# Stability and Failure of the Edge-Closed Honeycomb Sandwich Panels with Face/Core Debonding
## 2 Experimental Procedures  
### Subsection  
The specimens designed in this paper were divided into non-defective samples and samples with face/core debonding, which were consist of skin, honeycomb core and adhesive. The sheets were stacked by plain carbon fabric prepreg Cycom970/T300, provided by Cytec Industries Inc. (Paterson in United States). The thickness of prepreg was 0.216 mm and mechanical parameters are given in Table 1. Nomex honeycomb JY1-3.2-48 manufactured by Jiangsu Junyuan New Material Co., Ltd. (Nantong, China). was used in this study, and its equivalent mechanical properties [27] were given in Table 2. TS-JM-200 was used to adhere face-sheet onto core, and its mechanical properties are given in Table 3. All specimens were produced in autoclave. The basic configuration of the two type of test specimens is shown in Figure 1. The flat panel of specimens was the outer skin, and the convex panel was the inner skin. The square area between the inner and outer skins was the honeycomb core. The design bases [28] of specimens are summarized in Table 4. The stacking sequence of sheets in honeycomb area from outside to inside was [(45/0)\({}_{2}\)/45/C\({}_{10}\)/45/0/45], and that of edge-closed area from outside to inside was [(45/0)\({}_{2}\)/45/(0/45)s/45/0/45]. More layers and reinforced plates were laid in the closed area to prevent the edge-closed area from destroy in advance. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**E\({}_{1}\) (GPa)** & **E\({}_{2}\) (GPa)** & **G\({}_{12}\) (GPa)** & \(\upsilon_{12}\) & **X\({}_{\text{T}}\)** = **X\({}_{\text{C}}\) (MPa)** & **Y\({}_{\text{T}}\)** = **Y\({}_{\text{C}}\) (MPa)** & **S\({}_{12}\) (MPa)** \\ \hline
49 & 49 & 3.6 & 0.044 & 676.2 & 615.5 & 261.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The mechanical parameters of plain carbon fabric prepreg. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**E\({}_{1}\) (MPa)** & **E\({}_{2}\) (MPa)** & **E\({}_{3}\) (MPa)** & **G\({}_{12}\) (MPa)** & **G\({}_{13}\) (MPa)** & **G\({}_{23}\) (MPa)** & **\(\upsilon_{12}\)** & **\(\upsilon_{13}\)** \(\equiv\) **\(\upsilon_{23}\)** \\ \hline
0.1953 & 0.1953 & 136 & 0.073 & 40 & 23 & 0.94 & 0.0003 \\ \hline \hline \multicolumn{2}{c}{**X\({}_{\text{TT}}\) (MPa)**} & \multicolumn{4}{c}{**S\({}_{\text{LT}}\) (MPa)**} & \multicolumn{4}{c}{**S\({}_{\text{WT}}\)(MPa)**} \\ \hline
1.93 & \multicolumn{4}{c}{1.26} & \multicolumn{4}{c}{0.62} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Equivalent mechanical properties of Nomex honeycomb. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Design Parameters** & **Reference** \\ \hline The minimum number of skin layers is 2 & Prevent moisture penetration and meet the minimum structural strength requirements \\ \hline The number of skin layers reaches 5 & Avoid damage caused by low energy impact \\ \hline The empirical height value of Non-metal core is about 12.7 mm & Provides appropriate shear strength and stiffness \\ \hline \hline \(\pm\)45 ply & Enhanced in-plane shear \\ \hline
0/90 ply & Strengthening structural bending \\ \hline Beveling angle is generally 20–30\({}^{\circ}\) & Minimize the bonding pressure on the inclined surface \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The design basis of specimens. \begin{table}
\begin{tabular}{c c c} \hline \hline
**E\({}_{1}\) (GPa)** & **E\({}_{2}\) (GPa)** & **G\({}_{12}\) (GPa)** & **\(\upsilon_{12}\)** & **X\({}_{\text{T}}\)** = **X\({}_{\text{C}}\) (MPa)** & **Y\({}_{\text{T}}\)** = **Y\({}_{\text{C}}\) (MPa)** & **S\({}_{12}\) (MPa)** \\ \hline
49 & 49 & 3.6 & 0.044 & 676.2 & 615.5 & 261.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The mechanical parameters of plain carbon fabric prepreg. Compared with non-defective specimens, specimens with debonding defects form debonding areas by prefabricating a polytetrafluoroethylene film with a diameter D between the outer skin and the honeycomb core.