关键词: 三维五向编织, 圆形编织, 三单胞法, 刚度体积平均法, 复合材料, 刚度预测

Abstract: As one of the main load-bearing components, 3D five-directional circular braided composites have great advantages in mechanical properties, economy and structure, and have been gradually applied in aerospace, maritime transportation and other fields. They are a typical 3D multi-directional circular braided composite material. But due to the high complexity of the internal structure, the research on the mechanical properties of the material is not sufficient, the theoretical prediction is difficult, and the relevant research literature is seriously insufficient, which greatly limits the application and development of 3D five-directional circular braided composites. Therefore, it is of great significance to improve the theoretical research of mechanical properties by studying the mechanical properties prediction and damage evolution law of 3D five-directional circular braided composites.
To effectively predict the mechanical properties of 3D five-directional circular braided composites, the topological structure of 3D five-directional circular braided composites with radial yarns was obtained based on the spatial structure of 3D five-directional circular braided yarns with radial yarns at the meso-scale, considering the cross-sectional shape of the yarns after squeezing each other. The periodic law of circular unit cell braiding was introduced, and the unit cell structure characteristics of 3D five-directional circular braided composites with radial yarns were obtained. The unit cell was divided into three seed cells including “the upper surface unit cell, the internal unit cell and the lower surface unit cell”. The unit cell geometric model and mesh model of 3D five-directional circular braided composites including upper and lower surface sub-unit cells and internal unit cells were established by ANSYS APDL. The appropriate periodic boundary conditions were applied to the geometric model. Starting from the unit cell model, based on the stiffness volume average method, the tensile stiffness prediction of 3D five-directional circular braided composites with pitch lengths of 0.6, 0.7 and 0.8 along the circular axis was carried out, and the results were compared with the results obtained by the theoretical calculation method of mechanical stiffness of composites. The results show that the fiber volume content of the three pitch lengths is 24.94%, 23.33% and 22.04%, respectively. The fiber volume content and braiding angle are inversely correlated with the pitch lengths. The elastic modulus prediction results of the unit cell model are 16.42 GPa, 15.63 GPa and 14.83 GPa, respectively. The theoretical results are 16.96 GPa, 16.25 GPa, and 15.34 GPa, and the longitudinal stiffness is inversely related to the pitch lengths. In the unit cell model, the mutual extrusion of fiber bundles is considered, which makes the fiber volume content in the unit cell model slightly smaller than the theoretical calculation method, resulting in the theoretical calculation results being slightly larger than the unit cell prediction results. The stress distribution of fibers and matrix in the composite is analyzed.
In this paper, the geometric model of the unit cell of the 3D five-directional circular braided composite material of the radial shaft yarn is established based on the microscopic scale. Based on the unit cell model, the stiffness of the 3D five-directional circular braided composite material of the radial shaft yarn is predicted by the stiffness volume average method, and the mechanical properties of the 3D five-directional circular braided composite material are improved.

Key words:  , 3D five-directional weaving, circular weaving, three-cell method, stiffness volume average method, composite materials, stiffness prediction