1、DRAFT FOR DEVELOPMENT Advanced technical ceramics - Mechanical properties of ceramic composites at high temperature under inert atmosphere - Determination of creep behaviour ICs 81.060.30 ID ENV 13235:2000 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PEBMIITED BY COPYBIGIW LAW STD-BSI DD ENV L3235-EN
2、GL 2000 Lb24bb9 0873248 031 DD ENV 13235:200 National foreword This Draft for Development is the English language version of ENV 13235 1998. This publication is not to be regarded as a British Standard. It is being issued in the provisional nature because it is considered further experience is requi
3、red 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 practical application may be obtained. In addition, after the ratified text had been approved by CEN, a small number of errors were found i
4、n the text and the opporhinity has been taken to correct the Draft for Development. Coments arising from the use of this Draft for Development are requested so tha UK experience can be reported to the European organizations responsible for its conversion into a European Standard. A review of this pu
5、blication wiil 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 threeyear life. The commencement of the review perid will be notified by an announcement in Update Standards. According to the replies received by th
6、e end of the review period, the responsible BSI Committee wiil decide whether to support the conversion into a European Standard, to extend the life of the prestandard or to withdraw it. Comments should be sent in writing to the Secretary of BSI Technical RFYl3, Advanced technical ceramics, at 389 C
7、hiswick High Road, London W4 U, giving the document reference and clause number and proposing, where possible, an appropriate revision of the text. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implemen
8、t intedonal or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “Inteniational Standards Correspondence Index”, or by using the “Find facility of the BSI Standards Electronic Catalogue. for Development series of publications an
9、d is of a Summary of pages This document comprises a i-ont cover, an inside front cover, the ENV title page, pages 2 to 14, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued This Draft for Development, having been p
10、repared under the direction of the Sector Committee for Materiais and Chemicals, was published under the authority of the Standards Committee and comes into effect on 15 September 2000 Amendments issued since publication Comments Amd.No* ID - the type of heating system ; - the type of gripping syste
11、m. The volume in the gauge length shall be representative of the material. Total length depends on the furnace and on the loading system. NOTE : Generally total length is greater than 150 mm. 8 Test specimen preparation 8. I M8Chhhg and pmpnition During cutting out, care shall be taken to align the
12、test specimen axis with the desired fibre related loading axis. Machining parameters which avoid damage to the material shall be established and documented. These parameters shall be adhered to during test specimen preparation. 8.2 Number of test specimens At least five valid test results, as specif
13、ied in 9.5 are required. By agreement between parties the number of valid test results per datum point may be reduced. 9 Test procedures 9. I Test Set-up: Tempemtun? considetations The following determinations shall be carried out under conditions representative of the tests, and shall be repeated e
14、very time there is a change in material, in specimen geometry, in gripping configuration, etc. Every time a test parameter of test material is changed, time shall be allowed for temperature stabilisation. 9.1.1 Controlled temperature zone Prior to testing, the temperature gradient within the calibra
15、ted length inside the furnace shall be established over the temperature range of interest. This shall be carried out by measuring specimen temperature at a minimum of three locations, which shall be the extensometer reference points and midway between the two. STD-BSI DD ENV 13235-ENGL 2000 II Lb24b
16、b9 O873258 T8O 81 Page 10 ENV 13235:1998 To establish the length of the controlled temperature zone, it is also necessary to measure temperature outside the gauge length. The temperature variation within the controlled temperature zone and the gauge length shall meet the requirements of 4.5 and 6.4,
17、 respectively. Temperatures shall be measured in accorcdance with 6.6. If thermocouples are used to measure the temperature at different locations on the specimen, they shall be embedded (and sealed if necessary) into the specimen to a depth approximately equal to half the specimen dimension in the
18、direction of insertion. 9.1.2 Temperature calibration The test temperature can be determined either directly by measurement on the specimen itself, or indirectly from the temperature indicated by the temperature control device. In the latter case, calibration is necessary. The relationship between t
19、he control temperature and test specimen temperature at the centre of the gauge length shall be established beforehand on a dummy test specimen over the range of temperature of interest. NOTE : The relationship between the temperature indicated by the temperature control system and the test temperat
20、ure is usually established simultaneously with the controlled temperature zone. 9.2 Test Set-up: loading consider8tions For a given test temperature, it is recommended that the loading rate is setfor the highest load level. Once these conditions are established they can be used for the lower load le
21、vels. Loading shall be sufficiently fast in order to insure that creep deformation does not add to the pure tensile deformation during the loading phase. To determine the loading rate which minimises the creep phenomenon; it is necessary to carry out two tests with different loading rates, at the hi
