PSY367: The figure below shows a 3-cell thin-walled tubular section subjected to a torque T about its twist center: Work Stress Essay, SUSS, Singapore

The figure below shows a 3-cell thin-walled tubular section subjected to a torque T about its twist center. The thickness of the outer walls is too and that of the inner walls is as shown. Given that L1=L2=100 mm, L3=50 mm, to=2 mm, ti=1 mm, shear modulus G = 28 GPa, the allowable shear stress is 60 MPa and the allowable relative angle of twist is 0.1 degree per meter. Determine :

• the shear flows in the walls based on strength (i.e. allowable shear stress) and its allowable torque. Plot the distribution of these shear flows in the walls.
• the shear flows in the walls based on stiffness (i.e allowable angle of twist) and its allowable torque. Plot the distribution of these shear flows in the walls.
• the allowable torque if both strength and stiffness are to be satisfied.
• A structural designer proposed to use a lower-grade material with an allowable shear stress of 20 MPa for the inner walls of this 3-cell section. Discuss the feasibility of such a proposal, assuming that the geometrical parameters, mechanical property G, and allowable twist remain unchanged.