GOST 25.506-85

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  ГОСТ 25.506-85

GOST 25.506−85 design and testing for durability. Methods of mechanical testing of metals. The determination of crack resistance characteristics (fracture toughness) under static loading

GOST 25.506−85

Group B09

INTERSTATE STANDARD

Calculations and strength tests

METHODS OF MECHANICAL TESTING OF METALS

The determination of crack resistance characteristics (fracture toughness) under static loading

Design, calculation and strength testing. Methods of mechanical testing of metals. Determination of fracture toughness characteristics under the static loading

ISS 77.040.10
AXTU 0809

Date of introduction 1986−01−01

Resolution of the USSR State Committee on standards dated March 27, 1985, 902 N date of introduction is established 01.01.86

Limitation of actions taken by Protocol No. 5−94 of the Interstate Council for standardization, Metrology and certification (ICS 11−12−94)

This standard specifies mechanical tests for determining the characteristics of crack resistance of metals under static short-term loading on the samples with a minimum thickness of 1 mm at temperatures from minus 269 °C to plus 600 °C.

1. GENERAL PROVISIONS

1.1. Designations and units of quantities used in this standard are listed in Appendix 1.

Note. Explanation of symbols is given in Appendix 2.

1.2. To determine the characteristics of crack resistance of test with recording of the diagram «load-displacement» («») or «load-deflection» («») samples with pre-applied fatigue crack.

1.3. According to the results of the tests determine the following main characteristics of fracture toughness:

power is the critical stress intensity factors (or ): , , , ;

deformation — disclosure at the crack tip ;

energy — the critical value of the integral Il

and .

1.4. The fracture toughness of metals is evaluated by one or more of force, deformation and energy quantities , , , , , .

Under the conditions of correctness of determination of crack resistance characteristics (section 5.1.3.2; 5.1.5.1 and 5.1.6), the main is the value .

In case of default of the conditions of correctness of the quantities , , the fracture toughness of metals is evaluated by the values , , .

Prim

acania:

1. To determine the fracture toughness of metals in a wide range of lengths of cracks are allowed to use the limit of fracture toughness (Appendix 3).

2. Methods for constructing the temperature dependence of fracture toughness and the critical temperature for carbon and low alloy steels described in Annex 4.

1.5. Determined by the characteristics of fracture toughness (along with other characteristics of the mechanical properties) can be used for:

comparison of different variants of chemical composition, technological processes of manufacturing, processing and quality control of metals and alloys;

matching materials in the rationale for their selection for machines and structures;

strength calculations of load-bearing elements of structures with regard to their defects, geometrical shapes and operating conditions;

analysis of the causes of accidents and destruction of structures.

1.6. For metals, intended for use in machines and structures with desired operating conditions, can be applied to test methods, specimen types and characteristics of fracture toughness of metals in accordance with industry normative technical documents.

2. THE SAMPLES AND THEIR FABRICATION

2.1. To determine the characteristics of fracture toughness used the following samples: type 1 — rectangular with a flat Central crack test, for axial tension (Fig.1); type 2 — cylindrical with a circular fracture test axial tension (Fig.2); type 3 — rectangular compact specimen with edge crack test eccentric tensile (Fig.3); type 4 is a flat rectangular specimen with edge crack test three-point bending (Fig.4).

Type 1

 — the distance between the parts serving for attachment to the gripper;

; ;

; ;

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Type 2

 — the distance between the parts serving for attachment to the gripper;

; ;

mm

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Type 3

; ; ; ;

; ; ;

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Type 4

 — distance between supports

; ; ;

; ;

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2.2. Aspect ratio and loading pattern of the samples shown in hell.1−4. In this case we recommend the following sample sizes:

type 1 width of not less than 50 mm;

type 2 diameter not less than 12 mm;

type 3 thickness not less than 20 mm;

type 4 thickness not less than 10 mm.

