89-1 The Torsion of Equal Section Pole 1. Stress Function A equal section straight pole, ignoring the body force, is under the action of torsion M at its two end planes. Take one end as the xy plane, as shown in fig. The other stress components are zero except for the shear stress txx, tzy o.=0.=0.=7=0 Substitute the stress components and body forces X-r-=Z-0 into the equations of equilibrium, we get7 §9-1 The Torsion of Equal Section Pole 1. Stress Function A equal section straight pole, ignoring the body force, is under the action of torsion M at its two end planes. Take one end as the xy plane,as shown in fig. The other stress components are zero except for the shear stress τzx、τzy = = = = 0 x y z x y     Substitute the stress components and body forces X=Y=Z=0 into the equations of equilibrium, we get x M M o y z