Study On The Equivalent Stiffness Of Filament Wound Composite Materials

The filament wound composite materials have been widely applied in pipes, pressure vessels, rocket cases and other revolved structures. For this kind of filament wound composite structures, the study of equivalent stiffness is very important for analysis and design. The winding fiber tows in different layers form the microscopic characteristics of fiber intersecting and undulating, which affects the calculating of macro equivalent stiffness. The traditional method is based on the classical laminated plate theory, neglecting the fiber intersecting and undulating, and only the in-plane stiffness is considered. In this paper, a calculating method of the equivalent stiffness of filament wound composite structure is established, considering the influence of the fiber intersecting and undulating. The main work of this article is as follows.Firstly, the two scales of the calculating method for the equivalent stiffness of filament wound composite structure are established based on the micromechanics finite element method (FEM). In the scale of fiber tows, the equivalent stiffness is calculated by the homogenization method. A hexagon representative volume element (RVE) is established to compute microscopic stress field by applying periodic boundary conditions. In the scale of filament wound structure, the equivalent stiffness is calculated according to the micro geometrical characteristics of the winding structure. The equivalent stiffness of filament wound composite materials can be obtained from elastic properties of component materials and microstructure characteristics of fiber tow.Secondly, effect of the fiber intersecting and undulating of filament wound composite material stiffness properties are analyzed. Comparing with the classical laminated theory, The in-plane stiffness calculated by the equivalent method is found decreasing. Besides, the out-plane stiffness of filament wound composite materials could be obtained.Finally, the factors that influence the equivalent stiffness of the filament wound composite materials are discussed, including winding angles, width of the fiber tow, undulating of the fiber tow and the fiber volume fraction.