GOST R 8.748-2011

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  ГОСТ Р 8.748-2011

GOST R 8.748−2011 (ISO 14577−1:2002) the State system of ensuring unity of measurements (GSI). Metals and alloys. Hardness and other characteristics of materials at instrumental indentation test. Part 1. Test method

GOST R 8.748−2011
(ISO 14577−1:2002)
Group T62.2

NATIONAL STANDARD OF THE RUSSIAN FEDERATION

State system for ensuring the uniformity of measurements

METALS AND ALLOYS. HARDNESS AND OTHER CHARACTERISTICS OF MATERIALS AT INSTRUMENTAL INDENTATION TEST

Part 1

Test method

State system for ensuring the uniformity of measurements. Metallic materials. Instrumented indentation test for hardness and materials parameters. Part 1. Test method

OKS 17.020
AXTU 0008

Date of introduction 2013−05−01

Preface

The objectives and principles of standardization in the Russian Federation established by the Federal law of 27 December 2002 N 184-FZ «On technical regulation», and rules for the application of national standards of the Russian Federation — GOST R 1.0−2004 «Standardization in the Russian Federation. The main provisions"
________________
* On the territory of the Russian Federation the document is not valid. Valid GOST R 1.0−2012. — Note the manufacturer’s database.
Data on standard

1 PREPARED by all-Russia research Institute of physicotechnical and radio engineering measurements of Federal Agency on technical regulation and Metrology on the basis of their own authentic translation into the Russian language of the international standard indicated in paragraph 4

2 MADE by the Department of Metrology Federal Agency for technical regulation and Metrology

3 APPROVED AND put INTO EFFECT by the Federal Agency for technical regulation and Metrology of December 13, 2011 N 1071-St

4 this standard is modified in relation to the international standard ISO 14577−1:2002* «the metal Materials. The definition of hardness and other materials parameters tool by indentation. Part 1. The method of definition» (ISO 141577−1:2002 «Metallic materials — Instrumented indentation test for hardness and materials parameters — Part 1: Test method»). Additional words (phrase, indicators, their values) are included in the text of the standard to reflect the needs of the economy of the Russian Federation and/or the peculiarities of the Russian national standardization, which are underlined, solid horizontal line**.
** In the original paper the number of the standard in the section «Bibliography», underlined the solid horizontal line in the electronic version of a document is marked with the symbol «#". — Note the manufacturer’s database.

The name of this standard changed with respect to names specified international standard for compliance with GOST R 1.5−2004* (subsection 3.5)
________________
* On the territory of the Russian Federation the document is not valid. Valid GOST R 1.5−2012. — Note the manufacturer’s database.

5 INTRODUCED FOR THE FIRST TIME

Information about the changes to this standard is published in the annually issued reference index «National standards», and the text changes and amendments — in monthly published information index «National standards». In case of revision (replacement) or cancellation of this standard a notification will be published in a monthly information index «National standards». Relevant information, notification and lyrics are also posted in the information system of General use — on the official website of the Federal Agency for technical regulation and Metrology on the Internet

Introduction

Under instrumental indentation refers to the process controlled by special test setting, in which there is a continuous introduction of a tip (diamond pyramid Berkovich, Vickers, carbide ball, etc.) in the test sample under the action of the smoothly increasing load, followed by its removal and registration according to movement of the tip load.

Hardness is usually defined as the material resistance to indentation of another harder material. The results obtained from the hardness test according to Rockwell, Vickers and Brinell hardness, determined after removing the test load. Therefore, the influence of elastic deformation of a material under the influence of the tip (indenter) is not taken into account.

This standard is prepared to allow the determination of hardness and other mechanical characteristics of the material by simultaneous measurements of load and displacement of the tip during indentation. Tracing a complete cycle of loading and removing test loads, one can determine the hardness values equivalent to the values measured by classical methods of hardness measurement. Also this method allows you to define additional material properties, such as its modulus of elasticity indentation hardness and elastic-plastic. These values can be calculated without optical measurement of the imprint.

The standard is designed to enable many of the characteristics by the analysis of data after the test.

1 Scope

This standard specifies the test method instrumental indentation test for hardness and other characteristics of materials for three of the ranges specified in table 1.


Table 1 — Ranges of application of the method

Macrocapon	Microlepton	Nanorange
	; µm	µm
For nanoscale mechanical deformation strongly depends on the shape of the top of the tip, and the results of calculations of the parameters of the materials significantly affected the function of the area of the contacting region of the tip used in the test installation. Therefore requires careful calibration of the instrument and the shape of the tip to achieve the unity of the playback characteristics of the materials defined on different installations.

Macro — and microgeometry different test loads and indentation depth.

Note that microdamage is characterized by the upper limit of the test load (2 N) and the lower limit of the depth of indentation (0.2 µm).

Reference materials to determine the hardness and other characteristics is given in Appendix A.

