Page 93 - Plastics Engineering

76 Mechanical Behaviour of Plastics

Dia = 4h

+IF?

Fig. 2.25 (continued)

indeed ‘L‘ or ‘U’ sections) are very efficient at providing excellent stiffness
per unit weight. The following Example illustrates how such sections can be
designed into plastic products.
Example 2.11 An aluminium cantilever beam is 50 mm wide, 80 mm long
and 2 mm deep. The loading is 200 N spread uniformly over the cantilever.
If the beam is to be replaced by one made from acetal and the design criteria
is that the end deflections should be the same in each beam after one month,
calculate the dimensions (a) of a solid acetal beam and (b) an acetal beam with
unidirectional ribs. The modulus of the aluminium is 70 GN/m2.