Bsi bs en 00820 1 2002 (2003)

BRITISH STANDARD BS EN 820 1 2002 Advanced technical ceramics — Methods of testing monolithic ceramics — Thermomechanical properties — Part 1 Determination of flexural strength at elevated temperature[.]

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BRITISH STANDARD BS EN

820-1:2002

Advanced technical ceramics — Methods of testing monolithic

ceramics — Thermomechanical properties —

Part 1: Determination of flexural strength at elevated temperatures

The European Standard EN 820-1:2002 has the status of a British Standard

ICS 81.060.30

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Copyright British Standards Institution

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`,,,,``,`,,,,`,,,`,,`,`,``,,-`-`,,`,,`,`,,` -This British Standard was

published under the authority

of the Standards Policy and

Strategy Committee on

6 March 2003

ISBN 0 580 41375 6

National foreword

This British Standard is the official English language version of

EN 820-1:2002 It supersedes DD ENV 820-1:1994 which is withdrawn The UK participation in its preparation was entrusted to Technical Committee RPI/13, Advanced technical ceramics, which has the responsibility to:

A list of organizations represented on this committee can be obtained on request to its secretary

Cross-references

The British Standards which implement international or European

publications referred to in this document may be found in the BSI Catalogue

under the section entitled “International Standards Correspondence Index”, or

by using the “Search” facility of the BSI Electronic Catalogue or of British

Standards Online

This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application

Compliance with a British Standard does not of itself confer immunity from legal obligations.

enquiries on the interpretation, or proposals for change, and keep the

UK interests informed;

promulgate them in the UK

Summary of pages

This document comprises a front cover, an inside front cover, the EN title page, pages 2 to 10, an inside back cover and a back cover

The BSI copyright date displayed in this document indicates when the document was last issued

Amendments issued since publication

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`,,,,``,`,,,,`,,,`,,`,`,``,,-`-`,,`,,`,`,,` -EUROPEAN STANDARD

NORME EUROPÉENNE

EUROPÄISCHE NORM

EN 820-1

October 2002

ICS 81.060.30 Supersedes ENV 820-1:1993

English version

Advanced technical ceramics - Methods of testing monolithic ceramics - Thermo m echanical properties - Part 1: Determination

of flexural strength at elevated temperatures

Céramiques techniques avancées - Méthode d'essai des

céramiques monolithiques - Propriétés thermodynamiques

- Détermination de la résistance à la flexion à températures

élevées

Hochleistungskeramik Monolithische Keramik -Thermomechanische Eigenschaften - Teil 1: Bestimmung der Biegefestigkeit bei erhöhten Temperaturen

This European Standard was approved by CEN on 8 August 2002.

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 Management Centre 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 Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E F Ü R N O R M U N G

Management Centre: rue de Stassart, 36 B-1050 Brussels

worldwide for CEN national Members.

Ref No EN 820-1:2002 E

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Contents

page

Foreword 3

1 Scope 4

2 Normative references 4

3 Terms and definitions 4

4 Apparatus 5

4.1 General 5

4.2 Test jig 5

4.3 Heating device 6

4.4 Test machine 6

4.5 Linear measuring devices 6

4.6 Drying oven 7

5 Test pieces 7

6 Test temperatures and number of tests 7

7 Test procedure 7

8 Calculations 8

9 Accuracy and references 9

10 Test report 10

Copyright British Standards Institution Reproduced by IHS under license with BSI - Uncontrolled Copy Document provided by IHS Licensee=Bureau Veritas/5959906001, 11/08/2004 06:05:32 MST Questions or comments about this message: please call the Document

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EN 820-1:2002 (E)

3

Foreword

This document EN 820-1:2002 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 April 2003, and conflicting national standards shall be withdrawn at the latest by

April 2003

This document supersedes ENV 820-1:1993

This document has been prepared under a mandate given to CEN by the European Commission and the European

Free Trade Association

EN 820 'Advanced technical ceramics – Methods of testing monolithic ceramics – Thermomechanical properties'

consists of three Parts:

 Part 1 : Determination of flexural strength at elevated temperatures

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,

France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain,

Sweden, Switzerland and the United Kingdom

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4

1 Scope

This Part of this European Standard specifies a method of determining the three-point or four-point flexural strength of

advanced monolithic technical ceramics at elevated temperatures as agreed between parties to the test The test can

be performed in any appropriate atmosphere

2 Normative references

This European Standard incorporates by dated or undated reference, provisions from other publications These

normative references are cited at the appropriate places in the text, and in the publications listed hereafter For dated

references, subsequent amendments to or revisions of any of these publications apply to this European Standard 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 tests at room temperature – Part 1:

