Allows you to determine ultimate stress(), in which the sample material is directly destroyed or large plastic deformations occur in it.
Ultimate stress in strength calculations
As ultimate voltage in strength calculations the following is accepted:
yield stress for a plastic material (it is believed that the destruction of a plastic material begins when noticeable plastic deformations appear in it)
,
tensile strength for brittle material, the value of which is different:
To provide a real part, it is necessary to choose its dimensions and material so that the maximum that occurs at some point during operation is less than the limit:
However, even if the highest calculated stress in a part is close to the ultimate stress, its strength cannot yet be guaranteed.
Acting on the part cannot be installed accurately enough,
the design stresses in a part can sometimes be calculated only approximately,
Deviations between actual and calculated characteristics are possible.
The part must be designed with some design safety factor:
.
It is clear that the larger n, the stronger the part. However very big safety factor leads to waste of material, and this makes the part heavy and uneconomical.
Depending on the purpose of the structure, the required safety factor is established.
Strength condition: the strength of the part is considered ensured if . Using the expression , let's rewrite strength condition as:
From here you can get another form of recording strength conditions:
The relation on the right side of the last inequality is called permissible voltage:
If the limiting and, therefore, permissible stresses during tension and compression are different, they are denoted by and. Using the concept permissible voltage, Can strength condition formulate as follows: the strength of a part is ensured if what occurs in it highest voltage does not exceed permissible voltage.
To determine permissible stresses in mechanical engineering, the following basic methods are used.
1. The differentiated safety factor is found as the product of a number of partial coefficients that take into account the reliability of the material, the degree of responsibility of the part, the accuracy of the calculation formulas and active forces and other factors that determine the operating conditions of the parts.
2. Tabular - permissible voltages are taken according to standards, systematized in the form of tables
(Table 1 - 7). This method is less accurate, but is the simplest and most convenient for practical use in design and testing strength calculations.
In the work of design bureaus and in the calculations of machine parts, both differentiated and tabular methods, as well as their combination. In table 4 - 6 show the permissible stresses for non-standard cast parts for which special calculation methods and the corresponding permissible stresses have not been developed. Typical parts (for example, gears and worm wheels, pulleys) should be calculated using the methods given in the corresponding section of the reference book or specialized literature.
The permissible stresses given are intended for approximate calculations only for basic loads. For more accurate calculations taking into account additional loads (for example, dynamic), the table values should be increased by 20 - 30%.
Allowable stresses are given without taking into account the stress concentration and dimensions of the part, calculated for smooth polished steel samples with a diameter of 6-12 mm and for untreated round cast iron castings with a diameter of 30 mm. When determining the highest stresses in the part being calculated, it is necessary to multiply the nominal stresses σ nom and τ nom by the concentration factor k σ or k τ:
1. Permissible stresses*
for carbon steels of ordinary quality in hot-rolled condition
| Brand become | Allowable stress **, MPa | |||||||||||||
| under tension [σ p ] | during bending [σ from ] | during torsion [τ cr] | when cutting [τ avg ] | in compression [σ cm] | ||||||||||
| I | II | III | I | II | III | I | II | III | I | II | III | I | II | |
| St2 St3 St4 St5 St6 | 115 125 140 165 195 | 80 90 95 115 140 | 60 70 75 90 110 | 140 150 170 200 230 | 100 110 120 140 170 | 80 85 95 110 135 | 85 95 105 125 145 | 65 65 75 80 105 | 50 50 60 70 80 | 70 75 85 100 115 | 50 50 65 65 85 | 40 40 50 55 65 | 175 190 210 250 290 | 120 135 145 175 210 |
* Gorsky A.I.. Ivanov-Emin E.B.. Karenovsky A.I. Determination of permissible stresses in strength calculations. NIImash, M., 1974.
** Roman numerals indicate the type of load: I - static; II - variable operating from zero to maximum, from maximum to zero (pulsating); III - alternating (symmetrical).
