Dynamic Investigation For Laminated Composite Plate Multibody System Based On Global-local Displacement Yheory

Due to the characteristics of high strength and high modulus, composite materials have been more and more widely used for its excellent mechanical properties, especially in the field of aircraft and spacecraft, and other industry area. The wing of helicopter, wind turbine blade, solar panel are among the representatives. Composite blades can effectively reduce the vibration of blades, improve the stability of helicopter significantly, thus increase the reliability of the mechanism. With the increasing demand for wind power, better performance of wind turbine blade is urgently needed, meanwhile, the use of glass-fiber resign composite can effectively solve this problem. All these structures are not traditional static structures, they all have large length-to-thickness ratio, all are dynamic system undergoing large overall motion. Since the laminated composite plate is a special composite shell structure, the investigation of the dynamic performance of laminated composite plate multibody system has significant application importance.In the conventional research area of composite laminates, quantities of achievements have been made and have developed the use of the composite material. What is now paid more attention to is to accurately and conveniently calculate the interlaminar stress of the laminates, because a good result of interlamiar stress is quite important to the subsequent research, such as fracture and fatigue. To solve this problem, quite a lot of methods have been proposed for calculation of the interlaminar stress of the static structure, and greatly promoting people’s perception. However, in the area of multibody system dynamics, none of the related research work can be found. The investigations were mostly concentrated on isotropic materials, in which dynamic response or normal strain on the surface were paid attention to, and the variation of the transverse shear stress along the thickness is not taken into account. Although good results of the response or surface strain in laminates can be obtained, the results of interlaminar stress are not accurate. Thus, it is quite necessary to study the interlaminar stress of laminates in multibody system in order to predict the variation of interlaminar stress accurately in multibody system.Concerning the calculation of interlaminar stress, different methods are reviewed and compared. To extend to multibody system effectively, based on displacement modes, two-dimensional model are chosen for its convenience. Two principles are set that, first, displacement modes would have to reflect the zigzag change with thickness of interlaminar displacements. Then, the displacement modes must satisfy the continuity of interlaminar transverse shear stress. Furthmore, displacement modes could give good results without using three dimensional equilibrium equations. Based on these principles, global-local high order shear deformation theory is chosen for further research, which satisfies the continuity of interlaminar shear stress, since the number of the unknown variables does not change with the layer number of laminate. In addition, this theory can give perfect results of interlaminar stress. However, the previous work have not given the reason why they chose to add the local displacement modes by intercepting to triple, and did not tell the necessity to add the three terms, did not tell the importance of each term to revise either. In view of this, local displacement modes are focused on by studying three different situation of removing one term each time. By classical example, the three situations are compared with previous global-local modes and analytical solution. Conclusions are drawn that the first order displacement term and the third order displacement term have more influence than the second order displacement term. However, the neglect of any one of the three terms may lead to simulation error. Thus, it is necessary to add local modes to the third order. By comparison with exact solution, the accuracy of global-local modes can be easily seen, and the variation of interlaminar displacements and stresses along the thickness can also be obtained.Considering the use of laminates in multibody system based on hybrid coordinate formulation, and using the global-local displacement mode and four-node rectangular finite element, we use double linear shape function for interpolation of the in-plane displacement variables and use nonconforming element for the discretization of the out-plane displacement variables, which is quite different from traditional interpolation in multibody system. As to the volume integral, triple Gaussian integral is used instead of double Gaussian integral for its efficiency and feasibility. Ultimately, the virtual power of elastic force, the virtual work of inertial force, and the virtual work of external force can be obtained, through the use of the principle of virtual work, dynamic equations for multibody system can be obtained, which have taken into consideration of the continuity of interlaminar shear stress. Through simulation, composite laminate attached to a hub with rotational degrees of freedom under the action of external force is studied by three models, the first order shear deformation theory(FSDT), higher order shear deformation theory(HSDT) and global-local mode. It can be easily seen that the difference of the angular velocities obtained by different models is not significant, no matter the laminate is thick or thin. It is also shown that the traditional methods of FSDT and HSDT can be accurately used for calculation of dynamic response. However, the use of these methods to calculate the stress may lead to significant error, especially the FSDT. Even when the laminate is quite thin, there exists much inaccuracy by use of FSDT and HSDT especially for transverse interlaminar shear stress, which shows the necessity to take into consideration of the continuity of interlaminar stress and the importance of the present investigation.Finally, the research work is summarized and the contributions of the present investigation are concluded.