EN 12788:2005

SLOVENSKI STANDARD
01-december-2005
Advanced technical ceramics - Mechanical properties of ceramic composites at
high temperature under inert atmosphere - Determination of flexural strength
Advanced technical ceramics - Mechanical properties of ceramic composites at high
temperature under inert atmosphere - Determination of flexural strength
Hochleistungskeramik - Mechanische Eigenschaften von keramischen
Verbundwerkstoffen bei hoher Temperatur an inerter Atmosphäre - Bestimmung der
Biegefestigkeit
Céramiques techniques avancées - Propriétés mécaniques des céramiques composites
a haute température sous atmosphere inerte - Détermination de la résistance en flexion
Ta slovenski standard je istoveten z: EN 12788:2005
ICS:
81.060.30 Sodobna keramika Advanced ceramics
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 12788
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2005
ICS 81.060.99 Supersedes ENV 12788:1998
English Version
Advanced technical ceramics - Mechanical properties of ceramic
composites at high temperature under inert atmosphere -
Determination of flexural strength
Céramiques techniques avancées - Propriétés mécaniques Hochleistungskeramik - Mechanische Eigenschaften von
des céramiques composites à haute température sous keramischen Verbundwerkstoffen bei hoher Temperatur an
atmosphère inerte - Détermination de la résistance en inerter Atmosphäre - Bestimmung der Biegefestigkeit
flexion
This European Standard was approved by CEN on 18 July 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12788:2005: E
worldwide for CEN national Members.

Contents Page
Foreword .3
1 Scope .4
2 Normative references .4
3 Terms, definitions and symbols .4
4 Principle.5
5 Apparatus .5
5.1 Test machine .5
5.2 Test jig .5
5.3 Gastight test chamber .7
5.4 Set-up for heating .7
5.5 Temperature measurement devices .7
5.6 Data recording system .7
5.7 Micrometers.7
6 Test specimens .7
7 Test specimen preparation.8
7.1 Machining and preparation .8
7.2 Number of test specimens .8
8 Test procedures .8
8.1 Test set-up: Temperature considerations.8
8.2 Test set-up: Other considerations.9
8.3 Testing technique .9
8.4 Test validity .11
9 Calculation of results.11
9.1 Test specimen origin .11
9.2 Flexural strength.11
10 Test report .12

