3 DIMENSIONAL PREFORMS FOR NONUNIFORM SOLID CROSS-SECTIONS

The Navy"s Joint Strike Fighter (JSF) employs ceramic matrix composites (CMCs) in certain critical components like the flaps and seals of the engine exhaust nozzle. The CMC flaps and seals are attached to movable metal frames that can be actuated to vary the nozzle"s throat di-ameter and exit area. The design can benefit significantly from the use of CMC fasteners since they save weight, offer attractive high temperature strengths, and provide properties that are compatible with the CMC flaps and seals. Previous projects have addressed 3D braided CMC fasteners but these designs employed inserts to form the nonuniform cross-section required for the fastener head. While the braided material offered attractive strengths, the interface between the fibers and insert created a plane of weakness that limited their capabilities. CMC fastener preforms can be improved if the entire nonuniform cross-section, i.e. shaft and countersunk head, maintains a constant fiber volume fraction and contains interlocking fi-bers. This problem can be solved with 3D weaving technology that is routinely used to create multi-directional reinforced fiber preforms for complex nonuniform structures. Existing 3D wo-ven composite components include curved and twisted fan blades for turbine engine compres-sors, and lightweight high strength struts used on the landing gear of Boeing"s 787 Dreamliner. The goal of this proposed Phase I program is to demonstrate 3D woven preforms with nonuniform cross-sections for CMC fasteners. The Phase I Base program will size specific CMC fasteners to meet JSF nozzle requirements, design one or more 3D woven preforms that provide the necessary fastener strengths, fabricate several samples of selected of 3D preform designs, and microstructurally evaluate a few specimens of each design to quantify fabricated fiber volume fraction and fiber architecture. In the Phase I Option, the remaining 3D preforms will be densified as CMCs and characterized for critical fastener failure loads of tension, shear and head pull off. The test results will be correlated with the design theory and used to identify preform improvements. The Phase I Base effort will be performed by a team of Materials Research & Design, Inc (MR & D) and Albany Engineered Composites (AEC). MR & D will manage the pro-gram, size the fasteners, design the 3D fiber architectures, and evaluate the microstructure. AEC will fabricate the woven preforms. The Phase I Option will expand the team to include COI Ce-ramics (COIC) and Southern Research Institute (SoRI). COIC will densify the CMC fasteners and SoRI will measure fastener strengths. MR & D will correlate the data and define improved fastener preforms. If the Phase I results prove that the 3D preforms are feasible for CMC fasteners, the Phase II effort will continue the prototype development focusing on the needs of CMC compo-nents in the JSF nozzle.