# Design and Analysis of a Curved Composite Bracket
## 2 Applied Materials and Structural Design  
The bracket structure was designed using a carbon fiber composite. Numerical analysis was performed on the designed bracket, and structural analysis was carried out to evaluate its structural integrity. The method for manufacturing composite structures is the autoclave method. Therefore, the prepreg composite material underwent the autoclave manufacturing method. A TORAY in New York, USA carbon fiber and epoxy resin prepreg was used for the design and analysis, with a thickness of 0.2 mm. The mechanical properties were obtained via specimen testing [20]. The mechanical properties of the applied material, which were required for the design, are presented in Table 1, and the bracket was designed using these mechanical properties. The mechanical properties of the manufactured specimen were analyzed and reflected in the conceptual design. In addition, the mechanical property results obtained through specimen testing were applied as values for the structural analysis. The designed structure was manufactured using the presented prepreg. The specimen test was performed using static material testing system at the KSNU Advanced Technology Institute for Convergence. The bracket's structure, made from cylindrically curved composite, was designed. Figure 1 shows a model of the curved composite panel considering loading conditions. The length of the curved panel is a. The length of the mid-surface is b. The length of the radius is R. N\({}_{\rm x}\) is the uniaxial compressive load. N\({}_{\rm xy}\) is the shear load. The constitutive relation equation was calculated using the Kirchhoff hypothesis. The lamination and definition of the angle for the target structure was carried out by applying the constitutive relation equation. The constitutive equation of the thin curved panel was also applied [21]. The design of the panel was carried out based on the laminate theory presented above. It was designed on the basis of the yield strength of the material for the application load. The composite design method using classical laminate theory was applied to carry out the structural design. The initial design is defined under the assumption that the fabric laminated in the load direction bears all of the load. This was complemented with the use of the mixed design method, in which fabric laminated in different directions from the load direction also contributes to 10% of the strength, and fabric in the \(\pm\)45\({}^{\circ}\) direction was mixed with fabric in the 0\({}^{\circ}\) direction in order to determine the final number of layers. A total of six acceleration loads were applied to the designed structure and were set by analyzing the flight conditions of the target aircraft. The cases where a load of \(-\)6G and +3G in the \(z\)-axis direction and 2G in the \(y\)-axis direction are applied are considered the basic load. The ultimate load is the case where a load of 20G is applied in the \(x\)-, \(y\)-, and \(z\)-axes, respectively. And since a line was connected to the center of the bracket, a load of 700 g, which is the weight of the line, was applied. The load of the line was regarded as acting on the lower part of the inner cylinder. Figure 2 shows the configuration when applying the line. A margin of safety of 1.5 was applied to all respective loads. The load application condition is presented in Table 2. \begin{table}
\begin{tabular}{c c} \hline
**Carbon/Epoxy Fabric Prepre** & **Value** \\ \hline Longitudinal modulus [GPa] & 56.27 \\ Transverse modulus [GPa] & 54.86 \\ Shear modulus [GPa] & 4.21 \\ Longitudinal tensile strength [MPa] & 917.59 \\ Longitudinal compressive strength [MPa] & 708.86 \\ Transverse tensile strength [MPa] & 775.38 \\ Transverse compressive strength [MPa] & 702.97 \\ Shear strength & 132.57 \\ Ply thickness [mm] & 0.22 \\ Poisson’s ratio & 0.085 \\ \hline \end{tabular}
\end{table} 
Table 1: Properties of carbon fabric and epoxy resin prepreg [20]. Figure 1: Model of the curved composite panel considering loading conditions.