# Largest Allowable Square Cross Section

Determine the largest allowable square cross section of a steel shaft of length 6 m if the maximum shearing stress is not to exceed 135 MPa when the shaft is twisted through one complete revolution. Use G = 77.2 GPa.

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#### Solution Preview

Problem 160671

Consider the square shaft 6 metres long with each side being B cms.

The formula or shear stress due to torsion is

= T r / J (1)

where is the shear stress

T is the torque applied in Kg / cm2

. r is distance of the extreme point on the square shaft from the center of the shaft

J is the moment of inertia of the shaft

As the shaft is square in cross section the moment of inertia is

J = 1/12 ...

#### Solution Summary

Word doc attached gives calculations to find the largest allowable cross section of a described steel shaft in revolution.