Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for fracture resistance of monolithic ceramics at room temperature by indentation fracture (IF) method

This document describes a test method that covers the determination of fracture resistance of monolithic ceramics at room temperature by the indentation fracture (IF) method. This document is intended for use with dense monolithic ceramics and whisker- or particulate-reinforced ceramics which are regarded as macroscopically homogeneous. It does not include monolithic silicon nitride ceramics for bearing balls and continuous-fibre-reinforced ceramics composites. This document is for material development, material comparison, quality assurance, characterization and reliability data generation. Indentation fracture resistance, KI,IFR, as defined in this document is not to be equated with fracture toughness determined using other test methods such as KIsc and KIpb. NOTE KI,IFR is an estimate of a material's resistance to cracking as introduced by an indenter and has correlations with wear resistance and rolling contact fatigue performance as well as machining processes, since these properties are governed by the resistance to crack extension in localized damage areas[1]-[3]. By contrast, fracture toughness properties KIsc and KIpb are intrinsic properties of a material and are relevant to macroscopic and catastrophic fracture events with long cracks rather than those phenomena caused by microscopic and successive damage accumulation associated with short cracks.

Céramiques techniques (céramiques avancées, céramiques techniques avancées) — Méthode d’essai pour déterminer la résistance à la rupture par indentation (IF) des céramiques monolithiques à température ambiante

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Status
Published
Publication Date
28-Feb-2019
Technical Committee
Drafting Committee
Current Stage
6060 - International Standard published
Start Date
01-Mar-2019
Completion Date
01-Mar-2019
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ISO 21618:2019 - Fine ceramics (advanced ceramics, advanced technical ceramics) -- Test method for fracture resistance of monolithic ceramics at room temperature by indentation fracture (IF) method
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INTERNATIONAL ISO
STANDARD 21618
First edition
2019-02
Fine ceramics (advanced ceramics,
advanced technical ceramics) —
Test method for fracture resistance
of monolithic ceramics at room
temperature by indentation fracture
(IF) method
Céramiques techniques (céramiques avancées, céramiques techniques
avancées) — Méthode d’essai pour déterminer la résistance à
la rupture par indentation (IF) des céramiques monolithiques à
température ambiante
Reference number
ISO 21618:2019(E)
ISO 2019
---------------------- Page: 1 ----------------------
ISO 21618:2019(E)
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© ISO 2019

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Published in Switzerland
ii © ISO 2019 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 21618:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Apparatus ..................................................................................................................................................................................................................... 3

5.1 Testing machine ..................................................................................................................................................................................... 3

5.2 Indenter ......... ................................................................................................................................................................................................ 3

5.3 Verification by standard reference materials ............................................................................................................... 3

5.4 Metallurgical microscope or travelling microscope ................................................................................................ 3

6 Test specimen .......................................................................................................................................................................................................... 3

6.1 Thickness ..................................................................................................................................................................................................... 3

6.2 Surface finish ............................................................................................................................................................................................ 3

7 Procedure..................................................................................................................................................................................................................... 4

7.1 Specimen placement .......................................................................................................................................................................... 4

7.2 Specimen levelling ............................................................................................................................................................................... 4

7.3 Cleaning of the indenter .................................................................................................................................................................. 4

7.4 Adjustment of stage movement ................................................................................................................................................ 4

7.5 Application of test force .................................................................................................................................................................. 4

7.6 Acceptability of indentations ...................................................................................................................................................... 4

7.7 Number of indentations .................................................................................................................................................................. 5

7.8 Measurement of indentation size ........................................................................................................................................... 6

7.9 Measurement of crack size ........................................................................................................................................................... 6

8 Calculation .................................................................................................................................................................................................................. 8

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

Annex A (informative) General machining procedure for test piece preparation .............................................10

Annex B (normative) Adjustment of the axis of travelling-stage and calibration of the

length measurement using the travelling stage ................................................................................................................12

Annex C (informative) Interlaboratory evaluation of the indentation fracture (IF) test

procedure ..................................................................................................................................................................................................................14

Bibliography .............................................................................................................................................................................................................................16

© ISO 2019 – All rights reserved iii
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ISO 21618:2019(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

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.org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/members .html.
iv © ISO 2019 – All rights reserved
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INTERNATIONAL STANDARD ISO 21618:2019(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for fracture resistance of
monolithic ceramics at room temperature by indentation
fracture (IF) method
1 Scope

This document describes a test method that covers the determination of fracture resistance of

monolithic ceramics at room temperature by the indentation fracture (IF) method.

