A microstructurally based fracture model for polygranular graphites Original Research Article

The physical basis of, and assumptions behind, the Burchell fracture model for graphites are reported. The model combines a fracture mechanics failure criteria and a microstructurally based description of fracture. Microstructurally related inputs such as pore-size distribution, particle size, bulk density, particle fracture toughness, the number of pores per unit volume, and specimen geometry (size and stressed volume) are utilized in the model. Microstructural inputs to the model code, determined by quantitative image analysis of prepared specimens of the graphites, are reported. The Burchell fracture model was successfully applied to four graphites of widely different texture, ranging from a fine-grain, high-strength aerospace grade (POCO AXF-5Q) to a coarse-grain, low-strength electrode graphite (AGX). The excellent performance and versatility of the Burchell fracture model was attributed to its sound physical basis. The potential for applying the Burchell fracture model to irradiated graphites was explored and the model was shown to qualitatively predict the influence of neutron damage on the strength of a nuclear graphite.