prEN ISO 24370

Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for fracture toughness of monolithic ceramics at room temperature by chevron-notched beam (CNB) method (ISO 24370:2005)

This International Standard ISO 24370 specifies a test method for determining the fracture toughness of monolithic ceramic materials at room temperature by the chevron-notched beam (CNB) method.
This International Standard is applicable to monolithic ceramics and whisker- or particulate-reinforced ceramics that are regarded as macroscopically homogeneous. It is not applicable to continuous-fibre reinforced ceramic composites.
This International Standard is usually applicable to ceramic materials with a fracture toughness less than about 12 MPa(m1/2). The test method is applicable to materials with a flat crack-growth resistance curve and may be applicable to materials with a rising crack-growth resistance curve (R-curve).

Hochleistungskeramik - Prüfverfahren zur Bestimmung der Bruchzähigkeit monolithischer Keramik an Biegeproben mit Chevron-Kerb (CNB-Verfahren) (ISO 24370:2005)

Céramiques techniques - Méthode d'essai de ténacité à la rupture des céramiques monolithiques à température ambiante sur éprouvette entaillée en chevron (ISO 24370:2005)

Fina keramika (sodobna keramika, sodobna tehnična keramika) - Preskusne metode za ugotavljanje odpornosti monolitske keramike proti lomljenju pri sobni temperaturi z metodo upogibnega preskusa z zarezo (metoda CNB) (ISO 24370:2005)

General Information

• Status: Not Published
• Publication Date: 09-Aug-2023
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: CEN/TC 184 - Advanced technical ceramics
• Drafting Committee: CEN/TC 184 - Advanced technical ceramics
• Current Stage: 4060 - Closure of enquiry - Enquiry
• Start Date: 09-Feb-2023
• Due Date: 03-Sep-2023
• Completion Date: 09-Feb-2023
• Ref Project: oSIST prEN ISO 24370:2023 - Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for fracture toughness of monolithic ceramics at room temperature by chevron-notched beam (CNB) method (ISO 24370:2005)

Relations

• Revises: EN 14425-3:2010 - Advanced technical ceramics - Test methods for determination of fracture toughness of monolithic ceramics - Part 3: Chevron notched beam (CNB) method
• Effective Date: 18-Jan-2023

Standards Content (Sample)

SLOVENSKI STANDARD
oSIST prEN ISO 24370:2023
01-januar-2023
Fina keramika (sodobna keramika, sodobna tehnična keramika) - Preskusne
metode za ugotavljanje odpornosti monolitske keramike proti lomljenju pri sobni
temperaturi z metodo upogibnega preskusa z zarezo (metoda CNB) (ISO
24370:2005)
Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for
fracture toughness of monolithic ceramics at room temperature by chevron-notched
beam (CNB) method (ISO 24370:2005)
Hochleistungskeramik - Prüfverfahren zur Bestimmung der Bruchzähigkeit
monolithischer Keramik an Biegeproben mit Chevron-Kerb (CNB-Verfahren) (ISO
24370:2005)
Céramiques techniques - Méthode d'essai de ténacité à la rupture des céramiques
monolithiques à température ambiante sur éprouvette entaillée en chevron (ISO
24370:2005)
Ta slovenski standard je istoveten z: prEN ISO 24370
ICS:
81.060.30 Sodobna keramika Advanced ceramics
oSIST prEN ISO 24370:2023 en,fr,de

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

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oSIST prEN ISO 24370:2023
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oSIST prEN ISO 24370:2023
INTERNATIONAL ISO
STANDARD 24370
First edition
2005-06-01
Fine ceramics (advanced ceramics,
advanced technical ceramics) — Test
method for fracture toughness of
monolithic ceramics at room temperature
by chevron-notched beam (CNB) method
Céramiques techniques — Méthode d'essai de ténacité à la rupture des
céramiques monolithiques à température ambiante sur éprouvette
entaillée en chevron
Reference number
ISO 24370:2005(E)
ISO 2005
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oSIST prEN ISO 24370:2023
ISO 24370:2005(E)
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ii © ISO 2005 – All rights reserved
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oSIST prEN ISO 24370:2023
ISO 24370:2005(E)
Contents Page

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

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

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

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

4 Symbols ................................................................................................................................................. 2

5 Principle ................................................................................................................................................. 3

6 Apparatus............................................................................................................................................... 3

6.1 Test machine ......................................................................................................................................... 3

6.2 Flexure fixtures ..................................................................................................................................... 3

6.3 Micrometer............................................................................................................................................. 4

