mm beam with 10 supports

      The max. displacement is 1.404e-001mm

      ther1.png

      When I keep increase the length of beam to 5000mm with 50 supports, the max. displacement is similar to the model 1 and model 2. So, is it a reasonable result or something I have set wrong?

        • Re: Thermal expansion of beam
          Per Engberg

          It seems counter intuitive at first, but imagine an infinite version of this and look at some part. In which direction would it move (longitude wise)? None - because of symmetrical forces. Therefore it would seem that the only place you would have significant displacement would be at the free end.

            • Re: Thermal expansion of beam
              Chan Alex

              So, nothing I have set wrong in the simulation...

              Since thermal expansion=coefficient x beam length x temp.change , so I expect the max.displacement should be increased with the increase of beam length. But this simulation shows that no matter I increase the beam length, the max.displacement at the free end keeps not much different. Any maths principle can explain this result?

                • Re: Thermal expansion of beam
                  Nicholas Luyster

                  Hi Chan,

                   

                  This is a reasonable result with the way you have your simulation setup.

                   

                  The displacement is simply the amount of change from the original position.  If you have a fixed geometry fixture holding the closest support, you're defining the displacement to be 0 at this location.  The end of the beam is constrained by the fixtures and that is why the displacement is not proportional to the length of the beam. 

                   

                  The displacement will be proportional to the length of the beam if you eliminate the fixtures from the supports. 

                   

                  All the best,

                   

                  Nick

                  SolidWorks Simulation Training


                  • Re: Thermal expansion of beam
                    Jared Conway

                    what is the goal of your analysis?

                    what are you using as your test case? ie known results?

                      • Re: Thermal expansion of beam
                        Chan Alex

                        My purpose is to analyse the stress on every support due to thermal expansion(+30K).

                        I have created three models including

                        1000mm beam with 10 supports

                        2000mm beam with 20 supports

                        3000mm beam with 30 supports

                        a2.jpg

                        I have probed the max. stress on every support and found an impressive result.

                        First, the end support has the max. stress (it is expected)

                        Second, no matter I increase the beam length, the max. stress is similar (mentioned above, the max. displacement at the end is similar too) 

                         

                        So, I believe this solidworks result but I am looking for some maths principle to explain it. Does Solidworks provides some maths principle about its FEA simulation to support its result?

                        a1.jpg

                          • Re: Thermal expansion of beam
                            Jared Conway

                            validation examples are in the software

                            there is also the AFNOR document floating around

                            and also in 2014 there is a technical reference

                            all should give you confidence that the software is solving the problem correctly

                            but note, it is unlikely that you will find something that matches your case exactly

                             

                            i would add that you should look at displacement before stress as stress is prone to singularities..etc. displacement is what is calculated by fea

                    • Re: Thermal expansion of beam
                      bill campbell

                      Looks like you have everything set up correctly and I think the results are also correct.

                       

                      Trying to figure out what's going on is an issue with everything you analyze. Running the

                      analysis is only the beginning, understanding the results is more work. Welcome to the

                      world of analysis.

                       

                      Try looking at the strain plots and see if they are true. Displacement is the result of all

                      the strains, strain plots show how each node expanded. In your case it might be easier

                      to look at the strain to understand the truth.