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Wednesday, 11 October 2017 01:00

Scientists in Japan improve seismic resistance of metals

Scientists in Japan improve seismic resistance of metals Credits:

Researchers at Japan's Tohoku University have come up with a cheap way to improve the properties of some 'shape memory' alloys, often used in earthquake design due to their ability to return to their original shape after being deformed.

Shape memory alloys formed of a single crystal have improved properties over multiple-crystals metals, yet they are quite expensive to produce. The heating method developed by scientists at Japan's Tohoku University takes advantage of a phenomenon known as 'abnormal grain growth' to transform multiple-crystal materials to single-crystal materials in a simpler and thus, less expensive way. With this method, a metal's multiple crystals grow irregularly, some at the expense of others, when exposed to heat.

The team uses an alloy made of copper, aluminium and manganese, a well-known shape memory metal that is easy to cut with machines. The technique involves application of several heating and cooling cycles to the alloy. The metal is first heated to 900°C, then cooled to 500°C, five times. This is followed by four cycles of heating to 740°C then cooling to 500°C. Finally, the metal is heated one last time to 900°C.

This results in a single-crystal metal bar of 700mm in length and 15mm in diameter, with significantly enhanced elasticity. It was proven that by omitting the lower temperature heating /cooling cycles (740°C / 500°C) the single-crystal result could not be achieved.

Bending tests on an alloy bar produced by this method showed a super-elastic response with almost no residual strain for the material. Altering the metal's shape also helps towards increasing its strength, the scientists state. According to Toshihiro Omori, lead researcher of the study, the bar's size and enhanced properties make it highly suitable for seismic applications in civil engineering infrastructure, while its reduced cost stemming from the method's simplicity allows for mass production of such single-crystal bars.

Source: The construction Index

Read 421 times Last modified on Wednesday, 11 October 2017 13:44

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