## 3 Results
### Variation Laws of Surface Mechanical Properties Under Different Corrosion Mechanisms
#### 3.2.2 Variation Laws of Surface Longitudinal Wave Velocity Under Different Corrosion Mechanisms
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Dissolution Method**} & \multirow{2}{*}{**Dissolution Time (h)**} & \multicolumn{6}{c}{**P–Wave Velocity(m/s)**} \\ \cline{3-6}  & & & **2450–** & **2350–** & **2300–** & **2250–** & \multirow{2}{*}{**<2250**} \\  & & & **2550** & **2450** & **2350** & **2300** & \\ \hline  & 0 & 1 & 0 & 0 & 0 & 0 \\  & 24 & 0.53 & 0.47 & 0 & 0 & 0 \\  & 48 & 0 & 0.74 & 0.26 & 0 & 0 \\ Dynamic & 72 & 0 & 0 & 0.92 & 0.08 & 0 & 0 \\ Cyclic & 96 & 0 & 0 & 0.60 & 0.40 & 0 & 0 \\ Dissolution & 120 & 0 & 0 & 0.05 & 0.87 & 0.08 & 0 \\  & 144 & 0 & 0 & 0 & 0.03 & 0.88 & 0.09 \\  & 168 & 0 & 0 & 0 & 0.11 & 0.71 & 0.18 \\  & 192 & 0 & 0 & 0 & 0 & 0.50 & 0.50 \\ \hline Static & 240 & 0 & 0.22 & 0.71 & 0.07 & 0 & 0 \\ Immersion & 480 & 0 & 0.02 & 0.32 & 0.34 & 0.31 & 0.01 \\ Dissolution & 720 & 0 & 0 & 0.18 & 0.26 & 0.42 & 0.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Area proportion of surface wave velocity segments under different dissolution methods. The above analysis shows that the distribution of P-wave velocity ratios progressively shifts toward lower values, with distinct differences between static and dynamic dissolution. (1) Dynamic Cyclic Dissolution:  
The shift toward lower values occurs in a staged and continuous manner. As cyclic dissolution time increases, the P-wave velocity ratio decreases, and the distribution range gradually expands, indicating an enlargement of the affected area. Critical turning points occur at 48 h, 72 h, 120 h, and 144 h of cyclic dissolution (equivalent to the duration of acid rain in Southwest China), where P-wave velocity ratios exhibit relatively concentrated distributions. At 48 h, ratios primarily range from 0.92 to 0.96; at 72 h, they shift to 0.88-0.92; at 120 h, the main distribution moves to 0.85-0.9; and, at 144 h, ratios are predominantly in the range of 0.84-0.86. Combined with contour map analysis, the regions above the two sides of the rock slab are identified as areas with the lowest dynamic dissolution intensity. (2) Static Immersion Dissolution:  
A significant decrease in P-wave velocity is observed at 240 h of immersion, with ratios mainly distributed between 0.88 and 0.92. Subsequently, although P-wave velocity ratios continue to decrease, the distribution range broadens, and no concentrated areas of P-wave velocity ratios emerge. Figure 15: Variation in P–wave velocity ratio under different dissolution conditions. (**a**) Dynamic cyclic dissolution, (**b**) static immersion dissolution. In summary, dynamic cyclic dissolution results in a more complex P-wave velocity distribution, reflecting significant changes in the internal pore structure. Consequently, dynamic dissolution has a greater impact on pore structure evolution compared to static immersion dissolution. These findings highlight the importance of considering dissolution mechanisms when assessing sandstone degradation and developing preservation strategies for sandstone-based cultural heritage. 2.3 Research on Differences in Distribution Laws of Mechanical Parameters Under Different Corrosion Mechanisms  
To comprehensively analyze the variation in corrosion influence range with static and dynamic corrosion time and the differences between static and dynamic corrosion, the distribution of mechanical strength affected by static and dynamic corrosion is analyzed by combining surface hardness and surface P-wave velocity analyses. From the above analysis, the following can be concluded:  
(1) During dynamic cyclic corrosion, the distributions of surface hardness and surface P-wave velocity show relatively consistent changes. Specifically, the maximum values of surface hardness and surface P-wave velocity are concentrated in the central area, and the positions of minimum values correspond closely, with the strength distribution showing good integrity. However, the distribution range of low P-wave velocity values gradually decreases, while that of low surface hardness values gradually increases.