Modulus of Rupture:

What is the Modulus of Rupture?

Sol.: The maximum fictitious shear stress which can be calculated by torsion formula by using the experimentally found maximum torque required to rupture the shaft.

If,
τr  = Modulus of rupture in torsion (Also called as computed ultimate twisting strength)

Tu = Ultimate torque at failure

R  = Outer radius of the shaft

Then,                                    T_u/J =   τ_r/R

The expression for Är gives fictitious value of shear stress at ultimate torque as the torsion formula T/J =   τ/R is not applicable beyond limit of proportionality.

The actual shear stress at ultimate torque is different from shearing modulus of rupture as the shear stress does not vary linearly from zero to maximum but it is distributed uniformly at ultimate torque.