Sofia Martinez
Plastic deformation is the process by which an object changes shape or size under force in a way that is not reversible. It is a type of permanent deformation that occurs when the elastic limit of a body is exceeded, causing it to experience a permanent set or change in shape even after the applied load is removed. This happens when the applied load is sufficient to break the bonds between atoms and form new ones, preventing the object from returning to its original shape. Plastic deformation is observed in most materials, particularly metals, soils, rocks, concrete, and foams, and is characterized by a uniform flow of the material without any change in its volume.
| Characteristics | Values |
|---|---|
| Definition | Plastic deformation is a process in which an object changes its size or shape in a way that is not reversible due to applied force. |
| Other names | Plasticity, permanent deformation |
| Occurrence | Plastic deformation occurs in most materials, especially metals, soils, rocks, concrete, and foams. |
| Causes | Plastic deformation is caused by the breaking of a limited number of atomic bonds by the movement of dislocations. |
| Types | Elongation, contraction, expansion |
| Examples | Bending of steel rods, bending a metal hanger, pounding a solid piece of metal into a new shape |
| Related terms | Elastic deformation, elastic limit, plastic limit stress (PLS), ductility, malleability |
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What You'll Learn
Plastic deformation is a non-reversible change of shape
When a material undergoes plastic deformation, it does not return to its original shape even after the removal of the applied load or stress. This is because the deformation occurs at the atomic level, with bonds between atoms being broken and new ones formed, preventing the material from returning to its initial state. The force required to cause plastic deformation is typically very high, as it involves breaking the bonds between atoms in a crystal plane.
Plastic deformation is observed in a wide range of materials, particularly metals, soils, rocks, concrete, and foams. However, the mechanisms behind plastic deformation can vary depending on the material. In metals, plastic deformation is often caused by dislocations, which are defects in the crystal structure that allow planes of atoms to slip past each other. This results in a uniform flow of the metal and a permanent change in shape without any change in volume.
In contrast, brittle materials such as rock, concrete, and bone exhibit plastic deformation due to the slippage of microcracks. Cellular materials like liquid foams or biological tissues undergo plastic deformation through bubble or cell rearrangements. Ductile materials, on the other hand, can recover their original shape after deformation, as long as the load applied does not exceed their yield strength.
Plastic deformation can be studied experimentally using springs and Hooke's law, which helps differentiate between plastic and elastic materials. Plastic deformation is characterized by a strain hardening region and a necking region, eventually leading to fracture or rupture. The amount of load required to cause plastic deformation is known as the plastic limit stress (PLS).
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It occurs when a material's elastic limit is exceeded
Plastic deformation is a process in which an object changes shape in a way that is not reversible. It occurs when a material's elastic limit is exceeded, resulting in a permanent deformation that persists even after the applied load is removed. This phenomenon is also known as yielding in engineering terms.
When a sufficient load or stress is applied to a material, it undergoes deformation. Elastic deformation is temporary and self-reversing, allowing the object to return to its original shape once the force is removed. However, when the load exceeds the material's elastic limit, it enters the realm of plastic deformation. At this point, the deformation becomes irreversible, and the object remains permanently altered even after the load is released.
The malleability and ductility of a material contribute to its propensity for plastic deformation. Materials with higher ductility and malleability are more susceptible to irreversible changes in shape and are said to exhibit plasticity. In metals, plasticity is often a consequence of dislocations, where the force breaks a limited number of atomic bonds, allowing the material to deform.
Plastic deformation can be observed in various materials, particularly metals, soils, rocks, concrete, and foams. It is characterized by a uniform flow of the metal material without any change in its volume. The amount of load required to initiate plastic deformation is known as the plastic limit stress (PLS).
The transition from elastic behaviour to plastic behaviour is marked by the yield point or yield strength. Below the yield point, the relationship between stress and strain is generally linear and reversible, characteristic of elastic deformation. However, once the load surpasses the yield strength, the extension increases more rapidly, resulting in plastic deformation.
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Plastic deformation is caused by the breaking of atomic bonds
Plastic deformation is a process in which an object changes its size or shape in response to an applied force in a way that is not reversible. It is a type of permanent deformation that occurs when the elastic limit of a body is exceeded, resulting in a permanent alteration of shape, form, or texture. This phenomenon is observed in most materials, particularly metals, soils, rocks, concrete, and foams, and is characterized by a uniform flow of the material with no change in its volume.
