High-Strength, Lightweight Metal Matrix Composites (MMC) Material for Bridge Applications

The Army is in need of an improved material for use in bridge structures. Key requirements are reduced weight relative to current metallic structures (steel and aluminum), high strength, resistance to catastrophic failure, attractive cost, and resistance to environmental factors (weather, corrosion, erosion, extreme temperatures, UV, etc.). To meet this need, the use of macro-composite structures of Al/SiC MMC and steel are proposed. The structures could consist of Al/SiC reinforced with steel (e.g., rebar), or hollow steel structures filled with Al/SiC. Such a product will possess the low weight, high specific stiffness and strength, and excellent corrosion resistance of Al/SiC; together with the resistance to catastrophic failure (i.e., high strain to failure) of steel. A key processing advantage of this system is the ability to match the thermal expansion properties of Al/SiC to steel (by selecting proper Al:SiC ratio), which allows the fabrication of large structural elements without residual stress. A five task Phase I program is proposed, namely (1) design of macro-composite structural elements, (2) finite element analysis of the designs, (3) manufacturing trials, (4) mechanical testing to generate stress-strain behavior and assess failure mode, and (5) development of a cost model.