Fractal analysis of fracture surface of aluminum alloy amg6 under fatigue and dynamic loading

In this paper we investigated the localization of deformation during high-speed deformation and fatigue crack propagation in gigacycle loading regime in the aluminum-magnesium alloy AMg6. Localization of plastic deformation under conditions closely approximating simple shear was investigated using the shear-compression specimens (SCS) tested on the split-Hopkinson bar device. After the experiment the maintained specimens were subject to microstructure analysis using the NewView-5010 optical interferometer. Fatigue tests were conducted on Shimadzu USF-2000 ultrasonic fatigue testing machine. This machine provides 109-1010 loading cycles with the amplitude from 1 to several dozens of microns and frequency of 20 kHz, which reduces testing time to a few days, as opposed to the classical fatigue testing machines, in which the same number of cycles can be reached only in few years. The New View 5010 interferometer-profiler of high structural resolution (resolution of 0,1 nm) was used as an instrument of qualitative analysis, which provided data allowing us to find correlation between the mechanical properties and scale-invariant characteristics of defective structures formed under dynamic and gigacycle fatigue loading conditions. The authors propose an original form of writing the kinetic equation, which relates the rate of the fatigue crack growth with a change in the stress intensity factor. The scale invariance of defect structures responsible for the formation of the fracture surface relief under gigacycle fatigue loading was found to be related to the power exponent of the Paris law.