Deformations are divided into reversible (elastic) and irreversible (plastic, creep). Elastic deformations disappear after the end of the applied forces, but irreversible deformations remain. Elastic deformations are based on reversible displacements of metal atoms from the equilibrium position (in other words, the atoms do not go beyond the limits of interatomic bonds); Irreversible are based on irreversible movements of atoms to significant distances from the initial equilibrium positions (that is, going beyond the boundaries of interatomic bonds, after removing the load, reorientation to a new equilibrium position).
Plastic deformations are irreversible deformations caused by changes in stress. Creep deformations are irreversible deformations that occur over time. The ability of substances to deform plastically is called plasticity. During plastic deformation of a metal, simultaneously with a change in shape, a number of properties change - in particular, during cold deformation, strength increases.
Types of deformation
Most simple types deformations of the body as a whole:
In most practical cases, the observed deformation is a combination of several simultaneous simple deformations. Ultimately, however, any deformation can be reduced to two simplest ones: tension (or compression) and shear.
Study of deformation
The nature of plastic deformation may vary depending on temperature, duration of load or strain rate. With a constant load applied to the body, the deformation changes with time; this phenomenon is called creep. As temperature increases, the creep rate increases. Special cases of creep are relaxation and elastic aftereffect. One of the theories that explains the mechanism of plastic deformation is the theory of dislocations in crystals.
Continuity
In the theory of elasticity and plasticity, bodies are considered “solid”. Continuity (that is, the ability to fill the entire volume occupied by the material of the body, without any voids) is one of the main properties attributed to real bodies. The concept of continuity also refers to elementary volumes into which a body can be mentally divided. The change in the distance between the centers of each two adjacent infinitesimal volumes in a body that does not experience discontinuities should be small compared to the initial value of this distance.
The simplest elementary deformation
The simplest elementary deformation is the relative elongation of some element:
In practice, small deformations are more common - such that .
Strain measurement
Deformation is measured either in the process of testing materials to determine their mechanical properties, or when studying a structure in situ or on models to judge the magnitude of stresses. Elastic deformations are very small, and their measurement requires high accuracy. The most common method for studying deformation is using strain gauges. In addition, resistance strain gauges, polarization optical stress testing, and X-ray diffraction analysis are widely used. To judge local plastic deformations, knurling a mesh on the surface of the product, covering the surface with easily cracked varnish or brittle gaskets, etc. is used.
Notes
Literature
- Rabotnov Yu. N., Strength of Materials, M., 1950;
- Kuznetsov V.D., Solid State Physics, vol. 2-4, 2nd ed., Tomsk, 1941-47;
- Sedov L.I., Introduction to continuum mechanics, M., 1962.
see also
Links
Wikimedia Foundation. 2010.
Synonyms:See what “Deformation” is in other dictionaries:
deformation- deformation: Distortion of the shape of a bar of soap compared to that intended technical document. Source: GOST 28546 2002: Solid toilet soap. Are common technical specifications original document De... Dictionary-reference book of terms of normative and technical documentation
- (French) Ugliness; change in shape. Dictionary foreign words, included in the Russian language. Chudinov A.N., 1910. DEFORMATION [lat. deformatio distortion] change in the shape and size of the body under the influence external forces. Dictionary of foreign words. Komlev... Dictionary of foreign words of the Russian language
Modern encyclopedia
Deformation- – change in the shape and/or size of the body under the influence of external forces and various types of influences (changes in temperature and humidity, settlement of supports, etc.); in the strength of materials and the theory of elasticity - a quantitative measure of dimensional change... Encyclopedia of terms, definitions and explanations of building materials
Deformation- (from Latin deformation distortion), change relative position particles of matter due to any external or internal reasons. The simplest types of deformation of a solid body: tension, compression, shear, bending, torsion.... ... Illustrated encyclopedic Dictionary
- (from Latin deformatio distortion) 1) a change in the relative position of points of a solid body, in which the distance between them changes, as a result external influences. The deformation is called elastic if it disappears after the impact is removed, and... ... Big Encyclopedic Dictionary
Cm … Synonym dictionary
- (from lat. deformatio distortion), change in the configuration of the kl. object resulting from external influences or internal strength D. may experience TV. bodies (crystal, amorphous, organic origin), liquids, gases, physical fields, living... ... Physical encyclopedia
deformation- and, f. deformation f. lat. deformatio distortion. 1. Changing the size and shape of a solid body under the influence of external forces (usually without changing its mass). BAS 1. || In the visual arts, a deviation from the natural one perceived by the eye... ... Historical Dictionary of Gallicisms of the Russian Language
deformation- deformation, deformed. Pronounced [deformation], [deformed] and obsolete [deformation], [deformed] ... Dictionary of difficulties of pronunciation and stress in modern Russian language
Rocks (from Latin deformatio change in shape, distortion * a. rock deformafion; n. Deformation von Gesteinen; f. deformation des roches; i. deformacion de las rocas) a change in the relative position of rock particles, causing a change ... Geological encyclopedia
Books
- Plastic deformation of metals, R. Honeycombe, For engineering and technical and scientific workers of factories and research institutes, university teachers, graduate students and senior students. Reproduced in original... Category:
Under external influences, bodies can become deformed.