Determination of flexural strength

ENV 843-5, Advanced technical ceramics – Monolithic ceramics – Mechanical tests at room temperature – Part 5:

Statistical analysis of fracture data

EN 10002-2, Metallic materials – Tensile testing – Part 2: Verification of the force measuring system of the tensile

testing machine

EN ISO 17025, General requirements for the competence of testing and calibration laboratories

IEC 60584, Thermocouples - Part 1: Reference tables

IEC 60584, Thermocouples - Part 2: Tolerances

ISO 3611, Micrometer callipers for external measurement

3 Terms and definitions

For the purposes of this European Standard, the following terms and definitions apply

3.1

nominal flexural strength

maximum nominal stress at the instant of failure supported by the material when loaded in elastic bending

NOTE It is recognised that flexural strength tests on ceramics at elevated temperature may reveal inelastic behaviour in

the material Under such conditions, the nominal flexural strength calculated in accordance with this standard is not strictly a

valid result, since it tends to overestimate the true surface stress in the test piece This method requires that the

load/displacement relationship for each test piece at each temperature is inspected, and the validity of the result determined

3.2

three-point flexure

means of bending a beam test piece whereby the test piece is supported on bearings near its ends, and a central load

is applied

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EN 820-1:2002 (E)

5

3.3

four-point flexure

means of bending a beam test piece whereby the test piece is supported on bearings near its ends, and is loaded

equally at two points symmetrically disposed about the centre of the supported span

3.4

inelastic deformation

for the purposes of the test, the deformation of a test specimen under load which is not entirely elastic and reversible on

removal of the load

3.5

subcritical crack growth

extension of existing cracks or flaws under a stress which does not produce instant failure

NOTE This effect can be due to the intrinsic crack propagation of the material, additionally influenced by the environment

4 Apparatus

4.1 General

The test is carried out in a similar manner to that prescribed in EN 843-1 for testing at room temperature, with the

exceptions that the test jig shall be constructed from materials which are capable of remaining linearly elastic at the

temperature of testing, and that a means of heating the test jig and test piece to the test temperature is required

4.2 Test jig

The test jig shall be of a design that allows full articulation for alignment of the support and loading rollers on the

surfaces of the test piece, and in which the rollers are capable of rolling to minimise friction between the rollers and the

test piece

NOTE 1 It is recognised that –practical limitations can restrict the design of the test jig, and oxidation effects can restrict its

function In such cases, alternatives may be employed, but deviations from the function specified above should be reported in

the report (see clause 10, d))

The outer span of the test jig shall be either 20,0 mm ± 0,5 mm (span A) or 40,0 mm ± 0,5 mm (span B) For three-point

flexure the loading roller shall be centralised relative to the span to within 0,2 mm For four-point flexure, the inner span

shall be 10,0 ± 0,2 mm (span A) or 20,0 mm ± 0,2 mm (span B) The inner rollers shall be symmetrically positioned

relative to the outer rollers to better than 0,2 mm

NOTE 2 This represents a relaxation of centralisation requirements compared with room temperature testing (requirement

0,1 mm, see EN 843-1) because it can become relatively more difficult to set up test jigs inside furnaces

Measurements of the positions of the rollers shall be made with a travelling microscope (4.5.2)

The rollers shall be made from a material which is capable of remaining linearly elastic up to the maximum temperature

of the series of tests For tests to 400 °C, hardened steel rollers as in EN 843-1 shall suffice For higher temperatures it

is recommended that the test jig is constructed from fine-grained strong refractory ceramic materials

NOTE 3 For temperatures up to 1 400 °C, high-purity high-alumina ceramic materials can be used For temperatures up to 1

500 °C in air or up to 1700 °C in neutral atmospheres, sintered silicon carbide is recommended

Consideration should be given to any potential reaction between the test material and the rollers at the maximum test

temperature, and the choice of roller material shall be made such that reactions are minimised In particular, non-oxide

ceramic materials may tend to oxidise, and the oxide then may react with the loading rollers Rollers shall be

maintained with a clean smooth burr-free surface for all tests They shall be inspected before any test to ensure they

are undamaged, and are capable of rolling freely in the jig at the start of the test If necessary, rollers should be

replaced to maintain correct jig function Similarly, reactions between the main ceramic components of the test jig shall

be minimized by appropriate choice of material

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6

NOTE 4 At very high temperatures, the progressive oxidation of non-oxide jig components can lead to the development of

frictional effects due to inability of the rollers to roll freely Such effects can lead to uncertainties in nominal flexural strength of

up to 5% It is not possible to quantify this effect, which is likely to be time, temperature and material dependent Jig components

can be found to have welded together on cooling to room temperature They should be gently separated and cleaned before

re-use

The load shall be applied to the test jig through solid or hollow columns which are loaded by the test machine These

columns shall be of a material which remains linearly elastic to the maximum testing temperature

