Advanced technical ceramics - Mechanical properties of monolithic ceramics at room temperature - Part 4: Vickers, Knoop and Rockwell superficial hardness

This part of EN 843 defines conditions for conducting, and provides guidelines concerning the value that may be ascribed to the results of, standard hardness tests when applied to advanced monolithic technical ceramics. It is assumed that the calibration and test procedures employed are exactly those for metallic materials. This European Standard refers to Rockwell A, Rockwell N-scale, Vickers, and Knoop hardness testing, as described in existing international standards.

Hochleistungskeramik - Mechanische Eigenschaften monolithischer Keramik bei Raumtemperatur - Teil 4: Härteprüfung nach Vickers, Knoop und Rockwell

Dieser Teil von EN 843 definiert Bedingungen für die Durchführung von Härteprüfungen an monolithischer
Hochleistungskeramik und gibt Richtlinien für die Bewertung der erhaltenen Ergebnisse. Es wird voraus-
gesetzt, dass Kalibrierung und Prüfablauf exakt denen für metallische Werkstoffe entsprechen. Diese
Europäische Norm nimmt Bezug auf die Härteprüfung nach Rockwell A, Rockwell N, Vickers und Knoop in
Übereinstimmung mit den einschlägigen Internationalen Normen.

Céramiques techniques avancées - Propriétés mécaniques des céramiques monolithiques a température ambiante - Partie 4 : Essais de dureté Vickers, Knoop et Rockwell superficiel

Advanced technical ceramics - Mechanical properties of monolithic ceramics at room temperature - Part 4: Vickers, Knoop and Rockwell superficial hardness

General Information

Status
Published
Publication Date
31-Oct-2005
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Nov-2005
Due Date
01-Nov-2005
Completion Date
01-Nov-2005

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SLOVENSKI STANDARD
SIST EN 843-4:2005
01-november-2005
1DGRPHãþD
SIST ENV 843-4:2000
Advanced technical ceramics - Mechanical properties of monolithic ceramics at
room temperature - Part 4: Vickers, Knoop and Rockwell superficial hardness

Advanced technical ceramics - Mechanical properties of monolithic ceramics at room

temperature - Part 4: Vickers, Knoop and Rockwell superficial hardness
Hochleistungskeramik - Mechanische Eigenschaften monolithischer Keramik bei
Raumtemperatur - Teil 4: Härteprüfung nach Vickers, Knoop und Rockwell
Céramiques techniques avancées - Propriétés mécaniques des céramiques

monolithiques a température ambiante - Partie 4 : Essais de dureté Vickers, Knoop et

Rockwell superficiel
Ta slovenski standard je istoveten z: EN 843-4:2005
ICS:
81.060.30 Sodobna keramika Advanced ceramics
SIST EN 843-4:2005 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 843-4:2005
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SIST EN 843-4:2005
EUROPEAN STANDARD EN 843-4
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2005
ICS 81.060.30 Supersedes ENV 843-4:1994
English version
Advanced technical ceramics - Mechanical properties of
monolithic ceramics at room temperature - Part 4: Vickers,
Knoop and Rockwell superficial hardness

Céramiques techniques avancées - Propriétés mécaniques Hochleistungskeramik - Mechanische Eigenschaften

des céramiques monolithiques à température ambiante- monolithischer Keramik bei Raumtemperatur - Teil 4:

Partie 4: Essais de dureté Vickers, Knoop et Rockwell Härteprüfung nach Vickers, Knoop und Rockwell

surperficiel
This European Standard was approved by CEN on 29 April 2005.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the Central Secretariat or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official

versions.

CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,

Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,

Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 843-4:2005: E

worldwide for CEN national Members.
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SIST EN 843-4:2005
EN 843-4:2005 (E)
Contents
Page

Foreword.......................................................................................................................................................... 3

1 Scope................................................................................................................................................... 4

2 Normative references......................................................................................................................... 4

3 Terms and definitions ........................................................................................................................ 5

4 Significance and use.......................................................................................................................... 5

4.1 General points .................................................................................................................................... 5

4.2 Verification of test equipment ........................................................................................................... 5

4.3 Conversion of hardness numbers to other scales........................................................................... 6

5 Test method: method A: Vickers test................................................................................................ 6

5.1 Principle .............................................................................................................................................. 6

5.2 Machine calibration ............................................................................................................................ 7

5.3 Test piece............................................................................................................................................ 7

5.4 Test procedure.................................................................................................................................... 8

5.5 Accuracy and uncertainties............................................................................................................... 8

6 Test method: Method B: Knoop test .................................................................................................9

