Evaluation of Fiber/Matrix Interfacial Fracture Toughness and Its Contribution to Composite Toughness by Using Two and Four-Fibers Model Composite Specimens

Abstract

Fiber/matrix interfacial crack propagation behavior was investigated by using a model composite specimen. The model composite specimen used in the present study consists of two fibers bonded by matrix resin, and an interfacial crack can propagate without resin fracture in this specimen. Model composite specimens with an initial crack were successfully fabricated from glass fibers of about 200∼400μm in diameter and vinylester resin. Crack propagation tests were carried out by the DCB method for mode I loading and the ELS method for mode II. The average value of interfacial fracture toughness obtained from model composites with silane-treated fibers was much higher than that with untreated fibers for both mode I and II propagation. Thus, the characteristics of fiber/matrix interfacial crack propagation are successfully evaluated by the present test method. The crack propagation tests were also conducted by using another model composite specimen with four parallel fibers distributed in a square array in the cross section. As expected, fracture toughness of four-fibers model composites in which the crack propagation is a combination of interfacial debonding and matrix fracture was higher than interfacial fracture toughness because of large energy dissipation by matrix fracture. Using the interfacial fracture toughness, Gi, the fracture toughness of four-fibers model composites, Gc, and the fracture surface ratio of fiber/matrix debonding in four-fibers model composites, γi, the fracture toughness of matrix resin, Gm, was estimated on the basis of the rule of mixture, Gc = Giγi + Gm(1 + γi).