19/30371866 DC - BS ISO 23102. Fine ceramics (advanced ceramics, advanced technical ceramics). Weibull statistics for strength data of porous ceramics

19/30371866 DC

BS ISO 23102. Fine ceramics (advanced ceramics, advanced technical ceramics). Weibull statistics for strength data of porous ceramics

Status : Current, Draft for public comment   Published : June 2019

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This international standard describes the procedure for determining shape parameter m and scale parameter β when a 2-parameter single mode Weibull distribution is used to express the strength distribution characteristics of porous ceramics that undergo brittle fracture macroscopically. By plotting fracture probability Fi given by the median rank method against fracture strength data σi of the porous ceramics (called the Weibull plot: plotted for lnln(1/(1-Fi)) vs. lnσi), both parameters can be estimated from the slope and y-intercept by linear regression analysis. To apply this international standard to the strength data of porous ceramics, the linearity condition requiring that the square of the correlation factor of the Weibull plot is 0,90 or more shall be satisfied.

In extreme value statistics, the Weibull distribution is the third asymptotic distribution of the minimum value, and the weakest link model gives its physical interpretation where the largest-size defect in the original defect size distribution of a specimen determines its fracture strength. This model undoubtedly represents dense ceramics, but it is not clear regarding a porous ceramic because its fracture process must be changed with increasing porosity (from single fast fracture to multiple stable fracture). However, many porous ceramics have already been analysed by a 2-parameter single mode Weibull distribution, such as reactor-grade polycrystalline graphite. Therefore, in this international standard, Weibull statistics are used extensively relative to porous ceramics that fracture in a brittle manner, on the condition that linearity is attained in the Weibull plot. This is the similar situation that the failure rate of vacuum tubes (called a bath tub curve) can be expressed by the Weibull distribution with different shape parameters (early failure: 0 < m < 1, chance failure: m = 1, wear-out failure: m > 1). In reliability engineering, the Weibull distribution is one of the expressions to show the data.

NOTE 1

The preceding ISO standard for strength reliability of advanced ceramics is ISO 20501Fine ceramics (advanced ceramics, advanced technical ceramics) -- Weibull statistics for strength data, which is based on a 2-parameter Weibull distribution. Recently, however, a counter example has been reported in porous ceramics, which is not expressed by a 2-parameter Weibull distribution (rather a 3-parameter Weibull distribution). For such the data, meaningless parameters are obtained if ISO 20501 is applied. This is because ISO 20501 does not have its valid condition of applying a 2-parameter Weibull distribution, just directly calculating the parameters by maximum likelihood method from the strength data list. Therefore, it is necessary to set another international standard (and separate it from ISO 20501) for the strength reliability of porous ceramics, including the valid condition of applying a 2-parameter Weibull distribution. That is, the square of the correlation factor of the Weibull plot is calculated, and then its linearity is confirmed (the valid condition is satisfied), in such the case, the parameters can be estimated from regression analysis of the Weibull plot (or, applying maximum likelihood method, if necessary). This is the best way for the preceding ISO 20501 not to be revised largely.

NOTE 2

The preceding international standard ISO 20501Fine ceramics (advanced ceramics, advanced technical ceramics) -- Weibull statistics for strength data, is based not on only single mode Weibull distribution but also on multi-modal (competing mode) Weibull distribution to characterize the strength distribution of advanced ceramics. However, in porous ceramics, it is difficult to identify the fracture origin on the fracture surface, so this international standard only assumes single mode Weibull distribution.




Standard Number19/30371866 DC
TitleBS ISO 23102. Fine ceramics (advanced ceramics, advanced technical ceramics). Weibull statistics for strength data of porous ceramics
StatusCurrent, Draft for public comment
Publication Date03 June 2019
Normative References(Required to achieve compliance to this standard)ISO 20501
Informative References(Provided for Information)JIS R 1601:2008, JIS R 1664:2004
International RelationshipsISO/DIS 23102
Draft Expiry Date22 July 2019
DescriptorsAnalysis, Data, Statistics, Special ceramics, Ceramics
ICS81.060.30
Title in FrenchTitre manque
CommitteeRPI/13
PublisherBSI
FormatA4
DeliveryYes
Pages16
File Size428 KB
NotesWarning: this draft is not current beyond its expiry date for comments.
Price£20.00


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