## 3 Results
Figure 27: Distortion distribution for a Skin3 with fiber variable volume fraction: (**a**) bottom 3 plies\({}^{*}\) variation: 56–52%; (**b**) bottom 3 plies\({}^{*}\) variation: 56–54%. Figure 25: Response of the embedded FBG sensors during the manufacturing process of the Skin3 coupon: (**a**) bottom surface; (**b**) top surface. After simulating several scenarios and by varying different types of parameters, the final and most suitable approach was chosen due to its good prediction of the spring-in:  
* The definition and introduction of the gel point of the resin in the simulation was essential for the accuracy of the results;
* The definition of a constant fiber volume fraction showed better results when compared to the measured coupons, even if the initial approach indicated possible model tuning leverage by varying this parameter;
* The definition of a variable friction coefficient was dependent on the gel point of the resin. In Figure 30, the results obtained with the strain FBG sensors embedded on a C-spar2 coupon are presented. Similarly, as for the skin coupons, it is possible to identify the manufacturing phases through strain measurements. Nevertheless, the values on these graphs were calculated considering the strains inflicted on the coupon and sensors due to the fabrication process (after the gel point). Figure 28: **(a)** Distortion distribution for variation in fiber volume fraction from 56% to 54% (applied to 1 pJy) with a variable friction coefficient between the tool and the part. **(b)** Distortion distribution for a constant volume fiber fraction with a variable friction coefficient between the tool and the part. Figure 29: Friction coefficient evolution. Following the C-spar coupon manufacture and measurement, the data shown in Figure 31 were used as a reference for evaluating the distortion numerical simulation values. We completed experimental vs. numerical distortion results for numerical comparison in the Tables 10-12. --see Figures 32 and 33 for the numerical results. Figure 31: Three-dimensional CMM contour plots for evaluation of shape distortions on web, R 12, mm, and R 5 mm flanges on a C-spar2 coupon. Figure 22:0 FBG strain monitoring results for full LRI cure cycle of a C-spar2 coupon. To compare the experimental data and the computed values, a set of nodes in the numerical model was defined very close to the points where the sensors were placed on the coupon in the experiment, as shown in Figure 22:1 The strain was measured in the experiment along the X direction (the long edge of the coupon). For this reason, in the numerical model, the strain principal value was aligned with the experiment. This followed the defined element orientation of the numerical model. The experimental data contained strain values from both sides of the coupon:  
* Bottom face--the side that is in contact with the tool;
* Top face--the side in contact with the vacuum bag. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Flange/Web Corner Radius** & **Flange/Web Corner Radius** & **Condition** \\  & **5 mm** & **12 mm** & **Condition** \\ \hline
**C-shape tool angles (\({}^{\circ}\))** & 94.970 & 94.810 & \\ \hline
**Experimental average (\({}^{\circ}\))** & 93.821 & 93.702 & Measured on the day of manufacturing \\ \hline
**Experimental average (\({}^{\circ}\))** & 93.813 & 93.693 & Measured 3 days after manufacturing \\ \hline
**Measured spring-in (\({}^{\circ}\))** & 1.16 & 1.12 & \\ \hline
**Computed angle (\({}^{\circ}\))** & 93.645 & 93.679 & \\ \hline
**Computed spring-in (\({}^{\circ}\))** & 1.325 & 1.131 & \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Summary of 3 mm thick C-shape test specimen—measured and computed values.