13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- of main and secondary cracks (Fig. 4d). Final failure is obtained by means of a crack propagation from one side to the opposite side of the specimen (―fracture ending zone‖). In Fig. 5, the ―fracture ending zone‖ is shown. For eng = 0, 5 and 10%, corresponding respectively to Fig. 5a, b and c, no transformations are evident: surface modifications due to phase transformations are not observed in this zone. For eng = 14% (Fig. 5d), it is possible to observe a localized ductile deformation. a) b) c) d) Figure 4. Fracture initiation zone: a) eng = 0%, b) eng = 5%, c) eng = 10%, d) eng = 14% (failure). Evidence of structure transitions are in Fig. 6, where two diffractograms show respectively the undeformed and the deformed at eng = 5% specimen. The undeformed specimen spectrum shows four peaks corresponding to 42.35°, 43.71°, 70.39°, 80.23°. The eng = 5% deformed specimen shows also four peaks but corresponding to different diffraction angles (42.27°, 43.43°, 43.85° and 85.71°). Peaks modifications (considering both angles and intensity) show the mechanical deformation influence on the microstructure modifications. Fracture surfaces are characterized by a brittle morphology, as the intergranular cleavage shown in Fig.7a, which confirms the path observed on the lateral surface (Fig. 4c, d). According to the LOM damaging micromechanisms analysis and to SEM fracture surface analysis, grains decohesion seems to be main damaging micromechamisms. Inclusions presence implies the initiation of secondary microcracks (Fig. 7b), probably due to the same mechanism which characterizes the grains decohesion.
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