When using the tip of a pyramidal or conical shape in the contact zone there is a high concentration of mechanical stresses, resulting in possible damage, so macrodiakonia often use ball tips.

For test specimens with very high hardness and modulus of elasticity should take into account the effect of deformation of the tip on the measurement results.

Note — Instrumental method of indentation can also be used to thin metal coatings and non-metallic materials. In this case, you should take into account the features specified in the relevant standards (see also 6.3).

2 Normative references

This standard uses the regulatory references to the following standards:

GOST 9450−76 the microhardness measurements by indentation of the diamond tips

GOST 25142−82 surface Roughness. Terms and definitions

Note — When using this standard appropriate to test the effect of reference standards in the information system of General use — on the official website of the national body of the Russian Federation on standardization in the Internet or published annually by the information sign «National standards» published as on January 1 of the current year and related information published monthly indexes published in the current year. If the reference standard is replaced (changed), when using this standard should be guided by replacing (amended) standard. If the reference standard is cancelled without replacement, then the situation in which the given link applies to the extent that does not affect this link.

3 Refer

Table 2 provides the basic notation used in the standard (see also figures 1 and 2).


Table 2 — Designations

Marking	Name	Unit
	The vertex angle of the tip	°
	The radius of the spherical tip	mm
	Test load	N
	Maximum test load	N
	The depth of the indentation under the applied test load	mm
	The maximum depth of the indentation at	mm
	The point of intersection of the tangent to the curve 2 when the axis displacement (see figure 1)	mm
	The residual depth of imprint after removing the test load	mm
	Immersion depth of tip in the test sample when	mm
	The cross-sectional area of the tip at a distance from the top	mm
	The cross-sectional area of the tip at a distance from the top	mm
	The hardness Martens	-
	Elastic modulus during indentation	N/mm
	Creep during indentation	%
	Relaxation during indentation	%
	The total mechanical work of indentation test	N·m
	The work of elastic deformation during indentation	N·m
	Attitude	%
	The hardness Martens, determined by the slope of the curve of loading on chart	-
	Hardness indentation	-
Notes 1 allowed the use of multiple or fractional units. 2 1 N/mm=1 MPa.

Figure 1 — test Methods (F-h-diagram — load dependence on the depth of the indentation)

1 — curve corresponding to the increase in test load (loading); 2 — curve corresponding to the decrease in test load (unloading); 3 — the tangent to the curve 2 in

Figure 1 — test procedure (diagram — load dependence on the depth of the indentation)

Figure 2 — Scheme of the longitudinal section area indentation

1 — tip; 2 — the surface of the imprint in the test sample after complete unloading; 3 — the surface contact of test sample with the tip at the maximum indentation depth and test load

Figure 2 — Scheme of the longitudinal section area indentation

4 Main provisions

Continuous measurement of the values of load and depth of indentation allows to determine the hardness and material properties (see figures 1 and 2). You need to use the tip from a material harder than the test material having the following form:

a) a diamond tip in the form of a regular tetrahedron with the angle ° between the opposite faces at the vertex (diamond tip Vickers, see figure A. 1),

b) diamond pyramid with a triangular base (for example, the pyramid Berkovich, see figure A. 1),

c) a ball of solid alloy (especially for materials research in elastic region),

d) a spherical diamond tip.

This standard does not preclude the use of tips of different shape, however this form need to be considered when interpreting the results obtained by using these tips. You can also use other materials of the tip, such as sapphire.

Note — due To the crystalline structure of the diamond spherical tips not have a perfect spherical shape and are often polyhedra.


The measurement technique can be implemented in two ways:

— setting the load, measure the resulting displacement of the tip, and

— setting the displacement of the tip, causing it to measure a moving load.

The values of the test load and the corresponding indentation depth is fixed throughout the measurement. The result data for the applied load and the corresponding indentation depth as a function time chart (see figure 1 and Annex).

For reliable determination of the load and corresponding indentation depth, for each test cycle it is important to set the zero point of the indentation curve (see 7.3). When measuring time-dependent effects:

a) c using the method of control of test load the applied load is kept constant for a certain period of time and the change of depth of indentation is measured as a function of exposure time under load (see figures A. 3 and B. 1).

b) using the technique of controlled depth, the depth of indentation is kept constant for a certain period of time and the change in applied load is measured as a function of hold time a fixed depth of indentation (see figures A. 4 and B. 2).

The above two methods give different results in the segments (2) and (6) the curves in figure B. 1a) and B. 2b) or in figure B. 1b) and B. 2A).

5 Setup for testing

5.1 Design of the test rigs should enable the application of test loads specified and satisfy the requirements [1].

5.2 Design of test system for testing should provide the ability to measure and record the values of applied load, displacement and time for all cycle tests.

5.3 Design of test system for testing should provide the possibility of compensating for their own compliance and use of appropriate function area of the tip (see Appendix C of this standard and [1] (paragraphs 4.5 and 4.6)).

