A micromechanical model is implemented to indicate the progressive fatigue problem of a laminated composite with a central circular hole under fatigue loading based on a finite element model. The mechanical properties of the composite lamina are represented based on the characteristics of the fiber and the matrix through a micromechanics model. An appropriate algorithm is then adopted to simulate fatigue damage development in the composite lamina. According to this algorithm, the stress field of the composite subjected to fatigue load is initially obtained using the finite element method. Finally, the predicted results of the stresses in the constituents i.e. fiber and matrix are determined according to the micromechanical bridging model. Finally applying proper damage driving relations leads to damage degree in each element. The proposed model is proven to be successful in the observation of the fatigue behavior with stiffness degradation in each element of the composite in each cycle. Results are reported and validated using those micromechanical models and experimental data available in the literature.

As the aileron mass parameter and its position on the velocity and frequency of the flutter is an important problem in design of the aircraft wings, the optimization of the composite wing with an aileron is represented in this paper. Mass properties and its distribution have a great influence on the multi-disciplinary optimization procedure based on speed and frequency of flutter. At first, flutter speed was obtained with and without aileron, then aileron was mass-equilibrated and other studies were performed using the proposed method. It is deduced that changing the position and mass properties of the aileron the speed and frequency of the flutter changed. The position of the aileron was determined for better wing performance in flutter instability and minimizing the composite stress. In the present study, it has been attempted to model the aerodynamics of the problem under ultrasound with the panel method, and the structure has been modeled using finite element method and coupled with the aerodynamics. Using the p-k method, the equations are solved and the results are extracted.

In this study, the elastic properties of composite materials are investigated, considering the effects of separation of fiber-matrix joint boundary and matrix failure. In this method, by assuming periodic microstructure and using a linear approximation of the displacement field by applying continuity and equilibrium conditions, the composite fiber composite relation is determined. The effect of separation is assumed by introducing tangential and normal scalar parameters in the equations by assuming the displacement field jump at the common boundary. In order to express the effect of matrix micro-cracks, the fracture mechanics framework of continuous environments was used and the micro-cracks parallel to the fibers, perpendicular to the fibers and in the thickness direction with scalar parameters were expressed. At the end of the effect of these parameters the results are presented in graphs. The results show that the presence of defective joint at the joint boundary and the matrix micro-components reduce the hardness of the composite and thus it’s bearing load, which is more significant at the defective joint state.