## 3 Discussion of the Results  
### Deformation Energy Release  
Figure 2a shows a typical result for the LW-PLA specimens compared with the PLA reference when a 100% infill density is considered. Normalizing the load-bearing capacity by sample weight improves the relative resistance of the LW specimens. Still, the relative resistance of the lightweight structure did not reach the PLA reference (Figure 2b). Moreover, the noticeable increase in the resistance of the LW-PLA samples occurred after exceeding the 10 mm deformation limit, which corresponds to 25% of their length. Such a deformation degree is barely attainable under service conditions. This outcome aligns with the results in the literature [7; 13; 43]. However, the need to create a relatively sparse lattice structure highlights the brittleness issues of the PLA material (Figure 6). [PERSON]\(\tilde{\text{n}}\)[PERSON] et al. [34; 35] provided several characteristic examples of brittle PLA failure under compressive loads. In this context, LW-PLA emerges as a promising alternative to enhance energy absorption in the lattice structures under strict weight limitations [14]. This study expands the DfAM concept by developing a lightweight metastructure capable of absorbing a deformation energy equivalent to that released during drone collisions (Section 2.2). Remarkably, the theoretical  
Figure 11: The deformed internal structure of the modified prototypes: (**a**) Sample 3; (**b**) Sample 4. Figure 10: Compressive test results for the modified prototypes under monotonic and repeated loads. 300 J collision energy used in this study serves as a boundary condition to standardize the comparison of the deformation energy absorption values across different prototype configurations. It does not represent a realistic loading scenario but provides a consistent reference for evaluating the efficiency of internal structural modifications under quasi-static compression. The analysis of the test results for Sample 3 (Figure 9b) reveals a 2.4-fold decrease in the compression deformation required to release the 300 J impact energy equivalent compared with the Reference sample. In particular, the Reference PLA prototype must reach a deformation of 49.9 mm to absorb the collision energy, whereas the modified Sample 3 can absorb this energy after deforming by 20.8 mm. At the same time, this modification also reduces the sample's weight from 156.6 g of the reference to 144.0 g (Table 3). The modified prototype (Sample 4) demonstrates an even more efficient outcome when the target energy absorption is reached after the 15.1 mm deformation, which is comparable to Sample 2 (12.8 mm), selected as the modification target; simultaneously, the prototype weight of these specimens was reduced from 289.0 g to 181.0 g (Table 3). Figure 12 summarizes this discussion, presenting the normalized (by weight) load-displacement diagrams for all of the test specimens listed in Table 3. Notably, the compression deformation necessary to absorb the 300 J collision energy by the corresponding fuselage prototype limits these diagrams. Thus, a shorter diagram is preferred. Figure 12 reveals the following noticeable aspects:  
* The reference PLA could reach a relatively high load-bearing capacity in the \"elastic\" stage. This stage is not elastic in the general context, as the prototype represents a lattice structure without a definite area and is characterized by a complex deformation pattern [13; 34; 44; 45]. However, the structural resistance decreased suddenly after reaching its ultimate capacity, and the fracture of the internal lattice structure, along with a particular material consolidation, ensured further mechanical resistance. The resistance peaks and continuous increase in resistance (green diagram) reflect these mechanisms. * The alternative LW-PLA specimen (Sample 1) did not demonstrate exceptional performance, yielding a supremum diagram that approximates the resistance peaks of the reference diagram. * Sample 2 exhibits a similar relative resistance to Sample 1 during the \"elastic\" stage.