2. Mechanical properties and permissible stresses
carbon quality structural steels
3. Mechanical properties and permissible stresses
alloyed structural steels
4. Mechanical properties and permissible stresses
for castings made of carbon and alloy steels
5. Mechanical properties and permissible stresses
for gray cast iron castings
6. Mechanical properties and permissible stresses
for ductile iron castings
7. Permissible stresses for plastic parts
For ductile (unhardened) steels for static stresses (I type of load), the concentration coefficient is not taken into account. For homogeneous steels (σ in > 1300 MPa, as well as in the case of their operation at low temperatures) concentration coefficient, in the presence of stress concentration, is included in the calculation under loads I type (k > 1). For ductile steels under variable loads and in the presence of stress concentrations, these stresses must be taken into account.
For cast iron in most cases, the stress concentration coefficient is approximately equal to unity for all types of loads (I - III). When calculating strength to take into account the dimensions of the part, the given tabulated permissible stresses for cast parts should be multiplied by a scale factor equal to 1.4 ... 5.
Approximate empirical dependences of endurance limits for cases of loading with a symmetrical cycle:
for carbon steels:
- when bending, σ -1 = (0.40÷0.46)σ in;
σ -1р = (0.65÷0.75)σ -1;
- during torsion, τ -1 = (0.55÷0.65)σ -1;
for alloy steels:
- when bending, σ -1 = (0.45÷0.55)σ in;
- when stretched or compressed, σ -1р = (0.70÷0.90)σ -1;
- during torsion, τ -1 = (0.50÷0.65)σ -1;
for steel casting:
- when bending, σ -1 = (0.35÷0.45)σ in;
- when stretched or compressed, σ -1р = (0.65÷0.75)σ -1;
- during torsion, τ -1 = (0.55÷0.65)σ -1.
Mechanical properties and permissible stresses of anti-friction cast iron:
- ultimate bending strength 250 ÷ 300 MPa,
- permissible bending stresses: 95 MPa for I; 70 MPa - II: 45 MPa - III, where I. II, III are designations of types of load, see table. 1.
Approximate permissible stresses for non-ferrous metals in tension and compression. MPa:
- 30...110 - for copper;
- 60...130 - brass;
- 50...110 - bronze;
- 25...70 - aluminum;
- 70...140 - duralumin.
Table 2.4
Fig.2.22
Fig.2.18
Fig.2.17
Rice. 2.15
For tensile tests, tensile testing machines are used, which make it possible to record a diagram in “load – absolute elongation” coordinates during testing. The nature of the stress-strain diagram depends on the properties of the material being tested and on the rate of deformation. A typical view of such a diagram for low-carbon steel under static load application is shown in Fig. 2.16.
Let us consider the characteristic sections and points of this diagram, as well as the corresponding stages of sample deformation:
OA – Hooke’s law is valid;
AB – residual (plastic) deformations have appeared;
BC – plastic deformations increase;
SD – yield plateau (increase in deformation occurs under constant load);
DC – area of strengthening (the material again acquires the ability to increase resistance to further deformation and accepts a force that increases to a certain limit);
Point K – the test was stopped and the sample was unloaded;
KN – unloading line;
NKL – line of repeated loading of the sample (KL – strengthening section);
LM is the area where the load drops, at this moment a so-called neck appears on the sample - a local narrowing;
Point M – sample rupture;
After rupture, the sample has the appearance approximately shown in Fig. 2.17. The fragments can be folded and the length after the test ℓ 1, as well as the diameter of the neck d 1, can be measured.
As a result of processing the tensile diagram and measuring the sample, we obtain a number of mechanical characteristics that can be divided into two groups - strength characteristics and plasticity characteristics.
Strength characteristics
Proportionality limit:
The maximum voltage up to which Hooke's law is valid.
Yield Strength:
The lowest stress at which deformation of the sample occurs under constant tensile force.
Tensile strength (temporary strength):
The highest voltage observed during the test.
Voltage at break:
The stress at break determined in this way is very arbitrary and cannot be used as a characteristic of the mechanical properties of steel. The convention is that it is obtained by dividing the force at the moment of rupture by the initial cross-sectional area of the sample, and not by its actual area at rupture, which is significantly less than the initial one due to the formation of a neck.
Plasticity characteristics
Let us recall that plasticity is the ability of a material to deform without fracture. Plasticity characteristics are deformation, therefore they are determined from measurement data of the sample after fracture:
∆ℓ ос = ℓ 1 - ℓ 0 – residual elongation,
– neck area.
