On the Strength of Fiber/Matrix and FRP/FRP Interface of Roving Cloth FRP

Abstract

When the properties of FRP are discussed in terms of its interface, the following three kinds of interface in FRP must be taken into consideration: fiber/matrix interface as a constitution of FRP, matrix/matrix interface as a representative of laminating condition and FRP/FRP interface as a characteristics of adhesion. Since these interfaces are aligned in a series in the flatwise direction of FRP, the individual property of interface or the relation among the three interfaces can be evaluated by applying tensile load in this direction.
In this paper, the relation between fiber/matrix and FRP/FRP interfaces and its dependence on the type of matrix used were studied. Two types of matrices selected were orthophthalic and isophthalic unsaturated polyester resins which show obvious difference in their adhesiveness. The reinforcement was roving glass cloth. The results obtained showed the validity of the method used in the present study. The main conclusions were as follows:
(1) In the case of FRP having sufficiently high bond strength at fiber/matrix interface, the relation between fiber/matrix and FRP/FRP interfaces is affected by the matrix, adhesive and curing condition, so that the location of the weakest interface varies.
(2) The dependence of the bond strength of fiber/matrix interface on the type of matrix can be determined by testing FRP with various fiber/matrix ratios. But it must be cautioned that the fracture mode also depends on the type of adhesive and rigidity of FRP specimen.
(3) The property of matrix can be evaluated by changing the surface roughness of FRP, since the location of the weakest interface depends on the type of matrix.