In the samples of types 1 and 2, the shape and size of the parts, securing and loading, determined after selecting the design of the grips. The size is prescribed depending on the method of manufacture of the notch and mounting the sample so that it is not destroyed in the capture.

Notes:

1. For samples of types 1, 3, 4 the roughness of the side surface near the top of the incision and the source of a fatigue crack should correspond to the 8th grade.

2. Recommendations for the selection of samples is given in Appendix 5.

2.3. Initiating the incision in the sample of type 2 shown in hell.2, and the rest to hell.5. The orientation of the incision in the case of anisotropy of mechanical properties should be the same for all samples during these tests.

For samples of type 1 is used incisions of options 1, 2, 3 (Fig.5), for samples of type 3 and 4 variants 1and 2.

The incision is manufactured using a special milling cutters (see the devil.5, options 1and 2) or grinding wheel (variant 2), propilivanie from the center hole (option 2) or the electric-spark method (option 3). In some cases, combinations of different methods. Initiating the incision for sample type 2 are made on a lathe with the subsequent polishing.

Note. To reduce the load and time required for crack nucleation, it is possible to apply the laser, electron beam and other treatments the top of the incision, provided that the area of the broken condition of the original material at the apex of the notch is less than the length of the generated source of a fatigue crack.

mm

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2.4. When cutting and production of samples is necessary to ensure minimal work hardening, residual stresses, and changes in the structure and phase composition in the fracture zone of the sample. The final machining of the samples and the application of the initial fatigue crack is carried out after heat treatment of samples.

2.5. Fatigue crack is applied so that the contour of the incision was between straight lines intersecting at an angle 220° — 30° at the crack tip (Fig.5), and the difference was not less than 1.5 mm.

2.6. Fatigue cracks in flat specimens of types 1, 3 and 4 (Fig.1, 3, 4) is applied with variable tension with cycle asymmetry factor , and in samples of type 2 — with a circular bending . In this case, record the minimum and maximum effort cycle and number of cycles. The nominal voltage at the maximum stress of the cycle (must be greater than 0.5 (determined at the temperature at which cause fatigue cracks), and the recommended number of load cycles applied at fatigue crack is at least 5·10.

Notes:

1. In samples of type 4 may be applied of fatigue cracks under alternating console bending with observance of the requirements of this paragraph.

2. When applied to fatigue cracks on samples intended for testing to determine , , and , the maximum stress intensity factor cycle , designed to cut how to crack length , shall not exceed 0.75 , where is the expected value , and the final part of crack length less than 1.5 mm not to exceed of 0.6 . If the crack is applied at a temperature , and test the sample at the temperature , should not exceed 0.6 . where the values with index (1) refer to the temperature , and index (2) (see

Annex 6).

2.7. Deviation of the length caused fatigue cracks at each of the side surfaces of flat samples of a given length must not exceed 2% at mm and 0.5 mm at mm.

The deflection angle of the plane of the fatigue crack from the plane of the incision at all samples should not exceed 10°.

2.8. Recommendations for the design of devices for securing and loading during application of the fatigue cracks is given in Appendix 6.

3. TEST EQUIPMENT

3.1. To determine the characteristics of crack resistance of used machines with mechanical, hydraulic or electrohydraulic drive, the metrological parameters of which correspond to GOST 28840−90.

3.2. The required maximum force of the testing machine is calculated by the formula:

for samples of type 1

;

for samples of type 2

;

for samples of type 3

;

for samples of type 4

3.3. To measure displacements or deflections used double-cantilever transducers strain gauge type. The gripper part of the sensors, their installation on the samples and the dimensions of the sensors in the zone of their attachment shown in hell.6. The calculation of the remaining size of the sensor and connection diagram of strain gauges to provide temperature compensation are given in Appendix 7.

1 — sample; 2 -applied to the reference prism; 3 — displacement sensor; 4 — plane incision; 5 — prismatic protrusions

Damn.6

The difference between direct and reverse, and the non-linearity in the range of the stroke sensor and the measurement error of the sensor should not exceed 2% of the working range of the sensor. The sensor calibration is carried out with accuracy up to ±0,01 mm.

