A new test method for mode I dynamic fracture toughness of ceramic materials

Abstract: Based on the split Hopkinson pressure bar (SHPB) technique, Mode I dynamic fracture tests were carried out on alumina ceramic using a newly designed miniature three-point bending fracture specimen combined with a fixture. The fracture initiation time of the specimen was obtained by the strain gauge method. The accuracy of measured fracture initiation time was verified by a high-speed photography. The variation of the Mode I dynamic stress intensity factor at the crack tip and the dynamic fracture toughness of the material were obtained by the Experimental-numerical method. The results show that with the loading rate increasing from 0.45TPa·m1/2·s-1 to 1.83TPa·m1/2·s-1, the dynamic fracture toughness of alumina ceramic increased from 8.39TPa·m1/2 to 15.76TPa·m1/2, while the fracture initiation time decreases continuously. The analysis of fracture morphology shows that with the increase of loading rates, the failure mode of alumina ceramic gradually changes from domination of intergranular fracture to a mixture of transgranular and intergranular. During this period, more microdefects are activated at a higher loading rate, and eventually evolve into transgranular fractures. The transition of failure modes results in the consumption of more energy, and contributes to the elevation of fracture toughness of the material.