applied fracture mechanics

46Applied Fracture Mechanicscleavage steps, showing that for different magnifications the material shows differentmorphologies of the surface of fracture.Figure 14. Changings in pattern of irregularities with the magnification scale on a ceramic alumina, LotA8 [56].To approach this problem one must first observe that, what is the structure for a scale becomespattern element or structural element to another scale. For example, to study the material, thelevel of atomic dimensions, the atom that has its own structure (Figure 15a) is the element ofanother upper level, i.e., the crystalline (Figure 15b). At this level, the cleavage steps formed bythe set of crystalline planes displaced, in turn, become the structural elements ofmicrosuperfície fracture in this scale (Figure 15c). At the next level, the crystalline, is themicrostructural level of the material, where each fracture microsurface becomes the structuralmember, although irregular, of the macroscopic rugged fracture surface, as visible to the nakedeye, as is shown diagrammatically in Figure 15d. Thus, the hierarchical structural levels [69]are defined within the material (Figure 15), as already described in this section.Figure 15. Different hierarchical structural levels of a fracture in function of the observation scale; a)atomic level; b) crystalline level (cleavage steps); c) microstructural level (fracture microsurfaces) and d)macrostructural level (fracture surface).Based on the observations made in the preceding paragraph, it is observed that the fractalscaling of a fracture surface should be limited to certain ranges of scale in order to maintain