Structure and fracture property relation for silicon nitride on the microscale

The fracture toughness of silicon nitride ceramics is closely related to its microstructure, which is characterized by a bimodal distribution of partially large and elongated grains. In the first stage of fracture, these grains act as elastic bridges, which avoid a quick crack propagation. In order to improve the understanding of this R-curve effect, a unit cell approach for multiscale finite element simulation has been chosen. For the examination of the morphology influence on fracture stress and toughness unit cells with different mean aspect ratios have been utilized for the fracture simulations.As results, on the one hand effective stress–strain curves have been applied for the computation of the effective R-curves. On the other hand, these results have been compared with observations of the stress and strain fields on the local level. Findings on the local level support the concept of elastic bridging grains.

► Silicon nitride modeled by a highly detailed unit cell approach.
► Fracture of phases modeled by simple experiment-based assumptions.
► Effective fracture behavior determined by fundamental fracture mechanics.
► First simulation of evolution and fracture of elastic bridging grains.
► Structure–property relation observed and explained by micromechanic observations.