3.3.1. The installation of displacement transducers on the samples of the types 1−4 is carried out with the help of invoice reference prisms (Fig.6).

The samples of type 3 and 4 is possible to install the sensors on the prismatic projections made at the ends of the samples (Fig.6).

3.3.1.1. Of the axis holes for the installation of overhead supporting prisms or prismatic protrusions should be located at the same distance from the plane of the cut, with error not more than ±0.2 mm.

3.3.1.2. The distance between the axes of the holes (Fig.6) for mounting the overhead of the reference prism should be for samples:

type 1 — no more than 2;

type 2 — no more ;

types 3 and 4 — not more than 2.

Note. The samples of a type 2 allowed for the production of flats to a depth of not more than 0.15.

3.3.1.3. The distance between the edges of the prismatic projections of the samples of types 3 and 4 should be no more than 2.

3.3.2. Double-cantilever sensor deflection for specimens of type 4 is installed on the supporting prisms, one of which is rigidly mounted to the loading the knife and the other on the traverse of the testing machine.

3.4. Sensors of displacements or deflections , as well as devices for recording charts «» and «» should provide:

the tangent of the slope of the linear section of the chart «» and «» to the axis or in the range of 1−3;

the scale of the chart axis and not less than 25:1.

Note. When testing the scale along the axis increase by not less than two times compared to the above.

3.5. The temperature of the sample is measured thermoelectric sensors (thermocouples) welded to the specimen near the top of the initial fatigue crack.

Note. Allowed any other ways of mounting a thermocouple under the condition of ensuring reliable contact of the thermocouple with the sample surface. The sample temperature is measured by instruments of accuracy class not less than 0.5.

3.6. Fixture for mounting and loading samples (see Appendix 6) must provide an implementation for a given loading pattern, in particular, accurate centering of the specimen and to avoid its destruction in the grips.

When test specimens of type 4 nominal diameters of rollers and the Central load of the knife should be equal .

4. PREPARATION AND TESTING

4.1. The testing machine should be certified in accordance with GOST 24555−81*, this should be made requirements of sec. 3.
________________
* On the territory of the Russian Federation GOST R 8.568−97.

4.2. The dimensions of the samples and and the thickness of the invoices supporting the prisms before testing is measured with an accuracy higher than 0.1 mm.

4.3. The speed of loading samples, set the speed of the movable gripper in the range from 0.02 to 0.2 mm/s.

When the test to determine , , and loading rate should match the rate of growth of stress intensity factor in the range of 0.5−1.5 MPa·m/s on the linear part of the diagrams «» or «».

Note. If the NTD for steel special instructions testing is allowed at other loading rates. In these cases, the loading rate must be specified in the test Protocol.

4.4. When tested at temperatures different from room must comply with the test requirements established by GOST 22706−77, 11150−84 GOST, GOST 9651−84. During the test, monitor the temperature of the sample. The error of the observance of the set temperature of the sample in cross section with a crack should not exceed ±2°C at temperatures from minus 269 °C to 20 °C ±5°C at temperatures from 20 °C to 600 °C.

Note. Temperature range of testing fracture toughness tests should not include temperatures at which structural transformations occur and the deformations of creep.

4.5. In determining the characteristics , , and testing of samples and types 1−4 is carried out to failure with the registration charts «».

Typical chart types «(or») given on features.7.

Damn.7

The chart type I is characterized by the location of the vertex (point ) to the left of straight , inclined to the axis (or ) angle , whose tangent is 5% less than the tangent of the angle of inclination of the tangent to the initial linear portion of the graph. The destruction of the sample occurs at the point of the chart.

Diagram of type II is characterized by the local maximum load (point ), located to the left of straight . The destruction of the sample occurs at the point of the chart to the left of straight , inclined to the axis (or ) angle , whose tangent is 30% less than the tangent of the angle tangent (angle ).

