Plasticity (physics)

Plasticity or plastic deformation for the ability of substances to deform irreversibly under a force is exceeded by a flow limit ( to flow ), and maintain this shape after exposure. Below the yield point will not occur or only elastic deformations.

In contrast, an elastic material would take up its original shape again, and a brittle material to react with an immediate failure - this is referred to brittle fracture, which occurs for example in ceramics and body-centered cubic metals at low temperatures. Flowing a material under force immediately, not only after exceeding a yield point, then one speaks of viscous behavior.

In real materials, but these effects are practically always together.

Material behavior and its description

An ideal plastic body behaves as long as the applied voltage remains below the yield point, like a rigid, non- deformable solids. Reaches a value, it begins to deform irreversibly and unlimited.

This behavior can by a St. Venant - element, a friction pad, which also consists only after exceeding a static friction force in motion is modeled.

Ideal plastic behavior occurs as in nature but practically non-existent, but always together with elastic or viscous effects. An example of elastoplasticity is steel in the tensile test, while the Bingham fluids exhibit viscoplastic behavior, ie represent substances that behave below a yield stress like a solid, about like a liquid.

A model for the mathematical description of plasticity comes from Eugene C. Bingham. This is mainly used for finite element calculations of the viscoplasticity of materials such as Ziegelrohmassen. In continuum mechanics, the theory of plasticity involved in the irreversible transformation of matter.

Causes

The plastic deformation behavior depends on factors including the state of stress, temperature, type of loading and the loading rate. So you know in addition to the conventional plasticity, the high-temperature plasticity, creep and superplasticity.

Microscopically, the plastic deformation of the crystalline solids ( metals ) is described with reference to the dislocation theory. For energetic reasons, it is cheaper to drive individual defects ( dislocations) through the solid to move instead of all rows of atoms simultaneously. Commonly, the comparison to a large, long carpet is used here, which you want to move a piece. It would cost a lot of enormous strength to pull the whole carpet at once - instead you can push through a small fold effortlessly. ( See also strength)

Technical significance

The plasticity determines the ductility and formability of a material.

Examples

High plasticity:

• Dough
• Moist clay
• Metals and metal alloys with a suitable atomic lattice: hot steel forging
• Cold forming of plates when driving
• A thin metal wire can be bent into any shape

Low Plasticity:

• A rubber band is very elastic and therefore returns after load reduction back to its original shape.
• Ceramics break usually brittle without plastic deformation.