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In recent years, the damage caused by the earthquake has exposed the vulnerability of existing building structures in the face of strong ground movements. To address this situation, researchers at the Georgia Institute of Technology in the United States are analyzing shape memory alloy materials to understand their potential for use in seismic-resistant structural materials.
To analyze shape memory alloys, researchers developed a model that combines thermodynamic and mechanical equations to understand how shape memory alloys change under intense motion conditions. Using models, they analyzed the response of shape memory alloys to different external conditions in different building components (cables, rebars, plates, and coil springs). The researchers stated that based on this information, the best seismic properties of the material can be determined.
Developers of this analytical model include Reginald Desloches, Professor of the School of Civil and Environmental Engineering at Georgia Tech; Reza Mirzai, Faculty of Mechanical Engineering; Associate Professor, Arathi Yava, Faculty of Civil and Environmental Engineering. And Ken Woods, a professor of materials science and engineering. The article on analytical models was recently published in the online edition of the International Journal of Nonlinear Mechanics.
To improve the structural performance of materials in earthquakes, researchers around the world have studied the use of various “smart†materials, including shape memory alloys. The most common shape memory alloy is composed of a metal compound containing copper-zinc-aluminum-nickel, copper-aluminum-nickel or nickel-titanium. Potential applications of shape memory alloys in bridges and building structures include structural supports, pillars and beams, or connecting components between beams and columns.
Yavali explained that for standard civil engineering materials, one can measure the stress and deformation of a material by means of force and displacement through mechanics. However, for materials such as shape memory alloys whose characteristics change with the presence and absence of loads, one must consider both thermodynamics and mechanics.
The team found that the heat generation and absorption in the process from loading to no load create a temperature gradient in the shape memory alloy. This results in a non-uniform stress distribution in the material, even if the shape memory alloy is uniformly deformed. This is also the case.
Mirzaa Alpha believes that in the past, people have been deeply studying filament-shaped shape memory alloys, which can quickly exchange heat with the surrounding environment, so that people do not notice changes in temperature. However, when people start to study shape memory alloys that can become parts of civil engineering, their internal temperatures are no longer uniform, and this kind of non-uniformity must be considered within the scope of the study.
In order to anticipate the internal temperature distribution of the shape memory alloy in alternating cycles with/without load, which helps to understand the stress distribution, the research model developed by the researchers was able to input the material's surface thermal limit conditions, diameter, and shape memory alloy loading rate as input. parameter.
The reason why the research team puts the surrounding conditions into the research model is that the shape memory alloy will face various environments when it is used in seismic structures. For example, the bridge structure will come into contact with water and the building structure will encounter air. Different shape thermal conductivity of the shape memory alloy. In the study, the researchers used a thermal imager to record the change in surface temperature of the shape memory alloy when the load was present.
Using the developed model, researchers can accurately predict the temperature and stress distribution within the shape memory alloy. The results obtained by model analysis were confirmed by the experimental results. In one test, they discovered that when a shape memory alloy is slowly loaded, the alloy will have time to exchange heat with the surrounding environment, and a uniform stress distribution is generated inside; however, the alloy is rapidly loaded with heat. It is not possible to exchange with the surrounding environment in a short period of time, so that an uneven stress distribution occurs within the alloy.
Mirza Effie said that the model analysis method they developed was able to accurately and rapidly simulate the complex thermal/force coupling reactions of shape memory alloys when considering temperature changes and load-rate dependence.
Deschlochs said that shape memory alloys have demonstrated the unique properties required for earthquake-resistant buildings and bridge designs, as well as other applications: they have the ability to dissipate large amounts of energy, and they also undergo permanent deformation or severe degradation. Looking into the future, researchers plan to analyze more complex structural materials and the effects of multiple loads (including tension, bending, and torsion) to optimize the use of shape memory alloys in seismic structures. (Reporter in the United States, Mao Li)
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