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19-11-2007, 17:33   #1
sebastianlieken
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Shear modulus from a 'torque-angle of twist' diagram

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

Last edited by sebastianlieken; 19-11-2007 at 17:37.
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19-11-2007, 23:22   #2
chris85
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Quote:
Originally Posted by sebastianlieken View Post
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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