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As transport aircraft technology has progressed from subsonic to supersonic and now toward hypersonic applications, the demand for low-cost, lightweight, and high-strength materials for complex structural components has prompted the development of particulate-reinforced metal matrix composites (MMCs). Despite extensive room temperature evaluations of these MMCs, the toughness, creep, and welding properties of such materials when placed under high-temperature conditions have received little attention. In this paper, the effects of temperature on the tensile properties, fracture toughness, and related creep behaviors of a silicon carbide particulate reinforced 2124-T6 aluminum alloy matrix composite (SiCp/Al 2124-T6 MMC) are evaluated. To carry out this testing, variations in this material's mechanical properties, residual stresses and microstructure near welded joints and crack tips originating from machined notches were investigated.

Because of its low density and improved elastic modulus properties, use of aluminum-lithium alloys has good potential for substantial weight savings in aircraft, spacecraft, and missile applications. To study further the possible uses of this material, Douglas Aircraft Company conducted a program to investigate the effects of welding methods on the load-carrying capacities of welded joints made of aluminum-lithium alloy. In the study, laser-welded 2091-T8X aluminum-lithium sheet joints were fabricated and tested. The high-energy intensity and low-heat input generated by laser welding sharply narrowed the heat-affected zone and markedly improved the strength of the weld. Fracture toughness, Jlc, was determined by the J-integral procedure of ASTM E813. The fatigue crack growth rate, da/dN, was measured with precracked specimens and correlated by ΔK. The fracture toughness and fatigue crack growth in the welding zone and in the base metal section were compared.