CEN/TS 14425-3:2003

SLOVENSKI STANDARD
SIST-TS CEN/TS 14425-3:2005
01-januar-2005
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Advanced technical ceramics - Test methods for determination of fracture toughness of
monolithic ceramics - Part 3: Chevron notched beam (CNB) method
Céramiques techniques avancées - Méthodes d'essai de détermination de la ténacité a
la rupture des céramiques monolithiques - Méthode de l'éprouvette a entaille en chevron
Hochleistungskeramik - Prüfverfahren zur Bestimmung der Bruchzähigkeit von
monolithischer Keramik - Teil 3: Verfahren für Biegeproben mit Chevron-Kerb (CNB-
Verfahren)
Ta slovenski standard je istoveten z: CEN/TS 14425-3:2003
ICS:
81.060.30 Sodobna keramika Advanced ceramics
SIST-TS CEN/TS 14425-3:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TS CEN/TS 14425-3:2005

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SIST-TS CEN/TS 14425-3:2005
TECHNICAL SPECIFICATION
CEN/TS 14425-3
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
July 2003
ICS 81.060.30
English version
Advanced technical ceramics – Test methods for determination
of fracture toughness of monolithic ceramics – Part 3: Chevron
notched beam (CNB) method
Hochleistungskeramik - Prüfverfahren zur Bestimmung der Céramiques techniques avancées – Méthodes d’essai de
Bruchzähigkeit von monolithischer Keramik - Teil 3: détermination de la ténacité à la rupture des céramiques
Verfahren für Biegeproben mit Chevron-Kerb (CNB- monolithiques – Méthode de l’éprouvette à entaille en
Verfahren) chevron
This Technical Specification (CEN/TS) was approved by CEN on 19 April 2003 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available. It
is permissible to keep conflicting national standards in force (in parallel to the CEN/TS) until the final decision about the possible
conversion of the CEN/TS into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United
Kingdom.
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Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2003 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 14425-3:2003 E
worldwide for CEN national Members.

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SIST-TS CEN/TS 14425-3:2005
CEN/TS 14425-3:2003 (E)
Contents Page
Foreword. 3
1 Scope . 3
2 Normative references . 3
3 Terms and definitions. 4
4 Principle, significance and use . 4
5 Test apparatus. 4
6 Test pieces. 5
6.1 Material selection. 5
6.2 Test piece dimensions . 5
6.3 Sawn notch. 5
7 Procedure . 6
8 Calculation of results . 7
9 Interferences and errors. 7
10 Reporting . 8
Bibliography . 13
2

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SIST-TS CEN/TS 14425-3:2005
CEN/TS 14425-3:2003 (E)
Foreword
This document CEN/TS 14425-3:2003 has been prepared by Technical Committee CEN/TC 184 “Advanced
technical ceramics”, the secretariat of which is held by BSI.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Czech Republic, Denmark,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands,
Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom.
CEN/TS 14425 'Advanced technical ceramics — Test methods for determination of fracture toughness of
monolithic ceramics' consists of five parts:
Part 1: Guide to test method selection
Part 2: Single-edge pre-cracked beam (SEPB) method
Part 3: Chevron notched beam (CNB) method
Part 4: Surface crack in flexure (SCF) method
Part 5: Single-edge vee-notch beam (SEVNB) method
1 Scope
This part of CEN/TS 14425 provides a test method for fracture toughness determination based on the
chevron-notch method. For the purposes of this standard, the term monolithic includes particle and whisker
reinforced advanced technical ceramics which can be regarded as macroscopically homogeneous. It does not
included long-fibre reinforced ceramics.
2 Normative references
This Technical Specification incorporates by dated or undated reference, provisions from other publications.
These normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to
this Technical Specification only when incorporated in it by amendment or revision. For undated references
the latest edition of the publication referred to applies (including amendments).
EN 843-1 Advanced technical ceramics — Monolithic ceramics — Mechanical properties at room
temperature — Part 1: Determination of flexural strength
ENV 1006 Advanced technical ceramics — Monolithic ceramics - Guidance on the selection of test
pieces for the evaluation of properties
EN ISO 7500-1 Metallic materials — Verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines (ISO 7500-1:1999)
EN ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories (ISO/IEC
17025:1999)
ISO 3611 Micrometer callipers for external measurement
3

