Crack Paths 2012

In the case of corundum ceramic an essential and the most distinctive effect of the

critical stage of the structure destruction is the propagation of large cracks, starting from

the central part of the samples (Fig.5 at the left). Large cracks are at first of all of

intergranular type (intercrystalline cracking), but at the stage of rapid growth they also

pass through the grains, especially of larger diameter (transcrystalline cracking). The

growth of these cracks is the source of a series of strong A Esignals (Fig.5 at the right).

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Figure 5. Microstructure of corundum ceramic (at the left) and typical course

of A E (at the right) in the critical stage of degradation of the material.

A Ein Mg-Al A M Creinforced with carbon

Figure 7 shows the results of compression tests and A Ebehavior in the Mg2AlA M C

reinforced with carbon with a low concentration of order of 5.8 vol.%, situated

perpendicularly (Fig.7a) and parallel (Fig.7b) to the N Daxis.

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Figure 6. A Ecourses and compression force in the A M CMg2Alreinforced with

carbon of low density: (a) perpendicular and (b) parallel to the N Daxis.

The initial microstructures at the bottom part.

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