Omar Khalid
Plastic deformation is a process by which an object changes size or shape due to an applied force in a way that is not reversible. It is a common type of deformation that occurs in most materials, especially metals, soils, rocks, concrete, and foams. Plastic deformation is characterized by a uniform flow of the metal material and no change in its volume. It occurs when the deformation is beyond the elastic limit, and the load is too high compared to the amount of strain. This leads to a permanent alteration of shape, form, or texture, which persists even after the removal of the applied force.
| Characteristics | Values |
|---|---|
| Definition | Plastic deformation is a permanent alteration of shape, form, or texture of a material due to the action of stress. |
| Other Names | Permanent deformation, irreversible deformation |
| Process | Plastic deformation is the process by which an object changes its size or shape due to applied force, and this change is irreversible. |
| Plasticity | Plastic deformation is caused by the plasticity of a material. |
| Plasticity and Malleability | The malleability and ductility of a material are directly proportional to the plasticity of the material. |
| Plastic Limit Stress | The amount of load required to cause plastic deformation is called the plastic limit stress (PLS). |
| Ductility | Plastic deformation is said to be ductile if the material is able to undergo permanent deformation by a stress greater than the yield stress. |
| Irreversibility | Plastic deformation is irreversible, meaning the deformation stays even after the removal of the applied forces. |
| Types | Elongation, contraction, expansion, and thermoelastic deformation (or creep) are the four types of plastic deformation. |
| Materials | Plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, and foams. |
| Mechanisms | Different mechanisms that cause plastic deformation include dislocation motion, vacancy motion, twinning, phase transformation, or viscous flow of amorphous materials. |
| Temperature | Thermoelastic deformation or creep involves a change in material dimension with temperature change, with the material behaving elastically at low temperatures and more plastically with increasing temperature. |
| Hot vs. Cold Deformation | Most metals show more plasticity when hot than when cold. |
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What You'll Learn
Plastic deformation is irreversible
Plastic deformation is a change in the shape and dimensions of a material brought on by applied forces. It is the most common type of deformation, occurring in most materials, especially metals, soils, rocks, concrete, and foams.
Plastic deformation is characterized by a uniform flow of the metal material and no change in its volume. The amount of load required to cause plastic deformation is called the plastic limit stress (PLS). Plastic deformation occurs when the deformation is beyond the elastic limit. When the load is too high in comparison to the amount of strain, plastic deformation starts.
Plastic deformation is observed in most materials, but the physical mechanisms that cause it can vary. At a crystalline scale, plasticity in metals is caused by dislocations. Dislocations are relatively rare in most crystalline materials, but they are numerous in some and are part of their crystal structure. In brittle materials such as rock, concrete, and bone, plasticity occurs due to the slippage of microcracks.
The malleability and ductility of a material are directly proportional to its plasticity. Materials with perfect plasticity can undergo irreversible deformation without any increase in load or stress.
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It is caused by externally applied stress
Plastic deformation refers to the permanent change in the shape or dimensions of a solid material due to external stress. This deformation occurs when the elastic limit of the material is exceeded, resulting in an irreversible alteration. This means that once the deforming force is removed, the material does not return to its original shape or size.
Now, to focus on the role of externally applied stress:
Externally applied stress is indeed the primary cause of plastic deformation in materials. When a force is exerted on a material, it experiences stress, which refers to the internal resistance against deformation. There are different types of stress, including tensile, compressive, and shear stress, depending on the nature of the applied force. Tensile stress, for instance, stretches the material, while compressive stress squeezes it, and shear stress deforms it along a plane.
The amount of stress a material can withstand before deforming plastically is known as its yield strength or elastic limit. This value varies for different materials and is an important factor in engineering and design. If the applied stress exceeds this limit, the material will undergo plastic deformation. For example, imagine bending a metal rod. Initially, it may return to its original straight shape when the bending force is removed (elastic deformation). However, if you continue to apply force beyond its yield strength, the rod will stay bent even after you stop applying force – this is plastic deformation caused by externally applied stress.
The externally applied stress can be a result of various factors and forces. Common causes include mechanical loads, such as tension, compression, or torsion, which can be static or dynamic. Dynamic loads, like impact or cyclic loading, can be particularly detrimental as they may lead to fatigue and eventual plastic deformation. Other factors include environmental conditions such as temperature variations, chemical reactions, and the presence of impurities or defects within the material's microstructure, which can all influence its resistance to plastic deformation.
