Elastic deformation is a reversible change in shape of a material, with the ability to recover from low stress. Plastic deformation changes shape permanently. Material testing can determine elasticity and adjust it. Excessive elasticity can cause damage to structural components in buildings.
Elastic deformation is a reversible change in the shape of a material, where it bends out of position and snaps back after the deformation is released. A common example can be seen in memory-rimmed glasses, which the wearer can bend or crumple in the hand before releasing, allowing them to return to their normal shape. This property can be seen in a variety of materials, and evaluating the line between elastic and plastic deformation, where the change in shape becomes permanent, is an important part of materials testing.
For many materials, some elasticity is desirable. The ability to recover from relatively low stress can keep materials strong and useful for longer. Memory foams, metals and gels all display this trait. The material’s elasticity allows it to recover from stress to restore normal function, although over time and under certain conditions, the material can become brittle and may not have as large an elastic deformation range. Materials often become less pliable when cold or subjected to hardening chemicals that interfere with their elasticity.
With plastic deformation, the material changes shape permanently, even if it doesn’t fail. This can also be a useful trait with some materials; highway barriers, for example, are sometimes designed to give way under the pressure of a car while remaining in place, to stop the cars without bouncing them onto the roadway. When material breaks due to stress, this can pose a risk. Materials with a low breaking point are called brittle.
Material testing can determine how much elastic deformation a material exhibits, if any. It may be possible to change the configuration of the material to increase the elasticity. With polymer plastics, for example, special softening materials can be added to the mix to allow it to bend and sag under pressure without permanently changing shape. Elastic deformation under pressure can be useful for things like memory foams in seats, which can sag under weight and spring back to fit a different person.
Excessive elastic deformation can become a problem. With some materials, elasticity is not a desirable trait and the material is made more brittle, but stronger, so it can withstand stress. In a building, for example, a small amount of sagging can prevent problems, but if the beams bend and flex wildly, they could damage other structural components in the building. This could create cracks in the finish, damage to electrical systems, uneven walls and floors, and so on.
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