Oa ooN1k121

where N is the number of cycles to failure, oa denotes the stress amplitude level, and k, O0 are material constants.

Irrespective of stress level, the probability of survival after N cycles is assumed to be given by a two-parameter Weibull distribution:

Calculation of constants o0 and k of Eq. (1.21) is performed as follows:

A two-parameter Weibull distribution is fitted to the data of the i th stress level:

The parameters aand ;V, of each Weibull distribution are determined by the following maximum-likelihood estimators:

0 0

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