Relative elongation after break:
. (2.25)
This characteristic depends not only on the material, but also on the ratio of the sample dimensions. That is why standard samples have a fixed ratio ℓ 0 = 5d 0 or ℓ 0 = 10d 0 and the value of δ is always given with an index - δ 5 or δ 10, and δ 5 > δ 10.
Relative narrowing after rupture:
. (2.26)
Specific work of deformation:
where A is the work spent on destruction of the sample; is found as the area bounded by the stretch diagram and the x-axis (area of the figure OABCDKLMR). Specific work of deformation characterizes the ability of a material to resist the impact of a load.
Of all the mechanical characteristics obtained during testing, the main characteristics of strength are the yield strength σ t and the tensile strength σ pch, and the main characteristics of plasticity are the relative elongation δ and the relative contraction ψ after rupture.
Unloading and reloading
When describing the tensile diagram, it was indicated that at point K the test was stopped and the sample was unloaded. The unloading process was described by straight line KN (Fig. 2.16), parallel to the straight section OA of the diagram. This means that the elongation of the sample ∆ℓ′ P, obtained before the start of unloading, does not completely disappear. The disappeared part of the elongation in the diagram is depicted by the segment NQ, the remaining part by the segment ON. Consequently, the total elongation of a sample beyond the elastic limit consists of two parts - elastic and residual (plastic):
∆ℓ′ P = ∆ℓ′ up + ∆ℓ′ os.
This will happen until the sample ruptures. After rupture, the elastic component of the total elongation (segment ∆ℓ up) disappears. The residual elongation is depicted by the segment ∆ℓ os. If you stop loading and unload the sample within the OB section, then the unloading process will be depicted by a line coinciding with the load line - the deformation is purely elastic.
When a sample of length ℓ 0 + ∆ℓ′ oc is re-loaded, the loading line practically coincides with the unloading line NK. The limit of proportionality increased and became equal to the voltage from which the unloading was carried out. Next, straight line NK turned into curve KL without a yield plateau. The part of the diagram located to the left of the NK line turned out to be cut off, i.e. the origin of coordinates moved to point N. Thus, as a result of stretching beyond the yield point, the sample changed its mechanical properties:
1). the limit of proportionality has increased;
2). the turnover platform has disappeared;
3). the relative elongation after rupture decreased.
This change in properties is called hardened.
When hardened, elastic properties increase and ductility decreases. In some cases (for example, when machining) the phenomenon of hardening is undesirable and is eliminated by heat treatment. In other cases, it is created artificially to improve the elasticity of parts or structures (shot processing of springs or stretching of cables of lifting machines).
Stress diagrams
To obtain a diagram characterizing the mechanical properties of the material, the primary tensile diagram in coordinates Р – ∆ℓ is reconstructed in coordinates σ – ε. Since the ordinates σ = Р/F and abscissas σ = ∆ℓ/ℓ are obtained by dividing by constants, the diagram has the same appearance as the original one (Fig. 2.18,a).
From the σ – ε diagram it is clear that
those. the modulus of normal elasticity is equal to the tangent of the angle of inclination of the straight section of the diagram to the abscissa axis.
From the stress diagram it is convenient to determine the so-called conditional yield strength. The fact is that most structural materials do not have a yield point - a straight line smoothly turns into a curve. In this case, the stress at which the relative permanent elongation is equal to 0.2% is taken as the value of the yield strength (conditional). In Fig. Figure 2.18b shows how the value of the conditional yield strength σ 0.2 is determined. The yield strength σ t, determined in the presence of a yield plateau, is often called physical.
The descending section of the diagram is conditional, since the actual cross-sectional area of the sample after necking is significantly less than the initial area from which the coordinates of the diagram are determined. The true stress can be obtained if the magnitude of the force at each moment of time P t is divided by the actual cross-sectional area at the same moment of time F t:
In Fig. 2.18a, these voltages correspond to the dashed line. Up to the ultimate strength, S and σ practically coincide. At the moment of rupture, the true stress significantly exceeds the tensile strength σ pc and, even more so, the stress at the moment of rupture σ r. Let us express the area of the neck F 1 through ψ and find S r.
Þ Þ 
.
