Hoping for some help :-)

UGMENTALCASEUGMENTALCASE
Afternoon All,

Me again asking for help!

I have a small lifting set up which I have been testing. Basically this attaches to a larger frame, but I want to be sure this will handle the weights first. I've attached my file, loaded up with constraints. I've basically fixed it around one pin, and I'm pulling the other pin. The weight of the frame this lifts is around 3000 kgs. So I've converted that to force, and applied it to the top pin. Would you have used this approach to test the unit?

Also I have used bonded contact on the pin and holes, would you say this is good practice? Any pointers would be great.

Thank you

Comments

  • VictorVictor
    I'd say bonded contact for the pins is non-conservative since it distributes the force around the entire hole instead of concentrating it on one side. You could replace the lower pin with compression only support, or replace bonded contact with contact and use non-linear analysis with the CCX solver.

    A smaller issue that you can probably ignore is applying the distributed force to nodes. It won't end up distributed uniformly so spikes in stress in the area with the force may be spurious. It could also move the line of action if the nodes aren't uniformly spaced, though they're fairly close to that here. It's better to use faces for loads that are truly distributed and nodes for point loads.
  • UGMENTALCASEUGMENTALCASE
    Contact and non linear!! I knew that option was somewhere, sorry not used this for a while so missed that option. Thanks for the pointers Victor
  • disladisla
    Hi, UGMENTALCASE.

    Regarding the design of lifting devices there are some important considerations you should keep in mind.

    -Dynamic forces can double or triple the real weight you are lifting so use a minimum-minimum safety factor of 2 times your weight. (some codes impose K=3)

    -I see something wrong in the model. Stress appears in the wrong side of the Lifting Lug. Check force direction or contact condition.

    -Do not focus only on Pin and forget the rest of the elements. See note on the attached pdf.

    -Elements seems not properly proportioned. Prepare a predesign using some standard shackle catalogue based on allowable working load and recommended section required. Then use minimum distances as a guide on the lifting LUG. Finally use FEM to optimize.

    -Pay attention to the orange dot on the pdf. :# . (probably failing)

  • UGMENTALCASEUGMENTALCASE
    Excellent cheers!
  • disladisla
    You are welcome.

    Lifting devices are those kind of things in which safety of people are closely involved.
    If a chair or skateboard is broken people will probably laugh. 3 Tn machine falling is another thing.
    Do not hesitate to let us know your results or ask again. I will be pleased to help you as far as I can.

    Do not forget to check the frame where you are attaching this device.

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