Foreword
This European Standard (EN 12788:2005) has been prepared by Technical Committee CEN/TC 184
“Advanced technical ceramics”, the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by February 2006, and conflicting national standards shall be withdrawn
at the latest by February 2006.
This document supersedes ENV 12788:1998.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland
and United Kingdom.
1 Scope
This European Standard specifies the conditions for determination of the flexural strength of ceramic matrix
composite materials with continuous fibre reinforcement under three-point or four-point bending for
temperatures up to 2 000 °C under vacuum or a gas atmosphere which is inert to the material under test.
NOTE 1 The use of these environments is aimed at avoiding changes of the material affecting its flexural strength
caused by chemical reaction with its environment during the test.
This European document applies to all ceramic matrix composites with a continuous fibre reinforcement,
unidirectional (1D), bidirectional (2D), and tridirectional (xD, with 2 < x ≤ 3), loaded along one principal axis of
reinforcement.
NOTE 2 The method outlined in this document should not be used to obtain values of flexural strength for design
purposes.
2 Normative references
The following referenced documents are indispensable for the application of this European Standard. For
dated references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 12789, Advanced technical ceramics — Mechanical properties of ceramic composites at high temperature
under air at atmospheric pressure — Determination of flexural strength
EN 60584-1:1995, Thermocouples — Part 1: Reference tables (IEC 60584-1:1995)
EN 60584-2:1993, Thermocouples — Part 2: Tolerances (IEC 60584-2:1982 + A1:1989)
ENV 843-5:1996, Advanced technical ceramics — Monolithic ceramics — Mechanical tests at room
temperature — Part 5: Statistical analysis
EN ISO 7500-1:1999, Metallic materials — Verification of static uniaxial testing machines — Part 1:
Tension/compression testing machines — Verification and calibration of the force-measuring system
ISO 3611:1978, Micrometer callipers for external measurement
3 Terms, definitions and symbols
For the purposes of this European Standard, the following terms, definitions and symbols apply.
3.1
test temperature, T
temperature at the centre of the test piece
3.2
maximum flexural force, F
m
highest recorded force in a flexural test on the test specimen when tested to failure
3.3
flexural stress, σσ
σσ
nominal stress on the outer surface of the test specimen, calculated at mid span
NOTE This stress is conventionally calculated according to the simple beam theory, the basic assumptions of which
may not be met by ceramic matrix composite materials.
3.4
flexural strength, σσσσ
f,m
maximum flexural stress applied to a test specimen that fractures during a flexural test
4 Principle
A test specimen of specified dimensions is heated to the test temperature. It is subsequently flexion loaded to
fracture in such a way that failure occurs in tension, or in compression, along one principal axis of
reinforcement.
The test is performed at constant crosshead displacement rate.
The test duration is limited to reduce any time-dependent effects (e.g. creep).
5 Apparatus
5.1 Test machine
The machine shall be equipped with a system for measuring the force applied to the test specimen. The
system shall conform to grade 1 according to EN ISO 7500-1:1999.
5.2 Test jig
The test jig is composed of two parts, linked to the fixed and mobile parts of the machine. It has two outer
support rollers and one (three-point bending) or two (four-point bending) inner support rollers.
The material of the jig and that of the rollers shall not react with that of the specimen, or with the environment.
The cylindrical rollers shall have a diameter of 4 mm to 10 mm. Their length shall be at least equal to the width
of the specimen. They shall be made of a material with a hardness at least equal to that of the specimen. The
axes of the rollers shall be parallel to within 0,01 mm/mm.
The outer rollers (three and four-point bending) and inner rollers (four-point bending) shall be free to rotate
(see Figure 1).
Either two or three rollers, for three-point or four-point bending respectively, shall be free to pivot around an
axis parallel to the longitudinal direction of the test specimen, in order to adapt to the non-parallelism of the
upper and lower faces of unmachined test specimens (see Figure 1).
The rolling and pivoting ability of the rollers shall not be affected by heating. The distance between rollers shall
be in accordance with Clause 6.
The inner roller(s) shall be centred with respect to the outer rollers to within 0,2 mm. In the case of four-point
bending, a levelling system shall be used to ensure symmetrical loading of the test specimen.
The performance shall not change because of heating.

Key
1 Pivoting loading roller
2 Rolling and pivoting support roller
3 Rolling but non-pivoting support roller
a)
Key
1 Rolling and pivoting loading roller
2 Rolling and pivoting support roller
3 Rolling but non-pivoting support roller
b)
Figure 1 — Articulation required for jigs
5.3 Gastight test chamber
The gastight chamber shall allow proper control of the test specimen environment in the vicinity of the test
specimen during the test. The installation shall be such, that the variation of the load during the time of loading,
which may occur due to parasitic effects (e.g. variation of pressure, seals, etc.), is less than 1 % of the range
of the load cell being used.
Where a gas atmosphere is used, the gas atmosphere shall be inert to the specimen material and test jig
under test conditions.
Where a vacuum chamber is used, the level of vacuum shall not induce chemical and/or physical instabilities
of the test specimen material and test jig.
5.4 Set-up for heating
The set-up for heating shall be constructed in such a way that the variation of temperature of the test
specimen, which is between the outer support rollers, is less than 50 °C at test temperature.
5.5 Temperature measurement devices
For temperature measurement, either thermocouples conforming to EN 60584-1 and EN 60584-2 shall be
used or, where thermocouples not conforming to EN 60584-1 and EN 60584-2 are used, they shall be
calibrated appropriately.
5.6 Data recording system
A calibrated recorder shall be used to record force-time curve.
NOTE The use of a digital data recording system combined with an analogue recorder is recommended.
5.7 Micrometers
Micrometers used for the measurement of the dimensions of the test specimen shall conform to ISO 3611.
6 Test specimens
The amount of material under load shall be represent
...