For ductile steel ψ = 50 – 65%. If we take ψ = 50% = 0.5, then we get S р = 2σ р, i.e. the true stress is greatest at the moment of rupture, which is quite logical.
2.6.2. Compression test various materials
A compression test provides less information about the properties of a material than a tensile test. However, it is absolutely necessary to characterize the mechanical properties of the material. It is carried out on samples in the form of cylinders, the height of which is not more than 1.5 times the diameter, or on samples in the form of cubes.
Let's look at the compression diagrams of steel and cast iron. For clarity, we depict them in the same figure with the tensile diagrams of these materials (Fig. 2.19). In the first quarter there are tension diagrams, and in the third – compression diagrams.
At the beginning of loading, the steel compression diagram is an inclined straight line with the same slope as during tension. Then the diagram moves into the yield area (the yield area is not as clearly expressed as during tension). Further, the curve bends slightly and does not break off, because the steel sample is not destroyed, but only flattened. The modulus of elasticity of steel E under compression and tension is the same. The yield strength σ t + = σ t - is also the same. It is impossible to obtain compressive strength, just as it is impossible to obtain plasticity characteristics.
The tension and compression diagrams of cast iron are similar in shape: they bend from the very beginning and break off when the maximum load is reached. However, cast iron works better in compression than in tension (σ inch - = 5 σ inch +). Tensile strength σ pch is the only mechanical characteristic of cast iron obtained during compression testing.
The friction that occurs during testing between the machine plates and the ends of the sample has a significant impact on the test results and the nature of destruction. The cylindrical steel sample takes on a barrel shape (Fig. 2.20a), cracks appear in the cast iron cube at an angle of 45 0 to the direction of the load. If we exclude the influence of friction by lubricating the ends of the sample with paraffin, cracks will appear in the direction of the load and the greatest force will be less (Fig. 2.20, b and c). Most brittle materials (concrete, stone) fail under compression in the same way as cast iron and have a similar compression diagram.
It is of interest to test wood - anisotropic, i.e. having different strength depending on the direction of the force in relation to the direction of the fibers of the material. More and more widely used fiberglass plastics are also anisotropic. When compressed along the fibers, wood is much stronger than when compressed across the fibers (curves 1 and 2 in Fig. 2.21). Curve 1 is similar to the compression curves of brittle materials. Destruction occurs due to the displacement of one part of the cube relative to the other (Fig. 2.20, d). When compressed across the fibers, the wood does not collapse, but is pressed (Fig. 2.20e).
When testing a steel sample for tension, we discovered a change in the mechanical properties as a result of stretching until noticeable residual deformations appeared - cold hardening. Let's see how the sample behaves after hardening during a compression test. In Fig. 2.19 the diagram is shown with a dotted line. Compression follows the NC 2 L 2 curve, which is located above the compression diagram of the sample that was not subjected to work hardening OC 1 L 1 , and almost parallel to the latter. After hardening by tension, the limits of proportionality and compressive yield decrease. This phenomenon is called the Bauschinger effect, named after the scientist who first described it.
2.6.3. Hardness determination
A very common mechanical and technological test is the determination of hardness. This is due to the speed and simplicity of such tests and the value of the information obtained: hardness characterizes the state of the surface of a part before and after technological processing (hardening, nitriding, etc.), from which one can indirectly judge the magnitude of the tensile strength.
Hardness of the material called the ability to resist the mechanical penetration of another, more solid. The quantities characterizing hardness are called hardness numbers. Definable different methods, they are different in size and dimension and are always accompanied by an indication of the method of their determination.
The most common method is the Brinell method. The test consists of pressing a hardened steel ball of diameter D into the sample (Fig. 2.22a). The ball is held for some time under load P, as a result of which an imprint (hole) of diameter d remains on the surface. The ratio of the load in kN to the surface area of the print in cm 2 is called the Brinell hardness number
. (2.30)
To determine the Brinell hardness number, special testing instruments are used; the diameter of the indentation is measured with a portable microscope. Usually HB is not calculated using formula (2.30), but is found from tables.
Using the hardness number HB, it is possible to obtain an approximate value of the tensile strength of some metals without destroying the sample, because there is a linear relationship between σ inch and HB: σ inch = k ∙ HB (for low-carbon steel k = 0.36, for high-strength steel k = 0.33, for cast iron k = 0.15, for aluminum alloys k = 0.38, for titanium alloys k = 0.3).
