# Torsion rigidity

1. Feb 19, 2009

### tusharag171

please explain the concept of Torsion rigidity giving examples.

2. Feb 19, 2009

### Dr.D

If a round bar is twisted, it resists being twisted because it has torsional rigidity.

If the length of the bar is L, the applied torque is T, the angle of twist is phi, the area moment of inertia of the circular section is J, and the shear modulus of the material is G, then these variables are related by the linear elastic relation

phi = (T*L)/(J*G)

The torsional stiffness would then be

Kt = J*G/L