eFunda: Introduction to Fiber Reinforced Composite Materials
engineering fundamentals Fiber Reinforced Composites
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Composition of Fiber Reinforced Composites

Common fiber reinforced composites are composed of fibers and a matrix. Fibers are the reinforcement and the main source of strength while the matrix 'glues' all the fibers together in shape and transfers stresses between the reinforcing fibers. Sometimes, fillers or modifiers might be added to smooth manufacturing process, impart special properties, and/or reduce product cost.

Fibers of Fiber Reinforced Composites

The primary function of the fibers is to carry the loads along their longitudinal directions. Common fiber reinforcing agents include

  • Aluminum, Aluminum oxide, Aluminum silica
  • Asbestos
  • Beryllium, Beryllium carbide, Beryllium oxide
  • Carbon (Graphite)
  • Glass (E-glass, S-glass, D-glass)
  • Molybdenum
  • Polyamide (Aromatic polyamide, Aramid), e.g., Kevlar 29 and Kevlar 49
  • Polyester
  • Quartz (Fused silica)
  • Steel
  • Tantalum
  • Titanium
  • Tungsten, Tungsten monocarbide
Matrix of Fiber Reinforced Composites

The primary functions of the matrix are to transfer stresses between the reinforcing fibers (hold fibers together) and protect the fibers from mechanical and/or environmental damages. A basic requirement for a matrix material is that its strain at break must be larger than the fibers it is holding.

Most matrices are made of resins for their wide variation in properties and relatively low cost. Common resin materials include

  • Resin Matrix
    • Epoxy
    • Phenolic
    • Polyester
    • Polyurethane
    • Vinyl Ester

Among these resin materials, polyesters are the most widely used. Epoxies, which have higher adhesion and less shrinkage than polyesters, come in second for their higher costs.

Although less common, non-resin matrices (mostly metals) can still be found in applications requiring higher performance at elevated temperatures, especially in the defense industry.

  • Metal Matrix
    • Aluminum
    • Copper
    • Lead
    • Magnesium
    • Nickel
    • Silver
    • Titanium
  • Non-Metal Matrix
    • Ceramics
Modifiers of Fiber Reinforced Composites

The primary functions of the additives (modifiers, fillers) are to reduce cost, improve workability, and/or impart desired properties.

  • Cost Reduction:
    • Low cost to weight ratio, may fill up to 40% (65% in some cases) of the total weight
  • Workability Improvement:
    • Reduce shrinkage
    • Help air release
    • Decrease viscosity
    • Control emission
    • Reduce coefficient of friction on surfaces
    • Seal molds and/or guide resin flows
    • Initiate and/or speed up or slow down curing process
  • Property Enhancement:
    • Improve electric conductivity
    • Improve fire resistance
    • Improve corrosion resistance
    • Improve ultraviolet resistance
    • Improve surface toughness
    • Stabilize heat transfer
    • Reduce tendency of static electric charge
    • Add desired colors

Common materials used as additives include

  • Filler Materials:
    • Feldspar
    • Glass microspheres
    • Glass flakes
    • Glass fibers, milled
    • Mica
    • Silica
    • Talc
    • Wollastonite
    • Other microsphere products
  • Modifier Materials:
    • Organic peroxide, e.g., methylethylketone peroxide (MEKP)
    • Benzoyl peroxide
    • Tertiary butyl catechol (TBC)
    • Dimethylaniline (DMA)
    • Zinc stearate, waxes, silicones
    • Fumed silica, clays
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