A very convenient and widespread method for determining hardness according to Rockwell. In this method, a diamond cone with an apex angle of 120 degrees and a radius of curvature of 0.2 mm, or a steel ball with a diameter of 1.5875 mm (1/16 inch) is used as an indenter pressed into the sample. The test takes place according to the scheme shown in Fig. 2.22, b. First, the cone is pressed in with a preliminary load P0 = 100 N, which is not removed until the end of the test. Under this load, the cone is immersed to a depth h0. Then the full load P = P 0 + P 1 is applied to the cone (two options: A – P 1 = 500 N and C – P 1 = 1400 N), and the indentation depth increases. After removing the main load P 1, the depth h 1 remains. The indentation depth obtained due to the main load P 1, equal to h = h 1 – h 0, characterizes the Rockwell hardness. The hardness number is determined by the formula
, (2.31)
where 0.002 is the scale division value of the hardness tester indicator.
There are other methods for determining hardness (Vickers, Shore, microhardness), which are not discussed here.
To assess the strength of structural elements, the concepts of working (design) stresses, limiting stresses, permissible stresses and safety margins are introduced. They are calculated according to the dependencies presented in clauses 4.2, 4.3.
Operating (calculated) voltages And characterize the stressed state of structural elements under the action of operational load.
Ultimate stress lim And lim characterize the mechanical properties of the material and are dangerous for the structural element in terms of its strength.
Allowable stresses [ ] And [ ] are safe and ensure the strength of the structural element under given operating conditions.
Margin of safety n establishes the ratio of maximum and permissible stresses, taking into account the negative impact on the strength of various unaccounted factors.
For safe operation of machine parts, it is necessary that maximum voltages, arising in loaded sections, did not exceed the permissible value for a given material:
; 
,
Where 
And 
– the highest stresses (normal and tangential ) in the dangerous section; 
And 
– permissible values of these voltages.
For complex resistance, equivalent voltages are determined 
in a dangerous section. The strength condition has the form
.
Permissible stresses are determined depending on the maximum stresses
lim And
lim obtained during testing of materials: under static loads - tensile strength 
And τ
IN for brittle materials, yield strength 
And τ
T for plastic materials; under cyclic loads – endurance limit 
And τ
r :
; 
.
Safety factor 
appointed based on experience in the design and operation of similar structures.
For machine parts and mechanisms operating under cyclic loads and having a limited service life, the calculation of permissible stresses is carried out according to the dependencies:
; 
,
Where 
– durability coefficient, taking into account a given service life.
Calculate the durability coefficient according to the dependence
,
Where 
– basic number of test cycles for a given material and type of deformation; 
– the number of loading cycles of the part corresponding to the specified service life; m
– indicator of the degree of endurance curve.
When designing structural elements, two methods of strength calculations are used:
design calculation based on permissible stresses to determine the main dimensions of the structure;
verification calculation to assess the performance of an existing structure.
5.5. Calculation examples
5.5.1. Calculation of stepped bars for static strength
R
= 160 MPa and 
= 100 MPa.
For each of the presented schemes we define:
1. Type of deformation:
cx. 1 – stretching; cx. 2 – torsion; cx. 3 – pure bend.
2. Internal force factor:
cx. 1 – normal strength
N = 2F = 2800 = 1600 H;
cx. 2 – torque M X = T = 2Fh = 280010 = 16000 N mm;
cx. 3 – bending moment M = 2Fh = 280010 = 16000 N mm.
3. Type of stresses and their magnitude in sections A and B:
cx. 1 – normal 
:
MPa;
MPa;
cx. 2 – tangents 
:
MPa;
MPa;
cx. 3 – normal 
:
MPa;
MPa.
4. Which of the stress diagrams corresponds to each loading scheme:
cx. 1 – ep. 3; cx. 2 – ep. 2; cx. 3 – ep. 1.
5. Fulfillment of the strength condition:
cx. 1 – condition is met: 
MPa 
MPa;
cx. 2 – condition is not met: 
MPa 
MPa;
cx. 3 – the condition is not met: 
MPa 
MPa.
