Innovative Structural Joining Concepts and Analysis Techniques

A new structural joining technique is under development which employs a massive number of nanomaterials to achieve unique combinations of properties. One-dimensional nanomaterials (nanotubes, nanohelices, etc.) are anchored onto the opposite faces of the joint, and compatibly functionalized and engaged to form chemical bonds over their tremendous surface areas. The exceptional mechanical, physical and functional attributes as well as the tremendous surface area and aspect ratio of one-dimensional nanomaterials effectively restore the mechanical and physical (thermal, electric, etc.) continuity across the joint. The slender, compatibly functionalized nanomaterials act as flexible molecular chains with pronounced energetic preference (versus entropic resistance) toward chemical bonding at near-ambient conditions; the joining process thus minimizes any damage to materials, and offers major energy and environmental advantages. Nano-engineered joints embody several design variables which can be tailored to meet diverse performance requirements; they can effectively join dissimilar materials, and accommodate thermal expansion mismatch. Nano-engineered joints can complement high mechanical attributes with multi-functional features such as integrated health monitoring and thermal conduction (or insulation) for heat management. The Phase I project has developed: (i) a comprehensive theoretical framework for modeling the mechanical behavior of nano-enigneered joints; (ii) processing techniques for anchorage of aligned nanomaterials (carbon nanotubes and silica nanohelices) onto various substrates; (iii) methodologies to compatibly functionalize and engage nanomaterials for chemical bond formation (and mechanical interlocking in the case of nanohelices); and (iv) experimental data on progressively refined nano-engineered joints, yielding shear strengths of about 20 MPa which (at this early stage of development) compare well against modern aerospace adhesives. The proposed Phase II project will continue the Phase II research toward: (i) development of comprehensive design procedures for nano-engineered joints; (ii) establishment of versatile, high-throughput, low-cost, energy-efficient and environmentally benign techniques for production of broad categories of nano-engineered joints; (iii) design, fabrication and thorough characterization of representative aerospace joints within composite structures and also between structural composites and thermal protection ceramics (selected joint designs will be evaluated by Boeing under simulated service conditions); and (iv) assessment of the competitive performance, and the cost, energy and environmental implications of nano-engineered joints versus competing technologies, and development of refined strategies for market transition.