General Mechanical

General Mechanical

Contact issue

    • Talla
      Subscriber

      hi guys


      I have a question regarding the contact type in ansys. For example for a model of two blocks tighten by for bolts( A bolt in each corner). So normally I can’t have a sliding between the two blocks. When I do some research in the internet many people use a frictional contact between the two blocks to model this situation but when I try it I get a sliding between them. I were thinking that when I use a pretention bolt + a frictional contact normally the pretention load will create a limited zone between the two block (clamping cone) in which the two blocks will be bonded and so avoid the gliding. I notice that when I use the rough contact I have no more gliding between them. I think that this is due to the fact that the rough contact is with an infinite frictional coefficient.


      Any explanations will be really appreciate


      Thank you!

    • jj77
      Subscriber

      If you can upload your model then someone might be able to have a closer look. Go to file/archive in WB and save it as a .wbpz, and then use the attach button next to your post above to attach it here

    • Talla
      Subscriber

      Hi jj77, thank you for your response i can't share my real model because its confidential but this is a quick model with the same problem. you will see that because of the sliding there is non continuty in the displacement between the two blocks. thank you for you help

    • jj77
      Subscriber

      I saw that you are doing a pre-stressed modal analysis so you need to have in mind that modal is linear and contacts are nonlinear. Thus contacts are linearised.


      https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v193/wb_sim/ds_eigen_apply_pre_stress.html%23ds_restarts_mult_results


      Also the perturb command shows how contacts are treated - search for that in help or google (PERTURB and ansys)


      The sticking option valid for frictional contacts generates a frictional tangential contact stiffness at the interface thus the closed contact can not slide that much depending on the tangential contact stiffness.


       


       


       


      For more info on this see:


      https://www.simutechgroup.com/tips-and-tricks/fea-articles/160-fea-tips-tricks-ansys-14-pre-stressed-modal-analysis-nonlinear-static-analysis


       


      As for your set up and the behaviour it seems realistic  and behaves normal, and as one would expect. Also leave the contacts to default if you are not sure 100% what you are doing. Say bonded could be more ok with MPC not with penalty.

    • Talla
      Subscriber

      thank you jj77 and sorry for the late response i were out of th office. i will take a look into the link that you sent and let you know after

    • Talla
      Subscriber

      Helllo jj77 can you explain how to use this command please


       

    • jj77
      Subscriber

      To set it to sticking in WB go to the the initial conditions/pre-stress effect in the modal analysis and at the bottom there is something about contact treatment - change it to sticking

    • Talla
      Subscriber

      thank you jj77, thats works if I force the contact status to sticking. But i am still wondering something, actually i must have a sticking part just inside the clamping cone and if I force contact to sticking all surface will have the sticking status

    • jj77
      Subscriber

      read through the documentation on that part as I said:


      https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v193/wb_sim/ds_eigen_apply_pre_stress.html%23ds_restarts_mult_results


      Also the perturb command shows how contacts are treated - search for that in help or google (PERTURB and ansys)


      The sticking option valid for frictional contacts generates a frictional tangential contact stiffness at the interface thus the closed contact can not slide that much depending on the tangential contact stiffness.

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