SIST-TS CEN/TS 14425-1:2005

SLOVENSKI STANDARD
SIST-TS CEN/TS 14425-1:2005
01-januar-2005
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Advanced technical ceramics - Test methods for determination of fracture toughness of
monolithic ceramics - Part 1:Guide to test method selection
Hochleistungskeramik - Prüfverfahren zur Bestimmung der Bruchzähigkeit von
monolithischer Keramik - Teil 1: Leitlinie zur Auswahl des Prüfverfahrens
Ta slovenski standard je istoveten z: CEN/TS 14425-1:2003
ICS:
81.060.30 Sodobna keramika Advanced ceramics
SIST-TS CEN/TS 14425-1:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TS CEN/TS 14425-1:2005

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SIST-TS CEN/TS 14425-1:2005
TECHNICAL SPECIFICATION
CEN/TS 14425-1
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 1:Guide to
test method selection
Céramiques techniques avancées Hochleistungskeramik – Prüfverfahren zur Bestimmung der
Bruchzähigkeit von monolithischer Keramik – Teil 1:
Leitlinie zur Auswahl des Prüfverfahrens
This Technical Specification (CEN/TS) was approved by CEN on 19 January 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.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
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 14425-1:2003 E
worldwide for CEN national Members.

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SIST-TS CEN/TS 14425-1:2005
CEN/TS 14425-1:2003 (E)
Contents
Page
Foreword.3
1 Scope .3
2 Normative references .3
3 Terms and definitions.4
4 Significance and use .5
5 Test methods.5
5.1 Background .5
5.2 Test methods.5
5.3 Test-piece microstructure.8
5.4 Test-piece machining .8
5.5 Scatter of test results .8
6 Criteria for selection of an apparent fracture toughness test method.9
Bibliography .12
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Foreword
This document (CEN/TS 14425-1:2003) has been prepared by Technical Committee CEN/TC 184 “Advanced
technical ceramics”, the secretariat of which is held by BSI.
This document has been prepared under a mandate given to CEN by the European Commission and the European
Free Trade Association.
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
1.1 This part of CEN/TS 14425 provides information on the comparative value, and guidance on the selection, of
test methods for determining the apparent fracture toughness of monolithic advanced technical ceramics. For the
purposes of this Technical Specification, the term monolithic includes particle, platelet and whisker reinforced
advanced technical ceramics which can be regarded as macroscopically homogeneous. It does not include long-
fibre reinforced ceramics.
1.2 Reference is made in this part of CEN/TS 14425 to specific test methods described in other parts of this
Technical Specification.
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.
3

