IT 111 Composites

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IT 111 Composites

• Lecture 8
• Thomas E. Scott

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Composite Materials

• For situations where no single material has the
  required properties
• Two more materials combined
• Reinforce
• Bind together
• The whole is GREATER than the sum
• Natural composites
• Wood, celery, bamboo, corn

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Composite Material

• Two major components
• Matrix or binder
• Reinforcing material
• Advanced composite
• Directionally oriented and continuous fibers
• Examples
• Concrete with rebar
• Fiberglass with resin matrix and glass fibers

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Types of Fibers

• Resins can be almost any polymer
• High strength to weight fibers
• Glass Strong but heavy
• Kevlar (aramid) Expensive but light weight
• Graphite (Carbon) Expensive but light weight
• Hybrid
• Uses more than one type of fiber

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Hybrid Fibers

• Types
• Interply alternating layers
• Intraply different fiber intermixed
• Place fiber where it will contribute the best
• Expensive carbon where needed most
• Inexpensive glass everywhere else
• Interply Knitting
• Weaving strands to reduce lay-up time

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Hybrid Fibers

• Warp direction of stress application
• Weft perpendicular to stress direction
• Bias between warp and weft

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Fabrication of Composite

• Time consuming and labor intensive
• Hand Lay Up Oldest form
• Add filler to a mold
• Add resin
• Cures at room temp
• Examples Auto, boat
• Prepreg Woven fibers impregnated with resin
• Heated while being laid in place
• Cooled to set
• Cured at elevated temps and pressures (autoclave)

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Fabrication of Composite

• Resin Transfer Mold
• Place reinforcing material in two piece mold
• Matching mold injected with mixed resin and
  catalyst
• Fast curing times, less labor intensive
• Ultimately reinforced thermoset reaction
  injection (URTRI)
• Can use foam cores for cavity formation
• Injected resin

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Fabrication of Composite

• Sheet Molding Compound
• Material in continuous sheets made from resin,
  filler
• Covered with polyethylene film
• Cut to proper weight for final part
• Loaded in compression press, heated and pressed
  to form final part
• Examples auto body parts, appliance panels

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Strength Comparisons
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Ceramic Matrix Composite Constituents

• Composites consist of two or more materials or
  material phases combined to produce a material
  with superior properties to those of its
  individual constituents.
• The constituents are the matrix and the
  reinforcement.
• The matrix and reinforcement must be present in
  reasonable proportions to produce appropriate
  physical properties.
• MATRIX Portland Cement (Magnesia or
  Lithium-Alumina-Silicate)
• FIBERS SiC, SiNitride, Zirconium Oxide,
  Aluminum Oxide

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Metal Matrix Composites

• Consists of metal based reinforced with one or
  more other materials, such as graphite, ceramic,
  or metal.
• Most are relatively expensive.
• Some are difficult to fabricate with high degree
  of stability.
• MATRIX Materials Aluminum, Titanium, Copper,
  Silver
• FIBERS Boron, SiC, carbon, aluminum oxide