Experimental study on the mixed mode I-II fracture characteristics of dynamic ice

Abstract

The fracture and shedding of dynamic ice during flight is the main factor threatening flight safety. Clarifying the fracture mechanism of dynamic ice is of great significance for guiding the practice of aircraft icing protection engineering. Based on the linear elastic fracture theory, this paper combined icing wind tunnel tests with central cracked Brazilian disc (CCBD) tests to carry out the pure mode I, pure mode II and mixed mode I-II fracture tests of dynamic ice at different icing ambient temperatures T. The displacement and strain field evolution on the specimen surface during loading was monitored by digital image correlation (DIC) method, and the test results were more deeply understood from a theoretical perspective. Finally, combining the micro-characteristics of dynamic ice such as its pore structure and crystal structure, the connection between the macroscopic fracture mechanical properties and the microscopic scale was discussed, revealing the fracture mechanism of dynamic ice. The research results show that within the temperature range of −5 ℃ to −15 ℃, the pure mode I fracture toughness of the dynamic ice is in the range of 81.181–129.675 KPa·m^0.5, while the pure mode II fracture toughness is in the range of 110.802–189.565 KPa·m^0.5. Under various loading modes, as the T decreases from −5 °C to −15 °C, both the failure load and fracture toughness of dynamic ice exhibit a trend of first increasing and then decreasing, with the maximum values observed at −10 °C. It can be concluded that the decrease in failure load and fracture toughness of dynamic ice at −12.5 ℃ and −15 ℃ is mainly affected by internal pore defects, while the weakening of failure load and fracture toughness at −5 ℃ and −7.5 ℃ may be due to the combined action of the grain boundary weakening effect and the micro-interfaces formed during the freezing process.