Automated Surface Preparation of Organic Matrix Composites for Structural Adhesive Bonding

ABSTRACT: Peel ply, sanding and atmospheric plasma treatment have been examined as alternative methods for the surface preparation of bismaleimide carbon-fiber composites prior to bonding. It was found that atmospheric plasma treatment of the composite surface decreases the water contact angle from 822 to 202. X-ray photoemission spectroscopy of the treated composites revealed a 91% increase in surface oxygen fraction with plasma exposure. This surface oxygen increase correlated to the plasmas ability to recover the knock-down in double lap shear strength observed on peel plied and lightly sanded non-peel plied samples, from 1390210 psi to 209020 psi and from 2000100 to 225050 psi, respectively. Wedge crack extension testing after a seven-day hot-wet environmental exposure revealed that adding atmospheric plasma treatment after light sanding decreases the wedge crack length from 0.197 to 0.085 inches. In addition, oxygen plasma exposure on the peel ply composites increased the percent cohesive failure from an unacceptable value of 863% to an acceptable value of 981%. These results indicate that automated atmospheric pressure plasma treatment of organic matrix composites is a viable technology for surface preparation prior to structural adhesive bonding. BENEFIT: An exciting new technology is being developed for the automated surface preparation of organic matrix composites. This method will eliminate many of the problems encountered during joining of structural composites on jet aircraft, satellites, helicopters and other aerospace systems. The new preparation method greatly reduces manufacturing time and cost, and delivers systems with much stronger and tougher joints. In addition to aerospace, this process technology can be adapted to other industries, including renewable energy, automotive, and consumer electronics. The phase II project proposed herein aligns well with the government's Open Manufacturing initiative, since it will dramatically reduce the expense of acquiring future warfighter systems.