Nearly Isotropic Resin-Transfer-Molded Composites

NASA's Jet Propulsion Laboratory, Pasadena, California

Nearly isotropic matrix/fiber composite materials can be made quickly and at relatively low cost by resin-transfer molding. The fiber components of these materials are fine, loosely woven, three-dimensional preforms; the matrix components are epoxy or polycyanate resins. With proper tooling, these materials can be resin-transfer molded to net shape. Alternatively, they can be machined to net shape. The three-dimensional weaves enable the materials to withstand machining with minimal loss of mechanical properties. These materials are particularly suitable for lightweight, all-composite replacements for aluminum end fittings that have been used on tubular composite-material structural members.

Heretofore, resin-transfer-molded composites have been made with relatively coarse three-dimensional braided or angle-interlock woven preforms (see figure). These composites are so coarse that they cannot be machined and cannot be fabricated with fine details. For example, screw threads in these materials are useless because the threads contain no reinforcement and thus have insufficient strength.

The fine three-dimensional weaves of the present composites were developed previously for carbon/carbon composites, but have not been used heretofore in resin-transfer-molded composites. The method used heretofore to make carbon/carbon composites requires long processing times and expensive capital equipment, and the materials produced by this method are too brittle at room temperature to satisfy the requirements that prompted the development of the present nearly isotropic resin-transfer-molded materials.

The three-dimensional loosely woven preforms used in the present materials cost less than do the coarser three-dimensional preforms made by conventional three-dimensional braiding or weaving. In comparison with the coarser three-dimensional woven preforms, the present finer preforms are weaker on a large scale but stronger on a small scale like that of screw threads, where the fine weaves provide reinforcement that the coarser weaves cannot.

The Fine Weave of the newer composite is more conducive to fine machining and to retention of strength in fine details like screw threads.

This work was done by D. Kyle Brown of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Materials category, or circle no. 103on the TSP Order Card in this issue to receive a copy by mail ($5 charge). NPO-19918