1、 STD-BSI DD ENV 12788-ENGL 1998 m Lb24bb9 0711334 295 m DRAFT FOR DEVELOPMENT Advanced technical ceramics - Mechanical properties of ceramic composites at high temperature under inert atmosphere - Determination of flexural strength ICs 81.060.99 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED
2、BY COPYRIGHT LAW DD ENV 12788:1998 I l DD ENV 12788:1998 Ama No. This Draft for Development, having been prepared under the diredion of the Sector Board for Matenais and Chemicals, was published under the authority of the Standards Board and comes into effect on 15 July 1998 Date Text affected O BSI
3、 1998 National foreword This Draft for Development is the English language version of ENV 12788: 1998. This publication is not to be regarded as a British Standard. It is being issued in the Draft for Development series of publications and is of a provisional nature because it is considered that fur
4、ther experience is required in its application before it is converted into a British Standard. It should be applied on this provisional basis, so that information and experience of its prafAical application may be obtained. Comments arising from the use of this Draft for Development are requested so
5、 that UK experience can be reported to the European organization responsible for its conversion into a European Standard. A review of this publication will be initiated 2 years after its publication by the European organization so that a decision can be taken on its status at the end of its three-ye
6、ar life. The commencement of the review period will be notified by an announcement in Update Standards. According to the replies received by the end of the review period, the responsible BSI Committee will decide whether to support the conversion into a European Standard, to extend the life of the p
7、restandard or to withdraw it. Comments should be sent in writing to the Secretary of BSI Technicd Committee RPU13, Advanced technical ceramics, 389 Chiswick High Road, London W4 4AL, giving the document reference and clause number and proposing, where possible, an appropriate revision of the text. A
8、 list of organizations represented on this committee can be obtained on request to its secretary. Cross-references “he British Standards which implement intemationai or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “Internat
9、ional Standards Correspondence Index“, or by using the “Find“ facility of the BSI Standards Electronic Caaogue. Summary of pages This document comprises a hnt cover, an inside front cover, the ENV title page, pages 2 to 11 and a back cover. ISBN O 080 30013 7 STD.BS1 DD ENV 12788-ENGL 1998 = Lb24bb
10、0733336 Ob - set the displacement rate on the test machine ; - record the force versus time ; - load the test specimen up to failure ; - adjust the displacement to fully unload specimen and jig ; - read load signal at temperature and under inert atmosphere. NOTE 1 : This load value represents the tr
11、ue zero load on the specimen under the considered testing conditions. When the load cell is not housed in the test chamber, the final load value represents the effect of the gas pressure within the chamber, and the load measured during the flexure strength test has to be corrected by this value. Whe
12、n the load cell is housed in the test chamber, the specimen and the load cell experience the same load. When in this case, load control is used during setting of the inert atmosphere and during heating, the final load signal is zero within the measurement error. When load control is not STD.BSI DD E
13、NV 12788-ENGL 1998 3624bb9 0733344 334 Page 9 ENV 12788: 1998 used, the final load signal differs from zero and the load measured during the flexural strength test should be corrected by this value. NOTE 2 : When preloading is used and the load cell is not housed in the test chamber, the preload lev
14、el changes during setting of the inert atmosphere and during heating. The exact preload level can only be known after establishment of the variation of a nominal zero load during setting the environment and heating. In this case even load control of the machine does not suffice to maintain a constan
15、t preload. The latter can only be achieved when the load cell is housed in the test chamber and experiences the same environmental conditions as the test specimen. - Cool down under inert atmosphere down to a temperature where there is no more a risk of material degradation before opening the furnac
16、e ; - Note the position of fracture location relative to the mid-point of the specimen to the nearest 1 mm and the failure mode (tensile or compressive). 8.4 Test validity The following circumstances invalidate a test : - failure to specify and record test conditions ; - failure to meet specified te
17、st conditions ; - rupture of the specimen not occuring in the tensile or compressive mode ; - rupture occurring outside the zone where the bending moment is maximum (.e. outside the central part, 1/3 L, for three- point bending, and outside the inner span for four-point bending) ; - change in atmosp
18、here ; - rupture is initiated under a roller. 9 Calculation of results 9.1 Test specimen origin A diagram illustrating the reinforcement directions of the material with respect to the longitudinal axis of the specimen shall always accompany the test results. 9.2 Flexural strength Calculate the flexu
19、ral strength using the following expression : 9.2.1 Three-point bending 3FmL 0 f ,m =- 2bh2 where: ofrn is the flexural strength, in megapascal (MPa); Fh is the maximum flexural force, in Newton (N) corrected by the value of the load signal after specimen failure (see paragraph 8.3.4) ; L is the out
20、er span, in millimetres (mm) ; b is the mean width of the specimen, in millimetres (mm) ; h is the mean thickness of the specimen, in millimetres (mm). STDmBSI DD ENV 12788-ENGL 1998 3624669 0711i345 070 D Page 10 ENV 1 2788: 1 998 9.2.2 Four-point bending - 3Fm(L- Li) 2bh2 Oflm - where: ofm is the
21、flexural strength, in megapascal (MPa) ; FA is the maximum flexural force, in Newton (N) corrected by the value of the load signal after specimen failure (see paragraph 8.3.4) ; L is the outer span, in millimetres (mm) ; Lj is the inner span, in millimetres (mm) ; b is the mean width of the specimen
22、, in millimetres (mm) ; h is the mean thickness of the specimen, in millimetres (mm). In the case where the test specimen is protected by a coating intended for specific environmental conditions, the calculation procedure of the ENV 12789 shall be used. IO Testreport The test report shall contain at
23、 least the following information : a) name and address of the testing establishment ; b) date of the test, unique identification of report and of each page, customer name and address and signatory ; c) a reference to this Prestandard, .e. determined in accordance with ENV 12788 three-point or four-p
24、oint bending ; d) yest piece drawing or reference, test jig geometry ; e) description of the test material (material type, manufacturing cade, batch number) ; 9 load train, nature of inert gas and level of pressure or level of vacuum ; Description of the test set up : heating system, temperature mea
25、surement device, load cell, g) temperature gradient over length between outer rollers ; h) heating rate, test temperature, displacement rate ; i) number of tests carried out and the number of valid results obtained; j) force - time records ; k) valid results, mean values and standard deviations (for
26、 Gaussian distribution) ; i) results. mode of failure and failure location, of all the specimens used for obtaining the above STD-BSI DD ENV 12788-ENGL 1998 m 1624669 0711346 TO7 m Page II ENV 12788: 1998 O Pivoting loading roller O Rolling and pivoting support roller O Rolling but non-pivoting supp
27、ort roller O Rolling and pivoting loading roller O Rolling and pivoting support roller O Rolling but non-pivoting support roller o Figure 1: Articulation required for jigs DD ENV 12788:1998 BSI 389 Chiswick High Road London w4 4AL STD-ES1 DD ENV 12788-ENGL 1998 Lb24669 0711347 943 = BSI - British St
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