Studies on the fractal dimension and fracture toughness of steel

Abstract

The slit island method is employed to measure fractal dimensions D_F of fractured surfaces under plane strain conditions with the help of an image analysis technique for two high-strength steels under different heat treatment conditions and at different test temperatures. It is shown that the fractured surfaces are of fractal character. The values of D_F decrease smoothly with an increase of the logarithm of fracture toughness K_1C. This relationship may reflect the changes in the microstructure that occurred during different heat treatments and the changes in the fracture mechanism that occurred at different test temperatures. The fractal dimension D_F can be regarded as a measure of fracture toughness in steel. Finally, the experimental results are explained in terms of the relation of critical crack extension force to the true total area of the irregular fracture surfaces.