Finite element simulation of shaped ductile fiber pullout using a mixed cohesive zone/friction interface model

The fiber pullout test has long served as surrogate for estimating fracture toughness of fiber-matrix systems. In this paper, the quasi-static analysis of elastoplastic fiber pullout process is simulated by the finite element method based on an updated Lagrangian formulation. To approximate the non-linear behavior of the fiber-matrix interface, we propose a mixed 'cohesive' and 'Coulomb-friction' model. The use of such a model enables us to simulate the entire pullout process. A combination of von Mises yield criterion and associated flow rule is utilized as the constitutive model to describe the plasticity in the initially annealed copper-fiber. Through comparison with the experimental results from straight-fiber pullout, key parameters for describing the interface model are determined and the model is validated. The model is then applied to simulate the pullout of the 'nail-head' shaped fiber family. Simulation results are used to design an optimal shape of the head to maximize the pullout work.