`Smart' materials make for quick-thinking shock absorbers

THEY'RE called smart materials but they're destined for the most mundane places.

Take bulldozer seats. The Lord Corporation, a manufacturing company based in Erie, Pa., wants to sell a seat with ``smart'' shock absorbers. These shock absorbers change consistency whenever their sensors detect vibration, instantly damping the movement.

The company thinks heavy-equipment operators and truck drivers will pay a few hundred dollars extra for a seat that's ultrasoft but won't bounce them around when they hit a bump. Eventually, these smart materials could show up in car seats, shock absorbers, and brakes, says David Carlson, the company's senior staff scientist.

There are several kinds of products called smart materials. The secret behind these smart materials is liquid that changes to gel-like behavior when electricity or magnetism is applied. In a lab at North Carolina State University, Ying Chen picks up a glob of potato starch in silicon oil with a pair of tongs. When she applies an electric field to the tongs, the white foamy liquid instantly turns to a solid that looks suspiciously like Styrofoam.

But it's far stronger. The electric field causes the particles within the liquid to polarize so that they have a positive and a negative side. One particle's negative side attracts another's positive, whose negative side attracts another particle's positive and so on, forming a big chain. Dr. Chen, under the direction of Hans Conrad, professor of the university's materials science and engineering department, has measured the strength of these chains. They have discovered that the whole is greater than the sum of its parts: Three to five chains are 10 times as strong as an equal number of single chains.

Dr. Conrad is working on a beam that stiffens on demand. It is filled with one of the special fluids (called electrorheological or ER fluids). When the beam senses it is carrying a heavier load, it stiffens. Conrad sees many uses, from airplane wings that stiffen in rough weather to buildings in earthquake-prone areas that could soak up vibration.

One of the advantages of the technology is its speed. It takes a mechanical shock absorber one-tenth of a second or more to begin damping a shock, Conrad says. Smart materials react in 1/1000th or 2/1000ths of a second. That can reduce considerably the vibration. Another advantage: One can vary the stiffness of these materials over a wide range.

While ER fluids require electricity, Lord is among the leaders using magnetic fields to change liquids into a solid-like state. ``One of the questions about electrorheological fluids has been their temperature limits,'' Dr. Carlson says. A car or truck must operate in temperatures ranging from minus 40 degrees to 150 degrees C - temperatures that the magnetorheological fluids can handle easily. The company claims to have overcome the difficulties of the magnetic approach, including varying the field. Besides shock absorbers, which it hopes to market within the next year, Lord is also working on antivibration equipment and rotary-type products, such as brakes. Under normal circumstances, the brake disks would be separated by liquid. When the driver pushed the brake pedal, the liquid would turn to a peanut-butter consistency or, if needed, something stiffer.

``In five or 10 years, we could see extensive use of these within the transportation industry,'' Carlson says. But first ``they'll have to prove themselves in the niche markets.''

*``Smart'' comments or questions? Send them to CompuServe (70541,3654), Prodigy (BXGN44A), or via the Internet (laurentb @delphi.com).

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