This document is intended for use with dense monolithic ceramics and whisker- or particulate-

reinforced ceramics which are regarded as macroscopically homogeneous. It does not include monolithic

silicon nitride ceramics for bearing balls and continuous-fibre-reinforced ceramics composites.

This document is for material development, material comparison, quality assurance, characterization

and reliability data generation.

Indentation fracture resistance, K , as defined in this document is not to be equated with fracture

I,IFR
toughness determined using other test methods such as K and K .
Isc Ipb

NOTE K is an estimate of a material’s resistance to cracking as introduced by an indenter and has

I,IFR

correlations with wear resistance and rolling contact fatigue performance as well as machining processes, since

[1]-[3]

these properties are governed by the resistance to crack extension in localized damage areas . By contrast,

fracture toughness properties K and K are intrinsic properties of a material and are relevant to macroscopic

Isc Ipb

and catastrophic fracture events with long cracks rather than those phenomena caused by microscopic and

successive damage accumulation associated with short cracks.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements 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.

ISO 4287, Geometrical Product Specifications (GPS) — Surface texture: Profile method — Terms, definitions

and surface texture parameters

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

machines

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

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

monolithic ceramics at room temperature

ISO 17561, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for elastic

moduli of monolithic ceramics at room temperature by sonic resonance
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https: //www .iso .org/obp
© ISO 2019 – All rights reserved 1
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ISO 21618:2019(E)
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
fracture resistance
measure of resistance of extension of a crack introduced by an indenter
3.2
fracture resistance value
I,IFR
value of crack-extension resistance as measured by the IF method

Note 1 to entry: The indentation fracture resistance, K , as used here is not to be equated to fast fracture

I,IFR

toughness K . K is an estimate of a material’s resistance to cracking as introduced by an indenter. K is

Ic I,IFR Ic

considered to be an intrinsic property of a material and is independent of the test method.

4 Principle

This document is for material development, material comparison, quality assurance, characterization and

reliability data generation of dense monolithic ceramics. The method determines the indentation fracture

resistance value, K , from the elastic modulus and indentation force by forcing a Vickers indenter

I,IFR

(diamond pyramid) into the surface of a test piece and measuring the lengths of both the diagonals and

the associated cracks of the indentation that are left in the surface after removal of the indenter (see

[4]

Figure 1) . The method is applicable to the half-penny-crack type but not to the Palmqvist type. The

two types of crack profile can be estimated using the ratio of the crack length, 2c, to the diagonal length,

2a. If 2c/2a is more than 2,5, the crack is half-penny type. But the critical 2c/2a values can be smaller

than 2,5 for some ceramics. In such cases, direct observation of crack morphology by the decoration

technique or serial sectioning of the indented surface is also useful to differentiate the two crack profiles.

The measurement of the crack length and the observation of the crack tips are performed separately in

order to improve the accuracy. The crack length should not be measured in a single optical image because

doing so inevitably limits the magnification that can be used. Travelling microscopy is a solution that

allows both reading of the crack length and detection of the crack tips to be performed at high resolution,

albeit separately. Both an objective lens of 40 × or higher and a calibrated optical stage shall be employed

to ensure reliability. Both international and domestic interlaboratory comparison study (round robin)

projects on the advanced IF method are described in Annex C (see References [5] to [8]).

