## 3 Results and Discussion
### Influence of Rib Thickness on SIF of Crack Tip  
The bearing capacity, ability to delay crack propagation and the weight of the integral panel are directly influenced by the rib thickness. The rib of the integral wall panel can not only bear the load, but also plays a certain role in preventing crack. The thicker the rib is, the stronger its ability to delay the crack propagation is. Therefore, it is necessary to study the effect of the rib thickness on the stress field of the wall panel crack tip. Similarly, the thicker the rib, the stronger its bearing capacity, but also increase the weight of the rib, thus a reasonable rib thickness of the rib is very important, which is usually in the range of 2.5 mm-7 mm. The influence of rib thickness on SIF at the crack tip \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Groups**} & **Model** & **Model** & **Skin** & \multirow{2}{*}{**Rib Spacing**} & **Rib Height** & **Rib** \\  & **Length** & **Width** & **Thickness** & **\(d\)(mm)** & **\(h\)(mm)** & **Thickness** \\  & **\(L\)(mm)** & **\(W\)(mm)** & **\(t_{m}\)(mm)** & & & **\(t\)(mm)** \\ \hline
1 & 160 & 100 & 5 & 80 & 10 & 4 \\
2 & 160 & 100 & 5 & 80 & 20 & 4 \\
3 & 160 & 100 & 5 & 80 & 30 & 4 \\
4 & 160 & 100 & 5 & 80 & 40 & 4 \\
5 & 160 & 100 & 5 & 80 & 50 & 4 \\ \hline \end{tabular}
\end{table} 
Table 4: Structural parameters of integral wall panels at different rib heights. was analyzed by using a finite element model of integral panel with center penetration crack. Using the method of controlling a single variable, keep the dimensions of other parameters (\(L=120\), \(W=100\), \(t_{m}=5\), \(d=80\), \(h=30\)) of the panel unchanged, and set the ribbed height \(t\) as 2 mm, 3 mm, 4 mm, 5 mm and 6 mm respectively. The load on the model is \(M=7.81\times 10^{6}\) N\(\cdot\)mm. The specific parameters are shown in Table 5.  
Figure 6: SIF curves for crack lengths of (**a**) 5 mm, (**b**) 10 mm, (**c**) 15 mm, (**d**) 20 mm, (**e**) 25 mm, and (**f**) 30 mm. Figure 7: Comparison of the effect of rib height on SIF between FEM result and reference result. The SIFs at the crack tip under each group of parameters with different rib thickness were obtained by finite element calculation, as shown in Figure 8.  
It can be seen from Figure 8a that, when the crack length is 5 mm, the trend of SIF with skin thickness under different rib heights are relatively similar, with the SIF decreases approximately linearly with the change of thickness. With the increase of rib thickness, the slope of the curves decreases gradually, the curves tend to be flat. \(K_{I}\) value of the area below the skin thickness center decreases, while \(K_{I}\) of the area around the skin thickness center almost remains the same, and \(K_{I}\) of the area above the skin thickness center increases. The above result shows that the minimum \(K_{I}\) value of the crack tip increases with the increase of the rib thickness, while the maximum \(K_{I}\) value of the crack tip decreases with the increase of the rib thickness. In a certain range, the rib thickness has a certain influence on the stress field at the crack tip of the whole wall plate, but this effect weakens with the increase of the rib height. By comparing the six figures in Figure 8, it can be found that \(K_{I}\) value of the crack tip increases as a whole with the crack propagation, and the ratio of increase is close to each other, and the shape and slope of the curves change very little. The above results show that the effect of rib thickness on the change velocity of \(K_{I}\) value at each point is consistent during the crack propagation. The above analysis shows that when the rib thickness is small, the increase of the rib thickness can significantly reduce the overall crack tip \(K_{I}\) value, and the integral panel's fracture resistance can be enhanced.