Diagram type III is characterized by the presence of maximum load (point ) corresponding to failure of the specimen, lying to the left of straight .

Figure IV is a curve with the maximum load at the point . The destruction of the sample occurs at the point charts located to the right of point .

Note. Direct convenient to build in the following way: from the point down perpendicular to the axis (or ) and lay the cut . Through the point and draw . A straight carried out in the same way, but the amount to

have to be equal to 0.3 .

4.5.1. After the destruction of the samples is calculated, rounded to the nearest 0.1 mm, the length of the initial fatigue crack for plane samples of types 1, 3 and 4 or for samples of type 2 diameter of the sample .

4.5.1.1. Length in flat samples of type 1, 3, and 4 calculated with rounding to 0.1 mm as the arithmetic mean measurement (with an error of no more than 0.1 mm) in at least three points on the contour of fatigue cracks located at equal intervals on the thickness of the sample, excluding the lateral surfaces (Fig.8).

The scheme breaks

 — flat samples of types 1, 3 and 4;  — a cylindrical sample of type 2;
1 — border of the incision; 2 — contour of fatigue cracks; 3 — static $

Damn.8

If any two of these measurement results differ by more than 10%, the sample is discarded.

4.5.1.2. If the pattern type 1 in the value of the average length of the fatigue crack on each side of the centre of the sample differs by more than 10%, the sample is discarded.

4.5.1.3. In sample type 2 measure the distance between the centers of the cross-section and static doloma sample, and the diameters of the contour of fatigue cracks in two mutually perpendicular directions , and calculate their average value (Fig.8). If the magnitude and (or) value exceeds 0.08, the sample is discarded

.

4.5.2. All measured and calculated values are entered in the test report (Annex 8).

4.6. Values of the crack opening is determined by testing samples of the types 1−4 before the destruction of the recording charts «».

4.6.1. Measurement and calculation of the length of the initial fatigue cracks in samples of types 1, 3 and 4 and sizes and in samples of type 2 is carried out in accordance with clause 4.5.1.

4.6.2. All obtained during the test quantities (or ), together with diagrams «» are entered in the test report.

4.7. The critical values of the integral determined on samples of type 3 and 4 record charts «» for samples of type 3 «» type 4 samples.

4.7.1. The first sample brought to destruction. According to the obtained when testing the chart «» or «» analyze what distinctive type of charts it applies (see section 4.5).

4.7.2. In case of receipt at test charts type I (Fig.7) the fracture of the sample is carried out the calculation of the length of the initial fatigue cracks in accordance with paragraph 4.5.1.1.

Obtaining this type of chart check at least three identical specimens in the same test conditions. The values obtained for each sample, together with diagrams «» or «» are entered in the test report (Annex 8).

4.7.3. If the testing of the first sample according to claim 4.7.1 was resulting graph «» or «» II, III, or type IV, it is necessary to conduct additional tests on the same samples in the same test conditions.

4.7.4. The following sample statically loaded to a pre-selected displacement or deflection of not less than 0.9or 0.9to graphs of types III and IV and 0.9or 0.9to graphs of type II (Fig.9). The values and assign to the diagrams obtained by testing according to claim 4.7.1. Then the sample is unloaded, lock the circuit statically grown crack and break.

Note. The ways of fixing the static contour of the undergrowth of cracks shown in Annex 9.

Circuit loading and unloading of samples under test according to claim 4.7.4

diagram of type II;  — type III diagram; diagram of type IV

Notes:

1. The dotted line shows a chart obtained by testing the first sample according to claim 4.7.1.

2. on — point unloading of the samples.

Damn.9

4.7.5. The length of the initial fatigue crack is calculated in accordance with paragraph 4.5.1.1.

4.7.6. Static undergrowth cracks is calculated with rounding to 0.1 mm as the arithmetic mean measurement no less than five points on the contour are statically grown cracks located at equal intervals on the thickness of the sample, excluding the lateral surfaces (Fig.10). Each measurement should be performed with an accuracy of 0.1 mm.

