THE ELASTIC STRESS-FIELD ARISING IN THE SINGLE-FIBER PULL-OUT TEST

The stress field arising in the single-fiber pull-out test is analyzed within the framework of the linear theory of elasticity. Two fiber types with different elastic properties, an isotropic glass and an anisotropic carbon fiber, are studied. Both fibers are embedded in a polycarbonate matrix with a length to diameter ratio of 15. The solution of the boundary value problem is performed by means of the finite element method. It is shown that the stress distribution in the vicinity of the fiber is strongly inhomogeneous and exhibits severe concentrations of shear and radial stresses at the fiber entry and at the fiber end. The level of the stress concentrations is highly influenced by the axial stiffness ratio of fiber and matrix. The potential failure processes resulting from these stress concentrations are discussed. The von Mises yield stress and the principal stresses are also calculated. It is shown that the commonly calculated interface strength, utilizing experimental data only, results in an underestimate of the actual interface strength in the case of linear elastic material behavior.