02L2 oih I J 626

where o1Ll, o2Ll are the average strengths at a given failure probability for gage lengths L1 and L2 respectively. Assuming that af = afr, where afr is the fiber fracture strength, and applying an iterative method between Eqs. 6.22- 6.26, the critical COD necessary to fracture the fibers, is derived as a function of the Weibull modulus m (Fig. 6.22).

The above methodology makes clear that: (a) the interfacial shear strength and the debonding process, consequently, is responsible for the existence of bridging fibers; (b) the effectiveness of fiber bridging is controlled by the matrix material (G) and the strength of the fiber, and (c) the bridging life of each fiber row decreases for longer crack lengths (COD ^œ).

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