Industrial Applications of
3D Textiles for Composites
Christopher M. Pastore
Philadelphia University
Philadelphia, Pennsylvania, USA
Engineering @ Design Studio of Philadelphia University
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.
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History of Textile Composites
 The primary work in structural textile composites was
initiated in the 1960’s and 70’s
 The motivation was primarily elimination of
delamination
 From impact
 From ablation
 Many 3D textiles were developed in this activity
around the world.
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Advantages of 3D Textiles
 The use of textiles in composites revealed two sets of
benefits:
 Delamination resistance
 Primarily derived from through thickness orientation of yarns
 Potential for reduced cost
 Pre-assembled layers of fibers reduce touch labor
 Part consolidation can be realized with near-net-shape manufacturing
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Disadvantages to Textiles
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Crimp
Need for new machinery
Development cost
Difficulties in structural characterization
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Evaluation of Textiles
 The true effectiveness of textiles for applications is
very specific, depending on

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
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Fabric type
Size of part
Mechanical performance requirements
Availability of processing equipment
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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.
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XYZ Orthogonal Nonwoven
A variation on nonwovens is the XYZ
system which has no
interlacings, but uses
fibers or yarns to create
the structure.
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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.
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Conformable Rib Knit
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Warp Knits
 In the WIWK, the load bearing yarns are locked into
the structure through the knitting process
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Types of 2D Braids
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3D Braiding Machine
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Basic weave structures
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3D Weaves
Through thickness
Layer-to-layer
XYZ
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Crimp in Textiles
 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.
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New Machinery/Processes
 Very complex shaped objects can be produced with
textile processes
 Sometimes new processes or machinery are
required.
 Particular emphasis is on placement of bias yarns in
woven fabrics.
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Doubly Stiffened Woven Panel
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Variations in Weave Design
 Consider the formation of a tapered fabric
 Weaves can have gradients in a single or double axis by changing
yarn size in 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
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Gradations through yarn size
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Shape through floats
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Issues with shaping woven fabrics
 Tailoring the cross-section of a weave results 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.
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Mechanical Property Predictions
 to model the structural response it is necessary to
describe the mechanical properties of the material.
 The simplest form is to treat as homogenous medium
with anisotropic properties.
 This is termed homogenization of the material.
 If the volume of material to be homogenized is small compared to
the structural component, this approach seems reasonable.
 In the case of textile reinforced materials, the RVE is typically quite
large, on the order of cm in some cases. It may not be reasonable
to consider the RVE as representing the response of the material
 Special analytical tools need to be developed to understand the
local response within the RVE.
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Homogenization of Properties
 Analytical techniques have been developed to predict the elastic
properties of textile composite RVE's.
 averaging mechanical properties of the constituent materials,
 Bolotin (1966), Nosarev (1967), Tarnopol'skii et al. (1967), and Sendeckyj (1970), Roze and
Zhigun (1970), Kregers and Melbardis (1978), Kregers and Teters (1979), Chou et al. (1986),
Ishikawa and Chou (1982), Jortner (1984), Whyte (1986), Ko et al. (1987), Ko and Pastore
(1989) , Howarth (1991) , Jaranson et al. (1993), Singletary (1994), Pochiraju et al. (1993)
 property predictions based upon detailed geometric descriptions of the
reinforcement, and
 Foye (1991), Gowayed (1992), Bogdanovich et al. (1993), Carter et al. (1995).
 finite element methods treating matrix and fiber as discrete components.
 Kabelka (1984), Woo and Whitcomb (1993), Sankar and Marrey (1993), Yoshino and Ohtsuka
(1982), Whitcomb (1989), Dasgupta et al. (1992), Naik and Ganesh (1992), Lene and Paumelle
(1992), Blacketter et al. (1993) and Glaesgen et al. (1996), Hill et al. (1994), Naik (1994)
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Non-RVE Considerations
 The size of the RVE is relatively large compared to
test specimens and some actual structures.
