Alexei Volkov
Plasticity, also known as plastic deformation, is a property of materials in physics and materials science. It refers to the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces. A perfectly plastic body, therefore, is one that does not tend to regain its original configuration after the removal of a deforming force. Putty, mud, and paraffin wax are examples of nearly perfectly plastic bodies. Plastic deformation is observed in a wide range of materials, including metals, soils, rocks, concrete, and foams, and is of interest in various fields, including engineering and manufacturing.
| Characteristics | Values |
|---|---|
| Definition | A plastic body is a body that does not oppose a deforming force and remains deformed even after the removal of the deforming force. |
| Plastic Deformation | Plastic deformation is almost permanent, unlike elastic deformation, which can be altered. |
| Elasticity | Elastic bodies have restoring forces that allow them to return to their original shape. Plastic bodies lack this property and cannot regain their original shape and size. |
| Stress and Deformation | Plastic deformation is dependent on the deformation speed. Higher stresses are typically required to increase the rate of deformation. |
| Malleability and Ductility | The plasticity of a material is directly proportional to its malleability and ductility. |
| Temperature | Most metals exhibit greater plasticity when hot rather than cold. For example, lead shows sufficient plasticity at room temperature, while cast iron does not. |
| Materials | Plasticity is observed in various materials, including metals, soils, rocks, concrete, foams, and clays. |
| Mechanisms | The physical mechanisms underlying plastic deformation vary. In metals, it is often caused by dislocations in the crystal structure. In brittle materials like rock and concrete, it is caused by slip at microcracks. |
| Examples | Putty, mud, and paraffin wax are examples of nearly perfectly plastic substances. |
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What You'll Learn
Plastic deformation is almost permanent
In physics and materials science, plasticity, or plastic deformation, is the ability of a solid material to undergo permanent and almost irreversible deformation. This deformation is a non-reversible change of shape in response to applied forces. Plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, and foams.
The degree of plasticity differs from body to body, and plastic deformation is dependent on the deformation speed. Higher stresses are required to increase the rate of deformation. Plastic deformation in a metal has two prominent mechanisms: slip and twinning. Slip is a shear deformation that moves atoms through many interatomic distances relative to their initial positions. Twinning is the plastic deformation that occurs along two planes due to a set of forces applied to a given metal piece.
Plastic deformation is undesirable in many cases, as it can lead to a loss of mechanical energy and disrupt the material's structure. However, by deforming in response to applied stresses, plastic materials can reduce these stresses and withstand substantial mechanical work before failure.
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Plastic bodies cannot regain their original shape and size
Plasticity is also known as plastic deformation, and it is observed in most materials, particularly metals, soils, rocks, concrete, and foams. The transition from elastic behaviour to plastic behaviour is known as yielding. Plastic deformation is undesirable, and mechanical energy is lost whenever an item undergoes plastic deformation.
A perfectly plastic body is one that does not tend to regain its original configuration upon the removal of the deforming force. Putty, mud, and paraffin wax are examples of nearly perfect plastic bodies.
The concept of plasticity was first studied by Coulomb in the 18th century in relation to the stability of piles and embankments. Coulomb's work, along with later work by Mohr, has contributed to our understanding of elastic and plastic deformation, yielding, shear localization, and post-failure behaviour.
Plastic deformation is also dependent on the deformation speed, with higher stresses usually required to increase the rate of deformation. This is known as deforming visco-plastically. Additionally, the plasticity of a material is directly proportional to its ductility and malleability.
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Plasticity in crystalline materials
Plasticity refers to the ability of a solid material to undergo permanent deformation or changes in shape and structure without fracture when subjected to sustained or extreme mechanical stress. In the context of physics and materials science, the term "plastic body" is often used to describe the state or behaviour of materials that exhibit plasticity. This concept is particularly relevant in understanding the behaviour of crystalline materials, such as metals and alloys, under various conditions.
Crystalline materials are characterized by their ordered and periodic atomic structures, where the atoms are arranged in a regular, repeating pattern. The crystalline lattice structure gives these materials unique mechanical properties, including the ability to exhibit plasticity. Plasticity in crystalline materials can be understood by examining the behaviour of dislocations within the crystal lattice. Dislocations are defects or irregularities in the otherwise perfect crystalline structure. These dislocations can move and interact within the lattice when the material is subjected to stress, such as tensile or compressive forces.
The plasticity in crystalline materials can be attributed to two main mechanisms: dislocation glide and dislocation climb. In dislocation glide, the dislocations move through the crystal lattice in a direction parallel to the applied stress. This movement allows for the plastic deformation of the material, as the dislocations enable the sliding and rearrangement of the crystal planes. Dislocation climb, on the other hand, involves the movement of dislocations in a direction perpendicular to the applied stress. This type of movement allows dislocations to bypass obstacles or obstacles that impede their glide motion, providing an alternative mechanism for plastic deformation.
