Dynamic mixed mode I/II fracture toughness and failure behaviour of freshwater ice under impact loading

The dynamic mixed mode I/II fracture toughness of ice involves its fracture resistance under complex impact loading, which is essential for impact or blasting parameter selection and evaluation. The notched semi-circular bend (SCB) method was applied to determine the dynamic mixed mode I/II fracture toughness of freshwater ice based on a modified split Hopkinson pressure bar setup. The effects of loading rate and grain size on the mixed mode I/II fracture toughness of ice were comprehensively explored. A high-speed digital camera was adopted to record the crack propagation path and measure the crack propagation velocity. The experimental results indicate that the dynamic effective fracture toughness of SCB ice samples is dependent on the loading rate, particularly for mode I dominated loading. The dynamic fracture toughness decreases as the grain size increases from 0.8 to 4.5 mm. Subsequently, the fracture resistance was compared with the theoretical predictions based on some brittle fracture criteria. The generalized maximum tangential stress-based semi-analytical (SA-GMTS) criterion provides a good prediction for the dynamic mixed mode I/II fracture toughness of ice. For mixed mode I/II, the crack propagation velocities rise with the increase of loading rates. However, the grain size has little effect on the velocities. These results improve the understanding of the dynamic complex fracturing mechanism in ice engineering applications.