In-plane fracture resistance of a crossply fibrous monolith

The in-plane fracture resistance of a crossply Si3N4/BN fibrous monolith in the 0 degrees /90 degrees and +/-45 degrees orientations is examined through tests on notched flexure specimens. The measurements and observations demonstrate the importance of fiber pullout following fiber fracture. The mechanical response is modeled using a crack-bridging approach. Two complementary approaches to evaluating the bridging law are developed: one based on a micromechanical model of fiber pullout and the other based on the load versus crack mouth opening displacement response of the flexure specimens following fracture of all fibers. Both approaches indicate that the bridging law follows an exponential form, characterized by a bridging strength and an effective pullout length. An assessment of the bridging model is made through comparisons of simulations of the load-displacement response with those measured experimentally.