Today, plastics are an industrial and economic reality competing with traditional materials and in particular metals, among which steel is the most important.

Global consumption of plastics is roughly 170 million tonnes per annum, which is:

• intermediate between steel and aluminium consumption in weight, that is, roughly a sixth of the consumption of steel and six times the consumption of aluminium for recent years

• higher than steel and aluminium consumption in volume in recent years: roughly 1.4 times the consumption of steel and 16 times that of aluminium

• lower than steel and aluminium consumption if we reason in terms of equal rigidity: equivalent to roughly 1% of the consumption of steel and half that of aluminium

The growth of plastics is significantly higher than that of steel.

No engineer or designer can be ignorant of plastics, but the decision to use a new material is difficult and important. It has both technical and economic consequences. It is essential to consider:

• the actual penetration of the material category in the industrial area

• the functionalities of the device to be designed

• the characteristics of the competing materials

• the abundance or scarcity of the material and the process targeted

• the cost

• the processing possibilities

• the environmental constraints.

The intrinsic mechanical properties of plastics and composites are different from those of conventional materials:

• Expressed in the same units, the hardnesses of engineering materials cover a vast range broader than 1 to 100. Plastics are at the bottom end of the range but are of...