Specimen length effect on parameter estimation in modelling fatigue strength by Weibull distribution

The paper deals with the problem of estimating the S–N field based on samples with different lengths and testing the hypothesis of length independence of fatigue lifetimes. A Weibull model developed by Castillo et al. is used to discuss the problem and analyze two data samples of prestressing wires and prestressing strands. The analysis shows that in the first case the length independence assumption cannot be accepted while for the second case length independence seems to be a reasonable assumption. This shows that every case must be analyzed separately and that assuming length independence can lead to unsafe design.