Three dimensional characterization and modeling of particle reinforced metal matrix composites part II: damage characterization

This second paper of a two part sequence, attempts to quantitatively characterize 3-D microstructural damage in particle reinforced metal matrix composites using a combination of computational and experimental tools. It is perhaps the first studies providing quantitative 3-D characterization of phase and damage morphology for comparison with 2-D micrographs. Materials with different volume fractions and particle sizes, at different levels of deformation are considered. The serial sectioning method is used to obtain micrographs of a series of parallel sections of the sample material. 3-D computer images of the particles and the associated damage in the microstructure are constructed by digitally assembling the section micrographs. Equivalent microstructures with actual particles and cracks replaced by ellipses or ellipsoids are simulated for enhanced computational efficiency. The equivalent microstructures are meshed into Voronoi cells by a surface based algorithm. Various characterization functions of geometric parameters are generated to identify the damage size, shape, orientation and spatial distribution both in 2- and in 3-D. A sensitivity analysis is conducted to explore the influence of the morphological parameters on damage. Particle size, orientation and local volume fraction are found to play the most significant roles in the cracking process. Experimental observations of damage are compared with predictions by a probabilistic damage model viz. the Weibull model. Representative material elements, which correspond to the characteristic sizes for local continuum representation, are investigated through the use of variograms and marked correlation functions.