The fracture surface of PP was composed of the
expanding zone, the arc stripe zone and the last fracture
zone. With the crack extension, the morphology of
the expanding zone varied from coarse to flat. The
formation of the arc stripe zone corresponded to the
process of crack arresting and then initiating again w4x.
According to the LEFM, roughness on the fracture
surface reflects the level of energy consumption in the
process of materials cracking. The fractal dimension of
a fracture is a kind of metric parameter of roughness.
The fractal dimension D. and the size of the arc
stripe on the fracture surface with a filled quantity of
nucleating agent are shown in Figs. 7 and 8. From the
results, it can be seen that the fractal dimension of the
expanding zone exists at a maximum at the 0.4 wt.% of
the filled quantity of the nucleating agent. The size of
the arc stripe has nothing to do with the quantity of the
nucleating agent. Therefore, the results indicated that
the formation of the expanding zone is the principal
process in the change of energy consumption; the variation of the fractal dimension with the filled quantity of nucleating agent is just corresponding to the condition
of crystalline morphology and impact strength. It was
shown that the effects of microstructure on impact
behavior can be reflected by the variation in the characteristic
morphology of the fracture