# Solid shaft

for a solid shaft,the area moment of inertia is (pi*d^4) / 64 or (pi*d^4) / 32 ?? i mean in bending and buckling case.

ihave two formulas but don't know which one is correct??

does anybody has those formulas for other cross sections ??
pls help

Area moment of inertia is $$I=\frac{\pi*d^4}{64}$$ with unit $$mm^4$$
Widerstandsmoment, $$W=\frac{\pi*di^3}{32}$$ with unit $$mm^3$$
$$W_{by}=\frac{I_{y}}{C}$$ where C is the (maximum) distance from the neutral axis to the outermost fiber or layer of atoms.