The evolution of engineering materials

Throughout history, materials have limited design. The ages in which man has lived are named for the materials he used: stone, bronze, iron. And when he died, the materials he treasured were buried with him: Tutankhamen with shards of coloured glass in his stone sarcophagus, Agamemnon with his bronze sword and mask of gold, each representing the high technology of his day.

If they had lived and died today, what would they have taken with them? Their titanium watch, perhaps; their carbon-fibre reinforced tennis racquet, their metal-matrix composite mountain bike, their polyether-ethyl-ketone crash helmet. This is not the age of one material; it is the age of an immense range of materials. There has never been an era in which the evolution of materials was faster and the range of their properties more varied. The menu of materials available to the engineer has expanded so rapidly that designers who left college twenty years ago can be forgiven for not knowing that half of them exist. But not-to-know is, for the designer, to risk disaster. Innovative design, often, means the imaginative exploitation of the properties offered by new or improved materials. And for the man in the street, the schoolboy even, not-to-know is to miss one of the great developments of our age: the age of advanced materials.

This evolution and its increasing pace are illustrated in Figure 1.2. The materials of prehistory (> 10 000 BC, the Stone Age) were ceramics and glasses, natural polymers and composites.

Weapons - always the peak of technology - were made of wood and flint; buildings and bridges of stone and wood. Naturally occurring gold and silver were available locally but played only a minor role in technology. The discovery of copper and bronze and then iron (the Bronze Age, 4000 BC- 1000 BC and the Iron Age, 1000 BC-AD 1620) stimulated enormous advances, replacing the older wooden and stone weapons and tools (there is a cartoon on my office door, put there by a student, presenting an aggrieved Celt confronting a swordsmith with the words ‘You sold me this bronze sword last week and now I’m supposed to upgrade to iron!’). Cast iron technology (1620s) established the dominance of metals in engineering; and the evolution of steels (1850 onward), light alloys (1940s) and special alloys since then consolidated their position. By the 1960s, ‘engineering materials’ meant ‘metals’. Engineers were given courses in metallurgy; other materials were barely mentioned.

There had, of course, been developments in the other classes of’ material. Portland cement, refractories,

fused silica among ceramics, and rubber, bakelite, and polyethylene among polymers, but their share of the total materials market was small. Since 1960 all that has changed. The rate of development of new metallic alloys is now slow; demand for steel and cast iron has in some countries actually fallen’. The polymer and composite industries, on the other hand, are growing rapidly, and projections of the growth of production of the new high-performance ceramics suggests rapid expansion here also.

Fig. 1.2 The evolution of engineering materials with time. ‘Relative Importance’ in the stone and bronze ages is based on assessments of archaeologists: that in 1960 is based on allocated teaching hours in UK and US universities; that in 2020 on predictions of material usage in automobiles by manufacturers. The time scale is non-linear. The rate of change is far faster today than at any previous time in history. This rapid rate of change offers opportunities which the designer cannot afford to ignore. The following case study is an example. There are more in Chapter 15.

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MICHAEL F. ASHBY

Department of Engineering, Cambridge University, England

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