 The application of RVE based analysis may not be
appropriate
 Even experimental data can be effected by this
assumption
 The strain gage used in tensile testing usually covers
only a few RVEs of the textile, and sometimes even
less than 1.
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Measurements of Elastic Properties
 If the measurement system does not contain a large
number of RVEs, then the measurements do not
reflect a true average value.
 The location of the gage will affect the measured
values.
 Some of the perceived high variation in tensile
modulus may be due to the relationship between
strain gage and RVE size.
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Moiré Interferometry Field on Axially
Loaded Braided Composite
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Elastic Modulus vs. Gage Area for
Braided and 3D Woven Composites
1.3
1.2
1.1
Normalized
Tensile
1
Modulus
0.9
0.8
0.7
0
2
4
6
Gage Area/ Unit Cell Area
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8
Location of Test Cell with Respect to
Unit Cells in a Triaxial Braid
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Predicted Tensile Moduli for 60° Triaxial Braid AS-4/
Epoxy Test Cell with y1 = b and x1 = 4.1a
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Predicted and Experimental Tensile Modulus of a Triaxially Braided AS-4/
Epoxy Composite with 45° Braid Angle and 12% Longitudinal Yarns
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Predicted and Experimental Tensile Modulus of a Triaxially Braided AS4/Epoxy Composite with 45° Braid Angle and 46% Longitudinal Yarns
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Predicted and Experimental Tensile Modulus of a Triaxially Braided AS-4/
Epoxy Composite with 70° Braid Angle and 46% Longitudinal Yarns
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Outlook
 Tremendous variety of textile reinforcements
available for composites applications.
 Range from very traditional processes such as
weaving to novel techniques such as threedimensional fabrics.
 The most obvious advantage of these materials is
labor savings.
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Physical Limitations
 Current cost of production.
 modifications to machines are needed for shaping capabilities,
 capital cost is applied to a few prototypes, the unit cost is
tremendous (no economy of scale)
 Processing difficulties.
 infiltration at high pressure, and thermal effects during curing.
 frequently results in internal yarn geometry distortions.
 elastic and strength properties have high variation.
 thermal effects can result in local disbonds from yarns.
 One approach that seems promising is the use of cold cure systems such as ebeam curing to reduce the temperature of cure and thus reduce the effect of
different coefficients of thermal expansion between the fiber and resin.
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Analytical Shortcomings
 Analytical techniques are still not adequate to satisfy
structural analysts planning to apply these materials
to load bearing structures.
 Some “variation” in elastic performance is expected
due to a non-integer number of RVE's.
 the design allowables for the materials are greatly reduced,
frequently making them appear unsuitable for structural application
due to the perception of high weight penalty.
 It is possible to account for this behavior even with simple tools
such as stiffness averaging if the non-RVE element is modeled.
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Failure Analysis
 Understanding of failure initiation and growth is still
required.
 Greater resolution of the internal stress state is needed than that for
establishing homogenized elastic constants.
 Failure modes are poorly understood.
 These modes are associated with local curvature and distortion of the yarns at
crossover points, and cracking between yarn bundles (inter-bundle cracking).
 Transverse cracking and fiber failure within the yarns (intra-bundle cracking) are
also a function of the complex stress state inherent in a textile.
 An important issue is how curvature and inter-bundle cracking affect compression
by reducing the stability of the yarn.
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Conclusions
 Textile composites have been intriguing composites
researchers since the 1960s. However they have not
gained true acceptance in the industry as yet.
 Textile composites will remain only promises until:
 cost of production are greatly reduced,
 material forms are refined to meet arbitrary mechanical property
requirements, and
 analytical techniques are developed fully.
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Conclusions
 It seems that military demands will not drive the
necessary technology to turn these dreams into
reality.
 What is needed is aggressive development on the
part of the textile manufacturer to find appropriate
industrial placement.
 The most likely market forces driving future
development will be the biomedical, automotive, and
civil infrastructure industries.
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