An analysis of singularity in single fibre pull-out test using BEM

The single fibre pull-out test is one of the major mesomechanical methods which are designed to measure the interface properties between the fiber and matrix in composites. An axisymmetrical boundary element method is used for the single fibre composite model to obtain the stress distributions at the fibre-matrix interface. The numerical results show that the interface radial and shear stress components, sigma(r) and tau(rz), are singular at the fiber entry and the embedded fiber end, and vary linearly with the axial distance, z, in a log-log plot. It is proposed that the stress components, sigma(r) and tau(rz), have the form z(alpha)F(ij)(theta), where alpha is the singularity exponent and F-ij(theta) is the angular distribution function. It is shown that the singularity exponent depends on the loading geometry of the model and the properties of the composite constituents, especially the Young's modulus ratio of fiber to matrix