Composite Material Behavior

1
Composite Material Behavior

• Rule of Mixtures
• For fiber oriented composites, tested along the
  fiber direction
• Ruess Model (Inverse Rule of Mixtures)
• For fiber oriented composite, tested transverse
  to the fiber direction
• Applications

2
Concrete

• Components
• Aggregate
• Sand
• Cement
• Cement is the Matrix with aggregate and sand as
  reinforcements
• Cement Reaction with Water
• Flow Solidification

3
Pre-Stressed Concrete

• Concrete Metallic Reinforcement Rods
• Relaxation of rods following cure compresses the
  concrete making it stronger
• Rod corrosion an issue

Cement Forms are placed which allow for rods
to be placed through. Rods are stressed during
cure
4
Fiber Reinforced Composites

• Most important composite types
• Types of Fibers
• Graphite, Carbon, Glass, Boron, PE, Aramid
• Short fibers (whiskers) or continuous fibers
• Goal Low Density High Strength for the
  composite

5
Effect of Fiber Length

• The ability to strengthen a composite using a
  fiber reinforcement depends on several factors
• Fiber Properties
• Fiber Geometry
• Interfacial Shear Strength with the matrix
• Equation 17.3

6
The Matrix

• Can be a metallic, polymeric, or ceramic
• Is used to give composite some ductility
• Protects the fibers from mechanical damage
• Separates individual collections of fibers
  suppressing the catastrophic destruction of the
  fibers along when they begin to fail

7
Composite Applications PMCs

• Polymer Matrix Composites
• The easiest composites to form given the low
  temperatures needed to process the matrix
• Glass and Carbon reinforced composites
• Glass composites are more common in marine and
  other commodity applications for automobiles and
  other industrial applications
• Raw materials, cheap, relatively easy to make

8
Composite Applications PMCs

• When higher strength is needed, carbon fibers are
  commonly substituted for glass.
• Transparent change with respect to the matrix
  processing.
• Applications include sports equipment, airborne
  systems and structures.
• A function of who can pay

9
Composite Applications PMCs

• Kevlar An aramid (Nylon based) polymer that can
  be extruded and spun into a high strength fiber.
• Similar applications to carbon fibers for use in
  other high strength applications

10
Metal Matrix Composites

• In metal matrix composites, a metal is
  substituted for the polymeric matrix
• MMCs can be used in higher temp applications
  than the base metal and to improve specific
  stiffness, density, creep resistance, or to lower
  thermal coefficients of expansion.
• Matrices Al, Cu, Mg and Ti, low temp fluidity
• Reinforcements, Carbon, SiC, B, Al2O3...no glass

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Composite Applications MMCs

• Automotive engine and other under the hood
  components
• Electronic Heat Sink Materials
• Advanced Aerospace Composites for structural
  elements
• Largest limiting factor associated with
  acceptable quality

12
Ceramic Matrix Composites CMCs

• Goal To minimize catastrophic damage associated
  with the initial flaw formation and propagation.
• Common Particulates TiB2, Zirconia
• Common fibers SiC, SI3N4
• Most common matrices Al2O3, SiC
• Most important parameter K1c
• 2-3X improvement in toughness...still low