Key
2a diagonal length of the indent
2c diagonal length of the crack
Figure 1 — Crack lengths and diagonal sizes of the Vickers indentation
2 © ISO 2019 – All rights reserved
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ISO 21618:2019(E)
5 Apparatus
5.1 Testing machine

The testing machine shall be in accordance with ISO 6507-2. A suitable testing machine capable of

applying an indentation force of 49,03 N up to 196,1 N shall be used.
5.2 Indenter

The indenter shall meet the specification for Vickers indenters. See test method ISO 6507-2. The

diamond should be examined before the test, and if it is loose in the mounting material, chipped or

cracked it shall be replaced.
5.3 Verification by standard reference materials

The reference materials which are in accordance with ISO 6507-3 shall be used to verify the testing

machine and their Vickers hardness shall not vary from the hardness of the material to be measured by

more than 20 %.
5.4 Metallurgical microscope or travelling microscope

The metallurgical microscope equipped with calibrated stage movement or the travelling microscope

shall be employed for both detection of the crack tips and measurement of the crack length. The

magnification of the objective lens shall be 40 × or 50 × and the total magnification shall be 400 × or

more. The travelling stage shall move both vertically and horizontally and the readout resolution of the

table position shall be 1 μm or less. The coaxial vertical illumination with enough light intensity shall

be used for the observation of the crack tips.
6 Test specimen
6.1 Thickness

The thickness of the specimen shall be large enough so that the crack lengths are not affected by

variations in the thickness. As long as the thickness of the specimen is more than five times the crack

length (2c), the test will not be affected. In general, a specimen thickness of more than 3 mm is suitable.

6.2 Surface finish

Specimens shall have a ground and polished surface so that the crack lengths can be measured

accurately. The surface roughness, Ra, as defined in ISO 4287, shall be not more than 0,1 μm. Any

grinding-induced damage layer at the surface shall be removed completely by polishing so that the

crack lengths are not affected by any residual stress at the surface layer. The area fraction of tiny pits

due to dropout of a grain or fragmentation shall be as small as possible to enable the precious crack-

length measurement.
NOTE Annex A provides further information about a typical machining procedure.

The IF method is only applicable to dense ceramics. But if it is necessary to evaluate slightly porous

ceramics through the IF method, the porosity shall be described in the test report to show the precision

of measurements, because ceramics with some small porosity can experience local densification

beneath the indenter, which reduces the driving force for crack formation and results in overestimation

of K .
I,IFR
© ISO 2019 – All rights reserved 3
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ISO 21618:2019(E)
7 Procedure
7.1 Specimen placement

Place the specimen on the stage of the machine so that the specimen will not rock or shift during the

measurement. The specimen surface shall be clean and free from any grease or film.

7.2 Specimen levelling

The surface of the specimen being tested shall lie in a plane normal to the axis of the indenter.

7.3 Cleaning of the indenter

The indenter shall be cleaned prior to and during a test series. A cotton swab with ethanol, methanol or

isopropanol may be used. Indenting into soft copper can also help remove debris.
7.4 Adjustment of stage movement

Ensure that the horizontal movement of the stage of optics is coincident with the horizontal direction

in the field of optics. The magnitude of the stage movement shall be calibrated with an objective

micrometer. The procedures for the adjustment of the stage axis and for the length calibration shall be

carried out as specified in Annex B.
7.5 Application of test force

Indentations shall be made using a Vickers indenter under the following conditions:

Force: 196,1 N
Dwell time: 15 s

If indentations made at the test force of 196,1 N lead to no acceptable indentations (see Figure 2), use a

lower test force of 98,07 N or 49,03 N. The test force employed shall be described in the test report to

show the precision of measurements.

NOTE K measured at a force of 98,07 N or 49,03 N can be slightly smaller than that obtained at 196,1 N,

I,IFR

especially for those silicon nitrides with self-reinforced microstructures which produce rising R-curve behaviour.

Also, the accuracy of the measurement of crack length can become worse when the indentation size gets smaller

at the test force of 98,07 N or 49,03 N.
7.6 Acceptability of indentations

Only indentations whose four primary cracks emanate straight and radially from each corner shall

be accepted. Indentations with spalled edges, badly asymmetrical, split or forked cracks or gross

chipping shall be rejected, see Figure 2. If the difference between the horizontal crack length and the

vertical length is more than 10 % of the mean value of the horizontal and vertical lengths, the result

shall be rejected. If 2c/2a is less than 2,5, the results shall be rejected since the crack could

...

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