Question

Which of the following sections will be best in torsion?

• A. Solid circular
• B. Hollow circular
• C. Triangular
• D. Rectangular

Answer 1

The correct option is B Hollow circular

$\frac{T}{J}=\frac{\tau }{r}$

For a given amount of torsional moment, the section which develops least value of ${\tau }_{max}$ (maximum shear stress) will be best.

$J_{solidcircular}<J_{hollowcircular}$

(Considering same weight of solid & hollow sections)

${\tau }_{solidcircular}<{\tau }_{hollowcircular}$

Also, square, rectangular, triangular and other polygonal sections have sharp edges or fillets which reduce surface area, thus increasing the stress in those places. Hence, they are not very effective in resisting stress against the torque.
$\therefore Hollowcircularsectionwillbebestintorsion.$