Modeling and Modification of the Electromagnetic Properties of Advanced Composite Materials

摘要

The electromagnetic hazards involved in using composite materials in aircraft are considered. Attention is focused on the problems associated with the lower conductivities of composites in comparison to those of metals. The concept of a high conductivity composite is advanced as a solution to the electromagnetic problems associated with presently available composites. The electrical properties of available advanced composite materials, primarily graphite/epoxy and boron/epoxy, are presented. Basic deterministic models relating the electrical conductivities (D.C. to 50 MHz) of composites to the fiber conductivity, the matrix conductivity and the volume fraction of the fibers are developed. The electrical behavior of as-manufactured graphite and boron fibers is also detailed. The possibility of 'doping' fibers with suitable impurities to increase conductivity without an associated decrease in specific strength is explored. Boron fibers undergo a recrystallization when heated above 800 C and have, as a consequence, significantly reduced strengths. Since thermal diffusion of impurities requires temperatures above 800 C, significant effort was devoted to inhibiting this recrystallization. Diffusion of nickel impurities inhibited this process and resulted in increased conductivities.