Deformation- change in body shape and size. The reason for deformation is that different parts of the body make unequal movements when external forces act on the body.
Deformations that completely disappear after the force ceases - elastic that don't disappear - plastic.
During elastic deformations, the distance between the particles of the body changes. In an undeformed body, particles are in certain equilibrium positions (distances between selected particles - see Fig. 1, b), in which the repulsive and attractive forces acting from other particles are equal. When the distance between particles changes, one of these forces begins to exceed the other. As a result, a resultant of these forces arises, tending to return the particle to its previous equilibrium position. The resultant of the forces acting on all particles of a deformed body is the elastic force observed in practice. Thus, a consequence of elastic deformation is the emergence of elastic forces.
At plastic deformation, as observations have shown, the displacements of particles in a crystal have a completely different character than in an elastic one. During plastic deformation of the crystal, the layers of the crystal slide relative to each other (Fig. 1, a, b). This can be seen using a microscope: the smooth surface of a crystalline rod becomes rough after plastic deformation. Sliding occurs along the layers that contain the most atoms (Fig. 2).
With such displacements of particles, the body turns out to be deformed, but “returning” forces do not act on the displaced particles, since each atom in its new position has the same neighbors and in the same number as before the displacement.
When calculating structures, machines, machine tools, certain structures, when processing various materials, it is important to know how this or that part will deform under the influence of a load, under what conditions its deformation will not affect the operation of the machines as a whole, under what loads destruction occurs parts, etc.
Deformations can be very complex. But they can be reduced to two types: tension (compression) and shear.
Linear deformation occurs when a force is applied along the axis of a rod fixed at one end (Fig. 3, a, b). With linear deformations, the layers of the body remain parallel to each other, but the distances between them change. Linear deformation is characterized by absolute and relative elongation.
Absolute elongation, where l is the length of the deformed body, and is the length of the body in an undeformed state.
Relative extension- the ratio of absolute elongation to the length of the undeformed body.
In practice, crane cables are subject to tension, cable cars, tow ropes, strings of musical instruments. Columns, walls and foundations of buildings, etc. are subject to compression.
It occurs under the influence of forces applied to two opposite faces of the body as shown in Figure 4. These forces cause a displacement of the layers of the body parallel to the direction of the forces. The distance between layers does not change. Any rectangular parallelepiped, mentally identified in the body, turns into an inclined one.
The measure of shear strain is shear angle- angle of inclination of vertical edges (Fig. 5).
Shear deformation is experienced, for example, by rivets and bolts connecting metal structures. Shear at large angles leads to destruction of the body - shearing. The cut occurs when using scissors, saws, etc.
Bending deformation a beam is subjected, fixed at one end or fixed at both ends, to the middle of which a load is suspended (Fig. 6). The bending deformation is characterized by the deflection arrow h - the displacement of the middle of the beam (or its end). When bending, the convex parts of the bodies experience tension, and the concave parts experience compression; the middle parts of the body are practically not deformed - neutral layer. The presence of a middle layer has virtually no effect on the body’s resistance to bending, so it is advantageous to make such parts hollow (saving material and significantly reducing their weight). In modern technology, hollow beams and tubes are widely used. Human bones are also tubular.
