If displacements are not very high it is possible to use noncontact optical methods for displacement measurements (electron speckle-interferometry, speckle correlation methods ) and to calculate the angle. Also it is possible to use shearography for registration of dw/dx component which in some situation is proportional to the twist angle.

There are many methods for measuring that twist angle , each one depends on the accuracy of your needed results,

but the easier one is by using a simple pointer mounted on the twisted shaft and locating a graph paper behinf the pointer to show you the twist angle

As torsional loading, rosette strain gages can be apply at 45 degree to neutral axis.

In my opinion & to my under standing dr. Emad hussein's saying is more appopriate, because with out our need of accuracy method can be decided.

K C Gupta

Thank you dear Gupta for your reply, please keep in touch with me.

Yours

Emad

Thank you Dr. I will try to contact you. My e-mail Id is [email protected]

I am waiting you sir.