6.4 Optical microscope............................................................................................................................... 4

6.5 Stability detection equipment.............................................................................................................. 5

7 Test specimens ..................................................................................................................................... 5

7.1 Geometry, size, preparation and edge chamfering ........................................................................... 5

7.2 Number of specimens........................................................................................................................... 8

8 Procedure............................................................................................................................................... 9

8.1 Permitted test environments................................................................................................................ 9

8.2 Test specimen dimensions and alignment......................................................................................... 9

8.3 Post-test measurements .................................................................................................................... 10

8.4 Post-test interpretation....................................................................................................................... 10

9 Calculation........................................................................................................................................... 12

9.1 Calculations of the minimum stress intensity factor coefficient Y* ......................................... 12

min

9.2 Calculation of the fracture toughness value, K ....................................................................... 13

I,CNB

10 Test report............................................................................................................................................ 13

Bibliography ..................................................................................................................................................... 15

© ISO 2005 – All rights reserved iii
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oSIST prEN ISO 24370:2023
ISO 24370:2005(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 committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 24370 was prepared by Technical Committee ISO/TC 206, Fine ceramics.
iv © ISO 2005 – All rights reserved
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oSIST prEN ISO 24370:2023
INTERNATIONAL STANDARD ISO 24370:2005(E)
Fine ceramics (advanced ceramics, advanced technical
ceramics) — Test method for fracture toughness of monolithic
ceramics at room temperature by chevron-notched beam (CNB)
method
1 Scope

This International Standard specifies a test method for determining the fracture toughness of monolithic

ceramic materials at room temperature by the chevron-notched beam (CNB) method.

This International Standard is applicable to monolithic ceramics and whisker- or particulate-reinforced

ceramics that are regarded as macroscopically homogeneous. It is not applicable to continuous-fibre

reinforced ceramic composites.

This International Standard is usually applicable to ceramic materials with a fracture toughness less than

1/2

about 12 MPa(m ). The test method is applicable to materials with a flat crack-growth resistance curve and

may be applicable to materials with a rising crack-growth resistance curve (R-curve).

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.

ISO 7500-1:2004, Metallic materials — Verification of static uniaxial testing machines — Part 1:

Tension/compression testing machines — Verification and calibration of the force-measuring system

ISO 14704:2000, Fine ceramics (advanced ceramics, advanced technical ceramics) — Test method for

flexural strength of monolithic ceramics at room temperature
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
stress intensity factor

magnitude of the elastic stress field singularity at the tip of a crack subjected to opening mode (mode I)

displacement

NOTE It is a function of applied force and test specimen size, geometry and crack length.

3.2
fracture toughness
generic term for measures of the resistance of extension of a crack
© ISO 2005 – All rights reserved 1
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oSIST prEN ISO 24370:2023
ISO 24370:2005(E)
3.3
fracture toughness value
I,CNB

value of crack-extension resistance, i.e. fracture toughness, as measured by the CNB method

NOTE The measured stress intensity factor corresponds to a crack-extension resistance of a stably-extending crack

in a chevron-notched beam specimen. The measurement is performed to the operational procedure herein and satisfies all

the validity requirements.

NOTE The definition, interpretation and measurement of K assume a flat crack-growth resistance curve.

I,CNB
3.4
critical stress intensity factor
critical value of K at which fracture occurs
4 Symbols
l chevron tip dimension, CNB method (Figure 2)
l chevron dimension, CNB method, [l = (l + l )/2]
1 1 11 12
l chevron dimension, CNB method (Figure 2)
l chevron dimension, CNB method (Figure 2)
B test specimen thickness (Figure 2)
K stress intensity factor, Mode I
K critical stress intensity factor, Mode I
K fracture toughness value, chevron-notched beam method
I,CNB
S flexure fixture outer span
S flexure fixture inner span
L test specimen length

F maximum force applied to the test specimen by the test machine and thereby recorded (Figure 5)

max
F force applied to the test specimen by the upper fixture
Tare

F total force applied to the test specimen (F + F ). This value is used in calculation of K

max Tare I,CNB
T notch thickness or kerf resulting from cutting of the chevron notch (Figure 2)
W test specimen width (Figure 2)
Y* minimum value of the stress intensity factor coefficient Y*
min
2 © ISO 2005 – All rights reserved
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oSIST prEN ISO 24370:2023
ISO 24370:2005(E)
5 Principle

This International Standard is intended to be used for material development, material comparison, quality

assurance, characterization, reliability analysis and design data generation. The chevron-notched beam

(CNB) method measures the fracture toughness value K by fracturing a flexural specimen, that has a

I,CNB

chevron notch (Figures 1 and 2). The specimen is fractured by four-point flexure. Force versus displacement,

and backface strain or time are recorded in order to detect unstable fracture. The fracture toughness value

K is calculated from the fracture load and the minimum stress intensity factor coefficient. Background

I,CNB

information concerning this test method may be found in References [1] and [2]. An international

interlaboratory comparison study (round robin) project on the chevron-notched method is described in

Reference [3], and a comparison of this method to other standardized methods is given in References [2] and

[4].

