## 3 Results and Discussion
### Tensile Strength  
Figure 5A shows the tensile strengths of E51/PEPA resins with different mixing ratios of E51 and PEPA. The E51/PEPA (2:1) resin achieved the highest tensile strength compared with E51/PEPA (1:1), E51/PEPA (3:1), and E51/PEPA (4:1) resins. The result implies that the proper mixing ratio of E51/PEPA could bring forth the best curing effect. Although the E51/PEPA (2:1) resin achieved the highest tensile strength, it is still limited in many high-performance application fields. E-POSS and GF were employed to improve the tensile strength of epoxy resins [24; 25]. The influence of E-POSS and GF on tensile strength of epoxy resins was tested and the result is shown in Figure 5B and Table 1. The tensile strength of E51 resin is illustrated as the black column in Figure 5B, and the tensile strength of E51 resin was 60.1 MPa. The tensile strength of E51 + E-POSS composite is presented as the green column in Figure 5B, showing that the tensile strength increased with the increasing E-POSS content from 5 wt% to 10 wt%. However, an excessive amount of E-POSS (15 wt%) resulted in a slightly reduced tensile strength. The tensile strength of E51 + E-POSS composite with 10 wt% E-POSS content achieved the maximum value (92.5 MPa). Compared with the E51 resin, the tensile strength of E51 + E-POSS composites with 5 wt%, 10 wt%, and 15 wt% E-POSS increased by 30.3, 53.9, and 45.8%, respectively. Epoxy groups of E-POSS and E51 can react with PEPA to form the cross-linking network; E-POSS contains multiple epoxy groups and a network with high cross-linking grid density is formed around inorganic nanofiller (POSS). These grids break preferentially and consume energy during the tensile process, which leads to the high tensile strength of the epoxy resin. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample ID**} & **E-POSS** & **GF** & **Modulus** & **Tensile Strength** & \(\underline{\text{Ts}(\text{sample})}\) **100\%** \\  & **(wt\%)** & **(wt\%)** & **(GPa)** & **(MPa)** & **(MPa)** & \(\underline{\text{Ts}(\text{ESI})}\) **100\%** \\ \hline E51 & - & - & 3.7 \(\pm\) 0.1 & 60.1 \(\pm\) 6.5 & 100\% \\ E51 + E-POSS (5\%) & 5 & - & 4.5 \(\pm\) 0.2 & 78.3 \(\pm\) 7.4 & 130.3\% \\ E51 + E-POSS (10\%) & 10 & - & 4.9 \(\pm\) 02 & 92.5 \(\pm\) 7.8 & 153.9\% \\ E51 + E-POSS (15\%) & 15 & - & 4.7 \(\pm\) 0.2 & 87.6 \(\pm\) 8.3 & 145.8\% \\ E51 + GF (8\%) & - & 8 & 5.2 \(\pm\) 0.2 & 132.1 \(\pm\) 10.4 & 219.8\% \\ E51 + GF (16\%) & - & 16 & 6.6 \(\pm\) 0.2 & 186.7 \(\pm\) 11.5 & 310.6\% \\ E51 + GF (24\%) & - & 24 & 5.8 \(\pm\) 0.2 & 172.1 \(\pm\) 15.3 & 286.4\% \\ E51 + E-POSS (10\%) & 10 & 16 & 7.5 \(\pm\) 0.2 & 214.9 \(\pm\) 18.8 & 357.6\% \\ + GF (16\%) & & & & & \\ \hline \hline \end{tabular} NOTE: \(\underline{\text{Ts}}_{s}\) denotes the tensile strength.  
\end{table} 
Table 1: The data of tensile strength of different samples. Figure 5: (**A**) Tensile strength of E51/PEPA with different mixing ratios, (**B**) tensile strength of different samples. The blue column in Figure 5B shows the tensile strength of E51 + GF composite at different mixing ratios of E51/GF. With an increase in GF content (8 wt%-16 wt%), the tensile strength of E51 + GF composite became higher, while the tensile strength slightly decreased when the GF content was 24 wt%. The E51 + GF (16%) composite exhibited the highest tensile strength (186.7 MPa) compared with the E51 + GF (8%) and E51 + GF (24%) composites. The tensile strength of E51 + GF (16%) composite was increased by 210.6% compared with the E51 sample. The incorporation of GF could enhance the tensile strength due to the bridging mechanism. On the one hand, the addition of GF could scatter the extension of impact cracks and produce the fracture modes of multiple cracks. On the other hand, it could hinder the progress of the cracks in the direction of the cracks' fracture modes. The ternary composite of E51 + E-POSS + GF was prepared by adding 10 wt% E-POSS and 16 wt% GF.