Mechanical properties what. Mechanical properties of materials and their characteristics

Material selection criteria

Properties- this is a quantitative or qualitative characteristic of a material that determines its commonality or difference with other materials.
There are three main groups of properties: operational, technological and cost, which underlie the choice of material and determine the technical and economic feasibility of its use. Performance properties are paramount.
operational name the properties of the material that determine the performance of machine parts, instruments and tools, their power, speed, cost and other technical and operational indicators.
The performance of the vast majority of machine parts and products provides a level of mechanical properties that characterize the behavior of the material under the action of an external load. Since the loading conditions of machine parts are diverse, the mechanical properties include a large group of indicators.
Depending on the change in time, the load is divided into static and dynamic. Static loading is characterized by a low rate of change in its magnitude, and dynamic loads change over time at high rates, for example, during shock loading. In addition, loads are divided into tensile, compressive, bending, twisting and shear. The change in load can be of a periodically recurring nature, as a result of which they are called repetitively variable or cyclic. Under the operating conditions of machines, the impact of the listed loads can manifest itself in various combinations.
Under the influence of external loads, as well as structural-phase transformations, internal forces arise in the material of structures, which can be expressed through external loads. Internal forces per unit area cross section bodies are called stresses. The introduction of the concept of stresses makes it possible to carry out calculations on the strength of structures and their elements.
In the simplest case of axial tension of a cylindrical rod, the stress σ is defined as the ratio of the tensile force P to the initial cross-sectional area Fo, i.e.

σ = P/Fo

The action of external forces leads to deformation of the body, i.e. to change its size and shape. The deformation that disappears after unloading is called elastic, and the deformation that remains in the body is called plastic (residual).
The performance of a separate group of machine parts depends not only on the mechanical properties, but also on the resistance to the action of a chemically active working environment, if such an effect becomes significant, then physicochemical characteristics material - heat resistance and corrosion resistance.
Heat resistance characterizes the ability of a material to resist chemical corrosion in an atmosphere of dry gases at high temperature. In metals, heating is accompanied by the formation of an oxide layer (dross) on the surface.
Corrosion resistance- this is the ability of a metal to resist electrochemical corrosion, which develops in the presence of a liquid medium on the surface of the metal and its electrochemical inhomogeneity.
For some machine parts, important physical properties characterizing the behavior of materials in magnetic, electric and thermal fields, as well as under the influence of high energy flows or radiation. They are usually divided into magnetic, electrical, thermophysical and radiation.
The ability of a material to undergo various methods hot and cold working are determined by technological properties. These include casting properties, deformability, weldability and machinability with a cutting tool. Technological properties make it possible to perform form-changing processing and obtain blanks and machine parts.
The last group of basic properties includes the cost of the material, which evaluates the economics of its use. Its quantitative indicator is - the wholesale price - the cost per unit mass of materials in the form of ingots, profiles, powder, piece and welded blanks, according to which the manufacturer sells its products to machine-building and instrument-making enterprises.

Mechanical properties determined under static loads

Mechanical properties characterize the resistance of a material to deformation, destruction, or a feature of its behavior in the process of destruction. This group of properties includes indicators of strength, stiffness (elasticity), plasticity, hardness and viscosity. The main group of such indicators is the standard characteristics of mechanical properties, which are determined in laboratory conditions on samples standard sizes. The indicators of mechanical properties obtained during such tests evaluate the behavior of materials under external load without taking into account the design of the part and operating conditions.
According to the method of application of loads, static tests are distinguished for tension, compression, bending, torsion, shear or shear. The most common tensile tests (GOST 1497-84), which make it possible to determine several important indicators mechanical properties.

Tensile test. When stretching standard samples with a cross-sectional area Fo and a working (calculated) length lo, a tension diagram is built in the coordinates: load - elongation of the sample (Fig. 1). There are three sections on the diagram: elastic deformation up to load Rupr .; uniform plastic deformation from Rupr. to Рmax and concentrated plastic deformation from Рmax to Рк. The rectilinear section is maintained until the load corresponding to the proportionality limit Rpc. The tangent of the slope of the straight section characterizes the modulus of elasticity of the first kind E.

