# Study on Dynamic Splitting Properties of S-PP Hybrid Fiber Concrete after High Temperatures
## 4 Numerical Simulation
### Simulating Splitting Failure Process  
Figure 15 shows the failure process of PC and S1 PP0.2 concrete simulated by a dynamic splitting test under normal temperature and 800 \({}^{\circ}\)C. The numerical simulation results show that the concrete specimen first produces the crack initiation point from the end face in contact with the incident bar. Then the crack begins to crack in the center. The crack is derived from the contact surface at both ends. It penetrates the middle of the specimen, the transmission end is crushed, and the incident end and transmission end gradually to form a triangular failure area. This result is due to the stress concentration at the two contact end faces. When the strong compressive stress wave is transmitted to this position, the area of the crushing area presents a triangular shape. The specimen breaks when the crushing area gradually expands to the diameter direction. At the same time, it is found that the damage degree of the concrete specimen in contact with the incident bar and the transmission bar is inconsistent, and the damage degree of the end surface in contact with the incident bar is greater than that of the transmission bar. Comparing the splitting failure process of PC and S1 PP0.2 concrete, under normal temperature, the splitting failure crack of PC is long and wide, and the crack penetrates from the contact end face of the incident bar to the contact end face of the transmission bar. However, the destruction degree of S1 PP0.2 concrete is not as serious as that of PC, and there is no penetrating crack. Under 800 \({}^{\circ}\)C,  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Number** & **T** (\({}^{\circ}\)**C**) & \(\rho\) **(kg/m\({}^{3}\))** & \(G\) & \(f_{c}\) **(MPa)** & \(f_{t}\) **(MPa)** & \(p_{c}\) **(MPa)** & \(\mu_{c}\) & \(p_{l}\) **(GPa)** & \(\mu_{l}\) \\ \hline \multirow{2}{*}{PC} & 25 & 2310 & 13.5 & 41.6 & 3.99 & 13.89 & 0.000760 & 0.81 & 0.100 \\  & 800 & 2181 & 2.75 & 14.8 & 2.38 & 4.93 & 0.000675 & 0.81 & 0.121 \\ \hline \multirow{2}{*}{S1 PP0.2} & 25 & 2430 & 21.3 & 53.2 & 4.52 & 17.73 & 0.000894 & 0.81 & 0.100 \\  & 800 & 2317 & 4.28 & 27 & 3.22 & 9 & 0.000812 & 0.81 & 0.116 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Parameters of the concrete HJC material model.  
Figure 14: Comparison of experimental and simulated dynamic splitting stress–strain curves.  
the damage crack of PC runs through and has the trend of deriving to the surrounding, and the damage is more serious. S1 PP0.2 concrete has smaller main cracks and secondary cracks. The overall damage degree is lower than PC, and the two contact end faces still form triangular area damage. The failure results of LS-DYNA numerical simulation are matched with the experimental failure results, which shows that the modified HJC model effectively studies the dynamic tensile properties of concrete after high temperature. It can accurately reflect the change law of dynamic splitting tensile mechanical properties of concrete specimens during the impact process.  
Figure 15: Failure process simulated by splitting tensile test: (**a**) PC-25 \({}^{\circ}\)C; (**b**) PC-800 \({}^{\circ}\)C; (**c**) S1 PP0.2-25 \({}^{\circ}\)C; (**d**) S1 PP0.2-800 \({}^{\circ}\)C.