FRACTURE-BASED 2-WAY DEBONDING MODEL FOR DISCONTINUOUS FIBERS IN ELASTIC MATRIX

The mechanical performance of brittle and quasi-brittle materials can be significantly improved by the introduction of fibers. Fiber debonding, which results in the formation of bridging ligaments at the wake of cracks, is the major mechanism accounting for performance improvement. A strength-based two-way debonding theory, which accounts for fiber debonding at both the pulled and embedded ends, has recently been developed. In this paper, two-way debonding based on a fracture criterion is considered. With the fracture-based debonding theory, expressions for fiber stress and displacement, and thus the general debonding features, are found to be similar to those given by the strength-based theory. However, interpreting the same interfacial measurement (such as a pull-out test record) with the strength and fracture approaches will lead to predictions of different debonding behavior in composites with practical volume fractions. To determine whether debonding is governed by strength or fracture, interfacial properties should be measured from a number of specimens with different fiber sizes or fiber volume fractions.