Afrl-mn-eg-tp-2006-7407 a Study of Impact Response of Electrified Organic Matrix Composites (preprint)

The existing experimental evidence suggests that organic matrix composites sustain less impact damage when an electric field is applied. The intricate interaction of an electrical field and mechanical load is governed by coupling of the mechanical and electromagnetic fields via the Lorentz force as well as by the processes undergoing at the microscopic level: Joule heat, fiber-matrix interface changes, etc. The current work includes both experimental and theoretical investigations of the effects of an electric current on the impact response of carbon fiber polymer matrix composites. The experimental part of the work consists in low velocity impact tests of current carrying composite plates. We have developed a setup that allowed for effective application of an electric current to carbon fiber polymer matrix composites. A series of low velocity impact tests have been performed in order to assess the damage resistance of electrified carbon fiber polymer matrix composites. The tests have been carried out under 0 A, 25 A, and 50 A DC electric currents applied to the composite plates. The results of measurements have shown considerable dependence of the impact-induced damage upon the intensity of the electric field applied to the composite. The theoretical part of the work is concentrated on the analysis of the impact phenomenon in composite plates carrying an electric current. The system of governing equations under consideration consists of equations of motion, Maxwell’s equations, and heat transfer equations. We have investigated the effects of Joule heating in composites due to an externally applied electric field, which is especially important for carbon fiber polymer matrix composites because of relatively low electrical conductivity of fibers and thermal conductivity of the matrix. The results indicate that extensive Joule heating leads to significant temperature gradients across the composite plates. Aalysis of the Joule heat effects reveals that it is not a primary mechanism for the strengthening phenomenon observed in the experiments.