Change of the mechanism of accumulation of fatigue damages leads to sectional-linear description S-N curve view and change of functions of long life time distribution that have two-parametric bi-exponential distribution with logarithmic life time. The experimental estimations of durability mean and root-mean-square deviation under test condition are used as scale and position parameters of bi-exponential distribution. One of the advantages of this distribution is the smallest values of probabilities on the left tie of density of distribution compared with known ones.