6 Replies Latest reply on Jun 12, 2015 2:36 PM by Bill McEachern

    What material model should I use to preform nonlinear analysis of carbon fiber surface-to-surface contact?

    Tyler Chapman

      I am trying to model a set of nested carbon fiber half tubes that fold open into a ridged pole (utilizing the spring-like nature of the carbon fiber) with a nonlinear surface-to-surface study. The Solidworks materials library for carbon fiber is inadequate, so I am trying to create an accurate custom material but I am unsure what model type I should use. Due to carbon fiber being a composite material, I believe that the linear orthotropic model would be most appropriate, but again I'm unsure.

       

      Any and all help is greatly appreciated.

       

      Tyler

        • Re: What material model should I use to preform nonlinear analysis of carbon fiber surface-to-surface contact?
          Bill McEachern

          Since you are not trying to model failure linear orthotropic seems like the way to go. You may find that the very large displacement and rotations required in your description maybe a challenge in SWX NL with contact. Also you may have snap throughs to deal with as well - also challenging in SWX Sim NL with contact. ARC length and displacement control are not supported with contact.

            • Re: What material model should I use to preform nonlinear analysis of carbon fiber surface-to-surface contact?
              Tyler Chapman

              Thank you for the prompt response. I am looking for any instances of failure/buckling in the parts, so in linear still the way to go? And is there any way to probe for force translated during the model's interactions? On a similar note, I have the two tubes connected by a simple pin through both and I am using a concentric mate and non penetration contact set to restrict motion, but this disallows flexing/movement of the pin itself. Is there a better way to constrain this motion?

               

              Thanks again.

               

              Tyler

                • Re: What material model should I use to preform nonlinear analysis of carbon fiber surface-to-surface contact?
                  Bill McEachern

                  Now I am confused. What do you what to know about your device? I thought your joints were flexures. If it is just tubes with pins that is a whole different thing and maybe motion is the way to go. What question are you trying to answer?

                    • Re: What material model should I use to preform nonlinear analysis of carbon fiber surface-to-surface contact?
                      Tyler Chapman

                      Sorry for the confusion. Below is an image of the assembly. It starts from a nested configuration then rotates 180 degrees and locks in a linear configuration, the inner tube (full tube) being held in place by the spring force of the outer tube. They are joined by a pin, the assembly does not have flexure joints. I need to know, based on the geometry of the outer tube (and its resulting spring constant), the stress and strain on the system by unfolding then inner tube, as well as buckling/failure if it occurs (including the pin), and the force necessary to do so. This will ultimately be one piece of a larger support boom structure.

                      Boom 1-Nonlinear 2-Results-Stress1.analysis.jpg

                        • Re: What material model should I use to preform nonlinear analysis of carbon fiber surface-to-surface contact?
                          Bill McEachern

                          Well for starters you only have to simulate the range of motion that encompasses the two tubes in contact if I understand what you doing which I may not with fidelity.  What I think is going on is when you fold the two tubes to the extended position the outer tube flexes to allow the inner tube to pass and once the peak has passed it starts to grab the tube till it hits the 180 degree position or somewhere close and then you have large bearing contact between the two tubes with some contact pressure based on the different initial diameters. the outer tube having a smaller one than the inner so it grips the tube. Is that right?

                          If it is, then you want an orthotropic material model (cause that is what a fibre composite is) and you probably want to run this as a shell model so you can lay up the laminate in the shell definition. You then want to get the simulation to run for the region (angle) of interest. Then you want examine the failure index to see if the outer tube (most likely) ever has a failure index of 1 or look at some other quantity (stress, strain, whatever) that provides you with an indication of suitability. If you don't use a shell element you will have to rely on an approximation of the bulk orthotropic properties using a laminate calculator of something similar and then you have to rely on more derivative quantities to assess its performance (bulk stress, strain whatever).  With a non-linear analysis if buckling  is going to occur anywhere in the analysis it will likely fail to converge or advance past a point near there. I would try a half symmetry model and avoid edge to surface contact by shaping the outer tube with a bit of a flare so that edge contact is avoided. This will be a pretty challenging analysis to get to complete but it might be doable.

                          • Re: What material model should I use to preform nonlinear analysis of carbon fiber surface-to-surface contact?
                            Bill McEachern

                            Oh and one more thing - you probably want to do this as an NL dynamics study if you plan on getting it be a continuous thing. It might be a lot easier to use a shrink fit analysis or some sort of expansion type analysis at the angle where the largest separation occurs. You expanded and then let is settle in bearing against the smaller tube. That might be a lot easier to pull off. Might be a good place to start.