Page 370 - Engineered Interfaces in Fiber Reinforced Composites

Chapter 8. Improvement of interlaminar fracture toughness with interfuce control 35 I

8.4. Three-dimensional textile composites concept

8.4.1. Introduction

Three-dimensional textile preforms are continuous fiber assemblies which are fully
integrated with multi-axial in-plane and though-the-thickness fiber orientations. KO
(1989) and Chou (1992) presented comprehensive reviews on this topic, and a brief
summary is given in this section. Composites containing three-dimensional textile
preforms display many unique advantages which are absent in traditional two-
dimensional laminate composites, and they include:
(1) Enhanced stiffness and strength in the thickness direction due to the presence of
out-of-plane orientation of some fibers.
(2) Elimination of the interlaminar surfaces through the fully integrated nature of
fiber arrangement.
(3) Feasibilities of near-net-shape design and manufacturing of composite compo-
nents which, in turn, minimizes the need of cutting and joining of the parts.
Three-dimensional textile preforms may be divided into four groups according to
their manufacturing techniques, namely braiding, weaving, stitching and knitting, as
shown in Fig. 8.19 (Chou, 1992). A schematic drawing of a set up for the three-
dimensional braiding process is given in Fig. 8.20. It is shown that the axial yarns
are supplied directly into the braiding structure from the package placed below the
track plate, while the braiding yarns are supplied from bobbins mounted on carriers
which move with the track plate. The type and microstructure of the braids are
controlled by the presence of axial yarns and the pattern of motion of the braiders.
In three-dimensional weaving, a high degree of integration in fiber geometry
through the thickness is achieved by modifying the traditional weaving techniques
for producing two-dimensional fabrics. Fibers are incorporated at an angle and
parallel to the thickness directions, respectively, in two major weaving techniques,
namely angle-interlock and orthogonal weaving. Fig. 8.2 1 schematically illustrates
an orthogonal woven fabric with yarns placed in three mutually orthogonal
directions. Matrix rich regions are often created in composites containing
orthogonal woven fabrics due to the nature of fiber placement.

Three-dimensional textile preforms

I I I I
Braiding Weaving Stitching Knitting
I
A 4-l 1
4-step 2-step Solid , Angle- Orthogonal Lock Chain Multi-axial
I I interlock stitching stitching warp knit
Square Circular A,
Cartesian Cylindrical

Fig. 8.19. Three dimensional textile preforms. After Chou (1992). Reprinted with kind permission of
Cambridge University Press.