Which one of the following is the correct expression for direct Shear Stress induced in the wire of a closed-coiled helical spring of wire diameter d and mean coil radius R which carries an axial load W?
1
\(\frac{{16WR}}{{\pi {d^3}}}\)
2
\(\frac{W}{{\left( {\frac{{\pi {d^2}}}{4}} \right)}}\)
3
\(\frac{{\left( {\frac{W}{2}} \right)}}{{\left( {\frac{{\pi {d^2}}}{4}} \right)}}\)
4
\(\frac{{16WR}}{{\pi d}}\)