The Split Hopkinson Pressure Bar (SHPB) is an apparatus for testing the dynamic stress-strain response of the cement mortar specimen with pre-set joints at different angles to explore the influence of joint attitudes of underground rock engineering on the failure characteristics of rock mass structure. The nuclear magnetic resonance (NMR) has also been used to measure the pore distribution and internal cracks of the specimen before and after the testing. In combination with numerical analysis, the paper systematically discusses the influence of joint angles on the failure mode of rock-like materials from three aspects of energy dissipation, microscopic damage, and stress field characteristics. The result indicates that the impact energy structure of the SHPB is greatly affected by the pre-set joint angle of the specimen. With the joint angle increasing, the proportion of reflected energy moves in fluctuation, while the ratio of transmitted energy to dissipated energy varies from one to the other. NMR analysis reveals the structural variation of the pores in those cement specimens before and after the impact. Crack propagation direction is correlated with pre-set joint angles of the specimens. With the increase of the pre-set joint angles, the crack initiation angle decreases gradually. When the joint angles are around 30°–75°, the specimens develop obvious cracks. The crushing process of the specimens is simulated by LS-DYNA software. It is concluded that the stresses at the crack initiation time are concentrated between 20 and 40 MPa. The instantaneous stress curve first increases and then decreases with crack propagation, peaking at different times under various joint angles; but most of them occur when the crack penetration ratio reaches 80–90%. With the increment of joint angles in specimens through the simulation software, the changing trend of peak stress is consistent with the test results.

Rock failure phenomena are accompanied by abundant energy variation, and the energy dissipation can explain the dynamic mechanical characteristics of the rock. In this study, a series of granite specimens (a total of 60) with different aspect ratios were dynamically loaded by a split Hopkinson pressure bar (SHPB) to explain the energy dissipation and the rock-crushing degree under dynamic load. A new index, namely energy time density (w_td), is proposed to evaluate the energy dissipation considering the time factor. The relationships between strain rate, energy time density, and specific energy absorption are analyzed. A metric (K_u) is defined to describe the degree of rock fragmentation quantitatively. The correlations of fractal dimension and K_u with different impact pressures are compared. It was concluded that there is a noticeable peak point in the energy time density curve. The energy time density of the stress equilibrium point is three times that of the peak point. The energy time density declines after the peak point, then the energy consumption density tends to be stable. The linear relationship between strain rate and peak point energy time density is stronger. The new index can describe energy dissipation well under dynamic loading. In addition, the experimental results indicate that the degree of crush K_u can describe the degree of crush, and the effect of fractal dimension to quantify the fracture characteristics of the rocks is less good in this test. The crushing degree of rocks increases with the increase of strain rate. Furthermore, the prediction effect of energy time density is better than that of strain rate about K_u.

In order to explore the mechanical characteristics and failure characteristics of water-saturated frozen cement mortar with different transfixion degree joints under impact load, a cyclic freezing impact test was performed on six kinds of water-saturated frozen cement mortar specimens with different transfixion degrees (0%, 20%, 40%, 60%, 80%, 100%) by split Hopkinson pressure bar (SHPB), and the microscopic damage of specimens was tested by an MRI analyzer. The results show that the dynamic compressive strength of the water-saturated frozen cement mortar increases first and then decreases with the increase of the number of cycles, with the increase of joint transfixion degree the peak stress showing a clear linear downward trend. An 80% transfixion degree joint specimen has the weakest ability to carry impact loads, and the 40% transfixion degree joint specimen has the strongest ability to carry impact loads. With the increase of joint transfixion degree, there was a similar trend of first decreasing and then rising in the average change of porosity and the change of energy density per unit time index. The joint transfixion degree controls the crack development trend and the final destruction mode of the specimen. With the increase of joint transfixion degree, the failure sequence gradually evolved from pull-shear composite failure to split-tensioned failure.

Stress equilibrium time is an important index to judge the homogeneity of rocks. In order to study the relationship between stress equilibrium time and crushing energy consumption before rock destruction, Hopkinson tests were conducted on granite specimens with different length-to-diameter ratios. In this paper, by studying the size and strain rate effects of rocks, five different sizes of granite specimens with different aspect ratios were prepared and Hopkinson impact tests were conducted under four strain rate conditions. Data analysis and processing using the three-wave method to investigate the stress uniformity of granite specimens under impact loading. The energy balance factor was introduced to compare and analyze the stress equilibrium time of five kinds of long-diameter granite specimens, and it was found that the stress equilibrium time of rocks with the same length–diameter ratio decreased with the increase of loading strain rate, while the granite specimens with length–diameter ratio of 0.8 showed a better stress equilibrium time. In order to better find the aspect ratio and loading strain rate that can crush better and maintain a long equilibrium time, the energy consumption of rock crushing is further analyzed. The energy dissipation of granite specimens with loading strain rate of 156.8 s⁻¹ and 253.2 s⁻¹ was found to be more concentrated, and the energy dissipation rate was stable at about 48%. Subsequently, the relationship between stress equilibrium time and energy dissipation was established, and it was proved that the fastest growing time period of the energy dissipation curve was approximately equal to the rock stress equilibrium time, while the length-to-diameter ratio of the granite specimen that could better maintain the stress uniformity before rock crushing was 0.8 and the loading strain rate was 156.8 s⁻¹.

The experimental system of 3D digital image correlation (3D-DIC) is set up to eliminate a certain extent of out-of-plane motion for accurate measuring the full-field strain field during crack propagation, and the effect of blast loading rates of fracture behavior of granite rectangle plate with a crack (GRPC) is investigated. The experimental results indicated that the maximum values of the strain concentration zone do not fully represent the crack tip during the whole process of crack propagation. The axial strain threshold value tip (ASTVT) plotting with lines and coordinate contours corresponding with the actual crack at the shooting area can be used to describe the position of the crack. The axial strain 1.3% is more practical to obtain crack velocity and average crack velocity, and the average crack velocity decreases as the blast loading rates increase. Through observing the relationship between crack width and time, it can be found that there are three stages, and the crack width increases as the blast loading rates increase.

Drop hammer impact tests were conducted to study crack features and the ductile–brittle transition in sea ice under low-speed impact. Crack images were analyzed using Hessian filtering and Hough transform methods, and a finite element model was created. Material parameters were validated using the crack tip strength factor. Energy dissipation, focusing on kinetic energy, was analyzed to understand energy conversion and crack propagation in sea ice during low-speed impact. The results indicate that the angular distribution of the crack mode exhibits central symmetry, with the peak frequency at each angle approximately 5°. As the initial impact kinetic energy increases, the dynamic response of the sea ice plate transitions from toughness to brittleness; the kinetic energy dissipation increases linearly, while its utilization efficiency declines. The variation in the kinetic energy conversion rate (η) is associated with the mode of ice plate failure. The crack propagation rate follows a normal distribution in relation to changes in time and kinetic energy. The stress wave effect predominates in the fracture formation mode, further elucidating the ductile–brittle transition behavior of sea ice. This research holds significant implications for ice-breaking operations.