# Experimental Study on the Dynamic Characteristics of Fractured Coal Under Cumulative Impact
## 4 Conclusions  
This study investigates the effects of cumulative impacts on the wave velocity, dynamic compressive strength, fractal fragmentation characteristics and energy dissipation behavior of fractured coal through wave velocity measurement and dynamic impact tests. This study can, to some extent, reveal the dynamic failure mechanism of fractured coal samples under cumulative impact. The key conclusions are as follows:  
1. As the number of cumulative impacts increases, the wave velocity of coal samples continuously decreases, following a linear relationship. The rate of wave velocity reduction varies with fracture dip angles, demonstrating angular dependence in fractured coal samples under cumulative impacts.
2. Dynamic compressive strength progressively decreases with cumulative impacts, showing 25-40% reduction after five impact cycles. Specimens with 30\({}^{\circ}\) fracture dip angles exhibit the most significant strength reduction and the highest failure probability under equivalent impact cycles.
3. Fractured coal fragments demonstrate remarkable self-similarity under cumulative impacts, conforming to fractal distribution characteristics. Increasing impact cycles elevate the fractal dimensions while transforming the fragmentation patterns from large-block tensile failure to small-particle crushing with tensile-shear hybrid failure modes.
4. A progressive reduction in the energy dissipation rate reveals that cumulative impacts induce significant damage degradation, reducing the energy consumption required for failure. Pre-existing fractures cause measurable energy dissipation reduction, though dip angles show limited influence on the dissipation rates.  
The experimental data presented in this paper cannot yet be directly applied to the dynamic response analysis of actual coal-rock masses. However, the research conclusions reveal universal principles underlying the scientific problems studied. Future research will attempt to establish a correspondence between actual working conditions and experimental results, thereby providing a reference for further studies and engineering applications related to these issues.  
Conceptualization, J.M.; methodology, J.M.; software, L.S.; validation, J.M. and L.S.; formal analysis, L.S.; investigation, F.L.; resources, F.L.; data curation, J.M.; writing--original draft preparation, J.M.; writing--review and editing, J.M. and L.S.; visualization, F.L.; supervision, F.L.; project administration, F.L.; funding acquisition, F.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Natural Science Basic Research Plan in Shaanxi Province (No. 2023-YBGY-085) and the Scientific Research Program Funded by Shaanxi Provincial Education Department (No. 24 JK0529) and Xi'an Jiaotong University City College potential cultivation project (No. 2024 PY02), for which the authors are very thankful.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
Author [PERSON] was employed by the company Shaanxi Coal Chemical Industry Technology Research Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.