Short shaped copper fibers in an epoxy matrix: Their role in a multifunctional composite

Previous research indicates that short shaped copper fibers improve the fracture and impact toughness of brittle thermoset polymer matrix composites. This paper investigates the potential multifunctional ability of these same shaped copper fibers by determining their electromagnetic interference (EMI) shielding effectiveness (SE). Fiber shapes were selected based on previous single fiber pullout experiments where they displayed high toughness. The two fiber diameters tested were: 0.325 and 0.162 mm. Fiber shapes used in the experiments were: straight, flat end-impacted, rippled, and acid roughened. A SE of greater than 45 dB at 1.0 GHz was attained in epoxy that contained 15 vol% of 0.162 mm diameter shaped fibers. Composites with 15 vol% of the 0.325 mm diameter shaped fibers showed poor SE, less than 20 dB. Experimental results indicate that besides improving the fracture and impact toughness of a thermoset polymer matrix, short shaped copper fibers can also significantly improve the SE and electrical conductivity of the composite, resulting in a multifunctional material. This increase in SE and electrical conductivity can be attributed to: shape effects that increase the skin volume, surface discontinuities which increase the amount of electromagnetic (EM) wave scattering, and the fiber count which determines the number of conducting paths.