The Drill pipe has an outer diameter of 3 in., a wall thickness of 0.25 in., and a weight...

The Drill pipe has an outer diameter of 3 in., a wall thickness of 0.25 in., and a weight of 50 lb/ft. If it is subjected to a torque and axial load as shown, determine

(a) the principal stresses and

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(b) the maximum in-plane shear stress at a point on its surface at section a.