The Consolidation and Processing of Graphite Fiber/Polymer Composites By Controlled Mode Microwaves
- PDF / 1,111,941 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 96 Downloads / 190 Views
THE CONSOLIDATION AND PROCESSING OF GRAPHITE FIBER/POLYMER COMPOSITES BY CONTROLLED MODE MICROWAVES D.J. TREACY*, D.A. EVANS*, J.S. BOYCE*, 3.F. McCOY* AND B.W. TREADWAY* *Foster-Miller. Inc., 350 Second Avenue, Waltham, MA02154-1196 ABSTRACT Composite laminates have been cured under pressure in a tunable microwave cavity. A 7-in. diam cavity with a sliding short was tuned to produce single mode or controlled hybrid mode standing waves at 2.45 GHz. Graphite/epoxy laminates were processed with power inputs as low as 2 W/g. A low loss press was designed and built to operate inside the cavity. The press can apply 100 psi pressure on a 9-in. square laminate. An empirical approach has been used to develop processing conditions for high quality laminates. Graphite/epoxy composites were cured in 90 min or less. A simple on-off temperature control loop modulated power input to the cavity with a coaxial switch. Mechanical testing and differential scanning calorimetry have been used to evaluate the composites. The material properties have been related to processing conditions. INTRODUCTION AND BACKGROUND Foster-Miller is currently involved in a program to develop technology to cure polymeric composites using microwave energy. Because the energy is directly coupled into the material (as opposed to convective heating), the potential exists to shorten cure times. Since microwave radiation is penetrating, potential may exist for improved curing of thick structures, which is often problematic with conventional convective cures. Early work on cavity curing was performed at Michigan State University (MSU) by Profs. Assmussen and Hawley. Owing to problems with conventional microwave approaches, MSU focused on understanding and modelling the cure process in a 2.45 GHz single mode cavity of circular cross section. While MSU experiments and analysis furthered understanding of basic mechanisms and phenomena, a number of practical questions remained. The Air Force and DARPA enlisted Foster-Miller, Inc. to work in concert with MSU to help address some of these issues. In general, the interactions of microwaves with realistic part geometries and laminate constructions are thought to be too complex to be predicted analytically, especially when tooling is added to a cavity. As a result, an empirical approach is required to find conditions for optimum cure. For continuity, Foster-Miller began investigations in 2.45 GHz cavity similar to that used by MSU. Additionally, Foster-Miller was tasked to incorporate a mold tool to apply controlled pressure during cure and instrumentation to monitor temperature and control heating. This paper is a report of progress I-n this effort. INVESTIGATION APPROACH As considerable effort by others had gone into composite curing of unconsolidated samples in a single mode cavity, we concentrated our effort on development of techniques for consolidating test specimens which are then cured in a single mode or hybrid mode cavity; in particular, in a 7-in. diam cavity at 2.45 GHz. After consideration of several This i
Data Loading...
