Plasticity

(mechanics) The property of a solid body whereby it undergoes a permanent change in shape or size when subjected to a stress exceeding a particular value, called the yield value.

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The ability of a solid body to permanently change shape (deform) in response to mechanical loads or forces. Deformation characteristics are dependent on the material from which a body is made, as well as the magnitude and type of the imposed forces. In addition to plastic, other types of deformation are possible for solid materials.

One common test for measuring the plastic deformation characteristics of materials is the tensile test, in which a tensile (stretching) load is applied along the axis of a cylindrical specimen, with deformation corresponding to specimen elongation. The load is converted into stress; its units are megapascals (1 MPa = 10⁶ newtons per square meter) or pounds per square inch (psi). Likewise, the amount of deformation is converted into strain, which is unitless. The test results are expressed as a plot of stress versus strain. See also Stress and strain.

Typical tensile stress-strain curves have been calculated for metal alloys and polymeric materials. For both materials, the initial regions of the curves are linear and relatively steep. Deformation that occurs within these regions is nonpermanent (nonplastic) or elastic. This means that the body springs back to its original dimensions once the stress is released, or that all of the deformation is recovered. In addition, stress is proportional to strain (Hooke's law), and the slope of this linear segment corresponds to the elastic (Young's) modulus. See also Elasticity; Hooke's law; Young's modulus.

Plastic (permanent) deformation begins at the point where linearity ceases such that, upon removal of the load, not all deformation is recovered (the body does not assume its original or stress-free dimensions). The onset of plastic deformation is called yielding, and the corresponding stress value is called the yield strength. After yielding, all deformation is plastic and, until fracture, the curves are nonlinear. This behavior is characteristic of many metal alloys and polymeric materials. The concept of plasticity does not normally relate to ceramic materials such as glasses and metal oxides (for example, aluminum oxide). See also Plastic deformation of metal.

noun

The quality or state of being flexible: bounce, ductility, elasticity, flexibility, flexibleness, give, malleability, malleableness, pliability, pliableness, pliancy, pliantness, resilience, resiliency, spring, springiness, suppleness. Obsolete flexure. See flexible/rigid.

1. the quality of being moldable or workable. n 2. the degree of permanent deformation resulting from stress application, usually associated with substances that are classed as solids or semirigid liquids.

1. That property of freshly mixed cement paste, concrete, mortar, or soil which determines its resistance to deformation or its ease of molding.
2. The ability of a plaster or lime putty to hold or retain water, so that it can be troweled easily.

1. Property of a body that causes it to he deformed permanently when a force is applied. Compare elasticity.

2. In sociology and psychology, applied to the modifiability of human behaviour; plastic behaviour.

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Plasticity generally means ability to be shaped or formed. (It differs from "elasticity", which refers to ability to change temporarily and revert back to original form.) More specific meanings include:

In science

• Neuroplasticity, entire brain structures can change to better cope with the environment. Specifically, when an area of the brain is damaged and non-functional, another area may take over some of the function.
  • Metaplasticity, the plasticity of the plasticity of brain activity.
  • Synaptic plasticity, in neuroscience, plasticity is a property of a neuron or synapse to change its internal parameters in response to its history.
• Phenotypic plasticity, describes the degree to which an organism's phenotype is determined by its genotype.
• Plasticity (psychology), an intelligence factor that determines the ease of changing ones perception of a situation for finding a new solution to a problem. Lack of plasticity is termed rigidity.
• Plasticity (physics), in physics and engineering, plasticity is the propensity of a material to undergo permanent deformation under load. In civil engineering, plasticity of a soil is quantitatively determined by Atterberg Limits testing.
• Plasticity (tissues), in body tissues, plasticity refers to the ability of differentiated cells to undergo transdifferentiation.

In art

• The plastic arts are those, such as clay sculpture, in which material is formed or deformed into a new, permanent shape.
• Plasticity is an album by the band Cabaret Voltaire.

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