Chapter 16

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• Chapter 16 Composites Teamwork and Synergy in
  Materials

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Chapter Outline

• 16.1 Dispersion-Strengthened Composites
• 16.2 Particulate Composites
• 16.3 Fiber-Reinforced Composites
• 16.4 Characteristics of Fiber-Reinforced
  Composites
• 16.5 Manufacturing Fibers and Composites
• 16.6 Fiber-Reinforced Systems and
  Applications
• 16.7 Laminar Composite Materials
• 16.8 Examples and Applications of Laminar
  Composites
• 16.9 Sandwich Structures

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Figure 16.1 Some examples of composite materials
(a) plywood is a laminar composite of layers of
wood veneer, (b) fiberglass is a fiber-reinforced
composite containing stiff, strong glass fibers
in a softer polymer matrix (? 175), and (c)
concrete is a particulate composite containing
coarse sand or gravel in a cement matrix (reduced
50).
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Section 16.1
Dispersion-Strengthened Composites

• A special group of dispersion-strengthened
  nanocomposite materials containing particles 10
  to 250 nm in diameter is classified as
  particulate composites.
• Dispersoids - Tiny oxide particles formed in a
  metal matrix that interfere with dislocation
  movement and provide strengthening, even at
  elevated temperatures.

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Section 16.2
Particulate Composites
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Figure 16.4 Microstructure of tungsten
carbide20 cobalt-cemented carbide (1300). (From
Metals Handbook, Vol. 7, 8th Ed., American
Society for Metals, 1972.)
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Figure 16.5 The steps in producing a
silver-tungsten electrical composite (a)
Tungsten powders are pressed, (b) a low-density
compact is produced, (c) sintering joins the
tungsten powders, and (d) liquid silver is
infiltrated into the pores between the particles.
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Figure 16.6 The effect of clay on the properties
of polyethylene.
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Section 16.4
Characteristics of Fiber-Reinforced Composites

• Many factors must be considered when designing a
  fiber-reinforced composite, including the length,
  diameter, orientation, amount, and properties of
  the fibers the properties of the matrix and the
  bonding between the fibers and the matrix.
• Aspect ratio - The length of a fiber divided by
  its diameter.
• Delamination - Separation of individual plies of
  a fiber-reinforced composite.

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Figure 16.11 Effect of fiber orientation on the
tensile strength of E-glass fiber-reinforced
epoxy composites.
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Figure 16.12 (a) Tapes containing aligned fibers
can be joined to produce a multi-layered
different orientations to produce a
quasi-isotropic composite. In this case, a
0/45/90 composite is formed.
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Figure 16.10 Increasing the length of chopped
E-glass fibers in an epoxy matrix increases the
strength of the composite. In this example, the
volume fraction of glass fibers is about 0.5.
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Figure 16.13 A three-dimensional weave for
fiber-reinforced composites.
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Figure 16.14 Comparison of the specific strength
and specific modulus of fibers versus metals and
polymers.
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Section 16.5
Manufacturing Fibers and Composites

• Chemical vapor deposition - Method for
  manufacturing materials by condensing the
  material from a vapor onto a solid substrate.
• Carbonizing - Driving off the non-carbon atoms
  from a polymer fiber, leaving behind a carbon
  fiber of high strength. Also known as pyrolizing.
• Filament winding - Process for producing
  fiber-reinforced composites in which continuous
  fibers are wrapped around a form or mandrel.
• Pultrusion - A method for producing composites
  containing mats or continuous fibers.

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Figure 16.20 A scanning electron micrograph of a
carbon tow containing many individual carbon
filaments (x200).
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Figure 16.22 Producing composite shapes in dies
by (a) hand lay-up, (b) pressure bag molding, and
(c) matched die molding.
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Figure 16.24 Producing composite shapes by
pultrusion.
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Figure 16.23 Producing composite shapes by
filament winding.
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Figure 16.21 Production of fiber tapes by
encasing fibers between metal cover sheets by
diffusion bonding.
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Section 16.7
Laminar Composite Materials

• Rule of Mixtures - Some properties of the laminar
  composite materials parallel to the lamellae are
  estimated from the rule of mixtures.
• Producing Laminar Composites - (a) roll bonding,
  (b) explosive bonding, (c) coextrusion, and (d)
  brazing.

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Figure 16.30 Techniques for producing laminar
composites (a) roll bonding, (b) explosive
bonding, and (c) coextrusion, and (d) brazing.
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Section 16.8
Examples and Applications of Laminar Composites

• Laminates - Laminates are layers of materials
  joined by an organic adhesive.
• Cladding - A laminar composite produced when a
  corrosion-resistant or high-hardness layer of a
  laminar composite formed onto a less expensive or
  higher-strength backing.
• Bimetallic - A laminar composite material
  produced by joining two strips of metal with
  different thermal expansion coefficients, making
  the material sensitive to temperature changes.

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Section 16.9
Sandwich Structures

• Sandwich - A composite material constructed of a
  lightweight, low-density material surrounded by
  dense, solid layers. The sandwich combines
  overall light weight with excellent stiffness.
• Honeycomb - A lightweight but stiff assembly of
  aluminum strip joined and expanded to form the
  core of a sandwich structure.

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Figure 16.32 (a) A hexagonal cell honeycomb
core, (b) can be joined to two face sheets by
means of adhesive sheets, (c) producing an
exceptionally lightweight yet stiff, strong
honeycomb sandwich structure.
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Figure 16.33 In the corrugation method for
producing a honeycomb core, the material (such as
aluminum) is corrugated between two rolls. The
corrugated sheets are joined together with
adhesive and then cut to the desired thickness.