EFFECT OF LOADING FREQUENCY ON FATIGUE STRENGTH OF AGE-HARDENABLE STEEL.

To investigate the effect of loading frequency on fatigue strength of age-hardenable steel, rotating bending fatigue tests were carried out under two different frequency conditions (3000 and 300 rpm) by using the low-temperature quenched rimmed steel. Hardness change and crack propagation were observed during the fatigue process under both loading frequency conditions. The results obtained were as follows: At a high cyclic stress region, the effect of loading frequency on fatigue life was not observed. The rate of increase in hardness with number of cycles was larger in 300 rpm than in 3000 rpm. As the cyclic stress was lowered, the fagigue crack growth in 300 rpm became slower than that in 3000 rmp. The fatigue behavior mentioned above might be explained as follows: the effect of strengthening of material due to age-hardening on fatigue appears remarkably in 300 rpm when cyclic stress is low, owing to the time available enough for ageing than in 3000 rpm.