Rice. 1. Ductile metal tensile diagram (a) and diagrams
conditional stresses of ductile (b) and brittle (c) metals.
The diagram of true stresses (dashed line) is given for comparison.

Plastic deformation above R control. goes with increasing load, since the metal is strengthened in the process of deformation. Hardening of a material during deformation is called work hardening.

The work hardening of the metal increases until the sample breaks, although the tensile load decreases from P max to P k (Fig. 1, a). This is explained by the appearance of a local neck thinning in the sample, in which plastic deformation is mainly concentrated. Despite the decrease in load, the tensile stress in the neck increases until the specimen fails.
When stretched, the sample elongates, and its cross section continuously decreases. The true stress is determined by dividing the load acting at a certain moment by the area that the sample has at that moment (Fig. 1b). These stresses in everyday practice do not determine, but use the stress conditions, considering that the cross section F o sample remains unchanged.

Stresses σ control, σ t, σ in - standard strength characteristics. Each is obtained by dividing the corresponding load R ex. R t and R max to the initial cross-sectional area F O .

elastic limitσ ex. name the stress at which the plastic deformation reaches values ​​of 0.005; 0.02 and 0.05%. The corresponding elastic limits are denotedσ 0.005, σ 0.02, σ 0.05.

The conditional yield strength is the stress, which corresponds to a plastic deformation equal to 0.2%; it is designatedσ 0.2 . Physical yield strengthσ t determined from the tensile diagram when it has a yield plateau. However, when tested in tension, most alloys do not show a yield plateau on the charts. The chosen plastic deformation of 0.2% quite accurately characterizes the transition from elastic to plastic deformations.

The tensile strength characterizes the maximum bearing capacity of the material, its strength prior to destruction:

σ in \u003d P max / F o

Plasticity is characterized by relative elongation δ and relative contraction ψ:

where lk is the final length of the sample; lo and Fo are the initial length and cross-sectional area of ​​the sample; Fk is the cross-sectional area at the rupture site.
For low-plastic materials, tensile tests (Fig. 1c) cause significant difficulties. Such materials are usually subjected to bending tests.

Bending test. During a bending test, both tensile and compressive stresses occur in the specimen. Cast iron is tested for bending tool steels, became after surface hardening and ceramics. The determined characteristics are tensile strength and deflection.

The flexural strength is calculated by the formula:

σ and = M / W,

where M is the largest bending moment; W - section modulus, for the image of a circular section

W = πd 3 / 32

(where d is the sample diameter), and for rectangular samples W = bh 2 /6, where b, h are the width and height of the sample).
Hardness tests . Hardness is understood as the ability of a material to resist penetration into its surface by a solid body - an indenter. A hardened steel ball is used as an indenter or diamond tip in the form of a cone or pyramid. When indented, the surface layers of the material experience significant plastic deformation. After removing the load, an imprint remains on the surface. A feature of the ongoing plastic deformation is that a complex stress state arises near the tip, close to all-round non-uniform compression. For this reason, plastic deformation is experienced not only by plastic, but also by brittle materials.
Thus, hardness characterizes the resistance of a material to plastic deformation. The same resistance is also estimated by the temporary resistance, in the determination of which a concentrated deformation occurs in the neck region. Therefore, for a number of materials, the numerical values ​​of hardness and tensile strength are proportional. In practice, four methods of measuring hardness are widely used: Brinell hardness, Vickers hardness, Rockwell hardness and microhardness.
When determining the hardness according to Brinell (GOST 9012-59), a hardened ball with a diameter of 10 is pressed into the sample surface; 5 or 2.5 mm under load from 5000N to 30000N. After the load is removed, an imprint is formed on the surface in the form of a spherical hole with a diameter d.
When measuring Brinell hardness, pre-compiled tables are used indicating the HB hardness number. Depending on the indentation diameter and the selected load, the smaller the indentation diameter, the higher the hardness.
The Brinell measurement method is used for steels with hardness < 450 HB, non-ferrous metals with hardness < 200 HB. For them, a correlation has been established between the tensile strength (in MPa) and the hardness number HB:
σ in » 3.4 HB - for hot-rolled carbon steels;
σ in » 4.5 HB - for copper alloys;
σ in » 3.5 HB - for aluminum alloys.
With the standard Vickers measurement method (GOST 2999-75), a tetrahedral diamond pyramid with an apex angle of 139° is pressed into the sample surface. The imprint is obtained in the form of a square, the diagonal of which is measured after the load is removed. The hardness number HV is determined using special tables by the value of the imprint diagonal at a selected load.

