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Industrial Applications of 3D Textiles for Composites

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Title: 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.

4
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.
9
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.

10
Conformable Rib Knit
11
Warp Knits
  • In the WIWK, the load bearing yarns are locked
    into the structure through the knitting process

12
Types of 2D Braids
13
3D Braiding Machine
14
Basic weave structures
15
3D Weaves
Through thickness
Layer-to-layer
XYZ
16
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.

17
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.

18
Doubly Stiffened Woven Panel
19
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
22
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.

23
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.

24
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)

25
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.

26
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.

27
Moiré Interferometry Field on Axially Loaded
Braided Composite
28
Elastic Modulus vs. Gage Area for Braided and 3D
Woven Composites
29
Location of Test Cell with Respect toUnit Cells
in a Triaxial Braid
30
Predicted Tensile Moduli for 60 Triaxial Braid
AS-4/ Epoxy Test Cell with y1 b and x1 4.1a
31
Predicted and Experimental Tensile Modulus of a
Triaxially Braided AS-4/ Epoxy Composite with 45
Braid Angle and 12 Longitudinal Yarns
32
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
34
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.

35
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.

36
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.

37
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.

38
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.

39
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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