1、BRITISH STANDARDBS EN 12788:2005Advanced technical ceramics Mechanical properties of ceramic composites at high temperature under inert atmosphere Determination of flexural strengthThe European Standard EN 12788:2005 has the status of a British StandardICS 81.060.99g49g50g3g38g50g51g60g44g49g42g3g58
2、g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN 12788:2005This British Standard was published under the authority of the Standards Policy and Strategy Committee on 29 December
3、2006 BSI 2006ISBN 0 580 49862 XNational forewordThis British Standard was published by BSI. It is the UK implementation of EN 12788:2005. It supersedes DD ENV 12788:1998 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee RPI/13, Advanced technical cerami
4、cs.A list of organizations represented on RPI/13 can be obtained on request to its secretary.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 cannot confer immunity from legal
5、 obligations.Amendments issued since publicationAmd. No. Date CommentsEUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN 12788August 2005ICS 81.060.99 Supersedes ENV 12788:1998 English VersionAdvanced technical ceramics - Mechanical properties of ceramiccomposites at high temperature under inert atmo
6、sphere -Determination of flexural strengthCramiques techniques avances - Proprits mcaniquesdes cramiques composites haute temprature sousatmosphre inerte - Dtermination de la rsistance enflexionHochleistungskeramik - Mechanische Eigenschaften vonkeramischen Verbundwerkstoffen bei hoher Temperatur an
7、inerter Atmosphre - Bestimmung der BiegefestigkeitThis 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 EuropeanStandard the status of a national standard without any alterat
8、ion. Up-to-date lists and bibliographical references concerning such nationalstandards 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 translatio
9、nunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, I
10、celand, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart,
11、36 B-1050 Brussels 2005 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12788:2005: EEN 12788:2005 (E) 2 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
12、 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 procedu
13、res 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 results11 9.1 Test specimen origin 11 9.2 Flexural strength.11 10 Test report .12 EN 12788:2005 (E) 3 Foreword This European Standard (EN 12788:
14、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
15、 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, Belgi
16、um, 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. EN 12788:2005 (E) 4 1 Scope This European
17、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. NO
18、TE 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)
19、, 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 indispe
20、nsable 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 h
21、igh 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 cerami
22、cs 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
23、 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, Fmhighest recorded force in a flexural test on the te
24、st specimen when tested to failure 3.3 flexural stress, 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 materi
25、als. EN 12788:2005 (E) 5 3.4 flexural strength, f,mmaximum 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
26、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
27、 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
28、-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
29、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
30、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 th
31、e 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
32、 the test specimen. The performance shall not change because of heating. EN 12788:2005 (E) 6 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
33、non-pivoting support roller b) Figure 1 Articulation required for jigs EN 12788:2005 (E) 7 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 variati
34、on 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
35、 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
36、, 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 use
37、d, 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 dimensio
38、ns of the test specimen shall conform to ISO 3611. 6 Test specimens The amount of material under load shall be representative of the nature of the material and of the reinforcement structure. NOTE 1 This sets minimum limits to the span and to the width and thickness of the specimen. In the case of f
39、lexural, as opposed to tensile testing, the distribution of the longitudinal reinforcement through the thickness shall also be considered. When this distribution is not symmetrical with respect to the neutral plane, care shall be taken to insure that it is similar between specimens. The thickness an
40、d the distance between the inner and outer roller(s) shall be chosen so as to avoid shear failure. This is achieved by setting a minimum limit to the ratio between the moment arm and the specimen thickness. NOTE 2 A value of 10 is commonly used and translates into a minimum L/h ratio of 20 in three-
41、point bending, and a minimum (L Li)/h ratio of 20 in four-point bending with Li = L/3. NOTE 3 Other factors affecting the size and dimensions of the specimens are the type of the heating and of the loading system, as well as the size of the test chamber. Recommended specimen dimensions are given in
42、Table 1. EN 12788:2005 (E) 8 Table 1 Recommended test specimen and span dimensions Dimensions in millimetres 1D, 2D and xD Tolerance Lt, total length L + 10 1 b, width 10 0,2h, thickness 2,5 0,2 Inner span 25 0,1 Four-point bending, LiOuter span Four-point bending, L 75 0,1Outer span Three-point ben
43、ding, 50 0,1 NOTE 4 If it is necessary to define test specimens of different dimensions, the conditions of Clause 6 should be taken into account. 7 Test specimen preparation 7.1 Machining and preparation During cutting out, care shall be taken to align the longitudinal test specimen axis with one of
44、 the principal axes of reinforcement. Specimens may be tested with either machined or non-machined top and bottom surfaces. In some cases machining is not recommended because it may cause breakage of the fibres near the top and bottom surfaces. When machining these surfaces, care shall be taken to m
45、aintain a reinforcement geometry across the thickness of the specimen, which is representative of the material in the as-processed condition. In particular, the symmetry of an originally symmetric reinforcement geometry shall be preserved in the specimen cross-section after machining. Machining para
46、meters that avoid damage to the material shall be established and documented. These parameters shall be adhered to during test specimen preparation. 7.2 Number of test specimens At least five valid test results, as specified in 8.4, are required per loading condition. For specimens with a non-symmet
47、ric reinforcement geometry with respect to the neutral plane, tests in two orientations for which the tensile and compressive face are interchanged may be necessary. If a statistical evaluation of the flexural strength is required, the number of test specimens shall be in accordance with ENV 843-5.
48、8 Test procedures 8.1 Test set-up: Temperature considerations The following determination shall be carried out under conditions representative of the tests, and shall be repeated every time there is a change in, e.g. material, specimen geometry or loading attachments. In establishing the conditions,
49、 time shall be allowed for temperature stabilization. Prior to testing, the temperature gradient within the outer span shall be established over the temperature range of interest. This shall be done by measuring the specimen temperature at a minimum of three locations, which shall be the points over the supports and at the centre. The temperature variation within the outer span shall be in accordance with 5.4. EN 12788:2005 (E) 9 During a series of tests, the test temperature can be determined either directly by measurement on t