The Vickers method is used mainly for materials with high hardness, as well as for testing the hardness of parts with small sections or thin surface layers. As a rule, small loads are used: 10,30,50,100,200,500 N. The thinner the section of the part or the layer under study, the less the load is chosen.
The Vickers and Brinell hardness numbers for materials with hardness up to 450 HB are practically the same.
Rockwell hardness measurement (GOST 9013-59) is the most versatile and least labor intensive. The hardness number depends on the depth of indentation of the tip, which is used as a diamond cone with an angle at the top of 120 0 or a steel ball with a diameter of 1.588 mm. For various combinations of loads and tips, the Rockwell device has three measuring scales: A.V.S. Rockwell hardness is indicated by the numbers that determine the level of hardness, and the letters HR indicating the hardness scale, for example: 70HRA, 58HRC, 50HRB. Rockwell hardness numbers do not have exact relationships with Brinell and Vickers hardness numbers.
Scale A (tip - diamond cone, total load 600N). This scale is used for hard materials, for thin sheet materials or thin (0.6-1.0 mm) layers. The limits of measurement of hardness on this scale are 70-85.
Scale B (tip - steel ball, total load 1000N). With this scale, the hardness of relatively soft materials is determined (<400НВ). Пределы измерения твердости 25-100.

Scale C (tip - diamond cone, total load 1500N). This scale is used for hard materials (> 450 HB), such as hardened steels. The limits of measurement of hardness on this scale are 20-67. Determination of microhardness (GOST 9450-76) is carried out by pressing a diamond pyramid into the sample surface at low loads (0.05-5N), followed by measurement of the imprint diagonal. This method evaluates the hardness of individual grains, structural components, thin layers or fine details.

Mechanical properties determined under dynamic loads

During the operation of machine parts, dynamic loads are possible, under which many metals show a tendency to brittle fracture. The risk of destruction is increased by notches - stress concentrators. To assess the tendency of the metal to brittle fracture under the influence of these factors, dynamic impact bending tests are carried out on pendulum impact testers (Fig. 2). standard sample set on two disputes and strike in the middle, leading to the destruction of the sample. On the pendulum copra scale, work is determined TO spent on destruction, and calculate the main characteristic obtained as a result of these tests - percussion viscosity:

KS = K / S 0 1 , [MJ/m 2 ],

Where S 0 1, the cross-sectional area of ​​the sample at the notch.

Rice. 2. Scheme pendulum copra (a) and impact test (b):
1 - sample; 2 - pendulum; 3 - scale; 4 – scale pointer; 5- brake.

In accordance with GOST 9454-78, three types of samples are tested: U-shaped (notch radius r=1 mm); V-shaped (r \u003d 0.25 mm) and T-shaped (fatigue crack created at the base of the notch. Accordingly, impact strength means: KCU, KCV, KCT. Impact strength of all mechanical properties is the most sensitive to temperature decrease. Therefore, tests impact strength at low temperatures is used to determine the threshold cold brittleness- the temperature or temperature range in which the impact strength decreases. Cold brittleness- the ability of a metallic material to lose viscosity, brittle fracture with decreasing temperature. Cold brittleness is manifested in iron, steel, metals and alloys having a body-centered cubic (bcc) or hexagonal close-packed (HP) lattice. It is absent in metals with a face-centered cubic (fcc) lattice.

