Materials Selection problem for a torsion shaft

  • #1

Homework Statement


A drive shaft tube for a rear wheel drive high-performance sedan requires a lighter weight unit than one made from conventional steel. The requirements are that the applied torque be 814 N-m (600 ft-lbs) the factor of safety be 2 or more and the maximum angular displacement at full torque be no more than 3 degrees.
The shaft is 36 inches long (0.9144m) and has a fixed outer diameter of 67mm (2.637 in.).

Determine the material indices for
this application and calculate the inner diameter, weight and cost for tubes made from the candidate materials.


Homework Equations



(tau)f/N=2M/(pi)r^3

m=L(rho)(pi)r^2

minimize (rho)/(tau)f^2/3

The Attempt at a Solution



I can derive the term to be minimized using the above equations, just need to do it with the variables given in the problem. (especially with the inner diameter not given)
 

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