## 3 Results and Analysis  
### Dynamic Stress-Strain Curve Analysis  
The dynamic stress-strain curves of jointed specimens with various JRCs and joint inclination angles are illustrated in Figure 4.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Mix Proportion** & \(f\)**/MPa** & \(\rho\)**/(g:cm\({}^{-3}\))** & \(E\)**/GPa** & \(\mu\) \\ \hline cementwater:fine sand = 1:0.4:0.7 & 28.56 & 2.44 & 3.68 & 0.25 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical and static mechanical parameters of the cement mortar.  
Figure 3: Jointed cement mortar specimen. (**a**) Half jointed cement mortar specimen, (**b**) Jointed cement mortar specimen after bonding.  
As shown in Figure 4, dynamic stress-strain curves show no compaction form but an approximates linear shape in the initial stage. Therefore, the initial stage of the stress-strain curve under impact load is different from that under static load. This phenomenon is more pronounced in complete specimens, whereas jointed specimens exhibit a shorter linear elastic stage. Moreover, the dynamic stress-strain curves of both complete and jointed specimens can be classified into three stages, namely linear elastic, plastic deformation, and post-peak failure.  
In the plastic deformation stage, the dynamic stress-strain curves of both complete and jointed specimens exhibit a continuous increase in strain after the first peak, while the stress remains constant. Once the strain reaches a certain level, the stress further increases until the specimen's plastic deformation occurs. At joint inclination angles of 45\({}^{\circ}\) to 60\({}^{\circ}\), jointed specimens exhibit a higher susceptibility to sliding failure under impact conditions.  
After reaching the peak stress, jointed specimens exhibit softening behavior, characterized by distinct curve profiles with decreasing stress. The post-peak curves of jointed specimens with joint inclination angles of 0\({}^{\circ}\) or 90\({}^{\circ}\) exhibit an almost linear decline, which indicates pronounced brittle characteristics. Despite being affected by the sliding of the joint surface, jointed specimens with a joint inclination angle of 45\({}^{\circ}\) retain a certain load-bearing capacity during the softening stage, as the stress gradually decrease with the strain along the post-peak failure curve.  
As illustrated in Figure 4, the dynamic stress-strain curves of jointed specimens are notably influenced by JRC under the same joint inclination angles. When the joint inclination angle is 0\({}^{\circ}\) or 90\({}^{\circ}\), jointed specimens with various JRCs exhibit similar curve slopes, peak stresses, and post-peak failure stage slopes, which all indicates pronounced brittfulness. When the joint inclination angle is in the range of 30\({}^{\circ}\) to 60\({}^{\circ}\), the slope in the initial linear elastic stage of dynamic stress-strain curve progressively augments with JRC increasing, leading to an increase in the elastic modulus. The slope in the plastic deformation stage reveals an increasing resistant capability of deformation with JRC increasing, resulting in a gradual rise in the peak stress. During the post-peak failure stage, when the JRC is 0, jointed specimens exhibit a notable reduction in slope, indicating plastic failure characteristics. As the JRC increases from 0 to 20, the slope in the post-peak failure stage exhibits a significant increase, indicating a brittle failure.