This document discusses opportunities and challenges for textile reinforced composites. It describes how textiles can be formed using various processes like weaving, knitting, braiding, and direct forming to create structures with multiple fiber orientations. Textiles are considered to have cost advantages over tape layup methods. However, shaping textiles to create tapered or complex geometries can introduce variations in fiber volume fraction, weave angle, yarn distribution, and mechanical properties across the structure. Careful design is required to minimize these variations.

1. Opportunities and Challenges
for Textile Reinforced
Composites
Christopher M. Pastore
Philadelphia University
Philadelphia, Pennsylvania, USA

2. Textile Reinforced Composites
Fiber reinforced composites whose repeating volume
element (RVE) is characterized by more than one
fiber orientation.
Formed with hierarchical textile processes that
manipulate individual fibers or yarn bundles to create
an integral structure.
It is possible to join various sub-assemblies together
to form even more complex structures.

3. Hierarchy of Textile Materials

4. Perceived Benefits
Textiles are considered to have significant cost
savings compared to tape lay-up.
Individual layer of fabric is much thicker than tape.
Fewer lay-up steps are necessary to create the final structure.
Formed from dry fiber and infiltrated with resin in a secondary
operation.
Handling and storage requirements of the material are reduced
compared to prepreg.
A single product is suitable for a variety of matrix materials,
reducing inventory and manufacturing costs.

5. 2D and 3D Textiles
Textiles are frequently classified as either 2D or 3D.
Clearly all fabrics are 3D, but 2-D implies that the
fabric is fundamentally thin.
That is, the thickness of the fabric is formed by only 2 or 3 yarns in
the thickness direction.
A 3-D fabric can have substantial thickness, limited
only by the machine, not some fundamental physical
phenomenon.

6. Types of Textiles
Direct-formed fabrics are those made directly from
fibers.
Woven, knitted, and braided fabrics are made from
manipulation of yarns.
These four classes represent the vast majority of
fabrics used in composite materials.
woven fabrics are formed by inter-lacing yarns,
knitted by inter-looping yarns,
braided by inter-twining yarns, and
direct formed fabrics by inter-locking fibers.

7. Direct Formed Fabrics
Created directly from fibers without a yarn processing
step involved.
No interlacing, intertwining, or interlooping of fibers
within the structure.
These fabrics are called nonwovens in much of the
literature, despite the obvious inadequacy of this
term.

8. Direct Formed Fabrics
Generally there are 2 steps
First a web is constructed of fibers. This sets the distribution of inplane fiber orientation.
Next the web is densified. This typically involves through thickness
entanglement or bonding.

9. Web formation
Opening process: mechanically separates the fibers.
Deposit fiber mass onto a belt, creating a continuous roll of lowdensity material
width of roughly 1-meter and a thickness 10-20 cm called a picker lap.
The fibers have a virtually uniform, random orientation in the plane,
with substantial out of plane orientation.
To thin the picker lap, it may be passed through a card.
Individual fibers are mostly oriented in the direction of material flow
through the machine.
This orientation allows the fibers to pack closer than previously resulting in a
thickness reduction, increased density, and a preferred distribution of fiber
orientations in the machine direction.
The resulting material is called a carded web.

10. Densification of web
The carded web may be used as input to the needle
punch, or it may be cross-lapped first.
The cross-lapper places carded web transverse to the machine
direction allowing the preferred fiber orientation to be in the cross
direction.
Needle punch creates mechanical interlocking
through barbed needles
Bonding can be done to chemically adhere the fibers
Adhesive application
Thermal bonding (sacrificial low melt fibers are pre-included in the
web)

11. XYZ Orthogonal Nonwoven

12. Knitted Fabrics
There are two basic types of knitting - weft knitting
and warp knitting.
They are distinguished by the direction in which the
loops are formed.
Weft knitting, the most common type of knitting in the apparel
industry, forms loops when yarns are moving in the weft direction,
or perpendicular to the direction of fabric formation.
Warp knitting differs from weft knitting in that multiple yarns are
interlooped simultaneously. A set of yarns are supplied from a
creel or warp beam and interlooped in the cross (course) direction.

13. Jersey Knits
The simplest weft knit structure is
the jersey.
Inherently bulky due to curvature
of the yarn.
The “natural” thickness of a jersey
knit fabric is roughly three times
the thickness of the yarns,
resulting in maximum yarn
packing factors of 20-25%, and
thus Vf around 15%.
High extensibility (up to 100%
strain to failure) which allows
complex shape formation
capabilities.

14. Rib Knits
In a rib knit structure it is possible to incorporate large yarns in the weft
to create a weft inserted rib knit.
In such a way a “unidirectional” preform can be constructed. However
it is difficult to achieve fiber volume fractions greater than 30% in these
structures due to the inherent bulkiness of the fabric.

