Industrial Applications of 3D Textiles for Composites

1
Industrial Applications of 3D Textiles for
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
History of Textile Composites

• The primary work in structural textile composites
  was initiated in the 1960s and 70s
• 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

5
Disadvantages to Textiles

• Crimp
• Need for new machinery
• Development cost
• Difficulties in structural characterization

6
Evaluation of Textiles

• The true effectiveness of textiles for
  applications is very specific, depending on
• Fabric type
• Size of part
• Mechanical performance requirements
• Availability of processing equipment

7
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.

8
XYZ Orthogonal Nonwoven
A variation on non-wovens 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
13
3D Braiding Machine
14
Basic weave structures
15
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

20
Gradations through yarn size
21
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
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Location of Test Cell with Respect toUnit 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 AS-4/Epoxy Composite with 45
Braid Angle and 46 Longitudinal Yarns
33
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
  three-dimensional 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 e-beam 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.