Mesoscopic modeling of 3D four-directional braided composites

3D four-directional braided composites are becoming widely used in the aeroengines due to their excellent transverse properties such as stiffness, strength, fracture toughness and damage resistance. In spite of great achievements in composite materials, the model of 3D four-directional braided composites gives rise to considerable challenge in establishing interior fiber bundle structure which is curved and twisted in jamming condition. Original circular cross-section of fiber bundle is squeezed into oval shape ellipse in manufacturing process of the jamming action. Thus, a novel mesoscopic modeling approach for 3D four-directional braided composites was proposed in this study, which considered the fiber bundle cross-section's deformation. Firstly, an analytic equation to describe the transformation of fiber bundle cross-section was established based on the equal area of the ellipse and circle. Secondly, the parameters of this equation were achieved using the Matlab simulation. It was concluded that the compacted, non-interfered fiber bundle model constructed was in good agreement with actual structure. This paper provides the mathematical relationship between braiding parameters and geometric dimensions of unit cell model. Numerical results showed that the value of braiding pitch length has a relative calculation error less than 4% compared with test data. The modeling technique lays a foundation for further mesomechanics investigation on 3D four-directional braided composites.