Torsional deformation can be observed if a rod, one end of which is fixed, is acted upon by a pair of forces (Fig. 7) lying in a plane perpendicular to the axis of the rod. During torsion, the individual layers of the body remain parallel, but rotate relative to each other at a certain angle. Torsional deformation is uneven shear. Torsional deformations occur when screwing nuts and when operating machine shafts.
Strain is the displacement or disruption of bonds between atoms. It appears if an object is affected by external forces: temperature, pressure, specific load, magnetic or electric field. The main types of deformation are deformation, which in physics is called means that the disruption of bonds between atoms is insignificant and the integrity of the structure is not broken. Objects with this property are called elastic. Irreversible deformation in physics is called and means a serious violation of the bonds in atoms and, as a consequence, the integrity of the structure. Objects with such properties are called plastic.
Breaking atomic bonds is not always a bad thing. For example, damping (vibration damping) parts must have plasticity. This is necessary to convert impact energy into deformation energy. There are the following types of deformation solids: bending, tension/compression, torsion and shear. Depending on the nature of the acting forces on solids, corresponding stresses may arise. These stresses are called by the nature of the force. For example, torsional stress, compressive stress, bending stress, etc. When talking about deformation, we often by default mean the deformation of solids, because the change in structure is most pronounced in them.
In fact, all types of deformation are the result of the influence of stress created by an acting force. IN pure form deformation is rare. As a rule, the resulting deformation is of various stresses. As a result, they all lead to two main deformations - tension/compression and bending.
Physically, deformation is a result that is expressed in quantitative and qualitative equivalents. Quantitatively, this phenomenon is expressed in a numerical value. Qualitatively - in the nature of the manifestation (direction, critical moments, such as destruction, ultimate stress...). Possible deformation is preliminarily calculated in the strength calculation when designing any device or mechanism.
As a rule, loads and the result of deformation are displayed in the form of graphs - stress diagrams. The structure of such a graph: design diagram with applied loads, types of stresses and types of deformation. The distribution of loads gives an understanding of the nature of the work load of a device or element, and deformation. The results of deformation - stretching, compression, bending, torsion - are measured in distance units (mm, cm, m) or angular units (degrees and radians). The main task of the calculation is to determine the limiting deformations and stresses in order to avoid malfunction - rupture, shear, fracture, etc. Also important is the nature of the voltage and numeric value, because There is a concept of fatigue deformation.
Fatigue deformation is the process of changing shape due to long-term loads. Over time, they develop from non-critical stresses (constant minor disruption of interatomic bonds) into serious consequences. This concept is called accumulated fatigue and is regulated by such a parameter (from the material) as fatigue strength.
In order to take into account the influence that different kinds deformations on functionality and service life, carry out full-scale tests of material samples. From experience, all the strength characteristics for each material are obtained, which then become table values. In the era computer equipment Such analysis is carried out on powerful PCs. But still, the properties of the material can only be determined from full-scale tests. By already incorporating all the characteristics and properties into the calculation model, the strength engineer receives graphic model(sometimes in the dynamics of work) of all stresses and deformations.
In mechanical engineering, such calculations are already included in 3D design programs. Those. the designer makes a 3D model of all elements, each of which is reduced to a model of the unit. By applying loads in a separate program module, the designer receives the nature of stresses and all types of deformation.
Without going into theoretical basis In physics, the process of deformation of a solid body can be called a change in its shape under the influence of an external load. Any solid material has a crystalline structure with a certain arrangement of atoms and particles; when a load is applied, individual elements or entire layers are displaced relative to each other, in other words, material defects occur.
Types of deformation of solids
Tensile deformation is a type of deformation in which the load is applied longitudinally from the body, that is, coaxially or parallel to the attachment points of the body. The easiest way to consider stretching is on a tow rope for cars. The cable has two attachment points to the tug and the towed object; as the movement begins, the cable straightens and begins to pull the towed object. When in tension, the cable is subject to tensile deformation; if the load is less than the maximum values it can withstand, then after the load is removed the cable will restore its shape.
