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.

The dynamic fracture behavior of rocks subjected to impact loading is a fundamental issue within the field of rock dynamics. This study aims to construct microstructure models of heterogeneous minerals representative of various typical rocks and establish a coupled SHPB impact simulation system with FLAC-PFC to examine the mechanisms of fracture, energy dissipation law, and the characteristics of acoustic emission (AE) responses in rocks acted upon by impact loads. The main results obtained reveal the following: (i) The fracture mechanisms of various lithologies under impact loading exhibit common characteristics, predominantly behaving as composite failure mechanisms. The observed distribution characteristics are mixed and interwoven with shear-tension-implosion failures, with a tendency to aggregate from the boundaries towards the interior of samples. (ii) The AE fracture strength of various lithologies predominantly ranges from −8.25 to −5.25, with peak frequencies observed between −7 to −6. The sequence of AE-based B-values, ranked from highest to lowest, is as follows: red sandstone > green sandstone > slate > granite > blue sandstone > basalt. (iii) The T-k distribution for various lithologies follows CLVD (+)-first. (iv) A significant correlation exists between the energy-time density and the B-value. Rocks exhibiting high energy dissipation capacity are characterized primarily by small-amplitude AE events and small-scale fractures, whereas those with low energy dissipation capacity are mostly marked by large-amplitude AE events and large-scale fractures. These research findings provide a fairly solid theoretical basis for understanding the fracture mechanisms and energy dissipation behaviors of rocks subjected to impact loading.

To investigate the mechanical behavior and energy evolution characteristics of various rock materials under impact loading, dynamic impact tests were conducted on five representative rock types using a split Hopkinson pressure bar (SHPB) apparatus, combined with X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The dynamic mechanical response, energy characteristics, mineral composition, and associated microstructural features of these typical rocks were systematically analyzed. The results show that basalt exhibits the highest peak strength, followed by blue sandstone and granite; all three display typical brittle failure characteristics, whereas red sandstone and green sandstone demonstrate greater ductility and plastic deformation capacity. By introducing the energy-time density index, the energy-time density of the rocks ranks from strongest to weakest as follows: green sandstone, red sandstone, granite, blue sandstone, and basalt. An innovative dynamic strength–energy-time density mapping model was established to elucidate the clustering and distinguishing characteristics of these rock materials. Assay results and mesoscopic images confirm the relationship between mineral composition and the fine structure of rock fragmentation mechanisms, highlighting that the critical transition from intergranular to transgranular fracture is the key mechanism governing impact pulverization. Furthermore, fractal analysis reveals that higher fractal dimensions are associated with more complex microcrack structures and may correlate with the corresponding energy dissipation intensity. These findings provide profound insight into the failure mechanisms of rocks under dynamic loading, offering significant theoretical value and engineering application prospects, particularly in fields such as mining excavation and rock mass stability assessment.