Fiber pullout behavior and impact toughness of short shaped copper fibers in thermoset matrices

This paper considers the effectiveness of adding short shaped copper fibers to brittle thermoset polymer matrices to improve the composite's impact toughness. The low velocity impact response of each fiber-matrix combination has been investigated by conducting reversed notch Izod impact tests using a pendulum impact tester. The fiber pullout behavior and its effects on impact toughness with different fiber shapes as well as lengths were investigated. The matrices used in the experiments were polyester and two different types of epoxy. Fiber shapes and lengths were chosen based on previous single fiber pullout experiments that were conducted to determine shape families that improved the fracture toughness of thermoset polymer matrix composites. Results indicate that the most important factors for determining impact toughness were the matrix and interface behavior. This behavior determined the fiber debonding and pullout behavior, the fiber shapes which gave increased toughness, and the length where fibers failed rather than pulled out of the matrix. The fiber shape was also important because when a fiber debonds from the matrix, it must be able to pull out to improve toughness. Because of the high effectiveness of shaped fibers, composites with such fibers, many of which fail during impact, can still perform better than composites with straight fibers, all of which pull out during impact.