A technique for depositing materials into position using a positive-displacement extruder to build up a body has been developed. This technique also includes a process to prepare composite materials through a solid free-body forming process containing directionally aligned short-fiber reinforcement and ceramic-particulate reinforcement (of which at least a portion is derived from an alkoxide precursor).
With this newly developed technique, the matrix resin contains fiber and/or high loadings of ceramic particulate (precursor). The fiber reinforcement is oriented by shear stresses in the extrusion process. The matrix resin has very low shrinkage and is capable of being cured in a short time after deposition.
This new technique for depositing materials into position uses a stereolithography system, comprised of a table and computer-controlled gantry system, a vertical slide and resin dispenser, and a heated platen. A computer-aided-design package is used to make a virtual image of a solid body. The computer translates the virtual image into motion instructions, which are, in turn, converted to indexer commands and motions of the resin dispenser. The resin dispenser extrudes resin through a needle while sweeping out a path to build up the solid body on the heated platen. The resulting part is thermally cured during or after deposition.
Composite resin systems were developed for this process based on specialty acrylic monomers. These monomers combine short chains of structural polymers with acrylate end groups. Upon curing, the acrylate end groups join, forming a polymer with properties similar to the structural polymer. A cross-linking agent was used to promote rapid curing. This resin system produces a tough, strong polymer within several minutes when heated, with very low shrinkage upon curing.
An advantage of this resin deposition system is that it has a low viscosity. A viscosifier is required to lay the material up. It was found that the addition of 1.66 volume percent fumed silica provided sufficient viscosity so that beads of the material could be neatly laid up. The viscosified resin was reinforced with chopped carbon or glass- fiber and ceramic particulate.
This solid free-body-forming process was used to produce controlled-alignment fiber-reinforced composites. Also, highly loaded ceramic particulate reinforced composites were prepared using this method.
Flexure testing of composite specimens showed the properties to be quite respectable when compared to traditional structural polymer materials. These tests also demonstrated that the specimens were far better than the materials that are currently produced by other solid free-body-forming technologies.
This work was done by Kevin Stuffle, Gabriel Chambers, John O'Kelly, John Lombardi, Anthony C. Mulligan, and Paul Calvert of Advanced Ceramics Research, Inc., for Marshall Space Flight Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to
the Patent Counsel
Marshall Space Flight Center; (205) 544-0021.