Much as earlier eras were characterized as the ages of stone, iron, and copper, it may be that the term that best characterizes the 20th century is "the age of engineered materials." But choosing just one material to define the century would be difficult. Steel for skyscrapers? Copper for electrical conduction? Silicon for chips? Plastics and polymers? Biomaterials for medical implants? In one way or another, all of these materials have been crucial to the inventions and innovations that have transformed the century.
The materials revolution that took hold in 1900 began with the heavy building blocks of iron and steel and ended with lighter weight metal alloys and exotic high-strength composites. Throughout the century, engineers learned new methods to analyze, process, refine, and add to materials in ways that maximized their properties, enhanced their performance, and met design challenges. They set about to reshape skylines with sleek architecture of steel and glass, forge great sheets of metal for airplane wings, fabricate plastics into heart valves and computer circuits, and create new composites for spacecraft.
It is a major engineering enterprise to design, analyze and test materials. Analytical methods coupled with the powerful computational tools that allow detailed imaging and simulation have completely revolutionized materials research. They have changed an empirical methodology into a directed, rapid approach to the materials requirements, and we can see the results everyday:
The interior of a jet engine is one of the most ferocious environments on Earth, reaching temperatures of 3600°F while exhaust gases rush past turbine blades, making them spin thousands of times per minute. The material for the blades must be strong enough to withstand the stress and force of the gases and heat, light enough to maximize efficiency, and durable enough for extensive use.
Copper is a highly conductive metal, but it is soft. Mixing it with a minute amount of silver makes it strong enough conduct electricity without melting. The wrong material, or the wrong amount of copper to silver, could spell disaster in many areas, including disconnecting a telephone call or causing the lights to go out.
Engineers are involved in solving such needs precisely. Because materials have different properties, some are better than others for certain things. Computers using plastic photonic circuits handle data more rapidly than electronic devices - photons travel much faster, and plastic components are lighter than metals, can store information more compactly, and are not subject to magnetic interference. Ceramic materials, in another example, enable engines to run hotter, therefore burning fuel more efficiently than do metal engines.
Adjusting carbon and other elements in steel produces many new alloys, allowing steel to be used in countless industries from shipbuilding to watchmaking. Adding tin to copper makes bronze, ideal for gears and bearings in places where strength counts, as in industrial machinery. Additives can turn some materials into shape-shifters -- for example, polyvinylchloride (PVC) used in gutters, pipes, and panels can be turned into clothing by adding plasticizers, or be used as the tubing that forms the circuit of the heart-lung machine.
More of the world's products are made with composites that combine different types of strength or resilience. These include exotic amorphous metals and shape-memory alloys — "smart" materials that can actually respond to changes in their environment and "remember" their shape. They are being applied to many products, such as stents used to keep human arteries open.
The greatest leaps in technological innovation occur as improved materials become available. This is especially true in the semiconductor business, where engineering silicon to make microprocessors is a delicate process. Silicon must be purified to produce crystals, then sliced into wafer-thin chips. With the recent "lab on a chip" technologies, the ability to build and use micromachines will soon move from a curiosity to specific applications.
One of the greatest examples of materials engineering responding to a crisis occurred during the early 1940s. Polymer chemistry and engineering took on critical new importance as the United States entered World War II. The seizure of rubber plantations in the Malay Peninsula and East Indies cut off the source of nearly 90 percent of America's natural rubber supply. A massive national research and engineering effort was undertaken to produce enough synthetic rubber to meet the needs of the country. A collaborative government-industry synthetic rubber program was put in place that called for the construction of four plants, each with a yearly capacity of 10,000 tons. Before the war, no more than 6,000 tons had ever been produced in a single year. By 1945, annual synthetic rubber production in the United States exceeded 600,000 tons.
At the end of World War II, the U.S. military released to the public many "high tech" synthetic materials that were previously restricted or unavailable. These state-of-the-art materials included silicones, Dacron, polyurethanes, nylon, titanium, and Teflon (which was discovered purely by accident). Physicians quickly saw the possibilities of using many of these in medicine. Engineers translated their vision into useful devices, first by analyzing the properties, then by figuring out how to manufacture them. Remarkable new biomaterials continue to be developed for use in making heart-assist devices, artificial kidneys, contact lenses, vascular grafts, shunts, sutures, prostheses, and hundreds of other products.
The space age has spawned important new materials and uncovered new uses for old materials. Fiberglass-reinforced plastics have been molded into rigid shapes to provide car bodies and hulls for small ships. Carbon fiber has demonstrated remarkable properties that make it an alternative to metals for high-temperature turbine blades. Ceramics research has produced materials resistant to high temperatures and suitable for heat shields on spacecraft. New analytical techniques, molecular and atomic imaging, and quantum calculations for atomic and molecular systems are available to help optimize materials choices and manufacturing approaches.
Materials development today is much closer to engineering science than in the past. The engineer's ability to translate that science into applications is now approaching the level of atomic and molecular design — the frontier of the future. The availability of new analytical and computational techniques has enabled engineers to take the study of material properties to new heights, and holds tremendous potential for the future.
