Considering a cylindrical bar with one end being twisted as shown in figure 6, the twisting
moment MT is resisted by the shear stress τ existing across the specimen section. This shear stress is
zero at the center of the bar, increases linearly with its radius and finally reaches its maximum value at
the peripheral of the bar. If the cylindrical bar with a length of L, the twisting moment can be related
to the shear stress as follow