Lattice models allow the incorporation of length-scale-dependent microstructural features and damage mechanisms into analyses of the mechanical behavior of materials. We describe our 3D lattice implementation and its use in fracture simulations. The method is particularly suitable for modeling fractures of nuclear graphite. This is a quasi-brittle material in which there is considerable non-linearity prior to final fracture caused by the inherent porosity, which triggers a field of local distributed failures upon mechanical and thermal loading. Microstructure representative models are generated with experimentally measured particle and pore size distributions and volume densities in two graphite grades. The results illustrate the effect of distributed porosity on the emerging stress–strain response and damage evolution. It is shown how the failure mode shifts from graceful, plastic-like behavior associated with substantial energy dissipation via distributed damage at lower porosities, to glass-like behavior with negligible energy dissipation at higher porosities. Thus, the work proposes a microstructure-informed methodology for integrity assessment of aging structures, where porosity increase is driven by environmental factors, such as radiation of nuclear graphite components.
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