Multi-fiber Pull-out Test

The fracture toughness of laminated composites can be dramatically increased by using thermoplastic micro-fibers (flock fibers) as a z-directional reinforcement of the matrix. Toughening of the interlaminar matrix is enabled through various mechanisms: flock fiber pull-out; fiber stretching; debonding; and fiber/matrix interaction. The multi-fiber pull-out test is more suitable for studying these mechanisms in the z-directional micro-fiber reinforced composites than the traditional single-fiber pull-out test. Starting with the procedures of the multi-fiber pull-out test, this paper presents a detailed analysis to determine which fiber properties significantly increase the fracture toughness. The results show that energy dissipation during fiber pull-out increases with the number of flock fibers per unit area up to a specific value and then it is nearly constant for higher fiber densities. The results also show how the fiber elastic and geometric properties and debonding strength affect the fiber pull-out for three different flock fiber materials at different fiber densities.