Unitized Composite Airframe Structures with Three Dimensional (3-D) Preforms for Elevated Temperature Applications

A novel method of manufacturing complex unitized composite structures reinforced with 3D non-crimp orthogonal woven fabric (serving as self-sustained single-ply skin preform) and 3D braided fabrics (serving as self-sustained unitary preforms for stiffeners, Pi-joints or other similar elements) is proposed. The method uses two consecutive steps: high temperature cure resin infusion and room temperature cure resin infusion into the same skin preform via high temperature and room temperature VARTM processes respectively. The 3D braided preforms are attached to the skin preform and co-infused in vacuum bag at room temperature. The skin preform can be a hybrid of PAN-based and pitch-based carbon fibers; the former type fiber is used for the inner part and the latter type faces elevated temperatures. Special attention is paid to the interface between two distinct matrix materials occupying different parts of the skin and to the interfaces between skin and stiffener (Pi-joint). Special methods of interface strength enhancement using sprayed carbon nanotubes and creating porous regions will be studied. Non-destructive evaluation and initial mechanical testing will be conducted. BENEFIT: The proposed out-of-autoclave manufacturing approach will enable production of complex unitary composite structures suitable for future supersonic transport applications. This will be achieved by a relatively simple process and equipment, with minimal labor involvement and at significantly reduced manufacturing cost. The use of thick self-sustained integrally woven and braided 3D fabric preforms is a key: it will completely eliminate the steps of stitching multiple layers of thin fabrics for the skin and stiffeners, Pi-joints, frames, etc. By use of different carbon fiber types and combining high temperature and room temperature cure resins in the same preform, it will become possible to optimize the whole complex of thermo-mechanical properties of this new type of unitary composite structures.