530 352 Materials Selection 530 352 Materials Selection Lecture 9 Structure

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530 352 Materials Selection 530 352 Materials Selection Lecture 9 Structure Powered By Docstoc
					530.352 Materials Selection

Lecture #9: Structure and elastic properties of CMC‟s
September 27th, 2005

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Composites are:

 Matrix                           +       Reinforcement
    Metal (MMC)                             Particulate (in MMC)
      Al (most widely used) and Ti          Whiskers (chopped fibers)
    Ceramic (CMC)                           Continuous fiber
    Polymeric (PMC)                           Fiberglass (cheap, most
      Thermoset                                common)
         Epoxy (most widely used),            Kevlar
          polyimides (max T stability),        Graphite
          cyanate esters, etc.
                                               Carbon
      Thermoplastic
                                               Poly Acrylic Nitrile (PAN)
         Poly Ether Ether Keytone
          (PEEK) – can be remolded             Boron
                                               SiC

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Matrix Types
Matrix                               Characteristics
Thermoset          Undergo irreversible chemical reaction when cured
Resin              Low temp, long time to cure, tend to be brittle
                   Epoxy, Bismaleimide, Polyimide, Polyester,
                    Phenolic, Cyanate Ester
Thermoplastic      Non-reacting reversible cure
Resin              High temp, short time to form, high toughness
                   Polyetheretherketone (PEEK)
Metal              Generally much more expensive than polymer
                   Higher use temperature and higher toughness
Ceramic            Used in highest temperature applications

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     Polymer Resin Comparison

From “PrePreg Technology”, Hexcel Composites
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Polymer Matrix Types
Matrix                               Characteristics
Epoxy           Most widely used matrix for composites
                Can be toughened with the addition of rubber
                 plasticizers to the matrix
                Cures at 250-350°F; 350°F max service temperature
                May be cured in oven or autoclave
                3501-6 (non-toughened) and 977-2 (toughened) are
                 most widely used
Bismaleimide    Improved thermal stability over epoxies
                350-450°F cure and service temp
                Must be cured at high pressure (autoclave)
                More brittle than epoxy
                5250 most widely used
Polyimide       Maximum temperature stability
                500-600°F cure and service temperature
                Cure is complicated and some forms give off toxic
                Must be cured in autoclave
                PMR-15 is most widely used
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Polymer Matrix Types
Matrix                            Characteristics
Cyanate        Moderate temperature stability with significantly
                reduced outgassing
               400-500°F cure and service temperature
               Virtually zero outgassing
               Used for satellite applications where sensitive
                optics are present
Polyester      Low cost matrix not used in aerospace
Phenolic       Low cost matrix with low mechanical properties
                used in the production of rocket nozzles
PEEK           Thermoplastic matrix of interest because it can be
                re-molded by the subsequent application of heat
                and pressure
               Complex, high temperature cure (700°F) and
                moderate service temperature (250°F) mean that it
                is not used extensively

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Other Matrix Types
Matrix                                  Characteristics
Aluminum             Most widely used metal matrix
                     Can be composited with fibers (Al/B, Al/Gr) or
                      particles (SiC, Alumina) or whiskers (SiC, Alumina)
                     Can lead to greatly improved stiffness, strength and
                      wear resistance when reinforced
Titanium             Used in small quantities for high temperature and
                      high strength applications
Carbon               One of very few viable materials for structural
                      applications at extreme temps (3000+°F)
                     Produced by lengthy iterative process of cure,
                      pyrolysis, impregnation, and coating
                     Used in aircraft brakes, Shuttle wing leading edge,
                      rocket nozzles
Silicon Carbide      Alternate matrix for high temperature applications

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Reinforcement Forms
Reinforcement                        Examples
Fiber          Fiberglass, Kevlar, Graphite, Carbon, or Silicon
                Carbide long or continuous fibers
               Most common in aerospace applications
Particulate    SiC, Quartz, or Alumina particles sometimes used in
                metal matrices
               Not used very extensively in aerospace
Whisker        Alumina or SiC short fibers sometimes used in metal
               Not used very extensively in aerospace

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Fiber Materials
Fiber Type                              Description
Fiberglass      Amorphous glass material, low cost, widely used, high
                 strength, moderate stiffness
                Used in general aviation or in applications where low
                 electrical conductivity is desired
                ~12 m diameter
Kevlar          High strength polymer used for impact resistance
(Aramid)        Low electrical conductivity
                ~12 m diameter

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Fiber Materials
Fiber Type                          Description
Graphite      Carbon fiber with high strength, high stiffness, and high
               temperature resistance
              Produced by “pulling” fibers from an organic precursor and
               heating away the radical group
              Pitch precursor leads to high modulus fibers (50-60Msi)
              Poly Acrylic Nitrile (PAN) based precursor leads to high
               strength fibers (700-800 ksi)
              Individual filaments are grouped into tows (1K, 3K, 6K,
               12K), tows grouped into fibers
              7-10 m diameter
Carbon        Rayon based precursor leads to low strength fiber used for
               C/C Composites

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Graphite Fiber Production

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Fiber Materials
Fiber Type                            Description
Boron           Formed by CVD of boron onto tungsten filament
                Very high stiffness but difficult to handle
                100-200 m diameter
Silicon         High temperature fiber used in ceramic composites
Carbide         Also grown by CVD onto tungsten filament
                100-200 m diameter

                   Boron                      b-SiC

                      Reaction Zone
                                   Reaction Zone

                      W Filament
                                   C Monofilament
                                Non-Stoichiometric SiC
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 SiC Fiber
Carbon Core         Coating


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     Fiber Comparison
                                                                  Carbon           Boron
                               700                          UHS
      Tensile Strength (ksi)

                               500                                                               PAN
                                                                    IM        HM      UHM
                               400            Aramid

                               200                                            Carbon MesoPitch

                               100   Carbon Pitch

                                0    10     20        30     40          50     60           70        80
                                                    Tensile Modulus (Msi)

From “Composite Materials: Science and Engineering”, K.K.Chawla
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Composite forms:
   Prepreg Tape
     Fibers are „pre-impregnated‟ into matrix which is partially cured but
     All fibers aligned in single direction
     Tape ~ 12” wide and any length
   Prepreg Cloth
       Fibers woven to provide strength/stiffness in 2 directions
       Woven cloth “pre-impregnated” w partially cured resin
       Cloth ~ 36” wide
       Different weaves give different drape
   Preform
     Fibers stitched, woven, or braded into complicated 3D shapes

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     What is a Prepreg?

From “PrePreg Technology”, Hexcel Composites
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Weave Styles

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3D Woven / Braided Forms

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Composite Fabrication:

               Lay up    Bagging

  Assembly     Inspect    Cure

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Voight Model
  A = B = 
  Av.  = VA  A + VB B
  Av. E = Av.  /  = VA A /  + VB  B / 

  Ecomposite = VA EA + VB EB                   A   B

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Reuss Model
 A = B =                           B
 Av.  = VA  A + VB B
 Av.    = VA A   + VB B  

 1 / Ecomposite = VA / EA + VB / EB

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