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ANSYS Workbench - 3D rope on a pulley with friction

  1. Feb 3, 2014 #1
    Hello everyone,

    First of all, I want to excuse for my not perfect English since it isn't my mother tongue.

    However, now to my problem, which I'm facing at the moment. As part of my master thesis I have to simulate the application of a fastening device, which I develope during my master thesis. It can be mechanically compared with a pulley problem in it basic concept, but instead of one rope, it uses two ropes, which lie on top of each other. Here is a sketch of the fastening device and the strapping put around it: https://www.dropbox.com/s/v78prd92q7dcgd9/aktuelle_loesung.jpg

    Before I model the whole fastening device, I want to model just one out of the three poles. It doesn't matter, if I choose the 90° or 180° setup. I already have a handwritten static mechanical calculation of the whole system, which I want to compare to the simulation. When I use just one rope instead of two and use a pretty stiff material (e.g. steel), I get results which differ just about 1% from the handwritten calculation. However, when I use two ropes, I get completly different results due to the fact, that in the model the friction is applied both ways - from the inner belt to the other belt and the other way round, while in the handwritten calculation only the normal force of the outer belt on the inner belt is taken into account. Sadly I'm really new to Ansys at all and do not know, how to set up the rope-like behaviour to continue this model. Furthermore I seek your advice on the setup of my model.

    I just know, that the material is a polyester, I sadly do not have more information. I tried to contact the manufacturer of the fibre and of the belt itself, noone knows the young's-modulus of the belt or the poisson ratio, from which I could make my own material. Due to the fact that polyester (the strapping is most likely from PET-fibers) normally shows an anisotropic behaviour, this gets even more complicated. But I contacted the professor, who does his research in this field of material science at my university, and even he couldn't help me with this material data. He suggested, that I just take into account the material data in direction of the pulling force, which I can determine from the material data sheet of the fiber-producer (young's modulus: 6.76 GPa; max tensile stress: 841.8 MPa).
    Here is a screenshot of my Ansys Workbench with the momentarily setup, I use: https://www.dropbox.com/s/4pdw118ne0l3js7/Screenshot 2014-01-09 14.20.14.png

    Here are my questions:

    1. How do I model a rope-like behaviour in Workbench? I read something about an APDL-command that could be inserted, however I can't find out, which one I have to use.
    2. Is it even possible to model this model in 3D or should I do it in 2D? Since I just know the basics in Workbench, I would like to keep using this programm instead of the Ansys Classic. I would have to learn this programm just like the other one from the start.
    3. Is it possible, as I described above, to set the contact friction acting just in one direction (screenshot 2 between the two belts) from the outer belt onto the inner belt, while when I apply a force to the inner belt, there is no friction acting on the outer belt. I want to apply it this way, because that is how the handwritten calculation was done.

    This is what I have done so far:

    - I tried to model the rope using LINK180, in which I was sucessfull. However, I didn't manage to apply any kind of friction to the model, which I need.
    - I read the Elementguide and found the Element SHELL41, which can be set to "cloth-like" behaviour. However when I try to do so, I just receive an error.
    - At the moment, I try to find out, how to set up the anisotropic stiffness matrix for a woven material as well as using the Mooney-Rivlin model.


    Any other hints would be really helpfull too and greatly appreciated!

    Thank you in advance!

    Johannes
     
  2. jcsd
  3. Feb 4, 2014 #2
    Do you not have a tension on both the inner belt and the outer belt?

    If you say pulling on the inner belt, no friction acts on the outer belt, then by what means does the inner belt not just slip out and release the tension in the strapping?
     
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