Finite Element Model Updating Study Of Composite Structures

Because of the advantages of high strength and high rigidity to weight, composite materials have been widely used in aeronautic and astronautic structures. The strength design of the composite structures is mainly through finite element technology. However, the analysis results are not accordance with the true data exactly sometimes, for the finite element model cannot simulate the real structures accurately. The basic approach of the finite element model updating method is to update the finite element model based on the response data from the test. In order to attain the best updating results, it's necessary to solve the problems of software implementation, test conditions, objective response selection, composite material parameters selection etc according to the characteristics of composite structures.This paper firstly established the model updating objective function based on static response which combined displacement, strain and internal force. Then the updating parameter selection method of orthotropic materials and the parameter selection method of damage identification were introduced according to the properties of composite structures. Besides, the optimization method was regarded as the basic algorithm.This paper established the foundational software platform which was more open and practical, and introduced two model parametric methods, which solved the problems of software implementation and model parameterization. Through performing the interface program of finite element analysis software and optimization program, this paper achieved the seamless integration of different processes used in model updating, including finite element model evaluation, parameters reading and writing, response reading, finite element pre and post processor, and optimization. Besides, this paper also introduced NASTRAN and PCL model parametric methods. The benchmark verified the correctness of the method in finite element model updating of composite structures.This paper proved that model updating method based on static response which combined displacement, strain, internal force could identify parameters conveniently and accurately, which solved the problems of test condition and objective function selection. The identification effects between static and dynamic response were compared in the damage identification example of composite solar array components, validating the method based on static response which combined strain and displacement could identify damage effectively. As another example, the finite element model boundary conditions of a composite rudder were identified by the model updating method according to the strength test data. The static strength test method was introduced firstly. Then the identified results of different objective functions and constraint conditions base on displacement data were compared. The root boundary conditions were further modified after combining displacement, internal force and strain data finally.This paper extended the application of the finite element updating method to the composite structures design based on response data. As the example, a metal beam widely used in aeronautics was replaced by equivalent composite foam sandwich structure. The stiffness requirement was regarded as the objective function, and the composite strength criterion and stability requirement were introduced as constraint conditions. Finally, optimal design parameters of the foam sandwich structures were obtained. Besides, through updating the thickness of the beam, skin and rib, including changing the structure form, a jig structure used in strength test of a composite horizontal tail was designed by the finite element updating method. The equality of the shear force was satisfied at the two sides of the center wing box, improving the design and analysis efficiency greatly.