21-06-2012, 02:00 PM
Seismic Resistance: Model Analyzes Shape-Memory Alloys Use in Earthquake-Resistant
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Researchers have developed a model that combines thermodynamics and mechanical equations to assess what happens when shape-memory alloys are subjected to loading from strong motion. The researchers are using the model to analyze how shape-memory alloys in a variety of components -- cables, bars, plates and helical springs -- respond to different loading conditions. From that information, they can determine the optimal characteristics of the material for earthquake applications.
To improve the performance of structures during earthquakes, researchers around the world have been investigating the use of "smart" materials, such as shape-memory alloys, which can bounce back after experiencing large loads. The most common shape-memory alloys are made of metal mixtures containing copper-zinc-aluminum-nickel, copper-aluminum-nickel or nickel-titanium. Potential applications of shape-memory alloys in bridge and building structures include their use in bearings, columns and beams, or connecting elements between beams and columns. But before this class of materials can be used, the effect of extreme and repetitive loads on these materials must be thoroughly examined.
The researchers were able to accurately predict internal temperature and stress distributions for shape-memory alloys. The model results were verified with experimental tests. In one test, they found that a shape-memory alloy loaded at a very slow rate had time to exchange the heat created with the ambient environment and exhibited uniform stress. If it was loaded very rapidly, it did not have enough time to exchange the heat, leading to a non-uniform stress distribution.