ISO 21618:2025

International
Standard
ISO 21618
Second edition
Fine ceramics (advanced ceramics,
2025-03
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 2025
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ii
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 . 3
7.1 Specimen placement .3
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 .5
7.9 Measurement of crack size.6
8 Calculation . 7
9 Test report . 8
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

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.
This second edition cancels and replaces the first edition (ISO 21618:2019), of which it constitutes a minor
revision. The changes are as follows:
— replacement of the withdrawn normative reference ISO 4287 by the current equivalent standard
ISO 21920-2:
— editorial changes.
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
International Standard ISO 21618:2025(en)
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 specifies a test method for determination of the fracture resistance of monolithic ceramics at
room temperature using the indentation fracture (IF) method.
This document is applicable to dense monolithic ceramics and whisker- or particulate-reinforced ceramics
which are regarded as macroscopically homogeneous. This document is not applicable to monolithic silicon
nitride ceramics for bearing balls and continuous-fibre-reinforced ceramics composites.
This document is applicable 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 correlations
I,IFR
with wear resistance and rolling contact fatigue performance as well as machining processes, since these properties
[1]-[3]
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 and catastrophic fracture
Isc Ipb
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 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
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms, definitions
and surface texture parameters
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp

— IEC Electropedia: available at https:// www .electropedia .org/
3.1
fracture resistance
measure of resistance of extension of a crack introduced by an indenter
3.2
fracture resistance value
K
I,IFR
value of crack-extension resistance as measured by the indentation fracture (IF) method
Note 1 to entry: The indentation fracture resistance, K , as used here is not to be equated to fast fracture toughness
I,IFR
K . K is an estimate of a material’s resistance to cracking as introduced by an indenter. K is considered to be an
Ic I,IFR Ic
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 Figure 1).
[4]
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
...