Measurements of the fracture of flat samples with a static young crack

1 — border of the incision; 2 — contour of fatigue cracks; 3 — the area of statically grown cracks; 4 — contour statically grown cracks; 5 — static $

Damn.10

4.7.7. In the case where the static undergrowth cracked sample, tested according to claim 4.7.4, turned out to be less than 0.3 mm for samples with thickness 30 mm max. or for samples with thickness more than 30 mm, the values of and obtained for PP.4.7.5 and 4.7.6, together with diagrams «"or „“ is entered into the test report

.

4.7.8. In the case where the static undergrowth cracked sample, tested according to claim 4.7.4, was greater than 0.3 mm for samples with a thickness of not more than 30 mm and for samples more than 30 mm, it is necessary to test additionally at least four identical samples in the same test conditions. The length of the source of the fatigue cracks measured on the lateral surfaces of the samples should not differ by more than 10%.

4.7.8.1. Each sample is loaded to a pre-selected displacement or deflection , the smaller is 0.9, or 0.9to graphs of types III and IV and 0.9or 0.9 to graphs of type II. The values , , or appoint diagrams obtained by testing according to claim 4.7.1. Then the sample is unloaded, lock the static undergrowth crack and break.

Notably,

niya:

1. Circuit loading and unloading of samples are given in hell.11.

2. The ways of fixing the static contour of the undergrowth of cracks is given in Appendix 9.

Circuit loading and unloading of the samples when tested according to item 4.7.8.1

diagram of type II;  — diagram type III  — type IV figure

Notes:

1. The dotted line shows a chart obtained by testing the first sample according to claim 4.7.1.

2. on — point unloading of the samples.

Damn.11

4.7.8.2. The length of the initial fatigue crack is calculated according to clause 4.5.1.1.

4.7.8.3. Static undergrowth cracks calculated in accordance with paragraph 4.7.6.

4.7.8.4. The obtained values of , , , , , , , , , for each sample, together with diagrams „“ or „“ are entered in the Protocol test

Tania.

4.7.9. In the case when when testing for I. 4.7.4 sample was destroyed before reaching the selected values or the chart „“ or „“ was a type IV, you must additionally experience at least five identical samples in the same test conditions. The length of the source of the fatigue cracks measured on the lateral surfaces of the samples should not differ by more than 10%.

4.7.9.1. Each sample is loaded to a pre-selected value or . Then the sample is unloaded, lock the static undergrowth crack and break.

Notes:

1. It is recommended that the first sample loading before the start of the recession burden on the charts,"» or «». Each of the successive samples sequentially loaded to a smaller magnitude of displacement or deflection , as shown in hell.12, and then the sample is unloaded.

2. Methods of fixing a static crack of undergrowth indicated in Annex 9.

Loading and unloading of samples under test according to claim 4.7.9.1

On — point unloading of the sample

Damn.12

4.7.9.2. The length of the initial fatigue crack is calculated according to clause 4.5.1.1.

4.7.9.3. Static undergrowth cracks is calculated according to claim 4.7.6.

4.7.9.4. The values obtained for each sample, together with diagrams «» or «» are entered in the test report.

4.7.10. In the case when when testing for I. 4.7.4 sample was destroyed before reaching the selected values or the chart «» or «» turned out II or type III, carry out the calculation of the length of the initial fatigue cracks according to claim 4.5.1.1.

4.7.10.1. The obtained values together with diagrams «» or «» are entered in the test report.

4.8. The thickness in the zone of maximum constriction of the destroyed flat samples of types 1, 3 and 4 (Fig.8) is determined as the arithmetic mean of the two measured thickness values at the top of the crack on both halves of the destroyed sample. The samples of a type 1 measurements were carried out at two vertices of the crack.

4.9. All measured and calculated during the test of the size and engine chart «» or «» are entered in the test report (Annex 8).

4.10. Requirements on safety when carrying out tests according to GOST 12.2.003−91.