Plasticity (physics)
Permanent deformation of solids under applied forces.
Plasticity, also known as plastic deformation, is the ability of a solid material to undergo permanent, non-reversible change of shape in response to applied forces. In physics and materials science, it describes how materials like metals, soils, rocks, concrete, and foams can be bent or pounded into new shapes, with permanent changes occurring within the material itself. The transition from elastic to plastic behavior in engineering is termed yielding. For many ductile metals, tensile loading initially causes elastic deformation, where extension is proportional to load and fully reversible upon unloading. Once the load exceeds the yield strength, extension increases more rapidly, and some extension remains after the load is removed. Elastic deformation is an approximation dependent on time frame and loading speed; when both elastic and plastic components are present, it is often called elasto-plastic or elastic-plastic deformation. Perfect plasticity describes irreversible deformation without any increase in stress, while materials hardened by prior cold forming may require higher stresses for further deformation. Plastic deformation is generally dependent on deformation speed, with higher stresses needed to increase the deformation rate, a behavior known as visco-plasticity. The physical mechanisms causing plasticity vary widely. In metals, it primarily results from dislocations at the crystalline scale, with slip and twinning as the main modes. Most metals become more plastic when heated, which is crucial for forming and shaping operations. In brittle materials like rock, concrete, and bone, plasticity is predominantly caused by slip at microcracks. In cellular materials such as liquid foams or biological tissues, plasticity arises mainly from bubble or cell rearrangements, notably T1 processes. On the nanoscale, reversible plasticity can occur in simple face-centered cubic metals without material transport, and shape-memory alloys exhibit a reversible form called pseudoelasticity.
- field
- Physics and materials science
- known_for
- Ability of solids to undergo permanent deformation; transition from elastic to plastic behavior known as yielding
- related_concepts
- Ductility, malleability, yield strength, dislocations, slip systems, twinning
Lore & Background
Plasticity, or plastic deformation, is the capacity of a solid material to permanently change shape under applied forces, a non-reversible process distinct from elastic deformation. In engineering, the shift from elastic to plastic behavior is termed yielding. This phenomenon is observed across many materials, including metals, soils, rocks, concrete, and foams, though the underlying physical mechanisms differ. In crystalline metals, plasticity primarily arises from the movement of dislocations—defects within the crystal lattice—or through twinning, where deformation occurs along specific planes. Metals generally become more plastic when heated, making hot forming operations possible; for instance, lead is highly plastic at room temperature, whereas cast iron lacks sufficient plasticity even when hot for forging. In brittle materials like rock, concrete, and bone, plasticity results from slip at microcracks. In cellular materials such as liquid foams or biological tissues, it stems from rearrangements of bubbles or cells. On the nanoscale, plasticity in simple face-centered cubic metals can be reversible if no material transport occurs. Amorphous materials, lacking long-range order, undergo plastic deformation through crazing, where regions of high stress form fibrils, giving a hazy appearance. Plastic deformation is also influenced by deformation speed; materials requiring higher stresses for faster deformation are termed visco-plastic. 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.
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