Abstract
Machines and structures often encounter repeated impacts in practice. So, it is very important to study fatigue fracture of steel under repeated impacts. Usually a rotating disk type impact fatigue testing machine is used for such study, but the analysis of the data obtained by using this machine is considerably difficult, because the impact phenomenon is transient and has complex characters. So, a new type of machine was made by modifying a rotating disk type impact fatigue testing machine, and fatigue tests under repeated impacts were carried out. Then, the influences of velocity of repeated impacts and stress ratio on the fatigue crack growth rate of stainless steel were investigated by means of fracture mechanics and fractography. The difference in crack growth rate between repeated impacts and more gradually-applied cyclic load was large. This difference was explained by the effective stress intensity factor based on the equivalent stress ratio which includes the repeated impact loading effect.
