# Design of Fiber-Composite/Metal-Hybrid Structures Made by Multi-Stage Coreless Filament Winding
## 3 Results
### Mechanical Evaluation  
To evaluate the structural performance of the component, two stiffness measurements were conducted. One to measure individual nodes to identify deviations in the fiber net and another measurement to evaluate the stiffness increase of the aluminum base plate by  
Figure 13: Comparison of the simulated (black outline, FVR of 37.96% based on nozzle diameter) and caliper-measured (colored bars) fiber segment cross-sectional areas for each winding stage. Regions of the fiber net: (**A**) longer lower outer edge; (**B**) shorter lower outer edge; (**C**) lower center rib (section 10–20); (**D**) lower transverse struts (e.g., section 2–18); (**E**) lower diagonal ribs; (**F**) raised outer edges of corners; (**G**) longer upper outer edge; (**H**) shorter upper outer edge; (**I**) upper center rib (section 10–20); (**J**) lateral cross-bracing; (**K**) diagonal inner struts; (**L**) vertical inner struts.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Parameter** & **Stage 1** & **Stage 2** & **Stage 3** & **Unit** \\ \hline \multirow{4}{*}{measured} & added resin per stage & 33.95 & 29.07 & 12.77 & g \\  & component mass 1  & 250 & 310 & 352 & g \\ \cline{2-5}  & composite mass & 62 & 122 & 164 & g \\  & fiber mass & 27.9 & 58.8 & 88.1 & g \\  & fiber length & 72.4 & 152.8 & 228.7 & m \\  & fiber volume ratio & 33.28 & 36.17 & 41.36 & \% \\ \hline \multirow{4}{*}{predicted} & composite mass & 74 & 140 & 172 & g \\  & fiber mass & 28.1 & 53.1 & 65.4 & g \\ \cline{1-1}  & fiber length & 96.6 & 182.4 & 224.7 & m \\ \cline{1-1}  & fiber volume ratio 2  & 37.96 & 37.96 & \% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Physical parameters of the fiber-composite demonstration component.  
the fiber-composite structure as well as the performance of the assembled component in relation to the state-of-the-art steel plate reference design. In both cases, several defined forces were applied, and the deformation was measured by one or two dial indicators. This was translated into a spring stiffness.  
For the first stiffness evaluation (Figure 14a) on individual winding pins, the fiber-composite structure was mounted to the winding fixture only at nodes 1, 2, 8-12, and 18-20 (Figure 10a). Single winding pins in region A (Figure 11c) were pulled upwards using a spring scale in the force range up to 50 N. On average, spring stiffness of 90.5 \(\pm\) 23.2 N/mm was measured for an individual pin. Lower values around 75 N/mm were found in the middle, and higher stiffness up to 140 N/mm at the sides. This trend was expected as no pins were fixed in the center, but significant differences in stiffnesses between the front and rear winding pin cluster of region A could be found. This is another quality control measure for monitoring the compliance of the winding plan and for identifying hidden damage or kissing bonds. This approach allows easily localizing weak points, unlike an eigenfrequency measurement by, for example, a laser vibrometer.  
For the second stiffness evaluation (Figure 14b) on the component level, the aluminum base plate was supported at its assembly interfaces. The orientation was upside down, neglecting the force of gravity. In a 3-point bending configuration, the plate was loaded in the center (Figure 9a). By installing the fiber-composite structure using all lower winding pins, the stiffness of the aluminum base plate could be increased by a factor of 1.76 in the covered force range up to 100 N. The mass-specific bending stiffness was increased by a factor of 2.5, although the stiffness of the state-of-the-art steel plate reference design remained 81% higher in absolute terms. The absolute mass of the total component in this design was 22% of the original steel component. Of the 4.13 kg component mass, only 0.35 kg is allocated to the fiber-composite structure, including the winding pins with 0.19 kg.