Numerical simulations of fracture-toughness improvement using short shaped head ductile fibers

Fibers can be shaped so as to anchor inside the matrix and resist pullout at a crack face, thus improving the fracture-toughness of the composites. This anchoring ability enables a greatly improved utilization of the plastic potential of ductile fibers, increasing fracture-toughness while maintaining stiffness. The purpose of this paper is to explore this property of shaped head fibers for composites with weak fiber-matrix bonding. Because of the difficulty in estimating the fracture-toughness contribution of shaped head fibers analytically or experimentally, we use a FEM based numerical scheme to investigate stress profiles induced during pullout of two chosen shaped head families. Annealed copper fiber with a large residual plastic potential and an elastic epoxy matrix have been used as representative materials. Using the computed strain energy distribution in the matrix as a measure of fracture-toughness contribution, we find that flat-head fibers out-perform ball-head fibers in minimizing failure potential. We have further discovered that within each shape family there exist optimal shapes. The optimal shape for the flat-head family is also computed for the example material system.