F (percent)

Figure 11.8. Influence of volume fraction of particles on fracture toughness [10]

Three aspects of this approach need further clarification.

a. In general the fracture toughness decreases with yield strength in contradiction to the prediction by eq (11.17).

b. The dependence of Klc on particle size is not yet experimentally established.

c. It is not clear yet which particles should be considered, nor is it established whether and how premature cracking of large particles should be accounted for.

These three aspects are interrelated and therefore they will be treated together in the following discussion. The effect of yield strength on toughness implies that eq (11.17) is not unique. This is expressed in figure 11.8 by the fact that Ku^Eays depends upon yield strength; the data of materials with different aVJE are on two separate lines. The yield strength dependence on toughness is further illustrated in figure 11.9.

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