Improved Miller Fasteners Based on 3-D Braided Preforms

Miller Fasteners made from 2-D laminates represent the state of the art in joining CMC panels to metal frames. Despite its success, the extant Miller fastener design is limited by its construction from a laminate of 2-D fabric. The resultant fastener part has poor interlaminar shear strength, and its manufacture and application entails high machining costs and high material scrap rates. 3TEX, in collaboration with COI Ceramics, will design, model, and demonstrate CMC Miller Fasteners based on 3-D braided fiber architectures. This improved fastener addresses each of the concerns with the existing design. The intertwined 3-D braided fiber architecture has no layers, thus no fracture-prone interlaminar regions. This will lead directly to higher out-of-plane stiffness and strength, and increased fracture toughness. The braided preforms are near net shape and would reduce costs through less machining and material waste. In Phase I, C/SiC 3-D braided Miller Fasteners demonstrated feasibility. For Phase II, SiC fiber 3-D braided preforms with integral head shaping will be manufactured, infiltrated with SiC matrix and tested. This effort will advance their Technology Readiness Level to 6 and perform subcomponent testing in a relevant environment.