I'm trying to develop a Matlab Simulink model which models the relationship between the voltage applied to a motor, and the voltage across a strain gauge connected to a shaft attached to the motor. So far, I have found the transfer function between voltage and motor torque, and the transfer function between strain on the shaft and voltage across the strain gauge. However, I cannot find a source that explains the transfer function between torque on the shaft and the resulting strain on that shaft. Can somebody please explain how I would go about finding this transfer function? The shaft is a 150mm long, 40mm diameter steel cylinder. Thanks!