# Solid shaft

1. Aug 15, 2006

### teng125

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

2. Aug 15, 2006

### Meson

For a shaft with cross section d,

Area moment of inertia is $$I=\frac{\pi*d^4}{64}$$ with unit $$mm^4$$

Widerstandsmoment, $$W=\frac{\pi*di^3}{32}$$ with unit $$mm^3$$

Relation between W and I, for the case of bending and bulking, is given by:
$$W_{by}=\frac{I_{y}}{C}$$ where C is the (maximum) distance from the neutral axis to the outermost fiber or layer of atoms.

Hence, do not be confused as they are different and yet related. If one is known, let's say I, the other can be found, W in this case.

Last edited: Aug 15, 2006