Self-Healing Material Developed

Wednesday, February 14th 2001, 12:00 am

By: News On 6

Researchers have developed the first material that automatically repairs itself, offering a potential way of fixing the hairline cracks that develop in the space-age composites used in everything from tennis rackets to aircraft.

The scientists' secret: tiny capsules of glue that are added to the composite material.

``It has just an enormous number of applications. That's probably one drawback for me, I don't know which direction to go,'' Scott White said, a professor of aeronautical engineering at the University of Illinois at Urbana-Champaign who led the study.

Composite materials consist of fibers of glass, carbon or other substances mixed with a resin. Fiberglass is one type of composite. Some tennis rackets and golf clubs are made of graphite composites.

Damage to composite materials often begins as tiny cracks. As they grow, they weaken the material until it breaks.

To heal tiny cracks automatically, the Illinois researchers sprinkled capsules about the thickness of a human hair throughout an experimental fiberglass-like compound. When a crack appeared, capsules in its path broke open, spilled their contents and sealed the cracks.

The compound retained 75 percent of its original strength after the cracks had healed for 48 hours, the researchers reported.

The study was published in Thursday's issue of the journal Nature.

The new material ``nips the damage in the bud,'' Richard P. Wool, a University of Delaware researcher, said in an accompanying commentary.

The material is not yet ready for commercial production, however. Temperatures higher than 200 degrees stop the setting agent from working, and the curing time is too long for many applications.

The material contains 100 to 200 capsules per cubic inch. While all of the capsules will eventually break, objects made with the material could last several times longer than those made of current composites, Wool said.

Materials such as the self-healing composite are part of the infant field of smart materials.

Objects such as spacecraft, artificial joints and bridge supports, which are difficult or impossible to reach, are prime candidates for self-healing materials.

White said researchers are also exploring the use of the material for computer circuit boards, many of which come off the production line with small cracks that make them unusable.

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