Plasticity (physics)

Lore & Background

Perfect plasticity is a property of materials to undergo irreversible deformation without any increase in stresses or loads. Plastic materials hardened by prior deformation, such as cold forming, may need increasingly higher stresses to deform further. Plastic deformation is also dependent on deformation speed, with higher stresses usually required to increase the rate of deformation—such materials are said to deform visco-plastically. The plasticity of a material is directly proportional to its ductility and malleability.

Reader's Guide

Plasticity is a fundamental concept in engineering and materials science, governing how materials are shaped, formed, and extruded. Most metals show more plasticity when hot than when cold, and are rendered plastic by heating for shaping operations. The transition from elastic to plastic behavior—yielding—is critical for structural design. The physical mechanisms include slip and twinning in metal crystals, microcrack sliding in rocks and concrete, and bubble rearrangements in foams. On the nanoscale, primary plastic deformation in simple face-centered cubic metals can be reversible as long as there is no material transport via cross-slip. Shape-memory alloys exhibit a reversible form of plasticity called pseudoelasticity. Understanding plasticity allows engineers to predict material failure, design forming processes, and develop materials with tailored properties for applications ranging from construction to biomedical devices.

Did You Know?

• Plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, and foams.
• In metals, plasticity is usually a consequence of dislocations within the crystal lattice.
• Perfect plasticity is a property of materials to undergo irreversible deformation without any increase in stresses or loads.
• Most metals show more plasticity when hot than when cold.