# Mechanical Behavior and Fracture Evolution of Artificial Rock Specimens Within 3D-Printed Fractures
## 6 Conclusions  
Using 3D printing technology, prefabricated fractured jointed rock specimens were fabricated with transparent crystal adhesive solution and full-size pulverized coal at ratios of 1:1 and 1:1.2. Uniaxial compression tests were performed to obtain stress-strain curves and mechanical parameters of samples with different shapes and ratios. DIC technology was used to study the change in full-field strain and the evolution of surface cracks during specimen failure. The effects of different proportions and low-temperature conditions on the mechanical properties of the specimens were discussed.  
1. The strength of the specimen increased as the pulverized coal content increased. When the ratio of AB adhesive to coal powder was 1:1.2, the peak compressive strength of the specimen approached that of natural coal rock. Compared with a solid sample, the introduction of a DFN model reduced the compressive strength of the sample.
2. The DFN model specimens mainly exhibited longitudinal fracture as the failure mode in uniaxial compression, while the solid model specimens exhibited shear fracture. The failure mode of the specimen changed when a DFN model was added compared with the solid specimen. Cylindrical specimens failed due to longitudinal and shear fractures that occurred during uniaxial compression. In addition, samples with low coal dust content exhibited transverse cracking during compression. Increasing the amount of pulverized coal in the mix increased the fragility of the sample, leading to predictable failure under rock compression.
3. The stress-strain curve of the DFN model coal rock sample became more similar to that of the actual coal rock after freezing treatment. A slight decrease in the average compressive strength was observed, while the average Young's modulus and the average peak strain increased. After freezing, the specimen experienced brittle failure, with a single slope shear failure as the failure mode.  
Figure 11: Stress-strain curves of different samples.  
**Author Contributions:** Investigation, writing--original draft, Y.G.; software, X.F.; data curation, Q.L. and Z.Q.; writing--review and editing, P.W.; project administration, M.C. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was financially supported by the National Key R&D Program of China (No. 2023 YFC2907400, 2021 YFC2900500), the National Natural Science Foundation of China (No. 52074020), the specific research fund of the Innovation Platform for Academicians of Hainan Province (YSPTZX202504), and the Hainan Province Science and Technology Special Fund (ZDYF2024 GXJS307).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Some or all data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.  
**Conflicts of Interest:** Author [PERSON] was employed by the company Anhui Magang Luohe Mining Industry 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.