# Numerical Analysis of Fatigue Life of Wind Turbine Blades Reinforced with Graphene Platelets
## 5 Conclusions  
In this study, the applicability of graphene platelet-reinforced composites (GPLRCs) to wind turbine blades as a next-generation material was examined by assessing the fatigue life of a wind turbine blade reinforced with graphene platelets (GPLs) using an effective and reliable numerical estimation method. The geometric dimensions and material properties of the finite element model were created based on the design of the SNL 61.5-m model, a 5 MW wind turbine blade. The effective elastic properties of GPLRCs were calculated by applying the Halpin-Tsai micromechanical model and modified linear rule of mixtures. The fatigue load spectrum was calculated based on 60 min wind speed data, and aerodynamic loads according to each wind speed were calculated using the BEMT. The fatigue load spectrum was then derived by applying the calculated loads to finite element analysis, and the fatigue cycle was calculated through an FFT. The equivalent stress acting on the \begin{table}
\begin{tabular}{c c c} \hline \multirow{2}{*}{**Location**} & \multicolumn{2}{c}{**Fatigue Life (Years)**} \\ \cline{2-3}  & **Without GPL** & **with 0.2\% wt. GPL** \\ \hline
1 & \(1.86\times 10^{8}\) & \(1.02\times 10^{10}\) \\
2 & \(9.05\times 10^{7}\) & \(4.71\times 10^{9}\) \\
3 & \(4.80\times 10^{7}\) & \(2.15\times 10^{9}\) \\
4 & \(2.00\times 10^{5}\) & \(7.18\times 10^{6}\) \\
5 & \(6.81\times 10^{1}\) & \(2.09\times 10^{3}\) \\
6 & \(1.06\times 10^{3}\) & \(3.42\times 10^{4}\) \\
7 & \(2.16\times 10^{3}\) & \(7.24\times 10^{4}\) \\
8 & \(9.71\times 10^{3}\) & \(3.26\times 10^{5}\) \\ \hline \end{tabular}
\end{table} 
Table 11: Fatigue life of GFRP in wind turbine blades with and without GPL reinforcement. Figure 9: S-N curves of GFRP with and without GPL reinforcement. blade was calculated based on the Goodman diagram, and cumulative fatigue damage was evaluated through the Palmgren-Miner rule. Finally, the reliability of the proposed analysis model and fatigue life assessment method was verified by comparing the fatigue life of wind turbine blades calculated in this study with the fatigue life results of Resor [26]. When the fatigue performance of the GPL-reinforced wind turbine blade was evaluated, GPLRCs exhibited similar or higher fatigue life compared to traditional materials in certain locations but showed poorer performance than traditional materials in other locations. In particular, the fatigue life of GPLRCs was significantly low near location 5 of the blade. This is due to the fact that the fatigue failure stress (S-N curve) and tensile strength of GPLRCs are lower than those of traditional materials. Additionally, an increase in the weight fraction of GPLs is highly likely to reduce tensile strength owing to their non-uniform distribution. This problem may have a more negative impact on fatigue performance in the actual manufacturing process. Despite these challenges, GPLRCs showed promising results in terms of material cost, weight reduction, and natural frequency. However, their poor fatigue performance highlights the need for further development. Thus, it is necessary to explore measures such as developing hybrid materials by mixing conventional fiberglass composites with GPLs or optimizing the volume fraction and reinforcement locations of GPLs. To address the fatigue life limitations of wind turbine blades with GPLRC, this study proposed incorporating GPLs into fiberglass composites rather than completely replacing the matrix with GPLRC. As a result, the fatigue life of wind turbine blades was significantly improved by adding GPLs to fiberglass composites. Nevertheless, given the limited research on the application of GPL-reinforced fiberglass composites for wind turbine blades, further studies are needed to explore this approach in greater detail and advance its practical implementation. Conceptualization, J.-R.C. ; Methodology, H.J.K. ; Software, H.J.K. ; Validation, H.J.K. ; Writing--original draft, H.J.K. ; Writing--review and editing, J.-R.C. ; Funding acquisition, J.-R.C.