Fracture toughness and failure mechanism of alumina and zirconia ceramics over a wide loading rate range

The split Hopkinson pressure bar (SHPB) system and a universal testing machine were used to measure the fracture toughness of zirconia (ZrO₂) and alumina (Al₂O₃) ceramics across a wide range of loading rates from 1.0 × 10^-8 to 2.0 TPa·m^1/2·s^-1. The experimental-numerical method was used to determine the dynamic fracture toughness of the materials. The results exhibit a positive relationship between fracture toughness and loading rate as well as a negative correlation between fracture initiation time and loading rate for both of the ceramics. The analysis of fracture morphology reveals different micromechanism in the failure of the materials under different loading rates. This analysis offers an explanation for the dependency of fracture toughness on loading rates. Additionally, the incubation time criterion and its modified version were employed to describe the effects of loading rate on fracture toughness and fracture initiation time.