A model was created to to analyze shape-memory alloys, which could be used in structures for stress distribution

Earthquakes, like other natural disasters, have proved to be destructive on several occasions. For instance, in March 2011, Japan suffered a 9.0-magnitude earthquake that damaged the Fukushima Daiichi nuclear plant, leading to a nuclear meltdown. With the development of earthquake-resistant structures, the threat of an oncoming earthquake might not be quite as bad -- and that's exactly what researchers at the Georgia Institute of Technology are working on.

Reginald DesRoches, study leader and a professor in the School of Civil and Environmental Engineering at Georgia Tech, along with Georgia Tech team Reza Mirzaeifar, Arash Yavari, and Ken Gall, have created a model that utilizes shape-memory alloys, which can be used to make seismic-resistant buildings.

Shape-memory alloys are materials that can bounce back after encountering extreme loads. They can be made of metal mixtures like copper-zinc-aluminum-nickel, and used in bearings, beams and columns.

"Shape-memory alloys exhibit unique characteristics that you would want for earthquake-resistant building and bridge design and retrofit applications," said DesRoches. "They have the ability to dissipate significant energy without significant degradation or permanent deformation."

The model mixed thermodynamics and mechanical equations to determine how shape-memory alloys react when taking on loading from powerful motion. The production and absorption of heat during loading and unloading led to a temperature gradient within the alloys, causing a non-uniform distribution of stress throughout the material despite the strain being uniform. The model was made to predict the internal temperature distribution of the shape-memory alloys when loading and unloading and determine the stress distribution.

"Shape-memory alloys previously examined in detail were really thin wires, which can exchange heat with the ambient environment rapidly and no temperature change is seen," said Mirzaeifar. "When you start to examine alloys in components large enough to be used in civil engineering applications, the internal temperature is no longer uniform and needs to be taken into account."

Ambient conditions were considered in the model, since structures would be located in different environments and thus produce different rates of heat transfer. A thermal camera was used to record surface temperature.

Tests verified that the model was able to predict stress distribution and internal temperature accurately. In one test, the shape-memory alloy loaded at a slow rate and had time to exchange heat produced with the ambient environment. It was able to show uniform stress. However, with more rapid loading, there was not enough time to exchange the heat and this led to non-uniform distribution of stress.

In addition to creating earthquake-resistant structures, scientists are constantly looking for new, better ways to prevent earthquake-related destruction. For instance, in 2010, Universidad Pablo de Olavide and Universidad de Sevilla researchers used clustering techniques to better understand the behavior patterns of earthquakes, which could lead to accurate forecasting and efficient preparation.

Source: Eurekalert

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