6.1 Principle .............................................................................................................................................. 9

6.2 Machine calibration .......................................................................................................................... 10

6.3 Test piece.......................................................................................................................................... 10

6.4 Test procedure.................................................................................................................................. 10

6.5 Accuracy and uncertainties............................................................................................................. 11

7 Test method: Method C: Rockwell tests......................................................................................... 11

7.1 Principle ............................................................................................................................................ 11

7.2 Machine calibration .......................................................................................................................... 11

7.3 Test piece.......................................................................................................................................... 12

7.4 Test procedure.................................................................................................................................. 12

7.5 Accuracy and uncertainties............................................................................................................. 12

8 Interpretation .................................................................................................................................... 13

8.1 Microstructural factors..................................................................................................................... 13

8.2 Interpretation of results ................................................................................................................... 13

9 Test report......................................................................................................................................... 13

Annex A (informative) Interlaboratory evaluation of hardness test methods ......................................... 19

Bibliography .................................................................................................................................................. 21

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SIST EN 843-4:2005
EN 843-4:2005 (E)
Foreword

This document (EN 843-4:2005) has been prepared by Technical Committee CEN/TC 184 “Advanced

technical ceramics”, the secretariat of which is held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by December 2005, and conflicting national standards

shall be withdrawn at the latest by December 2005.

EN 843 'Advanced technical ceramics – Mechanical properties of monolithic ceramics at room

temperature ' consists of six parts:
Part 1: Determination of flexural strength
Part 2: Determination of Young’s modulus, shear modulus and Poisson’s ratio

Part 3: Determination of subcritical crack growth parameters from constant stressing rate flexural

strength tests
Part 4: Vickers, Knoop and Rockwell hardness tests
Part 5: Statistical analysis
Part 6: Guide for fractographic investigation
This document supersedes ENV 843-4:1994.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech

Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,

Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia,

Spain, Sweden, Switzerland and United Kingdom.
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SIST EN 843-4:2005
EN 843-4:2005 (E)
1 Scope

This part of EN 843 defines conditions for conducting, and provides guidelines concerning the value that

may be ascribed to the results of, standard hardness tests when applied to advanced monolithic technical

ceramics. It is assumed that the calibration and test procedures employed are exactly those for metallic

materials. This European Standard refers to Rockwell A, Rockwell N-scale, Vickers, and Knoop hardness

testing, as described in existing international standards.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

EN ISO 6507-1, Metallic materials — Vickers hardness test — Part 1: Test method (ISO 6507-1:1997)

EN ISO 6507-2, Metallic materials — Vickers hardness test — Part 2: Verification of testing machines

(ISO 6507-2:1997)

EN ISO 6507-3, Metallic materials — Vickers hardness test — Part 3: Calibration of reference blocks

(ISO 6507-3:1997)

EN ISO 6508-1, Metallic materials — Rockwell hardness test — Part 1: Test method (scales A, B, C,

D, E, F, G, H, K, N, T) (ISO 6508-1:1999)

EN ISO 6508-2, Metallic materials — Rockwell hardness test — Part 2: Verification and calibration of

testing machines (scales A, B, C, D, E, F, G, H, K, N, T) (ISO 6508-2:1999)

EN ISO 6508-3, Metallic materials — Rockwell hardness test — Part 3: Calibration of reference

blocks (scales A, B, C, D, E, F, G, H, K, N, T) (ISO 6508-3:1999)

EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories

(ISO/IEC 17025:1999)
EN ISO 23878, Hardmetals — Vickers hardness test (ISO 3878:1983)
ISO 4545, Metallic materials — Hardness testing — Knoop test

ISO 4546, Metallic materials — Hardness test — Verification of Knoop hardness testing machines

ISO 9385, Glass and glass-ceramics — Knoop hardness test

ISO 14705, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for

hardness of monolithic ceramics at room temperature
OIML-36, Verification of indenters for hardness testing machines.

This international recommendation is available from the International Organization of Legal Metrology (OIML), 11, rue Tugot,

75009, Paris, France).
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SIST EN 843-4:2005
EN 843-4:2005 (E)
3 Terms and definitions

For the purposes of this European Standard, the following terms and definitions apply.