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3 Terms and definitions
For the purposes of this Technical Specification, the following terms and definitions apply.
3.1
stress intensity factor (K)
magnitude of the factor determining the ideal crack tip stress field (a stress-field singularity) for a particular mode in
a homogeneous linear-elastic body. This Technical Specification deals primarily with opening mode behaviour, K .
I
3.2
critical stress intensity factor (K )
c
magnitude of the stress intensity factor required to cause a crack to propagate at high velocity.
3.3
crack extension resistance
resistance to propagation of a crack expressed as either (1) the stress intensity factor for crack propagation
(commonly referred to as fracture toughness), or (2) the force per unit crack width required to extend a crack, or (3)
the value of J, the so-called J-integral.
3.4
fracture toughness
resistance displayed by a material to the propagation of a crack through it.
NOTE This term should normally be qualified with the conditions under which the test is performed since the value
obtained may depend on the crack size, geometry, stress field, crack velocity and test method.
3.5
apparent fracture toughness
fracture toughness determined by a particular method under the conditions imposed by that method.
3.6
work of fracture
external mechanical work performed on a test piece to produce unit area of new macroscopic crack face.
3.7
plane-strain fracture toughness
fracture toughness under conditions of crack tip plane-strain, i.e. where all strains are confined to a plane normal to
the crack front and containing the crack propagation direction.
3.8
stable crack growth
growth of a crack under known and controlled conditions by virtue of the experimental technique employed.
3.9
unstable crack growth
growth of a crack under conditions where the acceleration of the crack front is uncontrolled by virtue of the
experimental technique employed.
3.10
pop-in
sudden jump of a pre-existing crack front from an initial position or the development of a new crack to a stable
position on application of a force without catastrophic failure of the test-piece.
3.11
R-curve
plot of crack extension resistance as a function of stable crack extension.
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4 Significance and use
The toughness of a brittle, nominally crack-free material is not an engineering design parameter in the same sense
as might be the case for more ductile materials. The reason is that the microscopic flaws, such as grain
boundaries, large grains, pores, inclusions or processing defects, are too small to be measured non-destructively in
a meaningful way. Despite this, the toughness of relatively brittle materials is an important guide to other
mechanical properties, such as defect tolerance, abrasive wear and erosion resistance, impact resistance, fatigue
resistance, and thermal shock damage resistance.
5 Test methods
5.1 Background
It is recognised that the apparent plane strain fracture toughness of advanced technical ceramics may not be a
unique material property. The numerical value obtained in any particular test may be controlled by factors
associated with the test method, by the length of the crack, and by the velocity at which the crack propagates. Thus
the results from different types of test may not be numerically equivalent. Some of the important factors in test
method selection are given below.
NOTE The Bibliography contains a list of fracture toughness method assessments for advanced technical ceramics.
5.2 Test methods
5.2.1 The wide variety of possible test methods for determining opening mode apparent fracture toughness (K )
Ic
fall into two groups:
1) those which are considered to give good-quality determinations of critical stress intensity factor with
accurate and reliable calibrations;
2) those which are in wide-spread use but which are considered to have considerable calibration
uncertainties associated with them, or where the crack cannot be well characterised, or is pre-stressed by
the method by which it is introduced; such tests might be used for comparative purposes only.
5.2.2 This Technical Specification covers a total of six methods which can be applied to flexural test-pieces as
described in EN 843-1. Some of these are considered to behave in accordance with the first group, and some in
accordance with the second group. Table 1 lists the methods and their level of quality for apparent fracture
toughness determination. Figure 1 illustrates schematically the test-piece and crack geometries.
5.2.3 Methods which involve pre-cracks or developing cracks longer than a few tens of micrometres may be
influenced by so-called rising crack resistance (R-curve) behaviour. This occurs particularly in materials in which
crack face separation is incomplete behind the developing crack. This has been found to occur in coarse-grained
materials such as alumina, and in materials containing whiskers or platelet reinforcement, and in materials
containing metallic phase reinforcement. The effect may also be found in materials which undergo phase
transformation close to the crack tip as the crack propagates, e.g. in some zirconias. The R-curve effect may be
test piece geometry dependent, and is not a uniquely quantifiable material characteristic.
5

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SIST-TS CEN/TS 14425-1:2005
CEN/TS 14425-1:2003 (E)
SEPB
CNB
SCF
SEVNB
IF
IS
Figure 1 — Schematic diagrams of the range of apparent fracture toughness test methods.
For abbreviations see table 1
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Table 1 — Apparent fracture toughness tests performed on small test-pieces
Method Description Calibrations Uncertainties or difficulties
Single-edge pre- A flexural test on a Accurate calibrations Pre-cracking requires some skill
cracked beam beam into the tensile available for wide to obtain straight-fronted cracks.
(SEPB) side of which a short range of pre-crack Results are influenced by rising
straight sharp crack lengths; toughness at crack resistance behaviour
*
has been introduced a defined crack length
(CEN/TS 14425-2)
Chevron notched A flexural test on a Accurate calibrations Toughness at an ill-defined
beam (CNB) beam with two crack length; crack initiation
coplanar angled difficult in some materials; result
*
(CEN/TS 14425-3) notches leaving a influenced by rising crack
sharp-tipped triangular resistance behaviour
shaped region to
fracture
Sur
...