Influence of the material sensitivity factor on the stress ratio for different specimens geometries and materials under bending

In the paper, the influence of mean loads on the low cycle fatigue for notched specimens of different shapes of the cross section is analysed. The specimens are characterized by a similar value of the stress concentration factor $(K_t=2.46$ for round specimens and $K_t=3.27$ for specimens of the rectangular cross-section). A mathematical model describing the limiting stress plane under fatigue bending is applied, taking into account the influence of mean stresses. The model has been verified by 18G2A steel and PA6 aluminium alloy specimens via experimental test results under cyclic bending for stress ratios $R=-1$, $-0.5$, 0. The relationship between the stress amplitude and the stress mean value taking into account the number of cycles $N$ before failure is described by a linear model, for which good agreement of the
calculations with the experimental test results is achieved.