Evaluation of Mode i fiber/matrix interfacial fracture toughness and matrix toughness in FRP by using real-size model composites

Abstract

The model composite method for evaluating fiber/matrix interfacial fracture toughness and matrix toughness in FRP was applied to real-size model composites with glass fibers of 10∼15 μm in diameter used for chopped strand mat. Unsaturated polyester was used as matrix resin. Mode I crack propagation tests were carried out by using model composite specimens consist of two parallel fibers bonded by matrix resin, and interfacial fracture toughness was successfully evaluated on the basis of the compliance method. 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. Fracture toughness, Gc, obtained from 4-fibers model composites in which crack propagation is a combination of interfacial debonding and matrix fracture was higher than interfacial fracture toughness, Gi, because of large energy dissipation by matrix fracture. Using Gi, Gc. and the fractuit surface ratio of fiber/matrix debonding in 4-fibers model composites, γi,, matrix fracture toughness in FRP, G m was estimated on the basis of the rule of mixture, G c=Giγ i + Gm (1-γ i). The obtained G value was larger than that of bulk unsaturated polyester because of large roughness of fracture surfaces in FRP and a difference in resin deformation behavior between bulk resin and FRP. © 2011 The Japan Society of Mechanical Engineers.