3.1
hardness

resistance displayed by a material to penetration by a hard indenter of defined geometry and forced into

the test surface in a prescribed manner
3.2
hardness number

hardness calculated in a specified hardness test, usually without units specified, derived from the depth of

penetration of the indenter or lateral dimension of the indentation, and the applied force

3.3
hardness indenter

hard device of defined geometry, and for the purposes of testing ceramics usually fabricated from single-

crystal diamond

NOTE Types of hardness test are defined in clause 5, 6, and 7 for Vickers, Knoop and Rockwell tests

respectively.
4 Significance and use
4.1 General points

The three types of test defined in clauses 5, 6 and 7 have been standardised for metallic materials, and

are widely used as a guide to the state of thermal treatment or work-hardening. In advanced technical

ceramics they are also widely used, especially to describe materials for applications in a wear

environment. Whereas in a metal a hardness test is a measure of the yield stress, in a brittle material the

deformation tends not to be homogeneous. In addition to plastic flow, there is usually some cracking and

fragmentation occurring, the extent of which has a marked effect on the apparent hardness and the ability

to perform meaningful measurements.

A hardness test on a range of widely differing ceramics will enable them to be ranked in order of

resistance to localised penetration, which may be correlated with other behavioural characteristics of

similar type, e.g. abrasive wear or erosion resistance. Such an interpretation may not be possible if

materials show similar characteristics because the discrimination shown by hardness tests may be

inadequate.

Uses beyond this application should be viewed with caution. It is, for example, recommended that

hardness tests are not used as a pass/fail criterion in a specification. The potential differences between

observers and/or test machines, as explained below, are too great for high levels of confidence in the test

results, leading to possible dispute between parties to the specification.
4.2 Verification of test equipment

Hardness standard test blocks are usually supplied with the test machine. It is imperative that they be

used for checking the machine behaviour and, in the case of Vickers and Knoop tests, also the visual

criteria being employed by the operator for measurement. The test block should also be used to ensure

that the indenter is free from chips or cracks which might easily develop when used on very hard

materials. Very high hardness calibration blocks are recommended when testing ceramics.

The test force for hardness measurements on ceramics may not be the normal one for which the test

machine has previously been calibrated. If this situation occurs, it is desirable to carry out checks that the

intended force is actually being applied to the test surface for the required period of time.

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SIST EN 843-4:2005
EN 843-4:2005 (E)

Direct verification of test equipment is described in EN ISO 6507-2 (for Vickers tests), ISO 4546 (for

Knoop tests) and in EN ISO 6508-2 (for Rockwell N-scale tests). The procedure involves calibration of

force and of the reading system. This document does not deal directly with such issues.

Indirect verification of test equipment ensures that the equipment is reading correctly at the time of use,

by providing a check on the quality of indentations, particularly whether there is damage to the indenter

and whether the indenter is correctly aligned. It can also provide a check on the reading criterion being

used by the operator. Indirect verification is normally conducted using certified reference blocks, and by

ensuring that the indenter being used has previously been certified as being geometrically within the

tolerances defined in the above standards.

Calibration of standard reference blocks is described in EN ISO 6507-3 (for Vickers tests), and in

EN ISO 6508-3 (for Rockwell N-scale tests). There are currently no CEN or ISO standards for Knoop test

block verification and calibration. Verification of the geometry of indenters is dealt with in OIML-36.

4.3 Conversion of hardness numbers to other scales

Whereas for metallic materials there are conversion tables to convert between various hardness numbers

on particular alloy types, there is no equivalent for ceramic materials. Since ceramics tend to show a

strong force dependence of hardness characteristics, it is highly unlikely that there could be a unique

relationship between hardness values determined using different forces or different types of indenter.

NOTE Attempts to convert hardness numbers from one scale to another are strongly discouraged.

5 Test method: method A: Vickers test
5.1 Principle

A hardness test in which a square-based sharp pyramidal diamond indenter having specified face angles

is forced into the test-piece surface under a defined force, held for a defined duration and removed. The

indentation diagonal lengths are measured, the mean result calculated, and this value then employed to

calculate a hardness number which is equivalent to the mean force per actual unit area of indenter

surface contacting the test surface (no units are given, but kgf/mm are implied):

HV F = 1,8544 F/d (1)
where

HV F is the Vickers hardness number at applied force F (expressed as the mass in kg from which F is

derived), and
where
d is the mean length of the diagonals of the indentation (expressed as mm).

The Vickers test for metallic materials is described in detail in EN ISO 6507-1 for applied forces derived

from masses of 0,2 - 100 kg, in EN ISO 23878 for hardmetals, and in ISO 14705 for advanced technical

ceramics.

NOTE 1 Other references to the Vickers test method, including microhardness tests may be found in

references [1] and [2] of the Bibliography.

