Influence of the Loading Frequency on Very High Cycle Fatigue Behavior of Structural Steels

In ultrasonic fatigue tests, the VHCF properties can be determined in a reasonable time. Nevertheless, the high frequency can affect the fatigue behavior for some materials. This study investigated the fatigue capability of 34CrNiMo6 and 42CrMo4 steels, both of which find widespread applications in several mechanical components. These steels were carried out for conventional and ultrasonic fatigue tests under fully reversed testing conditions. A microplasticity strain amplitude was calculated, indicating an order of magnitude decreases around 10–100, when compared with the experimental results from low-frequency tests. Cyclic strain rates were estimated for each steel and correlated with the number of cycles to failure. A conversion constant was obtained by fitting a curve to convert the high frequency results into theoretical results at low frequency. The experimental and predicted results were evaluated. The results proved the relevance of the strain rate in frequency effect. The converted results showed strong agreement with the experimental results in low-frequency tests for the steels being studied.