5.4 Tips used in the test installation can have forms that are specified in [1] and GOST 9450. (For more information about the diamond tips is given in Appendix D).

5.5 Setup for testing must be calibrated in the working temperature range in accordance with the instruction Manual.

The test installation should work in the temperature range specified in 7.1, and be calibrated in accordance with the requirements of [1] (пункт4.4.3)

6 the test sample

6.1 Tests shall be performed in such a region of the sample surface, which will allow you to define chart of the indentation to the specified range and required uncertainty. In the area of the probe contacts the test sample should not be fluids or lubricants, with the exception of places where it is necessary to perform tests that must be recorded in the measurement Protocol. Do not allow foreign matter (dust particles) in contact area.

The influence of surface roughness of the test sample to the uncertainty of measurement results is given in Appendix E. Finishing the surface of the sample can have a significant impact on the measurement results.

The sample surface should be perpendicular to the axis of load application.

When the calculation of uncertainty should take into account the tilt of the sample surface. Usually the deviation of the perpendicular to the specimen surface from the axis of load application is less than 1°.

6.2 Preparation of the sample surface must be performed so as to minimize any change in surface hardness, for example, associated with cold treatment.

Due to the small depth of indentation into micro — and nanoscale during the preparation of the sample surface should take special precautions. You need to use a polishing process suitable for concrete materials (e.g., electropolishing).

6.3 the Thickness of the test sample should be sufficiently large (or sufficiently small to make the depth of the indentation) so that the effect of the substrate on the measurement result is small. The thickness of the test sample should exceed the depth of the indentation at least 10 times or 3 times greater than the diameter of the zone of the indentation(see note 7.7).

When testing coatings, the coating thickness should be considered as the thickness of the test sample.

Note — These restrictions are justified empirically. The exact limits of the influence of substrate on the measurement results of the mechanical properties of the test sample depend on the geometry of the tip used, and properties of materials the test sample and the substrate.

7 Method

7.1 the test Temperatures should be recorded. Typically, measurements are performed in the range of ambient temperature from 10 °C to 35 °C.

Instability temperature has a greater effect on measurement accuracy than the temperature measurement process. Any amendment made must be reported together with the corresponding uncertainty. It is recommended to carry out measurements, in particular in nano — and microdiamond, under controlled climatic conditions: temperature range (23±5) °C and relative humidity less than 50%.

Because of the requirements of high precision depth measurement of individual tests must be performed when the temperature is stable. It means that:

— the samples must acquire ambient temperature before the test;

— the temperature measurement system should be stable (consult user manual);

— should reduce the impact of external sources that can cause temperature change during individual measurement.

To minimize temperature drift, the temperature measurement system should keep constant during the whole measurement cycle or to correct for temperature drift (see 7.5 and [1] (paragraph 4.4.3).

You should record the uncertainty of measurement results caused by temperature drift.

7.2 the Sample shall be secured to the supporting surface of the measuring unit so that its work in strict conformity with specified conditions. The sample is mounted on a support surface or secured in the holder perpendicular to the direction of indentation. The contact surface between the sample support surface or holder shall not contain any foreign substances which may reduce the clamping of the sample.

7.3 the Zero point for measurements on the curve load/depth of indentation is set for each dataset according to the measurement results. It corresponds to the first contact of the tip with the sample. The uncertainty of finding the zero point should be recorded. This uncertainty must be less than 1% of the maximum depth of indentation for the macro — and microlepton. For nanoscale it may exceed 1%, and in this case, the uncertainty value should be recorded in the measurement Protocol.

Must be recorded a sufficient number of data when approaching the tip to the sample surface and in the area of the indentation to 10% of the maximum depth below the zero point can be set with the required uncertainty. We recommend one of the following methods:

1) the Zero point is calculated by approximation according to the load from moving on the diagram, for example, a polynomial of the second degree. The selection of polynomial coefficients is performed for indentation depths from zero to depths of no more than 10% of the maximum. The calculated uncertainty of the zero point depends on the parameters of the fit of the approximating function and region approximation.

In the initial part of the indentation curve (for example, up to 5%) can effect vibration orother interference. At the beginning of the measuring tip has to be held extremely close to the sample surface, avoiding the appearance of cracks or plastic deformation of its surface.

2) the Zero point is the touch point that is determined when you first recorded the value increase or the applied load or the contact stiffness. In this coordinate touch value step change of the applied load or displacement should be small enough so that the uncertainty of the zero point was less than the required value.

Note — Typical values of the minimum steps of changing the applied load to be macrodiakonia , and for micro — and nanoscale — less than 5 microns.

7.4 In the test cycle is set or the load applied, or the depth of the indentation. The controlled parameters may vary continuously or discretely. The Protocol should contain a detailed description of all features of the test cycle, including:

a) setpoint (load or displacement of the tip, as well as discrete or continuous change of the specified parameter);

b) the maximum load (or move head);

c) loading rate (or moving speed of the nozzle);

d) the duration and position of each loading step;

e) the frequency of data recording (or number of points).

