| This dissertation studies the impact of microstructure on macro-scale fracture parameters. Experimental and theoretical investigations of fracture toughness are carried out on a representative particulate composite material and reconciled by explicitly considering inclusions within the matrix. The reliability of any structure is a function of its resistance to fracture. Cracks resulting from stress concentrations are the major sources of fracture whether the material is classified as ductile, brittle, or quasi-brittle. The spatial distribution of inclusions in particulate composite materials, such as concrete and other heterogeneous materials, plays an important role in determining material fracture behavior due to the localized stress generated by the inclusion arrangement when cracks open. By controlling the spatial statistics of the inclusion microstructure in the matrix of a composite material, it is possible to control the amount or direction of crack development and may be possible to improve the material's reliability. As steps towards this goal this dissertation investigates the discrepancy between the micro-scratch and macro-scale three-point bending test methods due to the presence of matrix inclusions, applies the theoretical equations for fracture toughness which consider inclusions in the case of micro-particles in cement, and investigates how spatial statistic descriptions may be used to capture the impact of inclusions in a simple closed-form approach. The results of this work allow us to move towards a forward design method to design particulate composite micro-structures for improved resilience to local damage without fracturing. |
