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Thread: Trying to verify yield stress calculations for bending a pipe

  1. #1
    Tommy Boy
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    Trying to verify yield stress calculations for bending a pipe

    Hi All,

    I wanted to calcuate the maximum force I can place on a given iron pipe 2 ft away from a fixed end before it yields to plastic deformation and takes on a permanent set. I have enclosed 3 equations.

    The first equation shows how to calculate the moment of inertia of a pipe.

    Ip=pie*(Dout^4-Dinner^4)/64

    Dout = outer diameter
    Dinner=inner diameter

    The second formula shows deflection I would get for a given load.

    Deflection=F*L^3/3*E*Ip

    F=Force
    L=Lenght of pipe
    E=Modulus of Elasticity of Iron
    Ip=Moment of Inertia of pipe


    The third formula I am trying to use to calculate the maximum stress for a given force over a given length of pipe.


    Yield Stress Max for given load=((F*L)*h/2)/Ip

    F=Force
    L=Lenght of pipe
    h=height of pipe or outside diameter of pipe
    Ip=Moment of Inertia of pipe

    I am hoping that this 3rd formula is correct and that as long as the calculated value is less than the yield stress of a given pipe material i wouldn't deform the pipe.

    Any thoughts would be helpful.

    Thanks,
    Tom
    Last edited by Tommy Boy; 12-03-2012 at 08:51 PM.

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
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    Yes, I think...


    See:

    Moment of Inertia

    http://www.engineersedge.com/materia...gyration-3.htm

    Cantilever, single load at end

    http://www.engineersedge.com/beam_be...m_bending9.htm

    Cantilever, uniform load

    and

    http://www.engineersedge.com/beam_be...m_bending8.htm

    [quote]Yield Stress Max for given load=((F*L)*h/2)/Ip[\quote]

    I would just call this applied stress, as yield is a condition where the applied stress exceeds the yield stress and deformaton occurs.

    To get the yield stress of the material you need to find a stress-strain curve or the material specifications of the pipe.

    stress-strain.gif

  3. #3
    Lead Engineer RWOLFEJR's Avatar
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    Rochester Pennsylvania
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    Quote Originally Posted by Tommy Boy View Post
    Hi All,

    I wanted to calcuate the maximum force I can place on a given iron pipe.................


    ................Any thoughts would be helpful.

    Thanks,
    Tom
    Hi Tom,

    Remember that results from any formula regarding strength of materials are theoretical. So along came the safety factor...

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