Method for optimal design of composite structural elements based on strength and stiffness conditions

Abstract

The article considers a method for optimal design of composite structural elements under the conditions of strength and stiffness, in particular small-sized housings made of composite materials in CAD/CAE systems, the initial data for the calculation of which are the elastic constants of the fiber and matrix, as well as the volume content of the fiber in the composite. A model of a composite material (CM) has been developed to calculate the winding structure of structural elements. The choice of coordinate systems that ensure the winding process of structural elements has been justified. When calculating the CM in ANSYS, one of the necessary conditions is to define the model and specify the material properties. An orthotropic material was selected for the calculation. The elastic constants of the composite material were determined for modeling the winding process. The elastic moduli and Poisson's ratios of the fiber and matrix were determined, as well as the volume content of the fiber in the CM, and the elastic constants of the layer as a whole were calculated. A program was written in the Mathcad 15 environment to verify the calculation. The structure of the composite material of a small-sized housing was calculated. To verify the correctness of the approach when choosing the calculation method, a small-sized housing was calculated, conditionally reinforced with a layer [0°] and [90°] relative to the Z axis. The deformation of the small-sized housing loaded with internal pressure was analyzed and the operation of the layers of the composite material was shown. The liner calculation was carried out in the Cartesian coordinate system (CS), the cylindrical part of the layer [0°] and the layer [90°] in the cylindrical CS, and the circumpolar parts of the layer [0°] in spherical CS. The test calculation was carried out on a small-sized housing of the “balloon” type in the ANSYS software package using the finite element method (FEM). The stress-strain state of the small-sized housing loaded with internal pressure was obtained. The calculation performed allows optimizing the design based on the allowable stresses of the CM and liner layers in the ANSYS software package and obtaining the values of the structural parameters used for the composite hull and required for developing the winding program. To reduce the maximum stress that occurs in the liner in the area of the transition from the cylindrical part to the spherical part, a two-zone winding simulation was considered. At the same time, the nature of the distribution of equivalent stresses for the single-zone and two-zone winding schemes of the hull bottom was obtained. When winding the bottom in two zones, the stresses are reduced, which is associated with the formation of a more uniform bottom thickness. The developed method for designing structural elements from composite materials is suitable for modeling power elements of aircraft, such as high-pressure cylinders, pipes, solid propellant rocket casings, transport and launch containers and other hull structures.