Lifetime of amg6 alloy under consecutive shock-wave and gigacycle loading

The paper presents the experimentally implemented test program for very-high-cycle loading (number of cycles 107-109) samples produced from massive planar targets (aluminum alloy AMg6) and subjected to the plane wave loading method (explosive generator). Shock-wave loading modes provided a controlled damage to simulate structural changes in fan blade materials under conditions of a high-speed collision with solid particles. Very-high-cycle loading was performed using the ultrasonic testing machine Shimadzu USF-2000 that allows testing samples on the basis of 108-1010 cycles with an amplitude of up to several tens of micrometers and a frequency test of 20 kHz. A significant reduction by 34% of the fatigue strength on the basis of 109 cycles for the AMg6 alloy pre-loaded with a shock wave is shown. The technique of the "in situ" determination of fatigue damage is based on the analysis of the amplitude-frequency characteristics corresponding to the change in effective elastic properties. It allowed us to explore the damage development stages taking into account nonlinear kinetics of the defects accumulation in the process of cyclic loading in multi- and gigacycle fatigue modes. The anomalous change of elastic properties of the material at critical levels of damage is established. A quantitative correlation between mechanical properties and scale-invariant characteristics of the topography of the fracture surface are formed in the processes of dynamic loading and gigacycle according to profilometry (interferometer-Profiler New View 5010 with a resolution of 0.1 nm). For the samples subjected to the preliminary shock-wave deformation, a decrease in the Hurst index in comparison with the undeformed samples was established. The latter is associated with an intensive fragmentation in the formation of dislocation ensembles during shock wave loading, which complicates the formation of an ordered system of defects under the subsequent fatigue loading