Note — typical values: time of load application and its removal — 30 C; hold time the maximum load is 30 s; the interval of the exposure time with constant load to measure thermal drift — 60 sec (contact or after removing 90% of the maximum load).

To obtain comparable measurement results, consider the time spent on the measurement.

7.5 Test load should be applied without any bumps or vibrations, as they can significantly affect the results of measurement of load and displacement when reaching the specified values. The values of load and displacement of the tip should be recorded at intervals of time set by the Protocol.

During the determination of the coordinates of the touch of the tip with a sample feed rate of the tip should be low enough that the mechanical properties of the surface has not changed under the impact.

During indentation in microcapsule the speed of indentation should not exceed 2 µm/s. Typically, the feed speed of the tip before touching the measurements in the micro — and the nanoscale is 10 nm/s 20 nm/s or less.

Note — At present, the precise limits of the permissible feed speed of the tip of macrodiagonal unknown. Users are encouraged to contribute information on speed feed to the log.

The values of the load/indentation depth/time can be compared only if identical test cycles with the same profile. The test cycle described, or in the values of loads applied, or in the values of tip displacement as a function of time. There are two main types of cycle:

a) with a constant loading rate;

b) a constant probe speed.

The speed of the withdrawals applied loads can be arbitrary, depending on how to register the data sets during the load is removed for further analysis.

For each test cycle needs to be determined the drift velocity of the measurement results. This is done for micro — and nanoscale by removing the data for a certain time interval of exposure when an embedded terminal or during removal of the load (usually from 10% to 20% of the maximum load).

In macrodipole the drift velocity of the measurement results can be obtained on the basis of temperature measurements and knowledge of the drift characteristics of the device.

The data on applied load and depth of indentation should be adjusted by using the measured drift velocity.

Endurance at maximum load you can use in order to verify the completion of the transition of deformation processes prior to the removal of the load.

7.6 During the measurements, the test installation should be protected from shocks and vibrations, air currents and temperature fluctuations which can significantly affect the measurement results.

7.7 it is Important that the measurements are not affected by the presence in the contact area of the boundaries of the sample nodules and depressions, caused by previous intentionality in the series. Any of these factors affect the geometry of the imprint on the material properties of the sample. Prints must defend from the borders of the sample at a distance of at least three of their diameters, and the minimum distance between the footprints should, at least, five times larger than the largest diameter of the print.

The diameter of the imprint is the imprint diameter of the circular shape formed by indentation of a spherical tip on the surface of the test sample. For prints Nekropol shaped indentation diameter is the diameter of the smallest circle that describes the mark. At the corners of the print cracking may occur. In this case, the diameter of the print needs to describe cracks.

Note — the Specified minimum distances are most suitable for ceramic materials and metals such as iron and its alloys. As with other materials, it is recommended to postpone the prints from one another by a distance at least ten times the diameter of the imprint.


If there are doubts about the reproducibility of the measurements, it is recommended to compare the measurement result with the results of other intentioni in the same series. If the difference is significant, it is likely that the prints were too close to each other and increase the distance between them in half.

8 Uncertainty of measurement results

A full evaluation of uncertainty of measurement results is performed in accordance with[2] and [17].

The uncertainty of measurement results is the aggregation of uncertainties from a number of sources. They can be divided into two types:

a) uncertainty components of type A are:

— the uncertainty of the zero point;

— uncertainty measure applied load and displacement of the tip (under the influence of vibrations and magnetic field changes);

— the uncertainty of the approximation curves based on the load-depth indentation on the diagram;

— the uncertainty associated with the thermal drift;

— the uncertainty of the contact area taking into account surface roughness;

— the uncertainty associated with the heterogeneity of the test sample.

b) uncertainty components of type B are:

the uncertainty caused by the applied load and displacement of the tip;

— the uncertainty caused by the flexibility of the test system for testing;

— the uncertainty caused by determining the value of the area function of the tip;

— the uncertainty caused by the drift characteristics of the test system for testing after calibration. The drift associated with the temperature deviation from the nominal setup and the time elapsed since the last calibration;

— the uncertainty caused by the tilt of the sample surface.

Note — it is Not always possible to quantify the contribution of all these values in the uncertainty. In this case, the estimate of the standard uncertainty of type A can be obtained by statistical analysis with repeated intentioned in the subject material. You should remember that if the uncertainty type is already taken into account when calculating uncertainties of type A, it is not necessary to consider the second time (see пункт4 [2]).