NOTE 5 To ascertain this, the columns of the test jig can be brought into contact at the appropriate test temperature with or

without the jig in place A load equivalent to that estimated to be needed to fracture test pieces is applied, and the apparent load

displacement relationship is examined for evidence of non-linearity with increasing load (see clause 8)

4.3 Heating device

The test jig shall be contained within a furnace or suitable heating device of design appropriate to the maximum

temperature for the tests, and capable of reaching the maximum testing temperature within 3 h

NOTE 1 The use of very fast heating rates is not recommended because of risk of fracture of ceramic components in the test

jig or columns

The temperature control system used with the furnace shall be capable of controlling to within ± 5 °C using a suitable

thermocouple The temperature of the test piece shall be recorded using a second thermocouple manufactured in

accordance with the manufacturing tolerances stated in IEC 60584-2, allowing the use of reference tables in IEC

60584-1 or, alternatively, calibrated in a manner traceable to the International temperature scale ITS-90 The tip of the

thermocouple shall be close to but not touching the test piece It shall previously have been determined that the

temperature of the test piece shall not vary by more than ± 5 °C over its length after a 15 minute hold time at the

required testing temperature

NOTE 2 For use in an air atmosphere, the furnace can most conveniently be of a split design allowing access to the test jig

in the position for testing For a controlled atmosphere, a similar arrangement may be used with the test jig surrounded by a

gas-tight work-tube, or alternatively, a sealed atmosphere furnace may be employed The flow conditions for gas should also be

considered It should preferably be static or of limited flow rate to minimise problems of inhomogeneous test piece temperature

In all cases it is desirable to have ready access to the test jig during set-up A multiple test jig or hot specimen insertion system

can have some advantages in terms of total time required for testing, but care should be taken that the jig and test piece

alignment requirements are maintained for all jigs and/or test pieces, and the 15 min temperature equilibration time is used for

each test piece

NOTE 3 It is advisable to employ water cooling for parts of the furnace and loading column system to minimise the

temperature variations of the test machine and to protect load measuring devices

NOTE 4 It is permissible to employ a system for rapid cooling of the test piece fragments after failure to allow inspection of

fracture surfaces without subjecting them to further heating or to oxidation This can most readily be done by allowing the

fragments to drop out of the furnace down the support tube, preferably onto ceramic fibre blanket to avoid further damage

4.4 Test machine

The test machine shall be capable of applying a force to the test jig at constant loading or cross-head displacement

rate The test machine shall be equipped for recording the load and displacement output for inspection, and for

determining the peak load at fracture The accuracy of the test machine shall be in accordance with EN 10002-2,

Grade 1 (error limit of 1% of indicated load)

Ensure that the force calibration of the test machine has recently been checked in accordance with EN 10002-2

4.5 Linear measuring devices

4.5.1 A micrometer in accordance with ISO 3611, capable of recording to 0,01 mm and accurate to this level

Flat anvils shall be used to minimise risks of producing indentation damage in test pieces during measurement

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EN 820-1:2002 (E)

7

4.5.2 Travelling microscope or other suitable device reading to the nearest 0,05 mm (used for measurement of

the distance between loading rollers)

4.6 Drying oven

A drying oven capable of maintaining (120 ± 10) °C

5 Test pieces

Test pieces shall be prepared in accordance with the procedures defined in EN 843-1, according to agreement

between parties, and in the surface finish categories:

i As-fired;

ii Machined (agreed procedure);

iii.1 Standard finish by grinding;

iii.2 Standard finish by lapping and/or polishing

After machining they shall be washed free from cutting and grinding fluids, and dried in an oven at (120 ± 10) °C for 2 h,

followed by equilibration for at least 2 h in the laboratory atmosphere

NOTE If the test temperature is greater than about 120 °C, equilibration is generally not necessary

6 Test temperatures and number of tests

The test temperatures and the number of test pieces to be tested at each temperature shall be agreed between parties

At least 5 test pieces shall be tested at each temperature For statistical evaluation of strength data (e.g Weibull

parameters, etc.) the minimum number shall be 30 (see ENV 843-5)

