Effect of Fiber Inclination on Crack Bridging Stress in Brittle Fiber Reinforced Brtttle Matrix Composites

THE MECHANICAL behavior of brittle matrix composites is strongly affected by the bridging of cracks by fibers. In random fiber composites, libers can lie at an angle to the crack plane. Under such conditions, the bridging stress for a certain crack opening is governed by various micromcchanisms including fiber debonding, fiber bending and rupture as well as matrix spailing. While fiber debonding has been widely investigated, the coupled fiber bending~m~trix spaliing mcch~nism has received little attention. In this paper, the fiber bending/matrix spilling mechanism is analyzed by treating the fiber as a beam bent on an elastic foundation with variable stiffness and the possibility of spalling. The foundation stiffness and spalling criterion are derived from a tinite element analysis. The bridging stress due to bending alone as well as the total bridging stress are then obtained for the case with brittle fibers. Through this analysis. the effect of various microstructural parameters (such as fiber and matrix moduli, matrix spalling strain and fiber/matrix interfacial friction) on the behavior of random fiber composites cztn be studied. Prediction of ln~fx~rnurn bridging stress for inclined fibers based on the present model is shown to be in good agreement with experimental results.