Reduced-thermal-expansion, reduced-bulk-modulus silicone rubber for use in mold tooling made by incorporating silica powder into silicone rubber. Pressure exerted by thermal expansion reduced even further by allowing air bubbles to remain in silicone rubber instead of deaerating it. Bubbles reduce bulk modulus of material.

Continuous fiber web receives powder coat first on one side, then on other. Vibrating helical screw mechanism in powder feeder provides even flow of powder to form powder curtain that descends onto moving web. Small amount of powder that falls to side or through web recovered easily. Powder-curtain feeder part of apparatus similar to one described in System Applies Polymer Powder to Filament Tow (LAR-14231).

Tool converts partly formed towpreg into preconsolidated towpreg ribbon. In technique, towpreg coated with thermoplastic powder converted into preconsolidated ribbon without use of plasticizers or solvents. Relying on melt flow and proper application of tension, friction, and cooling, technique ensures both consistent distribution of polymer within, and consistent cross section of ribbon. Ceramic preconsolidation tool includes heated and cooled halves thermally insulated from each other.

Advance in polymer technology yields composites having relatively low dielectric constants. Reduction achieved by reducing interactions between linear polyimide chains and by incorporation of fluorine into polymer backbones. Further reductions obtained by physically incorporating selected diamic acid additives into polyimides. Strong potential for use in microelectronics industry for fabrication of printed-circuit boards and fabrication of components for military aircraft.

Powder prepregging processes being developed for advanced composite materials overcome many of the difficulties associated with melt, solution and slurry prepregging. In addition, studies have demonstrated that powder coating is applicable to thermoplastics and thermosets and that processing costs are comparable to conventional hot melt prepregging. The powder curtain prepreg process offers advantages in quality control and powder handling over other methods which utilize fluidized beds or slurries. The dry powder curtain feed method provides for the uniform metering and efficient application of polymer powder materials onto fiber webs for the manufacture of high quality composite towpreg. The process has been demonstrated for a wide variety of thermosets and thermoplastic resins. Towpreg, prepared. by the powder curtain method, has been made into unidirectional and woven composite test specimens that have exhibited excellent mechanical properties.

Polymer powder applied uniformly and in continuous manner. Powder-coating system applies dry polymer powder to continuous fiber tow. Unique filament-spreading technique, combined with precise control of tension on fibers in system, ensures uniform application of polymer powder to web of spread filaments. Fiber tows impregnated with dry polymer powders (towpregs) produced for preform-weaving and composite-material-molding applications. System and process valuable to prepreg industry, for production of flexible filament-windable tows and high-temperature polymer prepregs.

Proposed process suggests robotic placement processing improvements realized by altering cross-sectional shape of wide and flat ribbon materials. Angled cross-section helps composite ribbons to align themselves and correct adjacent tow gaps and overlaps. New prepreg architectures include isosceles triangles, parallelograms, hexagons, and variations of trapezoids.

The results from a study aimed at improving the dynamic and aerodynamic characteristics of composite rotor blades through the use of extension-twist coupling are presented. A set of extension-twist-coupled composite spars was manufactured with four plies of graphite-epoxy cloth prepreg. These spars were noncircular in cross- section design and were therefore subject to warping deformations. Three different cross- sectional geometries were developed: D-shape, square, and flattened ellipse. Three spars of each type were fabricated to assess the degree of repeatability in the manufacturing process of extension-twist-coupled structures. Results from free-free vibration tests of the spars were compared with results from normal modes and frequency analyses of companion shell-finite-element models. Five global modes were identified within the frequency range from 0 to 2000 Hz for each spar. The experimental results for only one D-shape spar could be determined, however, and agreed within 13.8 percent of the analytical results. Frequencies corresponding to the five global modes for the three square spars agreed within 9.5, 11.6, and 8.5 percent of the respective analytical results and for the three elliptical spars agreed within 4.9, 7.7, and 9.6 percent of the respective analytical results.

Part fabrication from composite materials usually costs less when larger fiber tow bundles are used. On the other hand, mechanical properties generally are lower for composites made using larger size tows. This situation gives rise to a choice between costs and properties in determining the best fiber tow bundle size to employ in preparing prepreg materials for part fabrication. To address this issue, unidirectional and eight harness satin fabric composite specimens were fabricated from 3k, 6k, and 12k carbon fiber reinforced LARC-TPI powder coated towpreg. Short beam shear strengths and longitudinal and transverse flexure properties were obtained for the unidirectional specimens. Tension properties were obtained for the eight harness satin woven towpreg specimens. Knowledge of the variation of properties with tow size may serve as a guide in material selection for part fabrication.