6. Minimum permissible diameter ensuring the fulfillment of strength conditions:
cx. 2: 
mm;
cx. 3: 
mm.
7. Maximum permissible forceFfrom the strength condition:
cx. 2: 
N;
cx. 3: 
N.
The online calculator determines the estimated permissible stresses σ depending on the design temperature for various brands materials of the following types: carbon steel, chromium steel, austenitic steel, austenitic-ferritic steel, aluminum and its alloys, copper and its alloys, titanium and its alloys according to GOST-52857.1-2007.
Help for website development of the project
Dear Site Visitor.
If you were unable to find what you were looking for, be sure to write about it in the comments, what is currently missing on the site. This will help us understand in which direction we need to move further, and other visitors will soon be able to receive the necessary material.
If the site turned out to be useful to you, donate the site to the project only 2 ₽ and we will know that we are moving in the right direction.
Thank you for stopping by!
I. Calculation method:
Allowable stresses were determined according to GOST-52857.1-2007.
for carbon and low alloy steels
St3, 09G2S, 16GS, 20, 20K, 10, 10G2, 09G2, 17GS, 17G1S, 10G2S1:- At design temperatures below 20°C, the permissible stresses are taken to be the same as at 20°C, provided acceptable use material at a given temperature.
- For steel grade 20 at R e/20
- For steel grade 10G2 at R р0.2/20
- For steel grades 09G2S, 16GS, strength classes 265 and 296 according to GOST 19281, the permissible stresses, regardless of the sheet thickness, are determined for thicknesses over 32 mm.
- The permissible stresses located below the horizontal line are valid for a service life of no more than 10 5 hours. For a design service life of up to 2 * 10 5 hours, the permissible stress located below the horizontal line is multiplied by the coefficient: for carbon steel by 0.8; for manganese steel by 0.85 at a temperature< 450 °С и на 0,8 при температуре от 450 °С до 500 °С включительно.
for heat-resistant chromium steels
12XM, 12MX, 15XM, 15X5M, 15X5M-U:- At design temperatures below 20 °C, the permissible stresses are taken to be the same as at 20 °C, subject to the permissible use of the material at a given temperature.
- For intermediate design wall temperatures, the permissible stress is determined by linear interpolation with rounding the results down to 0.5 MPa.
- The permissible stresses located below the horizontal line are valid for a service life of 10 5 hours. For a design service life of up to 2 * 10 5 hours, the permissible stress located below the horizontal line is multiplied by a factor of 0.85.
for heat-resistant, heat-resistant and corrosion-resistant austenitic steels
03X21H21M4GB, 03X18H11, 03X17H14M3, 08X18H10T, 08X18H12T, 08X17H13M2T, 08X17H15M3T, 12X18H10T, 12X18H12T, 10X17H13M2T, 10X 17H13M3T, 10X14G14H4:- For intermediate design wall temperatures, the permissible stress is determined by interpolation of two nearest values indicated in the table, with the results rounded down to 0.5 MPa towards a lower value.
- For forgings made of steel grades 12Х18Н10Т, 10Х17Н13M2T, 10Х17Н13М3Т, the permissible stresses at temperatures up to 550 °C are multiplied by 0.83.
- For long rolled steel grades 12Х18Н10Т, 10Х17Н13M2T, 10Х17Н13М3Т, permissible stresses at temperatures up to 550 °C are multiplied by the ratio (R* p0.2/20) / 240.
(R* p0.2/20 - the yield strength of the rolled steel material is determined according to GOST 5949). - For forgings and long products made of steel grade 08X18H10T, the permissible stresses at temperatures up to 550 °C are multiplied by 0.95.
- For forgings made of steel grade 03X17H14M3, the permissible stresses are multiplied by 0.9.
- For forgings made of steel grade 03X18H11, the permissible stresses are multiplied by 0.9; for long products made of steel grade 03X18H11, the permissible stresses are multiplied by 0.8.
- For pipes made of steel grade 03Х21Н21М4ГБ (ZI-35), the permissible stresses are multiplied by 0.88.
- For forgings made of steel grade 03Х21Н21М4ГБ (ZI-35), the permissible stresses are multiplied by the ratio (R* p0.2/20) / 250.
