# Delamination Effect on the Buckling Behaviour of Carbon-Epoxy Composite Typical Aeronautical Panels
## 4 Results and Discussion
### Cd11-CD16 Configurations  
In Table 6, the buckling loads and displacement obtained from the linear eigenvalue buckling analyses are reported for each configuration.  
According to Table 6, the local buckling load increases as the depth of delamination increases (from 0.33 mm in CD11-CD12, to 0.495 mm in CD13-CD14, to 0.66 mm in CD15-CD16). In the CD11-CD12 and CD15-CD16 configurations, the initiation of prop  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Configuration**} & \multirow{2}{*}{**Stiffness**} & \multicolumn{2}{c}{**Buckling Circular**} & \multirow{2}{*}{**Buckling Skin**} & \multirow{2}{*}{**Buckling Stringer**} & \multirow{2}{*}{**Delamination Initiation**} \\  & & & **Delamination** & & \\ \hline CD11 & 305,413 & 4.31 kN & 125.4 kN & 183.7 kN & 133.3 kN \\  & N/mm & 0.014 mm & 0.4107 mm & 0.6014 mm & 0.4437 mm \\ CD12 & 305,414 & 7.61 kN & 130.3 kN & 184.4 kN & 133.8 kN \\  & N/mm & 0.025 mm & 0.427 mm & 0.6039 mm & 0.4437 mm \\ CD13 & 304,877 & 14.3 kN & 124.18 kN & 183.1 kN & 113.4 kN \\  & N/mm & 0.047 mm & 0.4073 mm & 0.6006 mm & 0.375 mm \\ CD14 & 305,054 & 25.1 kN & 130.8 kN & 1842 kN & 119.4 kN \\  & N/mm & 0.082 mm & 0.429 mm & 0.6039 mm & 0.3937 mm \\ CD15 & 304,902 & 24.9 kN & 119 kN & 183 kN & 131.6 kN \\  & N/mm & 0.082 mm & 0.3907 mm & 0.6002 mm & 0.4375 mm \\  & 304,905 & 43.7 kN & 126.8 kN & 183.7 kN & 141 kN \\  & N/mm & 0.1434 mm & 0.4158 mm & 0.6025 mm & 0.4687 mm \\ \hline \hline \end{tabular}
\end{table}
Table 6: Buckling loads and displacements for CD11–CD16 configurations.  
Figure 10: CD9–CD10 configurations: (**a**) delaminated area vs. load curves; (**b**) delamination evolution at final analyses load (pink represent the delaminated area).  
agation occurs after the buckling of the skin, at loads of 133.3, 133.8, 131.6 and 141 kN, respectively, with respect to 125.4, 130.3, 119 and 126.8 kN, while in the CD13-CD14 configurations, characterised by the delamination located under the third layer, i.e., between two layers at \(90^{\circ}\) and \(-45^{\circ}\), the initiation occurs at a lower load (113.4 and 119.4 kN), and the propagation reaches its maximum extension before the global buckling of the panel. In Figure 11, the contour plots of the out-of-plane displacements are shown for each configuration, while in Figure 12 the delamination evolution is reported.  
Figure 11: Out-of-plane displacement contour plot: (1) buckling of circular delamination, (2) buckling of the skin, (3) global buckling including stringers and (4) delamination initiation, with (**a**) CD11, (**b**) CD12, (**c**) CD13, (**d**) CD14, (**e**) CD15 and (**f**) CD16.  
As Figure 12a shows, in two configurations characterised by delamination between \(45\)// \(-45\) (CD15-CD16), the propagation of delamination is triggered but does not evolve. Therefore, these configurations can be considered to be more conservative in terms of damage tolerance. Furthermore, the trend whereby an initial delamination with a lower radius exhibits a faster propagation is again confirmed, as shown by the curves in Figure 12a for the CD12 and CD14 configurations, both having a delamination radius of 30 mm. Figure 12b shows the final status of delamination for the CD11-CD16 considered configurations.