Structural Analysis of 3-D Braided Preforms for Composites Part II: The Two-step Preforms

Abstract

In Part I of this series of papers, structures and geometries of the four-step preforms were studied and analysed. In this part, an account is given of similar work conducted on the two-step preforms. Theoretical models for both regular and tubular two-step preforms are established with a few assumptions. Structu.ral geometries of the preforms are analysed aud discussed according to the theoretical models developed. Mathematical relations between the structural parameters, such as the fibre orientation, yam-volume ft-action, and prefoirm contour sizes, as well as their dependence on operating conditions, are derived. It is found that the preform structures are determined hy the constitucint yams, the braiding arrangements, and the process operating conditions. The extreme values ofthe parameters in the jamming conditions are also discussed. To verify the validity of the analytical models, experimental investigatic>ns were also carried out. The experimental results strongly support the theoretical predictions.

Finite Element Analysis of Mechanical Properties of 3D Four-Directional Rectangular Braided Composites Part 1: Microgeometry and 3D Finite Element Model

“…Take the hexagon yarn Y 3 as an example, Fig. 9b describes Y 3 is extruded by Y 1 and Y 7 , leaving two contacting planes which is taken as a couple of parallel surfaces to Y 3 ; Figure 9c shows another couple of parallel surfaces of Y 3 while it is bearing the extrusion from Y 4 and Y 5 . Similarly Fig.…”

“…Yang et al [4] developed ''Fiber incline model'' which was based on the simplified unit cell with four incline unidirectional laminas. Li et al [5] established the unit cell which was based on the assumption that yarns were straight rods with a circular cross-section and there were no lateral deformations at the yarn cross-over points. Lei et al [6] developed a finite cell model in which the composite was considered as comprising a finite number of brick-shaped structural cells.…”

Microstructure of 3D Braided Preform for Composites with Complex Rectangular Cross-section

“…Because the common four-step braiding procedures are followed to braid the preform, in most of the positions the microstructure of the preform is the same as those of a normal four-step braiding. For instance, as in Figure 1(a), the paths of carriers (7,4), (9,10), and (2,5) in the interior, corner, and surface regions, respectively, are the same as those of a common four-step braided preform with simple rectangle cross-section. However, in the joint region, the movement of carriers is quite different, such as carriers (4, 6) and (8,5) in the interior of the joint region, as in Figure 1(b), and carriers (7,5) and (4,2) in the corner and surface of the joint region, respectively, as in Figure 1(c).…”

“…The unit cell model of four-step 3D braided preforms established earlier was a cube containing four diagonally arranged yarns intersected at the center of the cube [1][2][3]. The unit cell model of Li et al [4] and Du et al [5] were also a cube, inside which yarns were inclined in four directions. The difference from the former cell model was that the dimension of yarns was taken into consideration so that the yarns did not intersect at one point.…”

Manufacturing processes for composite materials and components for aerospace applications

“…The vast majority of the tows employed in woven, braided or knitted reinforcements comprise low twist or untwisted continuous filament yarns. Three-dimensional technical textiles can be produced by weaving [5], knitting [6] and braiding [7] or as non-crimp fabrics.…”