Mechanical properties determined under variable cyclic loads

Many machine parts (shafts, connecting rods, gears) experience repeated cyclic loads during operation. The processes of gradual accumulation of damage in a material under the action of cyclic loads, leading to a change in its properties, the formation of cracks, their development and destruction, are called fatigue, and the ability to resist fatigue - endurance(GOST 23207-78). The ability of materials to work under conditions of cyclic loading is judged by the results of testing specimens for fatigue (GOST 25.502-79). They are carried out on special machines that create multiple loading in the samples (tension - compression, bending, torsion). Samples are tested sequentially for different levels stresses, determining the number of cycles before failure. The test results are depicted as a fatigue curve, which is plotted in the coordinates: maximum cycle stress σ max / or σ in ) is the number of cycles. Fatigue curves allow you to define the following endurance criteria:

- cyclic strength, which characterizes the bearing capacity of the material, i.e. the greatest voltage that he is able to withstand for a certain time of work.- cyclic durability- the number of cycles (or operating hours) that the material withstands before the formation of a fatigue crack of a certain length or before fatigue failure at a given stress.

In addition to determining the considered criteria for high-cycle endurance, for some special cases, tests for low cycle fatigue. They are carried out at high voltages (above σ 0.2 ) and low loading frequency (usually no more than 6 Hz). These tests simulate the operating conditions of structures (for example, aircraft) that perceive rare but significant cyclic loads.

Mechanical properties are manifested as the ability of a material to resist all types of external mechanical influences.

Mechanical effects characterize direction, duration And scope. In terms of direction, mechanical actions can be considered as linear(tension and compression) and corner(bending and twisting). According to their duration, they are divided into static And dynamic, by scope - on bulk and surface.

Mechanical properties determine the change in the shape, size and continuity of substances and materials under mechanical influences, and, consequently, the result of almost any mechanical action on substances and materials that occurs during their production and operation (use).

The main mechanical properties of substances and materials are elasticity, rigidity, elasticity, plasticity, strength, brittleness, toughness and hardness.

Elasticity- the property of materials to spontaneously restore their shape and volume (solids) or only volume (liquids and gases) when external influences cease. Elasticity is due to the interaction between the atoms (molecules) of a substance and their thermal motion.

As a measure of the ability of materials or products to change size and shape for a given type of load, the concepts "elasticity" And "rigidity".

Elasticity - the ability of a material or product to undergo significant changes in size and shape without destruction with a relatively small acting force.

Rigidity - the ability of a material or product to change less in size and shape for a given type of load. The more rigidity, the less change.

Elasticity- the ability of solid materials to retain their changed shape and volume without microscopic discontinuities after removing the mechanical loads that caused these changes.

Plastic deformation is associated with the breaking of some interatomic bonds and the formation of new ones. Accounting for plasticity makes it possible to determine the margins of strength, deformability and stability, and expands the possibilities of creating structures of minimum weight.

Mechanical strength solids - the property to resist destruction, separation into parts), as well as an irreversible change in shape under mechanical stress. The strength of solids is ultimately determined by the forces of interaction between their constituent structural units (atoms, ions, etc.).

fragility- the property of solids to break down under mechanical influences without significant preliminary changes in shape and volume.

Viscosity (internal friction)- the ability of materials to resist the action of external forces, causing:

In solids, the propagation of an already existing sharp crack (destruction);

In liquids and gases - flow.

Hardness - the property of materials to resist in the surface layer the contact action (indentation or scratching). The peculiarity of this property is that it is realized only in a small volume of matter. Hardness is a complex property of a material, reflecting both its strength and ductility.

In the absence of mechanical influences, the atoms in the crystal are in equilibrium positions. Under mechanical influences, a material object is deformed.

Deformation- a change in the relative position of a plurality of particles of a substance, which leads to a change in the shape and size of the body or its parts and causes a change in the forces of interaction between them. All substances are deformable.

If a compressive load is applied, then the particles of the structure of a substance (for example, atoms) will approach each other until such a distance at which the internal repulsive forces balance the external compressive forces. In tension, the distance between the structural particles increases until the attractive forces balance the external load.

In solids, according to the mechanism of flow, elastic and plastic deformations are distinguished. elastic deformation called deformation, the influence of which on the shape, structure and properties of the material is eliminated after the termination of the action of external forces, and plastic - such part of the deformation that remains after the removal of the load, irreversibly changing the structure of the material and its properties.