Sample stretching scheme
Tensile deformation is one of the main laboratory research physical properties materials. During the application of tensile stresses, the values at which the material is capable of:
- absorb loads with further restoration of the original state (elastic deformation)
- bear loads without restoring the original state (plastic deformation)
- break at the breaking point
These tests are the main ones for all cables and ropes that are used for slinging, securing loads, and mountaineering. Tension is also important in the construction of complex suspension systems with free working elements.
Compressive deformation is a type of deformation similar to tension, with one difference in the method of applying the load; it is applied coaxially, but towards the body. Squeezing an object from both sides leads to a decrease in its length and simultaneous strengthening; the application of large loads forms “barrel”-type thickenings in the body of the material.
Sample compression circuit
As an example, we can use the same device as in the tensile strain slightly above.
Compressive deformation is widely used in metallurgical processes for forging metal; during the process, the metal gains increased strength and welds structural defects. Compression is also important in the construction of buildings; all structural elements of the foundation, piles and walls experience pressure loads. Correct calculation of the load-bearing structures of a building allows you to reduce the consumption of materials without loss of strength.
Shear deformation is a type of deformation in which the load is applied parallel to the base of the body. During shear deformation, one plane of the body is displaced in space relative to another. All fasteners - bolts, screws, nails - are tested for maximum shear loads. The simplest example shear deformations - a loose chair, where the floor can be taken as the base, and the seat as the plane of application of the load.
Sample shift scheme
Bending deformation is a type of deformation in which the straightness of the main axis of the body is disrupted. All bodies suspended on one or more supports experience bending deformations. Each material is capable of withstanding a certain level of load; solids in most cases are able to withstand not only their own weight, but also a given load. Depending on the method of applying the load during bending, pure and oblique bending are distinguished.
Sample bending diagram
The value of bending deformation is important for the design of elastic bodies, such as a bridge with supports, a gymnastic bar, a horizontal bar, a car axle and others.
Torsional deformation is a type of deformation in which a torque is applied to a body, caused by a pair of forces acting in the plane perpendicular to the axis of the body. Torsion is produced by machine shafts, drilling rig augers and springs.
Sample torsion diagram
Plastic and elastic deformation
During deformation important has the magnitude of interatomic bonds, the application of a load sufficient to break them leads to irreversible consequences(irreversible or plastic deformation). If the load does not exceed permissible values, then the body can return to its original state ( elastic deformation). The simplest example of the behavior of objects subject to plastic and elastic deformation can be seen in a rubber ball and a piece of plasticine falling from a height. A rubber ball has elasticity, so when it falls it will compress, and after the energy of motion is converted into thermal and potential energy, it will again take its original shape. Plasticine has great plasticity, so when it hits a surface, it will irreversibly lose its original shape.
Due to the presence of deformation abilities, all known materials have a set of useful properties- plasticity, fragility, elasticity, strength and others. The study of these properties is sufficient important task, allowing you to select or make required material. In addition, the very presence of deformation and its detection is often necessary for instrument engineering tasks; for this purpose, special sensors called extensometers or otherwise strain gauges are used.
Deformations are divided into reversible (elastic) and irreversible (plastic, creep). Elastic deformations disappear after the end of the applied forces, but irreversible deformations remain. Elastic deformations are based on reversible displacements of metal atoms from the equilibrium position (in other words, the atoms do not go beyond the limits of interatomic bonds); Irreversible are based on irreversible movements of atoms to significant distances from the initial equilibrium positions (that is, going beyond the boundaries of interatomic bonds, after removing the load, reorientation to a new equilibrium position).
Plastic deformations are irreversible deformations caused by changes in stress. Creep deformations are irreversible deformations that occur over time. The ability of substances to deform plastically is called plasticity. During plastic deformation of a metal, simultaneously with a change in shape, a number of properties change - in particular, during cold deformation, strength increases.
Types of deformation
The simplest types of deformation of the body as a whole:
In most practical cases, the observed deformation is a combination of several simultaneous simple deformations. Ultimately, however, any deformation can be reduced to two simplest ones: tension (or compression) and shear.
