This proposal explores mixed-mode fracture in two aluminum alloys and a titanium aluminide alloy. Variations in microstructure allow for analysis of the role of second phase precipitates and dispersoids on the fracture process. Variables include particle shape and volume fraction, temperature, and matrix condition. Mechanical behavior to be examined includes fracture toughness, plane strain tension and compression behavior, and axisymmmetric tensile flow. Scanning and transmission electron microscopy are used to characterize the microstructure. Both theoretical and experimental approaches are outlined, the theory examining shear bands in such materials. The shear bands are represented by a tilt wall dislocation array, a portion of which can breakaway and propagate, interacting with dispersed particles in the vicinity. %%% The fracture of structural metal alloys is important to a wide variety of applications. This research advances our understanding of crack propagation in complex alloys and should provide avenues of applied research that will lead to improvement of mechanical properties of structural materials.