All real solids, even at small deformations, have plastic properties, which determines the mixed mechanisms of deformation - elastic-plastic deformation. Yes, in various details and structures, plastic deformations cover, as a rule, a small volume of material, the rest experiences only elastic deformations. If the amount of deformation explicitly depends on time, for example, increases at a constant load, but is reversible, it is called viscoelastic.

Plastic deformation in solids can be carried out, for example, by slip, which occurs in the crystal lattice of a substance along planes and directions with the most dense packing of atoms. The slip planes and the slip directions lying in these planes form sliding system. In metals, for example, one or several slip systems can act simultaneously.

The presentation of the sliding process as the simultaneous movement of one part of the crystal relative to another is purely schematic (Fig.

In real materials, sliding is carried out both as a result of the displacement of dislocations in one slip plane, and by transition to others. Dislocations moving in a deformed crystalline substance generate a large number of dislocated atoms and vacancies.

Most of the work (up to 95%) spent on deformation is converted into heat (heating occurs), the rest of the energy is accumulated in the form of an increased density of lattice defects (vacancies and mainly dislocations). The accumulation of energy is also evidenced by the growth of residual stresses as a result of deformation. In this regard, the state of the plastically deformed material is unstable and can change, for example, during heat treatment.

The simplest elements of deformations are:

relative elongation δ - the ratio of the increment in length (/, -/ 0) of the sample under the action of the load to its initial value / 0:

δ = (/,-/ 0)/ / 0

relative contraction ψ - the ratio of the reduction in the cross-sectional area of ​​the sample under the action of the load (S 0 -S 1) to its original value S 0:

ψ \u003d (S 0 -S 1) / S 0

The resistance to deformation is determined by the resistance to shear of one atomic layer relative to another, adjacent one. To estimate the value of this resistance, the concept " voltage".

Voltage - a measure of internal forces that arise during the deformation of a material, characterizing the change in the forces of interaction between particles of a substance during its deformation. The voltage is not measured directly, but is only calculated through the magnitude of the forces acting on the body or is determined indirectly - by the effects of its action, for example, by the piezoelectric effect.

Voltage is a vector quantity; the values ​​of the projection of this vector onto the normal and the tangent plane are called normal And shear stress..

The slip system during plastic deformation in a particular crystalline substance is characterized by the value of the minimum shear stress, which is necessary to start sliding. This critical shear stress t 0 , which does not depend on the orientation of the slip plane with respect to the applied load and is one of the fundamental characteristics of a crystalline material.

If slip in this system begins when the shear stress reaches the critical value t 0 , then the continuation of deformation requires a continuous increase in the shear stress, i.e. deformation is accompanied by continuous hardening ( strain hardening, or hardening).

hardening- change in the structure and properties with an increase in the density of defects in the crystal lattice in substances as a result of plastic deformation. Hardening reduces ductility and impact strength, but increases hardness and strength. Work hardening is used for surface hardening of products, but it should be borne in mind that work hardened metals are more susceptible to corrosion and are prone to stress corrosion cracking.

Stress characterize by origin And in relation to exposure time.

According to the source of voltage, they are divided into mechanical - under mechanical influences, thermal- due to a temperature gradient, for example during a rapid heating or cooling process between the surface and inner layers, and structural (phase) - during various physicochemical processes occurring in a substance, for example, a change in the volume of individual crystallites during phase transformations.

The magnitude of mechanical stresses in a material sample σ is directly proportional to the magnitude of the external force F, Pa:

σ = F/S,

Where S- sample area, m 2 .

The main mechanical characteristics of the resistance of the material to deformation and destruction: Young's modulus, Poisson's ratio, shear modulus, proportional limit, elastic limit, and yield strength And strength.

Under the mechanical properties understand the characteristics that determine the behavior of the metal (or other material) under the action of applied external mechanical forces. Mechanical properties usually include the resistance of a metal (alloy) to deformation (strength) and fracture resistance (ductility, toughness, as well as the ability of the metal not to collapse in the presence of cracks).

