## 5 Conclusions  
The current method enables a more precise description of the pattern of change and development of the data. Future studies may explore the angular and length variations of the cleavage. In this paper, five loading rate impact tests under preloaded axial pressure were carried out on fissured sandstones containing 45\({}^{\circ}\) dips using a combined dynamic-static SHPB test device. The test analyzed the dynamic parameters of the crushed specimens, including dynamic compressive strength, dynamic strain, dynamic modulus of elasticity, strain rate, and average grain size. The energy dissipation characteristics were also examined. The following are the main findings:  
1. Under static and dynamic combination conditions, the dynamic stress-strain curves of sandstone specimens were basically similar when loaded with five impact rates, which were mainly divided into three stages, which are elasticity, yielding, and damage. As the loading rate increases, the stress-strain curve of the specimen shifts to the upper right.
2. Five types of impact loading air pressure were used to drive the impact bar to accelerate the impact on the incoming bar, and the impact loading rates were 13.7 m/s, 15.1 m/s, 16.4 m/s, 17.1 m/s, and 18 m/s, respectively. The strain rate in the sandstone specimens grew from 53.5 s\({}^{-1}\) to 101.9 s\({}^{-1}\), with an increase of 90.6%, and the strain rate was quadratically related to the shock loading pressure.
3. Significant strain rate effects were observed on the dynamic compressive strength, dynamic strain, and dynamic modulus of elasticity of the sandstone samples. As the strain rate of the specimen increased, the dynamic compressive strength of the specimen increased from 74.02 MPa to 99.26 MPa, which was enhanced by a power function relationship; the dynamic strain increased linearly from 3.69 \(\times\) 10\({}^{-3}\) to 5.21 \(\times\) 10\({}^{-3}\); the dynamic modulus of elasticity increased quadratically from 23.15 GPa to 27.80 GPa.
4. When the loading rate increases, the incident energy increases as a power function. The sample's reflected, transmitted, and absorbed energies all increase with the incident energy. When the incident energy grew from 60.4 J to 109 J, the reflected energy increased from 20.4 J to 51.3 J, an increase of 151.5%; transmitted energy increased from 15.3 J to 23.9 J, an increase of 56.2%; the energy absorbed by the sample increased from 24.6 J to 33.8 J, an increase of 37.4%.
5. The degree of the sandstone fragmentation gradually increases with increasing loading rate and incident energy, as evidenced by a decrease in the scale of the fragments and an increase in the number of fragments. When loaded at five impact rates, the average crushed specimen sizes were 12.19 mm, 12.16 mm, 11.68 mm, 11.25 mm, and 10.89 mm. Specim absorption energy is mainly used for deformation damage of the rock; the more intense the specimen is broken, the more absorption energy is required.  
**Author Contributions:** Conceptualization, Q.P.; software, S.S.; formal analysis, X.L.; investigation, S.W.; data curation, J.H.; writing--original draft, Y.X.; writing--review and editing. Y.X. All authors have read and agreed to the published version of the manuscript.  
**Funding:** National Natural Science Foundation of China: no. 52074005 and no. 52074006; the Anhui Natural Science Foundation: no. 1808085 ME134; the Anhui Postdoctoral Science Foundation: no. 2015B058.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** All participants in the study agreed.  
**Data Availability Statement:** The corresponding author can provide the data that support the findings of this study upon request.  
**Acknowledgments:** Thanks to the editors and experts for their valuable comments.  
**Conflicts of Interest:** The authors declare no conflicts of interest.