It is also important to note that the extent of plastic deformation depends on the magnitude and duration of the applied stress. A higher stress applied for a longer duration will result in a more substantial deformation. Additionally, the rate at which the stress is applied can play a role, with rapid loading often leading to different deformation behavior compared to slow, gradual loading.
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It is observed in most materials
Plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, and foams. It is a change in shape and dimensions brought on by forces. It is the most common type of deformation and happens to most materials in most circumstances.
Plastic deformation is an intrinsic part of the processing of most metals. The aim is to achieve a change in shape by applying external stress, while also causing a controlled alteration in the mechanical properties of the material. Plastic deformation is also dependent on the deformation speed—higher stresses are usually required to increase the rate of deformation.
The physical mechanisms that cause plastic deformation vary widely. At a crystalline scale, plasticity in metals is usually a consequence of dislocations. Such defects are relatively rare in most crystalline materials but are numerous in some and are part of their crystal structure. In brittle materials like rock, concrete, and bone, plasticity occurs due to the slippage of microcracks. In ceramics, dislocation motion requires high shear stress due to covalent atomic bonds. Under specific loading conditions, plastic deformation and the formation of dislocations have been observed.
Plastic deformation can be studied with the help of springs, where Hooke's law is used to differentiate between plastic and elastic materials. Plastic deformation is characterized by a uniform flow of the metal material and no change in its volume. The amount of load required to cause plastic deformation is called the plastic limit stress (PLS).
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Plastic deformation is ductile
Plastic deformation is the permanent change in shape, form, or texture of a material due to the action of stress. It is the most common type of deformation, occurring in most materials and in most circumstances. Plastic deformation is observed in a wide range of materials, including metals, soils, rocks, concrete, and foams.
Ductility is a measure of the degree of plastic deformation that a material can sustain before fracture. It is often expressed as a percentage of elongation or reduction in area. Ductility is the ability of a material to deform plastically without failing under stress. This is in contrast to brittle materials, which tend to crack or shatter under stress.
The ductility of a material is directly related to its plasticity, or ability to undergo irreversible deformation without an increase in load or stress. Ductile materials can absorb more energy prior to failure than brittle materials, as they can undergo plastic deformation. This allows ductile materials to sustain more stress before failure.
Plastic deformation is said to be ductile when the material can recover its original shape without any residual stress after the load is removed. This is because ductile materials can undergo permanent deformation by a stress greater than the yield stress. On the other hand, brittle materials tend to undergo rapid failure below the ductile-brittle transition temperature (DBTT), where they are more likely to shatter on impact instead of bending or deforming.
The distinction between ductile and brittle behaviour depends on both the material itself and the temperature at which stress is applied. Metals like gold, copper, and platinum are generally considered ductile, while cast iron exhibits brittle behaviour. Polymers are also considered ductile materials, as they typically allow for plastic deformation.
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It is characterised by a uniform flow of metal material
Plastic deformation is a change in the shape or dimension of an object that is not reversible. It is observed in most materials, especially metals, soils, rocks, concrete, and foams. It is the most common type of deformation and occurs in most materials and circumstances.
Plastic deformation is characterised by a uniform flow of metal material and no change in its volume. It occurs when the deformation is in the elastic limit, and the load is too high compared to the amount of strain. The amount of load required to cause plastic deformation is called the plastic limit stress (PLS).
The malleability and ductility of a material are directly proportional to its plasticity. Plasticity is the property of a material to undergo irreversible deformation without any increase in load or stress. Fracture or rupture of the material may be caused by plasticity.
Plastic deformation is an intrinsic part of processing most metals. It is achieved by applying external stress to cause a controlled change in shape and material mechanical properties. Metal-working processes such as rolling, extrusion, and wire-drawing are used to shape metals.
Plastic deformation is also dependent on the deformation speed. Higher stresses are usually required to increase the rate of deformation. Materials that deform in this manner are said to deform visco-plastically.
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Frequently asked questions
Plastic deformation is the permanent change in shape, form, or texture of a material due to the action of stress. It is irreversible and stays even after the removal of the applied force.
Plastic deformation is observed in most materials, especially metals, soils, rocks, concrete, and foams. Examples include bending of steel rods, stretching of chewing gum, and the shaping of components by stretch-forming.
Plastic deformation is caused by the breaking of a limited number of atomic bonds and the movement of dislocations. The amount of load required to cause plastic deformation is called the plastic limit stress (PLS). It occurs when the deformation exceeds the elastic limit.
