# A Study on the Effects of Hob Temperature on the Rock-Breaking Characteristics of Sandstone Strata
## 2 Calibration of Mechanical Parameters
As shown in Figure 2, by comparing the indoor experiment and numerical simulation images, the numerical simulated stress and strain map, calibrated  
Figure 1: Numerical simulation of uniaxial compression and triaxial numerical simulation experiment. angle was calibrated by adjusting \(\varphi_{\text{P}}\) and \(\mu_{\text{P}}\), and the cracking strength was calibrated by adjusting \(R_{\text{sd}}\). The final calibration results are shown in Table 1 below, and we found that the errors of the macroscopic parameters are within 5%. The values of the relevant microscopic parameters are shown in Table 2.  
By comparing the failure modes of indoor experiments and numerical simulation experiments, we found that the calibrated numerical simulation model is basically the same in terms of crack development, as well as in terms of the failure mode, showing through-crack failure in oblique sections. The specific failure mode diagram is shown in Figure 4 below. As shown in Figures 5 and 6, from the numerical simulation analysis of three-dimensional grouping analysis, it is clear that the sandstone shows an overall distribution of contact numbers along the circumference before loading. After loading, the specimen as a whole undergoes penetration damage along the intermediate cracks due to the generation of intermediate assertive tensile cracks, and the circumferential particle contact bonds break and decrease sharply so that the contact number presents a tight up-and-down distribution, which is consistent with the damage simulation of indoor experiments. It can be seen from the contact forces that the member shows a damage pattern with concentrated forces around it due to the generation of the main crack in the middle. Furthermore, with the increase in temperature, the loss rate of sandstone gradually rises. In indoor experiments, this is manifested by the shedding of granular particles with a powdery appearance on the surface. In numerical simulations, it is reflected in the PFC particles' contact bonds reaching the fracture strength, leading to failure. This phenomenon is related to the composition of the rock. In sandstone, the clay components, under the influence of high temperatures, detach from the larger silica particles, subsequently detaching from the surface layer of the rock mass. At around 300 \({}^{\circ}\)C, the clay minerals undergo expansion, causing the rock mass to undergo a compacted state. However, with the continued increase in temperature, the rock mass develops penetrating cracks. At this point, internal pores gradually enlarge, which is the reason for the increase in particle porosity in the central part, as shown in Figure 4. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Micro-Parameter** & \(E_{\text{P}}\) (**GPa**) & \(\mu_{\text{P}}\) & \(k_{\text{P}}\) & \(C_{\text{P}}\) (**MPa**) & \(\sigma_{\text{P}}\) (**MPa**) & \(\varphi_{\text{P}}\) (\({}^{\circ}\)) & \(R_{sd}\) & \(\theta_{b}\) \\ \hline value & 1.20 & 0.97 & 1 & 16.64 & 8.32 & 75 & 0.42 & 0.7 \\ \hline \end{tabular}
\end{table} 
Table 2: Initial determination of microscopic parameters. Figure 4: Triaxial numerical simulation experiment.