# Simulation, Fabrication and Testing of UAV Composite Landing Gear
## 3 Results and Discussion  
### Finite Element Analysis of the Landing Gear  
The finite element analysis of the landing gear models was performed in the Static Structural module of the ANSYS 2021 R2 software system (ANSYS, Inc., Canonsburg, PA, USA). In the finite element analysis of the landing gear, the conditions of the experimental tests (three-point bending) were respected, considering the dimensions and constraints of the test machine. The most significant constraints imposed on the finite element analysis were the dimensions of the landing gear model, the properties of the five types of material (PLA GF, PP GF30, PET CF15, PAHT CF15, CFRP), the radius of the punch, the radius of the fixing plate and the distance between supports. The three-point bending finite element analysis of the landing gear models was carried out, considering two major objectives:  
Figure 3: Three-point bending test for the landing gears made of: (**a**) PLA GF; (**b**) CFRP. * The comparative analysis of the failure behavior obtained from the finite element analysis of landing gear models and the behavior observed during the experimental tests of the same models;
* A comparative analysis of the maximum reaction forces that appear in the fixing's structure plate from the finite element model and the reaction forces appearing at the break of the landing gear models. In the finite element analysis, frictionless support type boundary conditions (Figure 4a) were established for the landing gear in order to prevent rotation throughout the simulation. In order to simulate the conditions of the experimental testing, a displacement request was issued through the machine bed, in the middle of the landing gear, with a value of 5 mm/min (Figure 4a). Figure 4: Finite element analysis of landing gear models: (**a,b**) set up boundary conditions; (**c**) discretization of the model; (**d**) equivalent stress distribution for landing gear made of material PLA GF; (**e**) equivalent stress distribution for landing gear made of material PP GF30; (**f**) equivalent stress distribution for landing gear made of PET CF15 material; (**g**) equivalent stress distribution for landing gear made of material PAHT CF15; (**h**) equivalent stress distribution for landing gear made of CFRP material. The machine bed and the ground plate were assigned rigid body characteristics, and a fixed condition was established for the ground plate using the body-ground fixed joint option (Figure 4b). For the three-point bending simulation of the landing gear models, a discretization with three-dimensional elements of the Hexa type, with an element size of 1 mm, was used in FEA (Figure 4c). The punch and fixture plates were discretized using the same Hexa element type, having an element size of 2 mm (Figure 4c). A friction coefficient of 0.1 was established between the punch, the landing gear model and the mounting plate [37]. For the finite element analysis, the elastoplastic model was used, and the landing gear models were studied for 100% infill density. In this study, for the FEA simulation of the landing gear models, several simplifying assumptions were established and used in other studies too [38; 39; 40; 41]: the constituents show a linear elastic behavior, the matrix (PAHT CF15--polyamide; PET CF15--polyethylene terephthalate; PLA GF--polyplactic acid; PP GF30--polypropylene) has isotropic properties, short carbon/glass fibers are transversely isotropic, and the fiber matrix shows perfect adhesion and does not contain voids or defects. The values of modulus of elasticity and Poisson's ratio used in the material's definition, as well as in previous research [38; 39; 42], which is focused on FEA simulation, are outlined in Table 4.  
As a result, the outputs of the von Mises equivalent stress distribution on the landing gear models (Figure 4d-h) clearly identify the areas where the equivalent stress presents the highest values.