15. Conformable Rib Knit

16. Warp Knits
In the WIWK, the load bearing yarns are locked into
the structure through the knitting process

17. Braiding
Biaxial braided fabrics may incorporate a longitudinal
yarn creating a triaxial braid.
The braided fabric is characterized mainly by the
braid angle, θ, (10° - 80° ).
Braids are tubular and frequently compared with
filament winding. They have been shown to be cost
competitive.
The braided fabric is flexible before formation, and
thus the fabric can conform to various shapes. The
braided fabric may be formed around a mandrel, and
rather complex shapes can be formed.

18. Braiding
Braids are formed by a circular “maypole” pattern of
yarn carrier motions

19. Types of 2D Braids

20. 3D Braiding Machine

21. Woven Fabrics
Generally characterized by two sets of perpendicular
yarns systems
One set is raised and lowered to make “sheds” (these
are warp yarns)
The other set is passed through these sheds,
perpendicular to the warp yarns (these are fill, or pick
or weft yarns)

22. Elements of a loom

23. Woven Fabrics
The structure of the woven fabric is the pattern of
interlacing between the warp and weft yarns
Yarns can “float”, or not interlace for some distance
within a woven fabric

24. Basic weave structures

25. Crimp in Weaves
The crimp is defined as one less than the ratio of the
yarn's actual length to the length of fabric it traverses.
Crimp levels influence fiber volume fraction, thickness
of fabric, and mechanical performance of fabric.
High crimp leads to
Reduced tensile and compressive properties
Increased shear modulus in the dry fabric and the resulting
composite
Fewer regions for localized delamination between individual yarns.

26. Applications of Weaves
Weaves can be formed into composites with fiber
volume fractions as high as 65%.
High harness count satins – 8 and 12 –serve the role
previously held by 0/90 tape lay-ups.
There is a significant cost benefit to using the fabrics
in that much fewer layers need be applied because
the woven fabric is usually many times thicker than
the tape (depending on the yarns used in the fabric).

27. 3D Weaves
Layer-to-layer
XYZ
Through thickness

28. Doubly Stiffened Woven Panel

29. Variations in Weave Design
If large yarns are used in the warp direction and small
yarns are infrequently spaced in the weft direction,
the resulting fabric resembles a unidirectional
material.
Weaves can be formed with gradients in a single or
double axis by changing yarn size across the width or
length
Complex shapes can be achieved through “floating”
and cutting yarns to reduce total number of yarns in
some section of the part

30. Gradations through yarn size

31. Shape through floats

32. Issues with shaping woven fabrics
Tailoring the cross-section of a woven fabric will
generally result in
a change in weave angle,
a change in the distribution of longitudinal, weaver, and fill, and
a change in fiber volume fraction in consequence to the change in
thickness.
Some fiber volume fraction effects can be controlled
by tooling. The tailoring occurs in a discrete manner,
using individual yarns, whereas most tooling will be
approximately continuous.

33. Example of single taper weave
Consider a tapered panel where gradation in
thickness is achieved by changing yarn size/count
across the width

34. Design of tapered woven panel
Pick count is constant,
warps and wefts per
dent are modified to 18
17
16
taper
15
Z yarn path changes 14
13
to accommodate the 12
11
10
weave.
Number
Pick Columns per inch
Picks per column
Warp per dent
9
8
7
6
5
4
3
2
1
1
3
5
7
9
11 13
15
Dent
17 19
21
23 25
27
29 31

35. Variation in Fiber Volume Fraction
60%
This variation in
yarn packing results
in variations in Vf for
the resulting
composite.
Fiber
Volume
Fraction
58%
56%
54%
52%
50%
48%
Calculated
Target
46%
44%
42%
40%
0.000
0.500
1.000
1.500
Distance from Thin Edge (in)
2.000
2.500

36. Variation in weave angle
The weave angle will
55 °
also change throughout
the width of the part due 50 °
to varying warp yarn
count and part thickness.
45 °
Weave
Angle 40 °
35 °
Calculated
30 °
Target
25 °
0.0
0.5
1.0
1.5
Distance from Thin Edge (in)
2.0
2.5

37. Yarn Distributions
The distribution of warp,
weft, and Z yarn will also
vary throughout the part.
60%
55%
50%
45%
40%
Yarn
Distribution
35%
%Z
% Warp
% Fill
30%
25%
20%
15%
0.0
0.5
1.0
1.5
Distance from Thin Edge (in)
2.0
2.5

38. Variations in Modulus
All mechanical properties will vary throughout the part
14
12
10
E11
Tensile
Modulus
(Msi)
E22
E33
8
6
4
2
0
0.0
0.5
1.0
1.5
Distance from Thin Edge (in)
2.0
2.5