The temperature plays a crucial role in the plasticity of crystalline materials. At higher temperatures, the increased thermal energy provides the necessary activation energy for dislocation movement, making it easier for dislocations to glide and climb. This results in a higher plasticity and a decreased yield strength, which refers to the stress at which the material transitions from elastic deformation to plastic deformation. In contrast, at lower temperatures, the thermal energy is reduced, and dislocation movement becomes more difficult, leading to lower plasticity and increased yield strength.
The plasticity of crystalline materials also depends on the type and arrangement of the crystal lattice. Different crystal structures, such as cubic, hexagonal, or body-centred cubic, can exhibit varying plastic behaviours due to the unique arrangements of atoms and the resulting slip systems or preferred directions of deformation. Additionally, impurities or alloying elements within the crystal lattice can also influence plasticity by pinning or impeding dislocation movement, thereby affecting the overall mechanical properties of the material.
Understanding plasticity in crystalline materials is of significant practical importance, especially in engineering and materials science applications. By controlling and manipulating the plastic behaviour of materials, engineers can design structures and components that exhibit desired mechanical properties, such as strength, ductility, and toughness. Additionally, knowledge of plasticity helps in developing strategies for improving the performance and longevity of materials in various applications, including aerospace, automotive, and electronics industries.
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Plasticity in clay
In physics, plasticity is the ability of a solid material to undergo permanent deformation, a non-reversible change of shape in response to applied forces. Clay is a plastic material, and its plasticity is important in determining the quality of the final product and the time taken in processing.
The dispersion state of the clay particles, which is dependent on the ionic change capacity and the nature and proportion of additives, affects plasticity. Additionally, the application of pressure, body temperature, and the characteristics of additives used can influence the plasticity of clay.
Mathematical modelling and experimental testing, such as compression tests, are used to evaluate the plasticity of clay. The Atterberg's and Pfefferkorn's methods are commonly employed to characterise the plasticity of clay by determining the water content at which the clay can be rolled into threads without breaking (Atterberg's plastic limit) and the water content at which the clay begins to flow (Atterberg's liquid limit).
Understanding the plasticity of clay is crucial in optimising manufacturing processes and ensuring the quality of clay-based products.
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Plasticity in metals
In the context of physics and materials science, plasticity is the ability of a solid material to undergo permanent, non-reversible deformation in response to applied forces. This deformation is characterised by changes in the length, volume, or shape of the material. Plasticity in metals specifically refers to the ability of metallic structures to be moulded or reshaped under the influence of external forces, with the changes becoming irreversible once a certain threshold of force or stress is exceeded.
The plasticity of metals is influenced by various factors, including temperature and microstructure. Most metals exhibit greater plasticity when heated, as heat renders them more malleable and amenable to shaping. Lead, for example, demonstrates sufficient plasticity at room temperature, whereas cast iron typically requires higher temperatures for any significant plasticity to occur. The microstructure of a metal can also impact its plasticity. Nanostructured metals, for instance, tend to have high plasticity due to their unique microstructure, but they often exhibit low ductility because of their limited strain hardening capability.
The behaviour of metals under tensile loading provides insight into their plasticity. In ductile metals, when a load is applied, it is accompanied by a proportional increment in extension. Upon removal of the load, the metal generally returns to its original size and shape, demonstrating elasticity. However, when the load surpasses the yield strength, the extension increases more rapidly, and upon load removal, some degree of deformation persists, indicating plasticity. This transition from elastic behaviour to plastic behaviour is known as yielding.
Plasticity in a crystal of pure metal is predominantly governed by two modes of deformation in the crystal lattice: slip and twinning. Slip is a shear deformation that propels atoms through significant distances relative to their initial positions. Twinning, on the other hand, is a plastic deformation that occurs along two planes due to the application of forces on the metal piece. These deformations contribute to the overall plasticity of metallic materials.
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Frequently asked questions
A plastic body in physics refers to a body that does not have the property of opposing the deforming force. In other words, it remains in a deformed state even after the deforming force is removed.
Plasticity, also known as plastic deformation, is the ability of a solid material to undergo permanent deformation, or a non-reversible change of shape, in response to applied forces.
A perfectly plastic body is one that does not regain its original configuration when the external force is removed. Putty, mud, and paraffin wax are examples of nearly perfectly plastic bodies.
Elasticity is the property of a body that allows it to recover its original size and shape after the removal of external forces. Plasticity, on the other hand, is the tendency of a body to remain deformed and not recover its original shape after the removal of deforming forces.