As a result of mechanical tests, numerical values ​​of mechanical properties are obtained, i.e., stress or strain values ​​at which changes occur in the physical and mechanical states of the material.

When evaluating the mechanical properties of metallic materials, several groups of their criteria are distinguished.

1. Criteria determined independently of design features and nature of product service. These criteria are found by standard tensile, compression, bending, hardness tests (static tests) or notched impact tests (dynamic tests) on smooth specimens.

The strength and plastic properties determined during static tests on smooth samples, although they are important (they are included in the calculation formulas), in many cases do not characterize the strength of these materials in real conditions operation of parts of machines and structures. They can only be used for a limited number of simple-shaped products operating under static load conditions at temperatures close to normal.

2. Criteria for assessing the structural strength of the material, which are in the greatest correlation with the service properties of this product and characterize the performance of the material under operating conditions.

Structural strength criteria for metallic materials can be divided into two groups:

a) criteria that determine the reliability of metallic materials against sudden failures (fracture toughness, work absorbed during crack propagation, survivability, etc.). These techniques, which use the basic principles of fracture mechanics, are based on static or dynamic testing of samples with sharp cracks that occur in real machine parts and structures under operating conditions (cuts, through holes, non-metallic inclusions, microvoids, etc.). Cracks and microdiscontinuities greatly change the behavior of the metal under load, as they are stress concentrators;

b) criteria that determine the durability of products (fatigue resistance, wear resistance, corrosion resistance, etc.).

3. Criteria for assessing the strength of the structure as a whole (structural strength), determined during bench, full-scale and operational tests. During these tests, the influence on the strength and durability of the structure of such factors as the distribution and magnitude of residual stresses, defects in the manufacturing technology and design of metal products, etc., is revealed.

For solutions practical tasks metallurgy, it is necessary to define both standard mechanical properties and structural strength criteria.

All people are born differently. smart adults in different countries, such questions have been asked for a long time. They have long understood that all children differ from each other genetically, psychologically, physical development. And no moralizing, training, various scientific methods of education, and even a belt, will not make them the same. Different children need to be raised differently. When children grow up, professions will choose them. But from the abilities that manifest themselves from early childhood, we will not go anywhere. Abilities are technical, organizational, artistic and aesthetic. Almost all of them, in some way, influence the choice of our professions. It often happens that our abilities guide us in choosing professions. Let's take a closer look at technical abilities and their impact on our lives.

Imagine that you went to the courses customs clearance, subsequently a large amount will pass through your hands Vehicle. What will happen if you do not learn to understand everything. You simply will not be able to match the chosen profession. What does technical ability mean?

An indispensable attribute of technical abilities is an interest in technology, a desire to work on machines, with tools and equipment.

Components of technical abilities:
a) the ability to understand drawings, diagrams, graphs; b) the ability to read drawings, graphs, vividly imagine the real objects behind them, is very important for technical professions;
c) ability to physics, mathematics, chemistry. Technology is closely related to these sciences. You need not only a good mastery of mathematical material and memory, but also the ability to work with numbers and formulas;
d) the ability to understand and reason, analyze and generalize - logical thinking;
e) developed spatial imagination is a very significant component of technical abilities.

Such abilities are ideal for a person with a mathematical mindset who knows how to think. That is, if you choose courses customs declaration , and you consider yourself to be among people who have technical character traits, then you have chosen the profession correctly.

Diagnosis of one's own abilities is a very delicate matter. It is likely that you have not found the above technical abilities. Don't be scared. This is fine. Firstly, people with a full set of qualities are rare for only one profession - one in thirty. It's called a calling. The rest, as a rule, have a set of qualities that are equally suitable for several professions, and they have to either produce the missing abilities in themselves through constant training, or compensate for something else. You need to be wary if your abilities too clearly do not fit in with the requirements of the profession you want to choose. Listen to yourself, and everything will definitely work out, and you will become a master of your craft.

MECHANICAL PROPERTIES

MECHANICAL PROPERTIES

Materials - the reaction of the material to the applied mechanical. loads. Main mechanical characteristics. properties are stress and strain. Stresses are the characteristics of forces, which are attributed to a unit section of a sample of a material or product, a structure made of it. Deformation is most often assessed as a dimensionless quantity, such as changes in length, deflection, or angle of twist.

