Question

The maximum shear stress occurs on the outermost fibres of a circular shaft under torsion. In a close coiled helical spring, the maximum shear stress occurs on the

• A. Outermost fibres
• B. Fibres at mean diameter
• C. Innermost fibres
• D. None of these

Answer 1

The correct option is C Innermost fibres

In close coiled helical springs,

${\tau }_{max}={\tau }_{transverse}\pm {\tau }_{torsion}$

${\tau }_{torsion}$ will be maximum at outermost fibres of wire.
At innerside,
${\tau }_{max}={\tau }_{torsion}+{\tau }_{transverse}$

$=\frac{16PR}{\pi d^3}+\frac{4P}{\pi d^2}$

$=\frac{16PR}{\pi d^3}(1+\frac{d}{4R})$