9 measurement Protocol

The report must contain the following information:

a) reference to this standard;

b) all information necessary for identification of the sample;

c) the material and shape of the tip, and in case of need detailed information about the area function of the tip;

d) measurement cycle (method of control and complete description of the profile of the cycle); it should include the following:

1) the specified values;

2) the speed and time of application of the force or the displacement of the tip;

3) the commencement and duration of exposure under a certain load;

4) the intervals of data registration or the number of points recorded in each part of the cycle;

e) the obtained results, the expanded uncertainty and the number of tests;

f) method used for determining the zero point;

g) any additional operations not specified in this standard or are considered optional;

h) any details that may affect the results;

i) the temperature during the tests;

j) date and time of testing;

k) methods of analysis;

l) if necessary, all coordinated for more information, including the definition of values on -chart, and detailed information about budget uncertainties.

Note — it is Recommended to specify in the Protocol of measurements the location of the fingerprint on the sample.

Annex a (mandatory). Material parameters determined by the method of instrumental indentation

Appendix A
(required)

A. 1 General part

Sets values of data (load — depth of indentation), obtained with the help of instruments you can use to calculate the number of material parameters.

A. 2 Hardness scales Martens
________________
The previous designation of the universal hardness — see [3].

A. 2.1 hardness scales Martens,

Hardness scales Martens is measured under applied test load.Number of hardness scales Martens define on the chart during the growth test load (preferably after reaching the specified test force).When measuring hardness on the scale of Martens into account plastic and elastic deformation, so that the hardness value can be calculated for all materials.

Hardness scales Martens determined for both pyramidal tips are shown in figure A. 1. It is not determined to Coppa tip or ballpoint tips.

Figure A. 1 — Shape tips to determine NM

Figure A. 1 — Shape tips to determine

When calculating hardness scales Martens the applied load is divided into the function of the surface area of the working part of the tip. The number of hardness scalesMartens represent .

a) a Diamond tip Vickers b) a Diamond tip Berkovich

, ; (A1)

, . (A. 2)

For indentation depths of less than 6 microns it is impossible to use the theoretical function (A. 2) defining the cross-sectional area of the tip, because all the tips have a certain roundness of peaks and tips with a spherical end (spherical and conical) have a deviation from sphericity. Knowing the exact function that determines the cross-sectional area of this tip is especially important for indentation depths of less than 6 microns and is suitable for all depths (see 4.2.1 and 4.6 in [1]).

For indentation depths of less than 6 microns must use a real function of the area of the tip , see Appendix E and [4].

Notes

1 To provide measurements of the hardness values, it is recommended to use test load 1 N; 2,5 N; 5 N and 10 N and their decimal multiples of units.

2 In some cases, it may be useful to maintain a given test load for longer than the configured time interval. The duration of exposure under load should be recorded with an accuracy of 0.5 s. figure A. 2 shows the scope of hardness scales Martens.

Figure A. 2 — relationship between hardness scales Martens, depth of indentation and the test load

1 — macrogamete; 2 — microlepton; 3 — nanoscale; 4 — rubber; 5 — plastic; 6 — non-ferrous metals; 7 — steel; 8 — hard alloys, ceramics

Figure A. 2 — relationship between hardness scales Martens, depth of indentation and the test load

Designation hardness scales Martens,

A. 3 Hardness scales Martens, determined by the slope of the curve of loading on the chart

A. 3.1 hardness scales Martens,

Method for determination of hardness scales Martens, calculated by the slope of the curve of loading on the chart, need not be defined «zero point» in the case of homogeneous materials.

For homogeneous materials (sizes of inhomogeneities near the surface is small relative to the indentation depth) the following equation is indeed (at least in the area between 50% -90% ) for the curve of loading on chart

. (A. 3)

The slope can be determined by linear regression of the measurement results in accordance with equation A. 3. In this case it is possible to determine the hardness by using the following modification of the method of the slope of the loading curve on the diagram

, (A. 4)

26,43 for Vickers tip
where
Of 26.44 for Berkovich tip.

A. 3.2 Marking of hardness values according to the scales Martens,

Hardness scales Martens, determined by the slope of the loading curve on the diagram, denoted as

Notes

1 the Advantage of hardness scales Martens on the slope of the curve increases the load on the chart, lies in the independence of the obtained hardness values from the uncertainty associated with finding the «zero point» and the roughness of the sample. Vibration also have little effect on the results of determining hardness . For samples with different hardness at different depths of indentation, the hardness value will be different from the values defined for formula (A. 1).

2 In contrast to the hardness of Brinell, Rockwell, and Vickers hardness includes not only the resistance to plastic deformation, but the resistance to elastic deformation.

A. 4 Hardness indentation , determined by instrumental method for indentation

A. 4.1 hardness indentation

The indentation hardness is a characteristic resistance to permanent deformation or destruction of the sample.

, (A. 5)

where is the maximum applied load;

the cross — sectional area of the contact surface between the tip and the test sample determined by the curve increases the load on the chart, and the area function of the tip (see [1] 4.5.2).

Equation (A. 5) define the hardness as the ratio of the maximum applied load divided by the cross-sectional area of the contact surface between the tip and the test sample. This definition is consistent with proposed by Meyer (see [5]).

