Fractal characteristics of fracture toughness and crack propagation#br#
of saturated tuff under impact loads
WANG Hao1，ZONG Qi1，WANG Haibo1，WANG Mengxiang1，XU Ying1，WANG Feng1，2
(1. School of Civil Engineering and Architecture，Anhui University of Science and Technology，Huainan，Anhui 232001，China；
2. Beijing Zhongkeli Explosion Technology Engineering Co.，Ltd.，Beijing 101318，China)
Abstract：In order to explore the fractal characteristics of fracture toughness and crack propagation of saturated tuff under impact loads，the 50 mm diameter split Hopkinson pressure bar(SHPB) was used to carry out type I dynamic fracture toughness tests on dry and saturated straight channel semicircular bending tuff specimens(NSCB) under different impact pressures. The crack propagation process of the specimen was acquired by a high-speed camera，and the crack propagation trend and the micro structure of the fracture were analyzed by Image J software and electronic digital microscope. The results show that there is a linear positive correlation between the fracture toughness of the specimen and the loading rate. When the impact pressure is 0.2，0.3and 0.4 MPa，the average fracture toughness of the dry specimen is 1.08，1.10 and 1.10 times that of the saturated specimen. Water saturation reduces the ability of the specimen to resist crack propagation，and the fracture toughness decreases accordingly. Under the impact load，the crack propagation speed of the specimen increases first and then decreases rapidly to a stable development. The crack propagation length and opening width increase continuously with the increase of time. Water saturation can promote the crack growth and opening of the tuff samples. With the increase of the impact air pressure，the fractal dimension of the specimen increases. The mean fractal dimension of the water-saturated specimens at 0.2，0.3 and 0.4 MPa is 1.08，1.14 and 1.13 times that of the dry specimens. The saturated water effect increases the complexity of crack propagation in the specimens. Under the action of impact load，the crack propagates along the structural weak surface of the specimen，and the arbitrary distribution of the structural weak surface causes the crack propagation to produce a bending effect. The softening effect of water aggravated the bending degree of the specimen during crack propagation.
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2023, Vol. 42 
