
Selection of materials 379
183 Selection for stiffness
Stiffness can be considered to be the ability of a material to resist deflection
when loaded. Thus if we consider a cantilever of length L subject to a point
load F at its free end, then the deflection y at the free end is given by
FL
3
y
~3EI
with E being the tensile modulus and / the second moment of area of the beam
cross-section with respect to the neutral axis. Thus for a given shape and
length cantilever, the greater the tensile modulus the smaller the deflection.
Similar relationships exist for other forms of beam. Hence we can state that the
greater the tensile modulus the greate