Anisotropy of Fractal Dimensions of Fractures and Loading Curves of Steel Samples During Impact Bending

Abstract

This study aims to establish the correlation between the impact strength and texture, fractal dimensions of fractures (Df), fractal dimensions (DC) obtained from load-time diagrams P(τ) reflecting the applied load (P) dependence on time (τ) during the Charpy impact test of 20K steel at various temperatures as well as the comparison of the abovementioned fractal dimensions. The tests were carried out on a vertical impact testing machine with a multi-channel system for high-speed registration of forces and strains, as well as a heating and cooling system for samples in a wide temperature range. The load vs. time (load dependence on time) diagrams were obtained at an impact velocity of V0 = 4.4 m/s at temperatures of -50, +20, + 50С. The Charpy standard samples of 20K steel (analog to DIN17175, class St45.8) were cut in various directions out of a 12 mm thick the destroyed tank shell of a distillation column for oil refining. It was established that the behavior of both the abovementioned fractal dimensions depending on the cutting direction and test temperature coincides qualitatively. The trend of decreasing in fractal dimension with a more viscous nature of fracture was found. The effect of texture is discussed.