CHOBOT Karel VSB-Technical University of Ostrava

Spoluautoři KRAUS Martin

Geometry of the fracture surface morphology reflects the physical-metallurgical parameters of microstructure, as well as conditions of loading, which affect both the energy dissipation during crack propagation and fracture toughness, that’s why it is necessary to quantify occurrences of the unevenness on the fracture surface. In this paper, the geometry of fracture surface is assessed by fractal dimension, when the local value of fractal dimension is calculated using the test specimens cut from tests of fracture toughness. The analysis is performed on two types of specimens from measurements of static fracture toughness and dynamic fracture toughness on steel R7T. It appears that from the geometric point of view, and therefore from the perspective of energy dissipation, the difference exists in the area of initial propagation of the main crack between statically and dynamically loaded samples. Based on the Sih’s theory the density of strain energy was estimated for the crack loading modes I and II in dependence on the on the fractal dimension as an indicator of the angle of bending of the propagating crack. For the crack loading mode I; the direction with the minimum strain energy lies under the bending angle of 0° and fractal dimension approaches 1. In the case of the crack loading mode II the direction of crack propagation and the fractal dimension depend on the Poisson's number of the material.