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CEN/TS 14425-3:2003 (E)
ISO 4677 Atmospheres for conditioning and testing — Determination of relative humidity
3 Terms and definitions
For the purposes of this Technical Specification, the following terms and definitions apply.
3.1
chevron-notch test piece
test piece in which a two coplanar saw cuts are made at an angle to each other part way through a test piece
to leave a remaining cross-section with a sharp tip from which a crack may be initiated in a controlled or semi-
controlled manner.
4 Principle, significance and use
In the chevron-notched beam method, a crack is generated during the test from a sharp tip resulting when two
coplanar notches are cut in a test-piece (Figure 1). This overcomes the need to generate sharp planar cracks
before commencing the test.
During the test, the crack front widens as the crack propagates from the tip, resulting in an increase in the
force required to maintain growth. Countering this, the test-piece becomes more compliant as the crack
lengthens, and so the two effects result in a peak load being attained after some distance of propagation. The
toughness is determined from the peak force applied.
This test method employs the chevron notch in a flexural strength test-piece, loaded in four-point bending
geometry. The advantage is that it can be performed on standard flexural strength test pieces.
The test is most appropriate for homogeneous isotropic materials, but can be used with care on anisotropic
materials subject to the geometry of fracture remaining valid. In materials which are inhomogeneous on the
scale of the crack dimensions, a wide scatter of results and the development of invalid non-planar cracks may
occur. In addition, the test is valid primarily for materials which do not show rising crack resistance with
increasing crack length. Since the crack width progressively increases as propagation occurs, the concurrent
presence of rising crack resistance means that the crack front would no longer stay straight but would become
convex, producing an uncertainty in the calculated results.
It should be noted that this test employs a slowly moving crack. The numerical value for the fracture
toughness calculated from this method may not be the same as those from fast crack propagation tests,
especially if the susceptibility to subcritical crack growth is significant.
5 Test apparatus
5.1 Flexural strength test apparatus of four-point bending type in accordance with the requirements in EN
843-1.
5.2 Mechanical testing machine capable of accurate recording of load/displacement data for loads in the
range 0 N to 500 N. The load shall be calibrated in accordance with EN ISO 7500-1.
NOTE A stiff loading system (i.e. frame, load cell and fixtures, etc.) is advantageous for this test. The compliance is
-5
ideally less than 5 x 10 m/N (see [1]).
5.3 Micrometer in accordance with ISO 3611 but measuring to an accuracy of 0,002 mm.
5.4 Calibrated device for measuring dimensions of the cut chevron after fracture, reading to an accuracy of
0,002 mm or better.
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CEN/TS 14425-3:2003 (E)
NOTE This may be achieved by use of an appropriate travelling microscope, or a conventional microscope with a
calibrated stage micrometer, or a microscope with a micrometer eyepiece.
5.5 Humidity measuring device for measuring relative humidity to an accuracy of ± 2%, e.g. those according
to ISO 4677.
6 Test pieces
6.1 Material selection
Select the material or components from which test pieces are to be machined with reference to the
considerations given in ENV 1006.
6.2 Test piece dimensions
6.2.1 The test pieces shall preferably be of dimensions as for determination of flexural strength and
described in EN 843-1. Alternatively, if availability of material permits, the dimensions may be scaled larger for
convenience of machining of the notch.
NOTE It is usually advantageous to test coarse-grained or heterogeneous materials in larger test piece sizes
because it improves the chances of obtaining a valid test (see 7.9).
6.2.2 The standard size test pieces shall be 3,00 ± 0,15 mm x 4,00 ± 0,15 mm in cross-section, and have a
minimum length of 45 mm. The surfaces shall be machined to a flatness of better than 0,01 mm over the test
piece length, and opposite pairs of faces shall be parallel to better than 0,01 mm over the test piece length.
The section should be visibly rectangular.
NOTE Chamfering in accordance with EN 843-1 is unnecessary for this test.
6.2.3 The test piece surfaces shall be ground to a good quality finish using final grinding with a peripheral
wheel of grit size between 320 and 500 mesh grit, using a depth of cut of no more than 0,002 mm for the last
0,04 mm of material removed from each surface. No edge treatment is necessary.
NOTE Although a large notch is placed in the test piece, the quality of grinding remains import
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