22、ghest load level. If the longitudinal deformations differ by less than 10 % for the two tests, either of the two rates can be used for all tests. If the longitudinal deformations differ by more than 10 %, another test at a higher loading rate is carried out (and this until deformations fall within 1
23、 O %). Two cases can be distinguished : a) when using an universal test machine : in this case, it is possible to carry out tensile tests at the b) When using a creep testing rig : the same load shall be applied with two different time conditions. required load level according to ENV 1892. 9.3 Test
24、Set-up: otber consider8tions Measurement of test specimen dimensions The cross section area is determined at the centre of the specimen and at each end of the gauge length. The cross section area varies with temperature and the variation is very difficult to measure, for this reason, cross section a
25、rea is measured at room temperature. STD-BSI DD ENV L3235-ENGL 2000 Lb24bb7 0873259 917 Page Il ENV 13235: 1998 Dimensions are measured with an accuracy of $: 0,Ol mm. The arithmetic means of the measurements shall be used for calculations. If the test specimen is equipped with marks, the gauge leng
26、th measured at room temperature, shall be known with an accuracy of - zero the load cell ; - set the loading rate according to 9.2 ; - load the test specimen to the required load level ; - operate in load control at constant level during the entire test ; - zero the extensometer ; - record longitudi
27、nal deformation versus time ; - check temperature stability during the test according to 9.4.6 ; - record at the end of the test, the temperature, vacuum level and gas pressure ; - if the test is carried out until failure, record the failure position relative to the specimen centre to 1 mm; - cool u
28、nder inert atmosphere until the risk of degradation is removed before opening the test chamber. NOTE : When the load cell is not housed in the test chamber, the recorded load value is affected by the gas pressure within the chamber. It is therefore necessary to apply a correction factor. If the test
29、 is carried out until failure, the final load value represents this correction ; if the test is not carried out until failure, it is necessary to carry out a specific test to determine this correction. When the load cell is housed in the test chamber, the load cell and the specimen experience the sa
30、me load. 9.4.5.2 Creep testing rig When a creep testing rig is used, measurements shall be taken according to the following procedure : - Record temperature, vacuum level or gas pressure before starting the test ; - load the test specimen to the required load level according to 9.2 ; - zero the exte
31、nsometer ; - record longitudinal deformation versus time ; - check temperature stability during the test according to 9.4.6 ; - record at the end of the test the temperature, vacuum level and gas pressure ; - STD-BSI DD ENV 13235-ENGL 2000 = Lb24bb7 08732bL 575 Page 13 ENV 13235: 1998 - if the test
32、is carried out until failure, record the failure position relative to the specimen centre to 1 mm; - cool under inert atmosphere until the risk of degradation is removed before opening the test chamber. NOTE : In situations where the testing rig is equipped with a load cell and where the load cell i
33、s not houseU In Ihetest chamber, the recored loa value is avected by the gas pressure Within the chamber. It is therefore necessary to apply a correction factor. If the test is carried out until failure, the final load value represents this correction ; if the test is not carried out until failure,
34、it is necessary to carry out a specific test to determine this correction. When the load cell is housed in the test chamber, the load cell and the specimen experience the same load. 9.4.6 Monitoring of temperature stability During long-term testing, drifting of the temperature measurement signal ove
35、r time may affect conformity with 6.4. This shall be checked by comparing the temperature at or after the end of the test with the reading of a different calibrated temperature measurement device. 9.5 lest valldiity The following circumstances invalidate a test : - failure to specify and record test
36、 conditions ; - specimen slippage ; - extensometer slippage ; - failure in an area outside of the controlled temperature zone ; - change in atmosphere around the specimen ; - variation in temperature or in load outside tolerances during the test. 10 Calculation of results 70.7 test specimen origin A
37、 diagram illustrating the reinforcement directions of the material Mth respect to the longitudinal axis of the specimen shall always accompany the test results. 70.2 Results 10.2.1 Creep stress Calculate the applied stress according to the following formula : o = F/A, STDaBSI DD ENV L3235-ENGL 2000
38、Lb24669 08732b2 YOL Page 14 ENV 13235: 1998 where : Q is the applied stress in megapascals, (MPa); Fis the applied force in Newtons, (N); in millimetres (mm is the gauge length, in millimetres (mm) 10.2.3 Drawing of the creep curve Plot the curve versus time. 10.2.4 Creep strain at rupture Read cree
39、p strain at rupture from the curve. 10.2.5 Creep rupture time Read creep rupture time from the curve. 10.3 Creep strain rate curve Plot creep strain rate versus time. NOTE : This curve may help discriminate between primary, secondary and tertiary creep. 11 Test report The test report shall contain t
40、he following information : a) b) c) Name and address of the testing establishment ; Date of the test, unique identification of report and of each page, customer name and address and signatory ; A reference to this standard, .e. determined in accordance with ENV 13235 ; d) Test piece drawing or refer
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