M. s. construct. materials (metals and alloys, polymers, glass, ceramics, textile threads and fabrics, wood, etc.) establish a mechanical. tests, the purpose of which is most often to find a connection between the applied mechanical. stresses on the material and its deformation. M. s. essentially depend on the structure of the tested material and the scheme of applied forces. Therefore, they are not physical. constants and do not characterize the forces of interatomic interaction of the material. For ease of comparison M. with. different materials tests are carried out under simple, easily reproducible loading schemes (application of external forces) - uniaxial tension (or compression), bending, torsion. When comparing M. with. different materials or one material with a different structure, it should be borne in mind that the test conditions are met (the same stress pattern, load application rate and physical and mechanical conditions of the test environment, as well as geom. similarity - the shape and dimensions of the test sample). M. s. essentially depend on temperature and pressure.

Mechanical tests can be classified according to the stress state (scheme of applied forces), the method of loading during testing (deformation at a given rate and deformation resistance forces), the application of post, load (or stresses) and the measurement of deformation resistance forces, according to the nature of the change in static, dynamic.

M. s. classified according to physical the nature of the resulting characteristics.

Elasticity - the property of solids to resist a change in their volume or shape under the action of mechanical. voltages spontaneously restore the original state upon termination of the external. impacts. It is characterized by an elastic limit - max, tension, after removal to-rogo the form and the sizes of a sample are completely restored; modulus of elasticity- coefficient proportionality, linking and elastic deformation. Unity, characteristic of M. s., giving information about interatomic interaction in crystalline. the lattice of the material is the second derivative of the interaction energy of atoms (ions) but the distance between them.

In the region of elasticity, deviations from elastic properties often occur, which are characterized by stress relaxation, aftereffect elastic, internal friction, defect in the modulus of elasticity.

Strength - resistance to destruction (rupture); characterized by stresses corresponding to the maximum (before sample failure) load values ​​(the so-called tensile strength or ).

The nature of destruction in all types of tests (tensile, compression, bending, torsion) under the influence of normal (separation) and shear (shear) stresses can be ductile or brittle. The difference between ductile and brittle fractures lies in the amount of plastic. strain accumulated before failure. Both types of failure are associated with the initiation and development of cracks. Evaluation of resistance to destruction at conventional static. tests (ultimate strength, tensile strength) is often insufficient to determine the suitability of a material as a structural material, especially in the presence of notches, cracks, and other stress concentrators. In this case, fracture tests are used, in which samples with cracks created in advance are used, and the parameter ( TO), to-ry naz. coefficient stress intensity. Determine this coefficient. for flat ( K with) or bulk (A - Ci) stress states.

The strength properties also include plastic resistance. deformations. Usually plastic. the deformation is characterized by the stresses necessary to achieve a certain predetermined value of residual deformations. So, it determines the stresses that cause plasticity when stretched. deformation 0.2% (indicated by ).

Plasticity - the property of solids to irreversibly deform under the influence of external. forces or internal stresses. As characteristics of plasticity, elongation (attributes, change in length during tension) and attributes, narrowing in the neck - a change in the cross section of the sample after the termination of uniform elongation (buckling) and the formation of a neck are widespread.

Dynamic resistance loads are evaluated by the value of impact strength - specific fracture during impact bending of specimens with a notch (for relatively ductile materials) or without a notch (for less ductile materials).

Heat resistance - the ability of materials to work for a long time without deforming and but breaking down under applied loads and high temp-pax. Main the characteristics of heat resistance are creep limit and duration, . The creep limit, i.e., the magnitude of stresses, at which creep does not exceed a given value, is determined for each temperature from the dependence of the steady-state creep rate on stresses. Similarly, the value of the duration, the strength of the material for a given temperature is determined from the dependence of the time to failure on stresses. For example, they set the voltage (or load), at which destruction at a given post, temperature T happens in 100 hours

An important characteristic of heat resistance is also the duration, i.e., the amount of deformation accumulated during creep until the moment of failure. Often, heat resistance is simply characterized by the time to failure at given and constant stress and temperature. In many cases, heat resistance is evaluated by tensile strength or other similar characteristics at elevated temperatures. In this case, one speaks of a short time. heat resistance.

