Weibull modulus

Weibull modulus is a measure of the distribution of flaws, usually for a brittle material. The modulus is a dimensionless number corresponding to the variability in measured strength and reflects the distribution of flaws in the material.

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For brittle materials, the maximum strength (stress that a sample can withstand) varies unpredictably from specimen to specimen -- even under identical testing conditions. The strength of a brittle material is thus more completely described with a statistical measure of this variability, eg the Weibull modulus.

For example, consider strength measurements made on many small samples of a brittle material such as ceramic. If the measurements show little variation from sample to sample, the Weibull modulus will be high and the average strength of the material would be a good representation of the potential sample-to-sample performance of the material. The material is consistent and flaws -- due to the material itself and/or the manufacturing process -- are distributed uniformly and finely throughout the material. A low Weibull modulus reflects a high variation in measured strengths and an increase in the likelihood that flaws will tend to congregate and produce a weaker material. A material with a low Weibull modulus will more likely produce products where the strength is substantially below the average and show greater inconsistency of strength. Such products will exhibit greater variation in strength performance and will probably be less reliable.

Test procedures for determining the Weibull modulus are specified in DIN EN 843-5 and DIN 51 110-3.