Historical Perspective (material)

The designation of successive historical epochs as the Stone, Copper, Bronze,
and Iron Ages reflects the importance of materials to mankind. Human destiny
and materials resources have been inextricably intertwined since the daw^n of
history; how^ever, the association of a given material w^ith the age or era that
it defines is not only limited to antiquity. The present nuclear and information
ages ov^e their existences to the exploitation of tv^o remarkable elements,
uranium and silicon, respectively. Even though modern materials ages are
extremely time compressed relative to the ancient metal ages they share a
number of common attributes. For one thing, these ages tended to define
sharply the material limits of human existence. Stone, copper, bronze, and
iron meant successively higher standards of living through new^ or improved
agricultural tools, food vessels, and weapons. Passage from one age to another
was (and is) frequently accompanied by revolutionary, rather than evolutionary,
changes in technological endeavors.
It is instructive to appreciate some additional characteristics and implications
of these materials ages. For example, imagine that time is frozen at 1500 BC
and we focus on the Middle East, perhaps the world's most intensively excavated region with respect to archaeological remains. In Asia Minor (Turkey)
the ancient Hittites were already experimenting with iron, while close by to
the east in Mesopotamia (Iraq), the Bronze Age was in flower. To the immediate
north in Europe, the south in Palestine, and the west in Egypt, peoples were
enjoying the benefits of the Copper and Early Bronze Ages. Halfway around
the world to the east, the Chinese had already melted iron and demonstrated
a remarkable genius for bronze, a copper—tin alloy that is stronger and easier
to cast than pure copper. Further to the west on the Iberian Peninsula (Spain
and Portugal), the Chalcolithic period, an overlapping Stone and Copper Age
held sway, and in North Africa survivals of the Late Stone Age were in evidence.
Across the Atlantic Ocean the peoples of the Americas had not yet discovered
bronze, but like others around the globe, they fashioned beautiful work in
gold, silver, and copper, which were found in nature in the free state (i.e., not
combined in oxide, sulfide, or other ores).
Why materials resources and the skills to work them were so inequitably
distributed cannot be addressed here. Clearly, very little technological information
diffused or was shared among peoples. Actually, it could not have been
otherwise because the working of metals (as well as ceramics) was very much
an art that was limited not only by availability of resources, but also by cultural
forces. It was indeed a tragedy for the Native Americans, still in the Stone Age
three millennia later, when the white man arrived from Europe armed with
steel (a hard, strong iron-carbon alloy) guns. These were too much of a
match for the inferior stone, wood, and copper weapons arrayed against them.
Conquest, colonization, and settlement were inevitable. And similar events have
occurred elsewhere, at other times, throughout the world. Political expansion,
commerce, and wars were frequently driven by the desire to control and exploit
materials resources, and these continue unabated to the present day.
When the 20th century dawned the number of different materials controllably
exploited had, surprisingly, not grown much beyond what was available
2000 years earlier. A notable exception was steel, which ushered in the Machine
Age and revolutionized many facets of life. But then a period ensued in which
there was an explosive increase in our understanding of the fundamental nature
of materials. The result was the emergence of polymeric (plastic), nuclear, and
electronic materials, new roles for metals and ceramics, and the development
of reliable ways to process and manufacture useful products from them. Collectively,
this modern Age of Materials has permeated the entire world and
dwarfed the impact of previous ages.
Only two representative examples of a greater number scattered throughout
the book will underscore the magnitude of advances made in materials within
a historical context. In Fig. 1-1 the progress made in increasing the strengthto-
density (or weight) ratio of materials is charted. Two implications of these
advances have been improved aircraft design and energy savings in transportation
systems. Less visible but no less significant improvements made in abrasive
and cutting tool materials are shown in Fig. 1-2. The 100-fold tool cutting speed
increase in this century has resulted in efficient machining and manufacturing