In accordance with ISO 14705 and for the purposes of this document the use of SI units is preferred. In

the use of equation (1), when F is expressed in newtons ( = mass in kg × 9,807) and d is expressed in

mm, the hardness HV is then computed in MPa. The results shall be expressed as, for example: 15,0

GPa HV 1,0 for a test under a force of 9,807 N derived from a mass of 1 kg.
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SIST EN 843-4:2005
EN 843-4:2005 (E)

Unless otherwise agreed between parties, for the purposes of testing advanced monolithic technical

ceramics, the applied force shall be that derived from a mass of 1,0 kg (i.e. 9,807 N), i.e. test type HV1,0.

NOTE 2 If this force results in excessive cracking, or indentations which are not readable (see 5.4), then a

lower force is permitted. A higher force is permitted if there is minimal cracking associated (see 5.4).

5.2 Machine calibration
5.2.1 Direct verification

Ensure that the test machine is constructed and has been directly verified in conformity with

EN ISO 6507-2. Using a metallic reference block certified in accordance with EN ISO 6507-3, make at

least three indentations at a test force of HV 1,0. Ensure that the correct cross-hair positioning and

zeroing criteria are used (Figure 2). Calculate the hardness using equation (1) and ensure that the mean

value matches the certified value. If the apparent hardness does not match the certified value to within

the uncertainty envelope, the test machine should be serviced and re-verified before use.

5.2.2 Indirect verification

Using a high hardness reference test block certified in accordance with EN ISO 6507-3, make an

indentation at a test force of HV1,0 (unless otherwise agreed, see 5.1). Check that the indentation is

regular in shape and shows no damage to the indenter. If damage is suspected, change the indenter and

repeat. Measure the diagonal lengths to the nearest 0,2 µm using either the machine graticule or

micrometer stage, or using a separate microscope with a micrometer stage. If the indentation is

asymmetric, check the alignment of the machine or the indenter. Calculate the Vickers hardness in

accordance with equation (1). If there is a small difference (≤ 2 µm in diagonal length) between the test

block calibrated value and the observed value of hardness, check the visual reading criteria employed,

and adjust them appropriately. If there is a large difference (> 2 µm in diagonal length), first check the

function of the machine, particularly that the applied force is correctly calibrated.

NOTE 1 The use of hardmetal or ceramic reference blocks is recommended, especially to provide

appropriately small indentations when testing advanced technical ceramic materials.

NOTE 2 It may be helpful to mark the position of the calibration indentation with a pen if the measurement

of the diagonal lengths is made on a separate microscope.

NOTE 3 Adjustment of reading criterion may be necessary before beginning a measurement session on

test-pieces. The use of a reference block is considered to be a useful method of getting the eye accustomed

to making measurements before testing the test-piece.
5.3 Test piece

The test piece surface and the support surface shall be parallel to obtain symmetrical indentations (see

Figure 1, schematic 7 for limit of asymmetry). Irregular shaped fragments or components may be

mounted in mounting plastic for the purposes of this test. The thickness of the test piece should be at

least five times the distance that the radial cracking extends from the centre of the indentation, or ten

times the depth of penetration, whichever is greater. Polish the surface to be tested until it is scratch-free

in the region in which indentations are to be made, as observed at the magnification used for measuring

the indentation size.

NOTE The surface quality of ceramic test-pieces may affect the results. The test-piece should be neither

thermally nor chemically etched to reveal grain structure, as this can obscure the corners of indentations.

Note should also be made that it is possible that surface stresses produced by machining and polishing may

affect the indentation size. The test should preferably be performed on test-pieces prepared with prolonged

polishing such that at least 20 µm has been removed with an abrasive grit size of less than 3 µm, or which

have been annealed (but not thermally etched) if not polished as above. If annealing is used, the optimum

annealing temperature should be established by experiment as that which results in a maximum size of

indentation, or a minimum hardness.
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SIST EN 843-4:2005
EN 843-4:2005 (E)
5.4 Test procedure

Place the test piece in the test machine and make at least 5 indentations spaced apart by at least five

times the length of the radial cracking (see Figure 1, schematic 3). The indentations shall be randomly

positioned, and shall not be positioned over any particular microstructural feature.

NOTE 1 In coarse-grained or some multiphase materials the size of the indentation may be similar to or

smaller than the grain size or other microstructural features of the test material. The test then loses the

averaging element normally required for assessment of polycrystalline materials, and a larger spread of

results is obtained. Any bias towards preferential positioning of the centre of the indenter at particular

microstructure features will produce a bias in the test results. For material comparison purposes, where

possible it is advisable to ensure that the indentation diagonal size is at least five times the average grain

size of the test material.

