Calculation and Experimental Estimation of the Role of the Frequency Ratio in Changing the Durability at Two-Frequency Deformation Modes

Abstract

The cycle configuration at two-frequency loading modes depends on the number of parameters, including the absolute values of the frequencies and amplitudes of the low-frequency and high-frequency loads added during this mode, the ratio of their frequencies and amplitudes, and the phase shift between these harmonic components, with the latter having a significant effect only when the ratio of frequencies is small. Such two-frequency regimes of service loading of parts of machines and structures can significantly reduce their endurance. Using the results of experimental studies of changes in the endurance of a two-frequency loading of specimens of cyclically stable, cyclically softened, and cyclically hardened steels under rigid conditions, we have shown that decrease in the endurance under the aforementioned conditions depends on the ratio of frequencies and amplitudes of operating low-frequency low-cycle and high-frequency vibration stresses, and, moreover, the higher the level of the ratios of amplitudes and frequencies of those stacked harmonic processes of loading, the greater the effect. It is shown that estimation of such a decrease in the endurance compared to a single frequency loading equal in the total stress (strains) amplitudes can be carried out using an exponential expression coupling those endurances through a parameter (reduction factor) containing the ratio of frequencies and amplitudes of operation cyclic loads and characteristic of the material. The reduction is illustrated by a set of calculation-experimental curves on the corresponding diagrams for each of the considered types of materials and compared with the experimental data.