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Shear modulus from a 'torque-angle of twist' diagram

  • 19-11-2007 5:33pm
    #1
    sebastianlieken
    Registered Users, Registered Users 2 Posts: 1,778 ✭✭✭


    I hope i'm posting this in the right thread

    i have a question concerning torsion testing of a cylindrical shaft in relation to 'shear modulus'

    i have incremental data in tabular form with which ive converted to a graph. i have torque (Nm) on the x-axis, and angle of twist (degrees) on the y-axis. ive been told i should be able to find the shear modulus from the elastic region of the curve, allthough all my research has yielded that i need to derive a stress-strain curve for shear modulus.

    can anyone please tell me how i find shear modulus from a torque-angle of twist diagram


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  • #2
    chris85
    Registered Users, Registered Users 2 Posts: 4,502 ✭✭✭chris85


    sebastianlieken wrote: »
    I hope i'm posting this in the right thread

    i have a question concerning torsion testing of a cylindrical shaft in relation to 'shear modulus'

    i have incremental data in tabular form with which ive converted to a graph. i have torque (Nm) on the x-axis, and angle of twist (degrees) on the y-axis. ive been told i should be able to find the shear modulus from the elastic region of the curve, allthough all my research has yielded that i need to derive a stress-strain curve for shear modulus.

    can anyone please tell me how i find shear modulus from a torque-angle of twist diagram

    Yeah you picked the right place to post.

    Shear Modulus = Stress/Strain

    For the Stress you must use the applied load to and the dimensions of the bar. Im not sure whether it is a solid bar or not. For a cylinder with inside and outside diameter i think the equation for stress is:

    Stress = (Force)/(pi*OD*ID)

    Where OD and ID are the inside and outside diameter of the tube.

    Strain is just a change in angle relative to the length so strain is given by:

    Strain = (radius*angle)/length

    Need to do this for each of the data points you have. This will then allow you to produce a stress-strain graph. On the stress-strain graph the modulus is the slope of the elastic region (straight line).

    I am assuming the bar is a tube so correct me if i am wrong but you should be able to alter these if not.

    I think these are right but somebody let me know if I am wrong.

    Will that help?


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