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Plastic deformation is a process is which enough stress is placed on metal or plastic to cause the object to change its size or shape in a way that is not reversible. In other words, the changes are permanent; even when the stress is removed, the material will not go back to its original shape. Sometimes referred to simply as plasticity, this type of deformation can take be conducted under controlled circumstances as well as unintentionally.
Both the deformation of plastic and the deformation of metals involve changes to the makeup of the material itself. For example, metals that undergo this process of plastic deformation experience a condition known as dislocation. As stress of some type is exerted on the metal, the material reaches a point known as the yield strength. When this point is achieved, the pattern of the molecules that make up the metal begin to shift. The end result is that the molecules realign in a pattern that is shaped by the exterior stress placed on the object.
There are several ways to intentionally utilize plastic deformation in the creation of various types of goods. Heat is often used to shape objects into the desired form. As the metal cools, the shape is retained and becomes permanent. The use of pressure can also help to shape both plastic and metal into the desired shape.
The speed with which the plasticity takes place is also important. In situations where the stress causes changes rapidly, there is a chance that the material will be unable to conform to the pressure and may break. For this reason, plastic deformation as it is used in the manufacture of goods involves carefully controlling heat and pressure, allowing the structure of the material to adapt to the new conditions and incrementally bend until the desired shape is achieved.
In times past, the concept of plastic deformation was at the heart of many goods that were made by hand. This was true with horseshoes, for example. The metal was forged at particular temperatures by a trained ironsmith, rending the meal somewhat malleable. Mallets and other tools could then be used to shape the metal while it was still hot. Once the ironsmith had worked the metal into the desired shape and contour, it would be removed from the forge and allowed to cool, effectively setting the shape permanently.
Today, plastic deformation can be used in the creation of all sorts of goods constructed with metal or plastic. This includes metal sculpture, fittings for wood burning stoves, and some forms of wall art made from a combination of metals like tin and brass. Arts and crafts enthusiasts sometimes make use of heat or pressure to create objects using the principle of plasticity, often using methods that were routinely used in general before the dawn of mass production of goods.