1

or in terms of stress intensity factor as:

where x = an represents the statistical average of the projected area of defects on a plane normal to the maximum orm. To evaluate ain, the right part of Eq. 6.30 is set to be equal to the matrix fracture toughness, Km. Typical results of such methodology can be found in Fig. 6.23.

Even though the size of the radial cracks is small compared to the size of a broken fiber, at short crack lengths such cracks could make a difference in terms of crack arrest, as shown later [10, 11]. It should be noted that the above represents a typical practice for the evaluation of radial cracks. For a more thorough evaluation residual stress interactions, with neighboring broken or not fibers, should also be considered.

Effect of Manufacturing Defects Many workers [68, 108] have observed that manufacturing defects in uMMCs are characterized by varying sizes and types.

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