Dimensional Analysis of Bond Modulus in Fiber Pullout

Abstract

To evaluate the stress-crack opening relationship of fiber-reinforced composites, the properties of the constituents and the fiber-matrix interface should be known. The properties of the fibers and the matrix can fairly easy be determined, whereas those of the interface must be measured indirectly. In several fiber pullout analyses, a linear relationship between the bond shear stress and the slip is assumed in the elastic range. In this paper, the value of the bond modulus is studied using dimensional analysis and the finite element method. The value of the bond modulus was seen to depend on the fiber diameter, fiber volume content, and the modulus of elasticity of the fiber and the matrix. A diagram is shown, from which the values for the bond modulus can be read. The numerical results agree reasonably with the theory by Budiansky et al. However, the results are substantially higher than the limited available experimental data. A possible reason is that the Poisson's contraction can cause the debonding near the fiber free end even with low pullout loads.