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Mighty material breaks boulders.

Japanese scientists have developed a device that uses thin rods of a titanium-nickel alloy to break up room-size rocks and concrete structures. The alloy is a shape-memory material: It changes its shape in response to changes in temperature or pressure, but then "remembers" its original form when heated, explains Minoru Nishida, a metallurgist at Kumamoto University in Japan. Recognizing that the alloy recovers its shape with a force greater than what rocks can withstand, Nishida's team has built two rock-cracking devices.

The devices use three to nine alloy rods, each about 15 millimeters across and 29 millimeters long. The rods weigh about 35 grams each. The researchers first compress the rods to shorten them, and then mount them between and perpendicular to adjustable plates, Nishida says. For one type of breaker, the researchers insert the device into a small borehole drilled into the boulder. Then they heat the rods. As the rods "remember" their original shape and lengthen, they push the plates against the hole walls, and the increased pressure cracks the rock.

These devices have proved useful in breaking up large boulders at a golf course and concrete bases for power lines on private property, Nishida says. They work quietly and without much mess and so can be used in building renovations or underwater, he adds. Tokin Corp. in Sendai, Japan, now makes the devices.
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Title Annotation:titanium-nickel alloy
Author:Pennisi, Elizabeth
Publication:Science News
Date:Dec 14, 1991
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