In this dissertation the 3D microstructures of actual metal matrix composites (MMCs) are, in the first time, characterized and modeled and compared with their 2D micrographs. A serial-sectioning technique is developed for obtaining detailed 3D microstructural images from 2D sections of particle reinforced MMCs. Equivalent microstructures with actual particle or damage replaced by ellipse or ellipsoid are computationally simulated for efficiency. The equivalent microstructures are tessellated by a particle surface based algorithm. Various 3D characterization functions are developed to identify particle size, shape, orientation and spatial distribution in the actual materials and their relation with damage and compared with 2D micrographs. Si particle reinforced aluminum composites, varied in particle volume fraction and size and deformed into different strain levels, are employed to establish the differences between 2D and 3D characterization. Results indicate that it may not be sufficient to use 2D section information for characterizing detailed microstructural features. A sensitivity analysis is conducted to explore the influence of the microstructural variables on damage. Particle size, orientation and local volume fraction are found to play the most significant roles in the damage process.; Furthermore, commercial SiC particle reinforced aluminum composites are used to catch and characterize the dominant damage resulting in the final failure of the composites and reveal how the dominant damage path is formed and evolved. Interrupted test technique is developed to catch the dominant damage path. The materials are heat treated in naturally aged and annealed conditions. The formation and evolution of the dominant damage path in naturally aged material are investigated by serial sectioning and Voronoi Cell Finite Element Method (VCFEM) modeling. The results indicate that particle cracking is the main reason of failure and the linkage of large damage formed by the linkage of microcracks in particle clustered areas results in the dominant damage path. Besides, the characteristics of the microstructure forming the dominant damage and what kind of 2D section can give better prediction to 3D microstructure are studied. Representative material elements (RME) are investigated by marked correlation function and VCFEM analysis to find the suitable RME size of the material.
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