Inspect the shape of the indentations for regularity, and reject any that show suspected irregular shape,

displacement of one or more corners, loss of one or more corners or excessive radial cracking

(see Figure 1, schematics 6 to 14). If the indentations are asymmetric (see Figure 1, schematic 7), the

surface is not adequately flat or perpendicular to the axis of the machine, and the test piece should be re-

mounted or re-polished as appropriate. Repeat the tests until at least five acceptable indentations are

produced. Measure the lengths of both diagonals of each indentation to the nearest 0,2 µm using the

criteria appropriate to the test machine and the guidance shown in Figure 2.

NOTE 2 Most ceramics are translucent under the conditions of observation of the indentations in Vickers

(and Knoop) tests. This results in very poor contrast at the corners of the indentations compared with

metallic materials, and there are consequent difficulties in placement of measuring crosswires. Some

experience may be needed by an operator in order to develop a consistent criterion for measurement.

If damage to the indenter has occurred during the course of the tests, replace the indenter and repeat the

reference block tests and the tests on the test-piece.

Calculate the HV1,0 hardness in GPa or the hardness number for each indentation according to

equation (1), calculate the mean result and the standard deviation.
5.5 Accuracy and uncertainties

The principal errors arising in a Vickers hardness test on advanced monolithic technical ceramics vary in

magnitude according the size of the indentation, and thus the indentation force used. The Vickers

diamond geometry was originally chosen because natural cleavage planes of the diamond were

employed. Variations in geometry between indenters are therefore small, and can usually be ignored

except when indentations are of less than 20 µm diagonal length where the tip and edges near the tip

may be variable between indenters. In particular, the edges may have flats up to 1 µm across on them,

and this has the effect of cutting the corners off the indentation. The error that this introduces is

insignificant if the indentation is larger than about 30 µm, but increases rapidly in importance as the size

is reduced.

Determination of the diagonal lengths using cross-wires or other device attached to the instrument relies

on the operator positioning them at the "true" opposing corners of the indentation. There is a subjective

element in performing this task which increases with poor optical contrast and reducing size of the

indentation. The possible errors can be reduced by experience, and by consistent use of high-hardness,

preferably ceramic or hardmetal, test blocks to familiarise the eye at the start of measurement sessions.

In this way any systematic measurement bias can be reduced. In a round-robin exercise on high-alumina

ceramics (reference [3], Bibliography), it was found that when two individuals measure the same set of

indentations on different measurement equipment, a poor correlation was obtained unless the true sizes

of the indentations varied by more than ± 1 µm. It follows that, discounting differences between machines,

it cannot be guaranteed that any two observers will agree that one material is significantly harder than

another unless the average indentation sizes are systematically smaller by more than 1 µm. Thus even if

it is possible to measure the indentation diagonal length to an apparent precision of 0,1 µm, or the optical

resolution limit if larger, the ability to discriminate between materials is limited to an order of magnitude

greater in size. Errors of this size assume significance when the indentation size is less than about 20 µm.

In addition there is the actual scatter in indentation sizes as a result of local microstructure variations such

as grain size, grain orientation, secondary phase content, microcracking, porosity, etc. In a very uniform

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SIST EN 843-4:2005
EN 843-4:2005 (E)

and homogeneous, hard, fine-grained material, the scatter in actual indentation sizes may be less than

the potential measurement errors, and thus not be discernible. In a less-homogenous material, the true

indentation size may vary significantly. In such a case, the mean result may be determined by the choice

of measurement position, deliberate or inadvertent. The certainty of mean result can be improved only by

increasing the number of indentations, but the possibility of a human bias remains. The discrimination

between inhomogeneous materials is poorer than for homogeneous ones.

The use of thin metal coatings or alternative optical techniques (such as Nomarski interference

techniques) for improving the contrast of indentations prior to visual measurement is not allowed by

EN ISO 6507. In this document, the use of coatings is allowed for translucent or transparent ceramics

provided that it is less than 0,2 µm thick such that the dimensions of the indentation are essentially

unaffected. Nomarski interference techniques distort the image, and shall not be used.

The use of the scanning electron microscope is not recommended for a number of reasons. The principal

ones are that the topographic contrast produced by an indentation is not great, that the edges and

corners are not always clearly defined, and that the actual magnification of the image requires careful

calibration and checking for distortion in both directions.

In summary, the systematic and material inhomogeneity errors may be minimised by employing the

highest possible measurement force consistent with no chipping or displacement of corners of the

indentation. Under such conditions, the discrimination between materials is greatest. Tests at HV1,0

represent an optimum force in terms of the range of materials which can give acceptable indentatio

...

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