EMCs provide tougher alternative to shape-memory alloys and plastics

Composites Technology Development Inc. (CTD, Lafayette, Colo., U.S.A.) has developed TEMBO Shape Memory Polymers, elastic memory composites (EMCs) that are less dense and about one-fifth the weight of shape-memory metal alloys but deliver greater strength than other shape-memory plastics. "Most people think of composites as a rigid material," says Michael Tupper, vice president of CTD, but he explains that EMCs are being pursued for space applications because structures made from them can be folded and compacted into small spaces and will remain that way until heat is applied (see photo), at which time the product regains its original shape. Since it costs about $10/lb (USD) to launch objects into space, the lighter TEMBO components will help to reduce launch costs or allow larger structures to be built within the lifting capability of existing launch vehicles.

TEMBO composites feature a matrix of elastic memory thermoset resin developed by CTD, which allows them to withstand high packaging strains without damage. TEMBO structures can be reinforced with carbon, glass, aramid and organic fibers and manufactured like traditional composites, albeit with lower fiber volume fractions. "It was challenging because all of the processes are designed to give 60 percent fiber volume," Tupper says. TEMBO fiber loading is 40 to 50 percent to give the material sufficient flexibility for bending. Because different molding methods may prove more effective for particular designs, CTD is adapting TEMBO resins for wet layup, prepreg, vacuum-assisted resin transfer molding (VARTM), filament winding and pultrusion.

In development for five years, TEMBO EMCs are not yet commercially available, but prototypes and demonstration products are under review in automotive, industrial, sporting goods and other markets, with the first commercial products expected in 2005. Principal near-term applications are space and satellite programs: CTD is building five flight systems for U.S. Air Force missions. "Three of these will utilize hinges to deploy solar array panels," Tupper says. The fourth will be a 3.3m/10.8-ft-long gravity gradient boom for the U.S. Air Force Academy's FalconSat 3 satellite, and the fifth is a very large roll-out structure for use on a solar array system being developed by the Air Force and Lockheed Martin. CTD also is working on new EMC forms, using nanoreinforcement and foam materials. For product info, use goComp.biz: ctd-materials.gocomp.biz/1