Study of deformation
The nature of plastic deformation may vary depending on temperature, duration of load or strain rate. With a constant load applied to the body, the deformation changes with time; this phenomenon is called creep. As temperature increases, the creep rate increases. Special cases of creep are relaxation and elastic aftereffect. One of the theories that explains the mechanism of plastic deformation is the theory of dislocations in crystals.
Continuity
In the theory of elasticity and plasticity, bodies are considered “solid”. Continuity (that is, the ability to fill the entire volume occupied by the material of the body, without any voids) is one of the main properties attributed to real bodies. The concept of continuity also refers to elementary volumes into which a body can be mentally divided. The change in the distance between the centers of each two adjacent infinitesimal volumes in a body that does not experience discontinuities should be small compared to the initial value of this distance.
The simplest elementary deformation
The simplest elementary deformation is the relative elongation of some element:
In practice, small deformations are more common - such that .
Strain measurement
Deformation is measured either in the process of testing materials to determine their mechanical properties, or when studying a structure in situ or on models to judge the magnitude of stresses. Elastic deformations are very small, and their measurement requires high accuracy. The most common method for studying deformation is using strain gauges. In addition, resistance strain gauges, polarization optical stress testing, and X-ray diffraction analysis are widely used. To judge local plastic deformations, knurling a mesh on the surface of the product, covering the surface with easily cracked varnish or brittle gaskets, etc. is used.
Notes
Literature
- Rabotnov Yu. N., Strength of Materials, M., 1950;
- Kuznetsov V.D., Solid State Physics, vol. 2-4, 2nd ed., Tomsk, 1941-47;
- Sedov L.I., Introduction to continuum mechanics, M., 1962.
see also
Links
Wikimedia Foundation. 2010.
Synonyms:- Beta (letter)
- Bulgarian Commission for Antarctic Names
See what “Deformation” is in other dictionaries:
deformation- deformation: Distortion of the shape of a bar of soap compared to that provided for in the technical document. Source: GOST 28546 2002: Solid toilet soap. General technical conditions original document De... Dictionary-reference book of terms of normative and technical documentation
DEFORMATION- (French) Ugliness; change in shape. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. DEFORMATION [lat. deformatio distortion] change in the shape and size of the body under the influence of external forces. Dictionary of foreign words. Komlev... Dictionary of foreign words of the Russian language
DEFORMATION Modern encyclopedia
Deformation- – change in the shape and/or size of the body under the influence of external forces and various types of influences (changes in temperature and humidity, settlement of supports, etc.); in the strength of materials and the theory of elasticity - a quantitative measure of dimensional change... Encyclopedia of terms, definitions and explanations of building materials
Deformation- (from the Latin deformation, distortion), a change in the relative arrangement of particles of a substance, due to any external or internal reasons. The simplest types of deformation of a solid body: tension, compression, shear, bending, torsion.... ... Illustrated Encyclopedic Dictionary
DEFORMATION- (from Latin deformatio distortion) 1) a change in the relative position of points of a solid body, in which the distance between them changes as a result of external influences. The deformation is called elastic if it disappears after the impact is removed, and... ... Big Encyclopedic Dictionary
deformation- Cm … Synonym dictionary
DEFORMATION- (from lat. deformatio distortion), change in the configuration of the kl. object resulting from external influences or internal strength D. may experience TV. bodies (crystal, amorphous, organic origin), liquids, gases, physical fields, living... ... Physical encyclopedia
deformation- and, f. deformation f. lat. deformatio distortion. 1. Changing the size and shape of a solid body under the influence of external forces (usually without changing its mass). BAS 1. || In the visual arts, a deviation from the natural one perceived by the eye... ... Historical Dictionary of Gallicisms of the Russian Language
deformation- deformation, deformed. Pronounced [deformation], [deformed] and obsolete [deformation], [deformed] ... Dictionary of difficulties of pronunciation and stress in modern Russian language
Deformation- rocks (from Latin deformatio change in shape, distortion * a. rock deformafion; n. Deformation von Gesteinen; f. deformation des roches; i. deformacion de las rocas) a change in the relative position of rock particles, causing a change ... Geological encyclopedia
Books
- Plastic deformation of metals, R. Honeycombe, For engineering and technical and scientific workers of factories and research institutes, university teachers, graduate students and senior students. Reproduced in original... Category:
