Harvard, Princeton, the University of Virginia and, in the U.K, Cambridge. In the commercial sector, he has worked closely with General Electric Co., the world’s leading maker of jet engines. In the materials area, Evans has focused his research on the properties of brittle materials, such as ceramics. These are crucial elements in much of the new aerospace technology. They come into play in advanced jet engines – one of the last places you would want to see brittleness. But as Evans notes, ceramic compounds can take a lot more heat than metal can, and engines are much more fuel-efficient when they run hotter. Over the last decade, he says, engine manufacturers have learned how to couple the ceramic’s heat resistance with the metal’s strength by layering the two types of material on engine components. Combustion temperatures in engines are now 200° C above the melting point of nickel alloy, doubling fuel efficiency in the process. In the research phase are new ceramic composites, such as silicon carbide, that are lighter than nickel alloy and can operate at higher temperatures.
Tony Evans
Evans is also working with Boeing Aircraft Co. and Lockheed Martin Corp. on materials and design for new hypersonic craft, capable of flying up to eight times the speed of sound (just over 6,000 miles per hour at sea level). The technology they are developing would be used first in military aircraft but could also be applied later on to vehicles replacing the Space Shuttle. High speeds produce intense heat on the craft’s surface, and the heat-shielding solution for the shuttle – tiles – has an obvious and serious drawback: the tiles tend to fall off. Engineers, says Evans, are working
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to replace shuttle tile “with a materials concept that is much more robust and is able to withstand extremely high heat flux.” One candidate is hafnium boride, which has excellent heat-shielding ability and an extremely high melting point. But, like other ceramics, it’s fragile. As in the jet engine, the engineering challenge is to wed its heat resistance to a metal’s strength, without adding too much weight. Hypersonic and space flight also may make use of shapechanging structures. Jet engines that morph with changes in speed are one idea under development (as the jet goes hypersonic, the engine’s inlet size needs to decrease for optimum efficiency). The same principle could be applied to the craft as a whole, making it narrower with increasing speed. Taking flexibility to this level will challenge the engineers on several fronts. The surface material must be strong, light and thin, so that it can move without building up any internal stress. The underlying structure must be strong, light, and movable at many points. Traditional frames won’t do. Controlling the morphing process to keep the shape at its most efficient under changing speeds and conditions will require heavy-duty computing power. But advances of recent years in all these areas – materials, structure and computing – are putting such futuristic technology within reach. Already, the aerospace industry has made huge strides in fuel efficiency. With fuel getting more expensive all the time, and with Washington showing a renewed interest in space travel to the moon and beyond, the ideas once consigned to science fiction may soon, literally, take flight.