(R* p0.2/20 is the yield strength of the forging material, determined according to GOST 25054). - The permissible stresses located below the horizontal line are valid for a service life of no more than 10 5 hours.
For a design service life of up to 2*10 5 hours, the permissible voltage located below the horizontal line is multiplied by a factor of 0.9 at temperature< 600 °С и на коэффициент 0,8 при температуре от 600 °С до 700 °С включительно.
for heat-resistant, heat-resistant and corrosion-resistant steels of austenitic and austenitic-ferritic class
08Х18Г8Н2Т (KO-3), 07Х13AG20(ChS-46), 02Х8Н22С6(EP-794), 15Х18Н12С4ТУ (EI-654), 06ХН28МДТ, 03ХН28МДТ, 08Х22Н6Т, 08Х21Н6М2Т:- At design temperatures below 20 °C, the permissible stresses are taken to be the same as at 20 °C, subject to the permissible use of the material at a given temperature.
- For intermediate design wall temperatures, the permissible stress is determined by interpolating the two closest values indicated in this table, rounding down to the nearest 0.5 MPa.
for aluminum and its alloys
A85M, A8M, ADM, AD0M, AD1M, AMtsSM, AM-2M, AM-3M, AM-5M, AM-6M:- Allowable stresses are given for aluminum and its alloys in the annealed state.
- The permissible stresses are given for the thickness of sheets and plates of aluminum grades A85M, A8M no more than 30 mm, other grades - no more than 60 mm.
for copper and its alloys
M2, M3, M3r, L63, LS59-1, LO62-1, LZhMts 59-1-1:- Allowable stresses are given for copper and its alloys in the annealed state.
- Allowable stresses are given for sheet thicknesses from 3 to 10 mm.
- For intermediate values of the calculated wall temperatures, the permissible stresses are determined by linear interpolation with rounding the results to 0.1 MPa towards the lower value.
for titanium and its alloys
VT1-0, OT4-0, AT3, VT1-00:- At design temperatures below 20 °C, the permissible stresses are taken to be the same as at 20 °C, subject to the permissibility of using the material at a given temperature.
- For forgings and rods, the permissible stresses are multiplied by 0.8.
II. Definitions and notations:
R e/20 - minimum value of the yield strength at a temperature of 20 °C, MPa; R р0.2/20 - the minimum value of the conditional yield strength at a permanent elongation of 0.2% at a temperature of 20 °C, MPa. permissible
tension - the highest stresses that can be allowed in a structure, subject to its safe, reliable and durable operation. The value of the permissible stress is established by dividing the tensile strength, yield strength, etc. by a value greater than one, called the safety factor. calculated
temperature - the temperature of the wall of the equipment or pipeline, equal to the maximum arithmetic mean temperature value at its outer and internal surfaces in one section at normal conditions operation (for parts of nuclear reactor vessels, the design temperature is determined taking into account internal heat release as the average integral value of the temperature distribution over the thickness of the vessel wall (PNAE G-7-002-86, clause 2.2; PNAE G-7-008-89, appendix 1) .
Design temperature
- ,Clause 5.1. The design temperature is used to determine the physical and mechanical characteristics of the material and permissible stresses, as well as when calculating strength taking into account temperature effects.
- ,Clause 5.2. The design temperature is determined on the basis of thermal calculations or test results, or operating experience of similar vessels.
- The highest wall temperature is taken as the design temperature of the wall of the vessel or apparatus. At temperatures below 20 °C, a temperature of 20 °C is taken as the design temperature when determining permissible stresses.
- ,section 5.3. If it is impossible to carry out thermal calculations or measurements, and if during operation the wall temperature rises to the temperature of the medium in contact with the wall, then the highest temperature of the medium, but not lower than 20 °C, should be taken as the design temperature.
- When heating with an open flame, exhaust gases or electric heaters, the design temperature is taken equal to the ambient temperature increased by 20 °C for closed heating and by 50 °C for direct heating, unless more accurate data are available.
- ,section 5.4. If the vessel or apparatus is operated under several different loading conditions or different elements The devices operate under different conditions, for each mode you can determine your own design temperature (GOST-52857.1-2007, clause 5).
III. Note:
Source data block highlighted yellow , intermediate calculation block allocated blue , the solution block is highlighted in green.
