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Thread: How far can a round bar be rotated before deformation - formula

  1. #1
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    How far can a round bar be rotated before deformation - formula

    I have been trying to find a formula to work out how far can a round bar be twisted before being deformed.

    I have tried a few from various sources, with great varying results.

    Basically, I trying to find how far I can rotate one end of a round bar in DEGREES before it goes beyond its limits staying deformed.

    The round bar would be 330mm in length, but the diameters of the bars vary from ie: 15mm to 25mm.

    All the bars will be EN24T (4340/817M40).

    Once I know how far a bar can be twisted in DEGREES at one end, I can then design levers to ensure the bar is not overstressed using CAD.

    Can anyone help with a formula as the Torsion value applied at one end of the bar will be unknown.

    thanks

  2. #2
    Administrator Kelly Bramble's Avatar
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    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    thanks for that.

    But the Torsion/Torque is always unknown.

    If I can find the torsional limit in degrees or radiants of a bar before being deformed. I can then produce a lever of a certain length as I know the amount of travel/arc that will be applied at the end of the lever.

    example: the lever attached to the end of the bar could see travel/arc of 50mm, so a radius for the lever would have to be found as not to over torsion a bar deforming it and allowing it to return to rest. A short lever with the 50mm travel would have far greater torsion/torque than a longer lever with the same 50mm travel.

    If thats of any help of what I am trying to achieve.

    thanks

  4. #4
    Administrator Kelly Bramble's Avatar
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    Get the yield specification/characteristics of your target material under torsion loading..

    Then, determine the torsion to reach that yield strength.

    Apply a FOS and back calculate your angle of twist...
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  5. #5
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    thanks

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