For indentation depths of less than 6 microns it is impossible to use the theoretical function (A. 2) defining the cross-sectional area of the tip, because all the tips have a certain roundness of peaks and tips with a spherical end (spherical and conical) have a deviation from sphericity. Knowing the exact function that determines the cross-sectional area of this tip is especially important for indentation depths of less than 6 microns and is suitable for all depths (see [1] 4.2.1 and 4.6).

Note — the Function of the area of the tip is usually expressed as a mathematical function based on the cross sectional area of the tip of the distance to its vertices. If the function square is impossible to Express relatively simple (cubic or polynomial) function, then it must be determined graphically or by using a lookup table. Alternatively, you can use a different mathematical function or spline function is adopted to describe the different parts of the tip.

For indentation depths of more than 6 microns in a first approximation the square is determined from the theoretical shape of the tip:

for a perfect tip for Vickers and modified Berkovich tip (see [1] (4.2.3):

,

for a perfect Berkovich tip:

,

where the depth probe contacts the test sample, computed as follows:

.

Figure 2 schematically shows a longitudinal cross-section area of the indentation during the experiment. The theoretical basis of the method of determining depth of contact is given in [6]. Contact depth is evaluated by curve unloading on -a diagram using the tangent to the curve at the point and the maximum displacement less the elastic displacement of the surface in accordance with the analysis of Sneddon [7], where depends on the geometry of the tip (see table A. 1).


Table A. 1 — Correction factor for different tips

Tip type
Cylindrical with flat end	1
Conical
The paraboloid of revolution (including the spherical)	¾
Berkovich, Vickers	¾

derived from the diagram; the intersection of the tangent to the unloading curve with the axis of displacement. To determine the different possible methods that can be described in two ways:

a) method based on linear extrapolation (see [8]): assume the linearity of the initial part of the unloading curve on the chart, and this line is simply extrapolated to the intersection with the axis of displacement.

Note — This method can be a good approximation for ductile materials (e.g. aluminium, tungsten);

b) method based on power laws (see [6]): this method assumes that the initial part of unloading curve is nonlinear and can be described by a simple power dependence

,

where is a constant and is an exponent that depends on the geometry of the tip.

Typically, the regression procedures take the values of the test load exceeds 80% maximum values, the percentage of the maximum value of the load can vary based on the «quality» of the curve of discharge. If you want to use for regression curve data lifting load to 50% or less, then experiment with the indentation should be regarded as ambiguous and to decide on its interpretation. Find tangent by differentiation of the curve of the unloading diagram at . The intersection of this tangent with the axis of movement gives . Information regarding the correlation with other hardness scales are given in Appendix F.

Designation hardness indentation

A. 5 Modulus of elasticity , determined by instrumental method for indentation

A. 5.1 module Definition

The module can be calculated by the slope of the tangent to the unloading curve on the chart (see A. 4). Its value is close to the value of the young’s modulus of the material (modulus of elasticity). However, if the model contains nodules or dimples, it may be a significant difference between the modulus and young’s modulus.

The module value should be calculated according to the formula

, (A. 6)

where is the Poisson’s ratio of a material test sample (the value is known);

is the Poisson’s ratio of the material of the tip (for diamond 0,07) (see [9]);

the elastic modulus of the tip (the diamond of 1.14·10N/mm) (see [9]);

 — reduced modulus of elasticity in the region of the indentation;

 — compliance at the site of contact, i.e., determined from the curve of the lifting of the load at maximum load (the reciprocal of the contact stiffness);

the cross — sectional area of the contact surface between the tip and the test sample determined by weight-loading curve on the diagram and the area function of the tip, see [1] (пункт4.5.2).

For microns the following is true:

 — tip for Vickers and modified Berkovich tip;

for the Berkovich tip.

Note — the Ratio for written based on the assumption that the contact area is symmetrical relative to the axis of the tip. In [10] an amendment is proposed for pyramidal tips.

A. 5.2 Marking of the modulus of elasticity

Note — For some materials there is a correlation between the tabular values of young’s modulus for metals and metal alloys (see [11], [12]).

A. 6 Creep during indentation

A. 6.1 Definition of creep during indentation

If the depth of the indentation is measured at a constant test load, it is possible to calculate the relative change of depth of indentation. This value is called the creep of the material (see figure B. 1a), B. 1b), and calculated by the formula

, (A. 8)

where is the depth of indentation upon reaching the test load supported by a constant since , mm.

 — depth of indentation at the time after aging under load, mm.

Note — the Thermal drift can have a strong impact on the resulting value of creep.

A. 6.2 Marking of creep at instrumental indentation test

Figure A. 3 — Creep during indentation

1 — the increase of test load; 2 — endurance under load up to

Figure A. 3 — Creep during indentation

A. 7 Relaxation instrumental indentation

A. 7.1 Definition of relaxation by instrumental indentation test

If the change in applied load, measured at the constant depth of indentation, we can calculate the relative change in the test load. This is called relaxation of the material (see figure B. 2a), B. 2b) and calculated by the formula

, (A. 9)

where the load at a predetermined and maintained constant depth of indentation, H;

 — the load at which the indentation depth is held constant, N.

