In an earlier paper [1] the relation σB = σ∞ + const. tB−1/4 has been deduced for the time dependence of the strength decrease under a static load. In the formula σ∞ means the fatigue limit and σB is the stress causing a fracture after the loading period tB. By application of this formula the activation energy of the static fatigue of glass and of the creep of steel is calculated from experimental data at different temperatures. The activation energy determined for steel corresponds to activation energy for the diffusion of sulfur in iron but corresponds also to the half of the sublimation enthalpy for iron. Therefore, the rate limiting step of the creep of steel at elevated temperatures may be a diffusion of interstitial atoms as well as a quasi-sublimation. A theoretical model is given for the defect growth due to a quasi-sublimation.

In 1914 Stromeyer published the empirical relation ±Sn =Fl + C(106/n)1/4 for the mathematical description of fatigue (±Sn -nominal fatigue stress; Fl - fatigue limit; C - constant; n - number of stress cycles). In a previous publication Graefe has given a theoretical explanation of such a relation. In this paper the statistical distribution of the experimental fatigue data for steel is tested and no deviation from a normal distribution is found. The frequency dependence of the fatigue data is analyzed and is explained by temperature variations due to internal friction. Different models for defect growth are in concordance with the above-mentioned formulas.

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