Investigation of the Influence of Consecutive Dynamic and Gigacycle Fatigue Loads on the Lifetime of Titanium Alloy VT-8

An experimental and theoretical studies of fracture mechanisms at different structural levels of materials used in the aeronautical engineering (titanium alloy VT-8) were carried in the framework of laboratory experiments with the aim to simulate structural changes in the materials of fan blades under conditions of high-velocity impact of solid particles. The dynamic preloading test program for specially designed specimens of VT-8 alloy was implemented experimentally using the split Hopkinson (Kolsky) pressure bar. Very-high-cycle fatigue tests were conducted on the Shimadzu USF-2000 ultrasonic testing machine, in which specimens are subjected to 108–1010 cycle loading with amplitude of about several tens of micrometers and frequency of 20 kHz. Cyclic loading under these conditions showed a significant decrease in fatigue life in gigacycle fatigue tests at the critical number of cycles ranging from 2.23·109 in the initial (non-deformed) state of the VT-8 alloy specimen to 6.38·103 cycles for the preloaded specimen at a stress level of 585 MPa.