NOTE Weibull parameters estimated from the test data can be seriously in error if the number of nominally identical

tests-pieces is less than 30 The uncertainty in the parameters is sufficient as to render comparisons between materials meaningless

7 Test procedure

Assemble the furnace and the test jig in the test machine

Measure the width and thickness of each test piece at a minimum of three positions approximately equidistant along its

length, using the micrometer (4.5.1) Do not apply any marks to the test piece, e.g pencil marking, except to the ends

outside the test span, if the test temperature is to exceed 400 °C

NOTE 1 Marking materials that withstand high temperatures can contain a clay or other inorganic components which can

react with the test piece and influence the measured strength properties

Place each test piece in turn in the test jig orientated so that the appropriate face is subjected to tensile stress on

loading Ensure that both test piece and jig are centralised with respect to the loading axis, and that the test jig rollers

are in their correct starting positions as defined in 4.2

NOTE 2 If the available furnace arrangements do not allow convenient access to the test jig for aligning the test piece, an

alignment jig should be used Alternatively, the alignment can be performed out of the furnace, and then the whole arrangement

placed between the loading columns Care should be taken to ensure that the test piece does not move during this process If

there is a risk of movement, a temporary adhesive, such as polystyrene cement, can be used to fix the test piece and rollers in

position This burns out at 200 °C to 300 °C on heating in the furnace, leaving all components correctly positioned

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8

If necessary apply a small load not more than 5% of the expected fracture load to keep the test piece in position Raise

the furnace temperature to the required test temperature, and maintain this temperature for a period of 15 minutes to

ensure thermal equilibrium During heating ensure that any load applied to the test piece does not increase beyond 5%

of the expected failure load as a consequence of thermal expansion of the columns and the test jig

After stabilisation of the test temperature, select a rate of load application or cross-head displacement rate such that

fracture is obtained in a period of 5 - 15 s, this rate to be kept the same for all tests in the series Choose a recording

range on the test machine such that the expected average force at fracture is near the centre of the range If the

recordings of load and displacement are to be made using a chart recorder, select a speed range on the chart recorder

such that the load/displacement trace is drawn at about 45 o to the chart axis

NOTE 3 If the test machine does not have constant loading rate control, selection of a displacement rate may have to be

determined by experiment, depending on the elastic compliance of the test machine, the stiffness of the test jig and the loading

columns, and the elastic properties of the test piece A machine displacement rate of 0,5 mm/min is a convenient starting point

for most machines in cases where the expected strength of the material is 200 MPa to 400 MPa For materials which are much

weaker or much stronger than this, the displacement rate can have to be respectively decreased or increased by an appropriate

factor

NOTE 4 The strength of advanced monolithic technical ceramics can be markedly affected by the test rate as a consequence

of the phenomenon of sub-critical crack growth, especially at temperatures at which inelastic deformations become significant

The short time required by this test is intended to match the testing rate prescribed in EN 843-1, and to compromise between

the elimination of significant testing rate effects and the ability of test machines and load recording equipment to provide an

accurate measure of peak fracture load

Apply the test force at the chosen rate and record the load/displacement behaviour Record the peak load supported by

the test piece at the instant of fracture and the time to failure

Unless a multiple test piece system or a hot test piece insertion and rapid quench arrangement has been employed,

cool the furnace to ambient temperature and retrieve the broken fragments of test piece for later examination

Even if the test piece has failed away from the central loading roller in three-point bending or outside the uniformly

stressed zone between the two loading rollers in four-point bending, the result shall not be ignored, and shall be

included in the report of the test series and in the calculation of nominal mean strength

If the test pieces were in the as-fired condition before testing, remeasure the thickness and width of the test piece at the

fracture position

Inspect the test piece fragments for signs of oxidation and/or reaction with the loading rollers Inspect the loading rollers

for signs of reaction with the specimen or oxidation or flattening which would impair the performance of the jig

Renovate or replace the loading rollers if they do not conform to the requirements for free rolling movement

Repeat the procedure for each test piece

8 Calculations

Calculate the nominal flexural strength of each test piece from its dimensions and peak load at failure in accordance

with EN 843-1

For three-point flexure:

2

3

=

h b

l

Fm f

For four-point flexure:

2

3

=

h b

d

Fm

f

Tiêu đề	Advanced Technical Ceramics — Methods Of Testing Monolithic Ceramics — Thermomechanical Properties — Part 1: Determination Of Flexural Strength At Elevated Temperatures
Trường học	British Standards Institution
Chuyên ngành	Advanced Technical Ceramics
Thể loại	British Standard
Năm xuất bản	2003
Thành phố	London

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