Issue 43

P. Zampieri et alii, Frattura ed Integrità Strutturale, 43 (2018) 191-204; DOI: 10.3221/IGF-ESIS.43.15 197 In order to ensure the motion between the main fitting and the trailing arm a cylindrical pin has been modelled has shown in Fig. 8. In order to enable the model to simulate the sliding of the piston inside the cylinder tube, a contact surface has been modelled between them. A “contact-automatic-surface-to-surface-offset” algorithm has been defined; in particular, a master surface has been defined around the piston and a slave one inside the cylinder tube (Fig. 9). This type of contact algorithm allows modelling an offset between these two surfaces that will be kept constant during the sliding. In order to simulate the sliding, since the forces at stake are significantly severe, also a cylindrical joint has been introduced in the shock absorber constraining the piston to slide axially inside the cylinder tube (Fig. 9). Figure 8 : Pin linking the main fitting and the trailing arm. Figure 9 : Modelling of the shock absorber. In order to model the damping and elastic responses, the shock absorber has been modelled by placing a beam element between its ends. Such beam element allowed introducing the non-linear spring and damping properties characterizing the shock absorber. These non-linear properties have been modelled by setting a particular material card allowing the definition of the spring polytrophic curve (Fig. 10) and the damping factor, set equals to 150 kNms/mm. Figure 10 : Polytrophic curve. Moreover, differently from the stick model, in order to increase the landing gear stability during the drop test, the secondary actuation system has been modelled (Fig. 11) by introducing an elastic and a viscous finite element, characterized by a constant elastic stiffness and a damping factor of 50 kN/mm and 50 kN·ms/mm, respectively.