The paper presents the method of determination of two-dimensional probability distribution P_f of crack initiation versus fatigue life N and the fatigue damage parameter : P_f − N − ϭ. The proposed distribution P_f uses parameters of the standard fatigue characteristics and allows calculating fatigue life of elements with heterogeneous stress fields at any probability level. The model was successfully verified on experimental test results.

The critical plane orientations determined with account for maximum value of energy density parameters and the weight function method were compared to experimental fatigue fracture plane orientations. Energy density parameters used in two multiaxial fatigue failure criteria, i.e. (i) criterion of the maximum normal strain energy density on the critical plane and (ii) criterion of the maximum shear strain energy density on the critical plane were employed. In the other method, the weight functions were formed on the basis of energy parameters. These two methods were verified by experimental tests of 1802A steel. The material was subjected to cyclic and random bending, torsion and combined bending with torsion with different coefficients of cross correlation between normal and shear stresses. The calculated results are satisfactory for both methods.

The paper contains a comparison of the results of calculation and experiment for the IOHNAP alloy steel. Specimens made of this steel were subjected to uniaxial constant-amplitude and random loading with both zero and non-zero mean values of loading. For determination of the steel fatigue life, the energy parameter including the mean value of loading was proposed. Under random loading, cycles were counted with the rain flow algorithm, and fatigue damage was accumulated with the Palmgren-Miner hypothesis. For the registered stress histories, elastic-plastic strains were calculated with the kinematic hardening model proposed by Mróz.