# Mechanical Behavior and Fracture Evolution of Artificial Rock Specimens Within 3D-Printed Fractures
## 3 Experimental Tests
### Mechanical Properties
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \begin{tabular}{c} **Proportion of** \\ **AB** \\ **Glue and** \\ **Pulverized** \\ **Coal** \\ \end{tabular} & \begin{tabular}{c} **Peak** \\ **Compressive** \\ **Strength** \\ **(MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Elastic** \\ **Modulus** \\ **(GPa)** \\ \end{tabular} &
\begin{tabular}{c} **Poisson** \\ **Ratio** \\ **Ratio** \\ \end{tabular} \\ \hline Cubic DFN model & A1 & 1:1.2 & 32.70 & 1.12 & 0.29 \\ Cubic DFN model & A2 & 1:1 & 18.14 & 0.78 & 0.23 \\ Cubic DFN model & A3 & 1:1 & 12.94 & 0.59 & 0.25 \\ Cylindrical DFN model & B2 & 1:1.2 & 77.97 & 2.36 & 0.37 \\ Cylindrical DFN model & B3 & 1:1 & 61.09 & 1.03 & 0.31 \\ Cubic solid model & C & 1:1 & 78.96 & 3.70 & 0.37 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mechanical parameters of the sample. existence of the random fracture network model (DFN model) significantly reduced the compressive strength. The stress-strain curve of the solid cube model is also divided into four different stages: compaction stage, linear elasticity stage, yield stage, and residual stage. Compared with cubic DFN model samples, solid cubic samples featured a shorter compaction stage, longer linear elastic stage, and similar yield stage. At peak strength, the sample exhibited observable cracks, culminating in a shear failure. The post-peak axial stress-axial strain curve depicted simultaneous stress and strain reduction, suggesting that the material's plasticity triggered the post-peak expansion of the sample. During the residual stage, the compressive stress experienced a sudden decrease, followed by a significant, continuous deformation stage in the post-peak stage. Figure 5 shows the stress-strain curve of the cylinder model sample. The mechanical parameters of the cylinder model were given in Table 3. In particular, the B2 sample, with an AB glue to pulverized coal mixture ratio of 1:1.2, achieved a peak compressive strength, elastic modulus, and a Poisson's ratio of 77.97 MPa, 2.36 GPa, and 0.37, respectively. Moreover, the B3 sample, with an AB glue to pulverized coal mixture ratio of 1:1, demonstrated a peak compressive strength, elastic modulus, and a Poisson's ratio of 61.09 MPa, 1.03 GPa, and 0.31, respectively. It was found that increasing the pulverized coal content of the sample increased the strength of the sample by 0.28 times, the peak stress by 16.88 MPa, and the strain by 0.05. This indicated that the increase in pulverized coal content improved the mechanical properties of the sample. The stress-strain curve of the cylinder model sample was similar to that of rock in the compression process, which consisted of four stages: compaction stage, linear elastic stage, crack propagation stage, and post-failure stage. The slope of the sample curve gradually increased with the increase in stress in the compaction stage, indicating that the bubbles in the sample had burst, the microcracks had closed, and the strain had increased slightly after compression in this stage. In the linear elastic stage, the sample curve increases linearly with stress. In the crack propagation stage, the specimen was subjected to plastic deformation, new cracks appeared in the specimen, stress concentration occurred at the crack, and the specimen exhibited the maximum compressive strength. In the failure stage, the stress of the specimen decreases slowly while the strain continues to increase, and the crack continues to increase until it is completely destroyed. Figure 5: Stress–strain curve of cylindrical DFN model.