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Thermoelasticity is the change in the size and shape of a solid object as the temperature of that object fluctuates. Materials that are more elastic will expand and contract more than those materials that are more inelastic. Scientists use their understanding of thermoelasticity to design materials and objects that can withstand fluctuations in temperature without breaking.
Scientists have understood the equations that describe thermoelasticity for over 100 years but have only recently begun stress testing materials in order to determine how thermoelastic they are. By subjecting materials to rising and falling temperatures, engineers are able to predict how much these materials will expand or contract at different temperatures. This knowledge is important when building machines or weight bearing structures with pieces that need to fit closely together. Understanding the principles of thermoelasticity helps engineers design things that maintain their structural integrity for a range of temperatures.
The principles of thermoelasticity have affected the way engineers design a number of different objects. Knowing that concrete expands when it is heated, for instance, is the reason that sidewalks are designed with small spaces between the slabs. Without these spaces, the concrete would have no room to expand, causing a great deal of stress on the material, and leading to cracks, breaks or holes. Likewise, bridges are designed with expansion joints to allow for the components to expand as they are heated.
All materials that are elastic expand when heated and contract when cooled. The expansion that is described by thermoelasticity formulas is caused by an increase in the movement of the atoms in the material. These atoms remain linked to each other as a solid heats but the molecular bonds grow in size, allowing the atoms to move away from each other and causing the material to grow. Conversely, when a material is cooled, the atoms move less and the bonds pull them closer to each other.
The principles of thermoelasticity dictate that the expansion caused by an increase in temperature will cause an object to expand in all directions. Slabs of concrete expand out towards one another, up away from the ground, and down towards the ground when they are heated. Cups or other vessels will expand in all directions as well in such a way that the total volume they can contain increases along with the size of the vessel. Specific formulas are used in the study of thermoelasticity to describe how objects change in shape with changes in temperature.