Influence of grain-scale microstructural parameters on fracture toughness of polycrystalline ceramics: Dual scale finite element method

Fracture toughness is a basic property of ceramic materials, and it is strongly influenced by their microstructures. However, the influences of grain-scale microstructural factors, including grain fracture energy, boundary fracture energy, and grain size of the microstructure, on the fracture toughness remain unclear. To investigate this, a dual-scale finite element method was developed. Models were established to assess the microstructural mechanical properties, with an average grain size of 0.1-100 mu m, and different grain boundary fracture energies and grain fracture energies. Based on the microstructural mechanical properties, a macroscale three-point bending model, combined with the extended finite element method was used to evaluate the fracture toughness. The results indicated that fracture toughness increased with the decrease in the grain size when the grain size was below 5 mu m. Conversely, when the grain size was greater than 5 mu m, the fracture toughness remained relatively constant. Additionally, the grain boundary fracture energy played a more important role for the fracture toughness than the grain fracture energy. Finally, a formula that quantitatively describes the relationship between the microstructure and fracture toughness was obtained. This work provides a valuable reference for evaluating the performances of structural ceramics.