NOTE Ceramics generally exhibit stable crack extension from a chevron notch if the notch is sufficiently narrow

(< 0,30 mm), and the other notch dimensions are within the specified tolerances. If stable crack extension is not obtained,

then the fracture toughness cannot be directly measured.
6 Apparatus
6.1 Test machine

A suitable testing machine capable of applying a uniform cross-head speed shall be used. The testing

machine shall be in accordance with ISO 7500-1:2004 Class 1, with an accuracy of 1 % of the indicated force

at fracture.
6.2 Flexure fixtures

A schematic diagramme of a typical flexure fixture and test specimen is shown in Figure 1. Flexure fixtures

shall meet the requirements of ISO 14704. The fixtures should be semi-articulating. Test specimens shall be

contacted by smooth cylindrical bearings with a diameter between 4,50 mm and 5,00 mm. The diameter

should be uniform to ± 0,015 mm.

The bearings shall be free to roll in order to minimize friction, and the two inner bearings shall be free to roll

inward, and the two outer bearings shall be free to roll outward. The inner span, S, should measure

20 mm ± 0,5 mm and the outer span, S , should measure 40 mm ± 0,5 mm. Alternatively, the inner and outer

span may measure 10 mm and 30 mm, respectively.

When specific test environments other than the laboratory air are employed, an adequate chamber to hold the

environment around the test fixture is required. For gaseous environments such as dry nitrogen, a

polyethylene bag can be used. For liquid environments such as silicone oil or water, the specimen can be

coated and placed in the fixture or the fixture and test specimen can be immersed in a chamber containing the

liquid.
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oSIST prEN ISO 24370:2023
ISO 24370:2005(E)
Key
1 push rod
2 ball
3 test specimen
4 strain gauge
5 displacement transducer
6 support rod
7 flexure fixture inner span, S
8 flexure fixture outer span, S

Figure 1 — Schematic example of four-point flexure of a chevron-notched test specimen

6.3 Micrometer
[11]

A micrometer such as shown in ISO 3611 but with a resolution of 0,002 mm shall be used to measure the

[11]

test specimen dimensions. The micrometer shall have flat anvil faces such as shown in ISO 3611 . The

micrometer shall not have a ball tip or sharp tip since these might damage the specimen. Alternative

dimension-measuring instruments may be used provided that they have a resolution of 0,002 mm or finer.

6.4 Optical microscope

A travelling microscope or an optical microscope equipped with a calibrated filar eyepiece should be used to

measure chevron notch dimensions l , l , l and T. Magnifications of 10 × to 50 × are usually required. The

0 11 12

dimensional measurement performance of the measurement system shall be calibrated with a reference

standard.
4 © ISO 2005 – All rights reserved
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oSIST prEN ISO 24370:2023
ISO 24370:2005(E)
6.5 Stability detection equipment

The stability of the test is detected by monitoring the test specimen centre-point displacement, load-point

displacement, actuator displacement, cross-head displacement or backface strain. Alternatively, force can be

recorded as a function of time. Examples of force as a function of strain, actuator stroke and time are shown in

Figure 3.

Both backface strain and extensometers placed within or near the flexure fixture are excellent for detecting the

[5] [6] [7]

stability of the test . Test system extensometers that are placed remotely relative to the test specimen

are less sensitive to the local events in the test specimen and may not detect stable extension. Monitoring

force as a function of time is a less effective method of detecting stable crack extension. This is particularly

1/2

the case for materials with a low fracture toughness [e.g. < 3,0 MPa(m )] and high elastic modulus (e.g.

400 GPa). Reference [2] discusses experience with various monitoring methods.

If an extensometer contacting the test specimen is used, the force of the extensometer on the specimen

should be less than 0,2 N.
7 Test specimens
7.1 Geometry, size, preparation and edge chamfering
7.1.1 Recommended geometry
Rectangular beams with dimensions shown in
...