Structure Optimization Of The Main Frame Made Of Composite Material In The Pint-size UAV

How to reduce the structure weight of aircraft is the goal for plane designers. The main frame is head standing force element in fuselage. However, there should be a hole on the main frame because an oil box is placed through it. So it is necessary to carry out a structure optimization on the main frame. First, load boundary condition of the main frame was obtained from the full plane’s finite-element model by full-local analysis. Second, the location and the shape of the hole were obtained by step optimization. Third, a composite ply stacking optimization was taken on the main frame. Finally, an optimization was taken to strengthen the load-carrying capacity which was weakened by the hole. The main work of this paper consists of some parts as follows.The load boundary condition of the main frame was obtained. First, a finite-element analysis on the full plane was taken. Then the displacement boundary condition of the main frame was obtained from the full plane’s finite-element model with the method of full-local analysis. And the nodes force boundary condition was created from the displacement boundary condition.The location and the shape of the hole cut out from the main frame were obtained by step optimization. First, we realized the flow of stress in the main frame by a topology optimization. Then the form of the hole could be decided according to the result of the topology optimization and the function of the hole. And based on it, a shape optimization whose design variable is the primary size of the hole and whose design objective is the weight minimization was taken. Finally, in order to reduce the stress concentration in the chamfer angle, a particular shape optimization whose design variable is the parameter of the link curve and whose design objective is stress concentration minimization was taken. After optimization, the maximal stress reduced from300MPa to256MPa, and structure strength increased17.8%.A composite ply stacking optimization was taken on the main frame. Because of the capability of mechanics design, ply stacking optimization on the main frame can fully show the bearing capacity of composite material. After the optimization, the weight reduced39.8%. Then an optimization was taken on the main frame made of composite material to strengthen the load-carrying capacity which was weakened by the hole. A new strengthening form by symmetrical flange was taken instead of the strengthening form by unsymmetrical flange. Because the structure is symmetrical, there is no unsymmetrical moment, and the strengthening effect can be improved observably. After strengthening, the maximal stress reduced from40MPa to33.899MPa, and structure strength increased18.0%.The study in this paper has a extensive applicability, it has a reference to the design of standing force structure such as the frame.