Quote:
Originally Posted by sebastianlieken
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 xaxis, and angle of twist (degrees) on the yaxis. 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 stressstrain curve for shear modulus.
can anyone please tell me how i find shear modulus from a torqueangle 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 stressstrain graph. On the stressstrain 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?