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 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: