ISO 20501:2003

Foreword
1 Scope
2 Terms and definitions
  2.1 Defect populations
  2.2 Mechanical testing
  2.3 Statistical terms
  2.4 Weibull distributions
3 Symbols
4 Significance and use
5 Method A: maximum likelihood parameter estimators for single
  flaw populations
  5.1 General
  5.2 Censored data
  5.3 Likelihood functions
  5.4 Bias correction
  5.5 Confidence intervals
6 Method B: maximum likelihood parameter estimators for
  competing flaw populations
  6.1 General
  6.2 Censored data
  6.3 Likelihood functions
7 Procedure
  7.1 Outlying observations
  7.2 Fractography
  7.3 Graphical representation
8 Test report
Annex A (informative) Converting to material-specific
                      strength distribution parameters
Annex B (informative) Illustrative examples
Annex C (informative) Test specimens with unidentified
                      fracture origin
Annex D (informative) Fortran program
Bibliography

ISO 20501:2003 covers the reporting of uniaxial strength data and the estimation of probability distribution parameters for advanced ceramics which fail in a brittle fashion. The failure strength of advanced ceramics is treated as a continuous random variable. Typically, a number of test specimens with well-defined geometry are brought to failure under well-defined isothermal loading conditions. The load at which each specimen fails is recorded. The resulting failure stresses are used to obtain parameter estimates associated with the underlying population distribution.

ISO 20501:2003 is restricted to the assumption that the distribution underlying the failure strengths is the two-parameter Weibull distribution with size scaling. Furthermore, this International Standard is restricted to test specimens (tensile, flexural, pressurized ring, etc.) that are primarily subjected to uniaxial stress states.

Measurements of the strength at failure are taken for one of two reasons: either for a comparison of the relative quality of two materials, or the prediction of the probability of failure (or alternatively the fracture strength) for a structure of interest. ISO 20501:2003 permits estimates of the distribution parameters which are needed for either. In addition, this International Standard encourages the integration of mechanical property data and fractographic analysis.