Experimental and Numerical Study of Damage Evolution and Fracture Characteristics of Three-Layer Composite Rocks Under Dynamic Loading

In order to study the damage evolution and fracture characteristics of rock with different composite modes in three layers under dynamic loading, rock specimens with different composite modes were made by using three materials: sandstone, marble and granite. The dynamic fracture impact test was carried out by using the Hopkinson pressure bar impact loading system, the voltage signal on the Hopkinson pressure bar was calculated and processed, and the crack propagation mode of the specimen was captured by using a high-speed camera, and the stress wave characteristics, stress time–history relationship and energy change characteristics of rocks with different composite modes were studied. At the same time, combined with Distinct Lattice Spring Model numerical simulation, the fracture process of the specimen was inverted, and the changes in stress intensity factor, stress change and load–displacement change in monitoring point were analyzed to compare the dynamic fracture behavior differences between different composite rocks. The results show that the dynamic fracture process captured by the high-speed camera has a good fit with the crack propagation process simulated by numerical simulation. When marble is used as the upper material, the energy transmittance is larger, and the transmission energy ratio between sandstone and granite is basically the same due to the large difference in hardness. When the comprehensive hardness of the specimen is the same, the smaller the hardness of the material at the cracking position, the faster the cracking will be, and the smaller the hardness of the second layer of the specimen at the cracking position, the faster the cracking speed of the specimen. In terms of dynamic fracture toughness, for specimens with little difference in hardness, when the impact end material is sandstone, the dynamic fracture extreme value of the specimen is lower, and when the sandstone material is used as the impact end material, it is more likely to crack. When the first layer of material is the same, the dynamic fracture toughness of the specimen with less hardness of the second layer of material is smaller, and the easier the crack development is.