A. 7.2 Marking of relaxation at instrumental indentation test

Figure A. 4 — the Dynamics of relaxation during indentation

1 — increase the depth of indentation from zero to a predetermined value; 2 — the depth of indentation is kept constant in the time interval from to

Figure A. 4 — the Dynamics of relaxation during indentation

A. 8 the Plastic and elastic components of instrumental indentation test

A. 8.1 Determination of plastic and elastic components of instrumental indentation test

Mechanical work , done during indentation is only partially spent on the plastic deformation . When removing the applied load (elastic deformation ) is released. In accordance with the definition of mechanical work as both components of mechanical work represented by different areas in the figure A. 5. The ratio (A. 10) contains information describing the test sample

, (A. 10)

where .

The plastic component is equal to

. (A. 11)

A. 8.2 Marking elastic component of instrumental indentation test

Figure A. 5 — Plastic and elastic components of the indentation

Figure A. 5 — Plastic and elastic components of the indentation

Annex B (reference). Types of test cycles of instrumental indentation

Appendix B
(reference)

1 — application of test load; 2 — the maximum test load; 3 — removal of test loads; 4 — the test load is zero; 8 — creep during indentation; 9 — recovery at zero load test

Figure B. 1

5 — application of the depth of indentation; 6 — the maximum depth of indentation; 7 — reducing the depth of the indentation 8; 10 — relaxation at the maximum depth of indentation

Figure B. 2

Application (required). Give installation and function of the area of the tip

Application
(required)

C. 1 Compliance the installation

Applied test load affects not only the surface of the test sample, but also on the details of the test set, which in this case are elastically deformed.

Elastic deformation of the test setup causes an apparent increase in the measured depth of indentation, which does not occur with contact during indentation, and occurs between the reference planes in the test installation.

Usually additional apparent depth of indentation associated with the deformation of the test system for testing proportional to the applied force. This additional compliance installation must be taken into account at all loads, because it directly affects the increase and decrease in the slope of the tangent to the curve removing the test load. The absolute increase of the measured values is particularly significant at high loads attached.

Procedures for determining the compliance of the installation in accordance with accepted methods(see[1] (пункт4.5), [8], [13]) should be reported to the manufacturer settings for testing. Give installation can have a particularly significant impact on the results of measurements when the displacement of the tip measured from the lowest point. The manufacturer of the unit shall determine compliance for the installation before its delivery.

C. 2 a Function of the square of the tip

Calculation of parameters described in A. 2, A. 4 and A. 5 based on the determination of the contact area (or cross sectional area) of the tip. However, during indentation measure the depth of the indentation and not the area. Significant differences can be detected when comparing the actual contact area with the area calculated under the assumption of ideal geometry of the tip, particularly at small depths of indentation.

These differences are associated with rounding the top of the tip, in the case of a Vickers pyramid, on the web, and deviation from the specified angle of the tip that relates to normal production tolerances. In addition, the actual contact area changes due to deterioration the top of the tip.

To achieve comparability of results is necessary to determine the actual contact area (or projected area of contact) and use it in calculations of parameters of materials.

There are three method of determining the area function of the tip:

— the method of direct measurements using atomic force microscope (AFM) (see [14]);

indirectly using indentation in a material with a known young’s modulus (see [8]);

— indirectly, by observing the deviation of hardness calculated by means of the measured test load and the corresponding depth of indentation (hardness independent of the indentation depth). This method needs a special test materials (e.g., quartz glass, BK7), and is applicable for the determination of hardness indentation and Martens hardness (indirectly, through the use of indentation in a material with a known young’s modulus, (see [15]). If this method is used to determine hardness scales Martens, the function of the surface area of the tip can be calculated from the curve increases the load on diagram.

Notes

1 For determining the area function of the tip when defining the hardness scales Martens is recommended to use reference materials of high plasticity.

2 For all indirect methods, it is first necessary to determine the compliance of installation and properly adjust the data according to the depth of indentation. You can also use the iterative approach.

A function of the square of the tip, usually expressed as a mathematical function expressing the dependence of the cross sectional area of the tip distance from the apex of the tip. If the function of the area of the tip is impossible to Express relatively simple (cubic or polynomial) mathematical function, the assessment can be done graphically or by using a lookup table. Different parts of the tip can be described by various mathematical functions, or splines.

Procedure check the area function of the tip described in [1] (Appendix C).

3 Function square tip, and a correction for the compliance of the installation, you can determine simultaneously, using iterative procedure and the set of reference measures, [13].

Annex D (mandatory). Diamond tips. Notes

Appendix D
(required)

Experience shows that many of the past practice of the lugs during operation becomes defective in a relatively short period of time. This is due to small cracks, pits or other surface defects. If such defects are detected in time, the tip can be restored through regrinding. If this is not done, the small surface defects can reduce the quality of the tip, and he quickly destroyed.

