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ASTM C 1239 Document Information:
Title
Standard Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
ASTM International
Publication Date:
Feb 1, 2007
Scope:
This practice covers the evaluation and reporting of uniaxial
strength data and the estimation of Weibull probability
distribution parameters for advanced ceramics that fail in a
brittle fashion (see Fig. 1). The estimated Weibull distribution
parameters are used for statistical comparison of the relative
quality of two or more test data sets and for the prediction of the
probability of failure (or, alternatively, the fracture strength)
for a structure of interest. In addition, this practice encourages
the integration of mechanical property data and fractographic
analysis.
The failure strength of advanced ceramics is treated as a
continuous random variable determined by the flaw population.
Typically, a number of test specimens with well-defined geometry
are failed under isothermal, well-defined displacement and/or
force-application conditions. The force at which each test
specimen fails is recorded. The resulting failure stress data are
used to obtain Weibull parameter estimates associated with the
underlying flaw population distribution.
This practice is restricted to the assumption that the
distribution underlying the failure strengths is the two-parameter
Weibull distribution with size scaling. Furthermore, this practice
is restricted to test specimens (tensile, flexural, pressurized
ring, etc.) that are primarily subjected to uniaxial stress states.
The practice also assumes that the flaw population is stable with
time and that no slow crack growth is occurring.
The practice outlines methods to correct for bias errors in the
estimated Weibull parameters and to calculate confidence bounds on
those estimates from data sets where all failures originate from a
single flaw population (that is, a single failure mode). In samples
where failures originate from multiple independent flaw populations
(for example, competing failure modes), the methods outlined in
Section 9 for bias correction and confidence bounds are not
applicable.
This practice includes the following:
The values stated in SI units are to be regarded as the standard
per IEEE/ASTM SI 10.
Keywords:
- Weibull statistics
- censored data
- confidence bounds
- fractography
- strength
- Weibull characteristic strength
- Weibull modulus
- fracture origin
- unbiasing factors
- maximum likelihood
- advanced ceramics
- Weibull scale parameter
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