Fatigue is the process of accumulation of damage in materials under the influence of cyclically changing stresses, which in their magnitude do not exceed the elastic limit. The scheme of applied voltages and the nature of their change in time can be different. Fatigue resistance nav. in s-endurance. To study the fatigue of the material, diagrams are built depending on the number of cycles of stress changes on the value of max, cycle stresses. This dependence either begins to change insignificantly or remains constant. The level of such stresses is called. fatigue limit. The dependence of the number of cycles to failure on the deformation amplitude is also studied.

A very common characteristic of M. s. is , which is the resistance of the material to indentation. Despite some uncertainty in physical the nature of this property, due to its ease of measurement, ease of reproduction, and high correlation with strength, hardness has become a widespread characteristic of M. s.

In technology, the so-called. technol. samples showing the ability to construct. materials to certain deformations: Eriksen test, showing the ability of the material to deep drawing; plasticity in torsion, bend with an inflection - indicators of the plasticity of the material and its susceptibility to otd. types of pressure treatment.

Lit.: Bernstein M. L., Zaimovsky V. A., Mechanical properties of metals, 2nd ed., M., 1979; Zolotorevsky V. G., Mechanical properties of metals, 2nd ed., M., 1983. IN. M. Rosenberg.

Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Chief Editor A. M. Prokhorov. 1988 .

See what "MECHANICAL PROPERTIES" is in other dictionaries:

Mechanical properties- - reflect the ability of the material to resist power, thermal, shrinkage or other internal stresses without disturbing the established structure. Mechanical properties include deformation properties: strength, hardness, abrasion, ... ... Encyclopedia of terms, definitions and explanations of building materials

Materials, such as strength, fracture resistance, hardness, etc., are in many cases decisive for making a decision on the use of a material. Methods for testing mechanical properties The following main methods should be noted ... ... Wikipedia

Rocks (a. mechanical properties of rocks; n. mechanische Eigenschaften der Gesteine; f. proprietes mecaniques des roches; and. caracteristicas mecanicas de rocas, propiedades mecanicas de rocas) characterize changes in shape, ... ... Geological Encyclopedia

mechanical properties- material properties that show elastic and inelastic behavior when subjected to force, thereby indicating the suitability of the material for further applications; e.g. modulus of elasticity, tensile strength, elongation… Technical Translator's Handbook

MECHANICAL PROPERTIES- characteristics of the behavior of bodies (mostly solid) under the action of mechanical stresses. Mechanical properties are characterized mechanical stresses(see Strength), deformations (see Plasticity), work (see Impact ... ... Metallurgical Dictionary

Mechanical properties Mechanical properties. Material properties that show elastic and inelastic behavior when subjected to force, thereby indicating the suitability of the material for further applications; e.g. modulus of elasticity, limit... Glossary of metallurgical terms

mechanical properties- mechaninės savybės statusas T sritis automatika atitikmenys: engl. mechanical properties vok. mechanische Eigenschaften, f rus. mechanical properties, n pranc. propriétés mécaniques, f … Automatikos terminų žodynas

mechanical properties- mechaninės savybės statusas T sritis Standartizacija ir metrologija apibrėžtis Kūnų ir medžiagų reagavimo į mechaninius poveikius charakteristikos. atitikmenys: engl. mechanical properties vok. mechanische Eigenschaften, f rus. mechanical ... ... Penkiakalbis aiskinamasis metrologijos terminų žodynas

mechanical properties- mechaninės savybės statusas T sritis chemija apibrėžtis Kūno reagavimo į mechaninius poveikius charakteristika. atitikmenys: engl. mechanical properties mechanical properties … Chemijos terminų aiskinamasis žodynas

mechanical properties- mechaninės savybės statusas T sritis fizika atitikmenys: engl. mechanical properties vok. mechanische Eigenschaften, f rus. mechanical properties, n pranc. propriétés mecaniques, f … Fizikos terminų žodynas