# A Sensitivity Analysis of the Damage Behavior of a Leading-Edge Subject to Bird Strike
## 3 Starting Configuration Results  
In this section, the numerical results of the investigated phenomenon are reported and compared with respect to the experimental ones in order to highlight the model accuracy. These results are deeply discussed in [17]; however, hereafter, the most relevant aspects are proposed to serve as a basis for the sensitivity analysis, which is the focus of this work. Figure 3 shows the stress distribution and the damage status generated by the impact event. The last frame (right side of Figure 3) shows the time step corresponding to the maximum deformation state. In order to better appreciate the damage status, the bird was removed from the visualization. Regarding the damage status, the element painted in red are the ones where at least one layer is fully damaged (inner face, outer face or core). The elements which experienced the failure in all layers were removed from the analysis. According to the numerical results, no element is subject to a total failure (all layers failed). This result is confirmed by the experimental test, where no total failure can be appreciated, and only failures in one or at least two components can be observed in the same zone [20] (Figure 4). Figure 3: Results at different time steps. (**A**) Experimental deformations; (**B**) numerical—Von Mises stress; (**C**) numerical—damage status. Figure 5 shows the experimental-numerical comparison of the reaction forces recorded by the three installed load cells (Figure 1). The force's component reported is parallel to the impact direction, therefore normal to the plane of the mainframe. The experimental curves were offset over time in order to synchronize them with the numerical ones (the contact starts at about 1 ms). The main phenomenon lasts about 12 ms, in fact, the maximum deformation level, and therefore the maximum crushing is reached at about 9 ms. After this time step, the projectile starts to rebound and, consequently, the structure recovers elastically part of its deformation, and the reaction forces decrease. At about 12 ms, the reaction forces go to zero, and then they grow up again, all of which indicates that the first rebound is terminated. For this reason, only the first 15 ms are reported in the graphs. After this time step, the reaction forces exhibit several oscillations, which are influenced a lot by the dynamic behavior of the entire test rig, and so they are no too relevant for comparative scope. The graphs shown in Figure 5 highlight that the numerical model is able to capture the main structure response on the entire test article (the leading edge with test rig) with a good accuracy level; it is possible to note only a slight time shift. The errors related to maximum and minimum forces are smaller than 10%, that can be considered very satisfactory considering the complexity of the simulated test. The numerical model was proven to correctly describe the mechanical behavior of the leading edge, according to the good agreement between the experimental and the numerical model in terms of the global deformations experienced during the phenomenon, shown in Figure 4A. Comparisons were conducted in terms of post-impact permanent deformation, reported in Figure 4B and reaction forces (Figure 5) as well. Indeed, a good correlation can be found both in terms of deformed shape and dimension: the distance between the two tips of the ribs, in particular, gives information on the plastic deformation and of the failure of the structure. Figure 6 reports the numerical time-history of the principal data related to structural response, i.e., the skin apex displacement and the tip-web distance. Obviously, the distance between the two  
Figure 4: Experimental–numerical comparison. (**A**) Deformed shape during the test; (**B**) permanent deformation after the impact. Figure 5: Reaction loads comparison. (**A**) Load cell 01; (**B**) load cell 02; (**C**) load cell 03.  
frame tips can be obtained by subtracting the displacement of each tip from the initial distance (640 mm).