The force required to break the bonds of all the atoms in a crystal plane is very high. However, when a sufficient load is applied, it can cause a limited number of atomic bonds to break, resulting in plastic deformation. The amount of load required to initiate plastic deformation is called the plastic limit stress (PLS). It is important to note that plastic deformation is not one-dimensional, as the lateral contraction of the material and the substrate may differ, leading to lateral stresses.
The ductility and malleability of a material are directly proportional to its plasticity, which is the ability to undergo irreversible deformation. Materials with high plasticity can be deformed without any increase in load or stress, and they may need increasingly higher stresses to deform further after initial deformation. This property is known as perfect plasticity. Additionally, the deformation speed also plays a role, with higher stresses required to increase the rate of deformation.
Plastic deformation can be differentiated from elastic deformation, which is temporary and reversible. In elastic deformation, the bonds between atoms are stretched, but the atoms do not slip past each other. Elastic deformation occurs when the applied stress does not surpass the energy required to break molecular bonds, allowing the material to return to its original shape once the stress is removed.
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It is observed in most materials, especially metals
Plastic deformation is observed in most materials, especially metals. It is a type of deformation that occurs when a sufficient load is applied to a material, causing it to change shape permanently. This change in shape is irreversible, meaning that even after the load is removed, the material will not return to its original form. For example, a bent metal hanger will not regain its original straight shape.
Metals are particularly susceptible to plastic deformation due to their crystalline structure. In crystalline materials, uniform planes of atoms are organised with long-range order. These planes can slip past each other, resulting in a permanent change of shape within the crystal. Additionally, metals often undergo plastic deformation during various metal-forming processes such as forging, pressing, rolling, and swaging.
The ductility and malleability of a material are directly proportional to its plasticity. Ductile materials, such as metals, can undergo permanent deformation by a stress greater than the yield stress. They can recover their original shape without any residual stress after the load is removed. However, once the load exceeds the yield strength, some degree of extension will remain, resulting in plastic deformation.
Plastic deformation in metals is primarily caused by two mechanisms: slip and twinning. Slip involves the sliding of crystal blocks over one another along different crystallographic planes called slip planes. Twinning occurs when a portion of the crystals takes up an orientation related to the rest of the untwined lattice in a symmetrical and definite way. These mechanisms allow metals to be shaped into desired forms through controlled heat and pressure applications.
It is important to note that not all materials exhibit the same plastic deformation behaviour. For example, hard thermosetting plastics, crystals, and ceramics have minimal plastic deformation ranges. On the other hand, soft thermoplastics, such as wet chewing gum, have a large plastic deformation range.
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Plastic deformation is studied using springs and Hooke's law
Plastic deformation refers to the permanent change in shape, form, or texture of a material due to applied stress. It occurs when the deformation exceeds the elastic limit, and the material undergoes plastic deformation, no longer following a linear relationship between force and deformation. This phenomenon is observed in various materials, including metals, during processes such as forging, pressing, and rolling.
In the context of plastic deformation, Hooke's law is used to differentiate between plastic and elastic materials. While Hooke's law applies to elastic materials, it does not hold true for plastic or brittle materials. This distinction is essential because plastic materials may experience permanent deformation even within their elastic limit, which is the maximum deformation a material can undergo while still returning to its original shape. Once the elastic limit is surpassed, the material undergoes plastic deformation, and permanent changes occur.
By studying plastic deformation with springs and Hooke's law, scientists and engineers can gain insights into the behaviour of materials under stress. They can design efficient structures, accurately measure forces, and analyse the stress and strain distribution within various materials and systems. This understanding helps in predicting and managing the response of materials to external forces, ensuring the safe and optimal use of different materials in various applications.
Additionally, the concept of Hooke's law and its application in studying plastic deformation have practical implications in everyday objects. For example, the internal springs in retractable pens work based on Hooke's law, allowing the ink cartridge to be locked or released when the pen is clicked. Similarly, the balance wheel in clocks uses a spring that operates according to Hooke's law, ensuring consistent motion and accurate timekeeping.
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Frequently asked questions
Plastic deformation is the ability of a solid material to undergo a permanent and non-reversible change of shape in response to applied forces.
Plastic deformation can be observed in many objects, including a bent coat hanger, a steel rod, or wet chewing gum.
Elastic deformation is a temporary change in shape that is self-reversing after the force is removed, so that the object returns to its original shape. Plastic deformation is irreversible and the deformation stays even after the force is removed.