Therefore:

— the condition of the tip should be regularly checked for contamination or defects. For macrodiakonia the shape of the tips checked by indentation of the reference measure hardness as described in [1] (paragraph 6.3);

for bits the nano range it is recommended to conduct optical checks with 400x microscope to determine the presence of contamination significant defects;

— detection of submicroscopic damage or pollution is possible by conducting timely indirect and reference checks, as stated in [1] (paragraphs 6.2 and 6.3), or by using scanning microscopy prints or the tip;

— in case of detection of defects of the tip of its certificate of calibration is considered invalid;

— presledovanie or in any other way repaired the tips should believe again.

Contamination of the surface of the tip can distort the test results. The source of the contamination of the tip most often dirt on the test specimens.

For push-on micro — and nanoliposomal the cleaning procedure outlined below:

— firmly hold the tip of the handseveral times to push it just chipped off the surface of the polystyrene foam. The plasticizer is a good solvent, and the foam is unlikely to harm a diamond tip. To carry out an inspection using an optical microscope (400or more) and incentivate in a small piece of cotton moistened with acetone or pure alcohol (for example, high-purity ethyl alcohol or isopropanol), until then, until there is visible contamination;

— if, after conducting this process, the contamination still remains, the indentation in the aluminium, glass or a clean wooden Board will help eliminate pollution using the above procedure;

— when indentation is required to protect the tip from exposure to excessive loads, both normal and especially transversal, because they can cause damage to the tip. One of the safest ways is the use of the sample, the weight of which is less than the forces normally acting on the tip: slowly and smoothly lowering the specimen on an inverted tip, limit the weight of specimen maximum force acting on the tip.

Appendix E (mandatory). The influence of surface roughness of the test sample to the uncertainty of measurement results

Appendix E
(required)

The app is based on tests of the tips of the Vickers.

The surface roughness is caused by the uncertainty of the contact zone at very small depths of indentation. At a deeper indentation of the uncertainty of the contact zone is reduced, at most, the uncertainty of the depth of indentation is proportional to the arithmetic mean roughness of the surface profile.

To limit the contribution of surface roughness to the uncertainty of the measurement result of the depth of indentation (up 5%), should be more, at least 20 times, the arithmetic average roughness (see GOST 25142):

(E. 1)

Table E. 1 contains examples of surface roughness for various materials at different applied loads.


Table E. 1 — Examples of maximum allowable arithmetic average height of roughness surface for different test loads

Examples of materials	A valid arithmetic mean height of surface roughness , µm, for test loads			Hardness Martens
0.1 N	2 N	100 N
Aluminium	0,13	0,55	Of 4.00	600
Steel	0,08	0,30	2,20	2000
Hard alloy	0,03	0,10	0,80	15000

Notes

1 Test (see [16]) show that the standard deviation of the depth of the indentation is approximately equal to the arithmetic average roughness . The requirement that the uncertainty was less than 5%, one can estimate the minimum depth of the indentation.

2 For tests on the nano — and lower bounds of microcapsule may be impossible to satisfy the conditions of formula (E. 1) for test specimens with high hardness. To reduce the uncertainty of the average value of the measurement result, you can increase the number of measurements. It should be noted in the measurement Protocol.

3 In nano — and microdiamond it is recommended to measure surface roughness in the potential contact zone, or this zone must be investigated by any other means available. In many cases the surface roughness can be measured by comparison with measures of roughness. In macrodipole enough visual verification that determines the smoothness of the polished or «mirror» surface treatment.

Annex F (informative). Correlation between hardness H (IT) with a hardness on the Vickers

Appendix F
(reference)

Correlation of hardness with hardness Vickers

Hardness can be correlated with the Vickers hardness for a wide range of materials with a suitable ratio.

WARNING — Although can be correlated with this method, the equivalent value calculated as shown in this Appendix cannot be used as exact replacement for .

You can enter a simple function for the tip Vickers with a perfect geometry or tip Vickers with the usual geometry when the function square is known. In this case, hardness values are linked with hardness values in Vickers scale factor. The ratio of the cross sectional area to surface area is constantly on the any distance from the top of the tip Vickers with a perfect geometry.

. (F. 1)

The length of the diagonal in the hardness measurements by Vickers tied to the relationship:

; . (F. 2)

Thus,

, (F. 3)

where is the gravitational constant, usually taken equal to 9,80665 m/s.

For the Berkovich tip, the following relationship:

;

. (F. 4)

For a modified Berkovich tip, there are following relations:

;

. (F. 5)

Note that in the General case at small depths of indentation (<6 µm), one can assume that the tip has a perfect geometry, so a simple correlation function (F. 2)-(F. 5) may be incorrect. In the General case, the error caused by this assumption will be most significant at small depths of indentation.

For some materials the correlation between and demonstrated in [6] and [11].