Docstoc

530 352 Materials Selection 530 352 Materials Selection Lecture 9 Structure

Document Sample
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
Tuesday
September 27th, 2005




                                                  Page 1
Composites




             Page 2
Page 3
Page 4
Page 5
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


                                                                         Page 6
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
                    matrices
                   Higher use temperature and higher toughness
Ceramic            Used in highest temperature applications




                                                                    Page 7
     Polymer Resin Comparison




From “PrePreg Technology”, Hexcel Composites
                                               Page 8
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
                 fumes
                Must be cured in autoclave
                PMR-15 is most widely used
                                                                     Page 9
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


                                                                     Page 10
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




                                                                             Page 11
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
                matrices
               Not used very extensively in aerospace




                                                                  Page 12
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




                                                                         Page 13
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




                                                                       Page 14
Graphite Fiber Production




                            Page 15
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
                    SiC
                                Non-Stoichiometric SiC
                                                                     Page 16
 SiC Fiber
Carbon Core         Coating




              SiC


                              Page 17
     Fiber Comparison
                               800
                                                                  Carbon           Boron
                               700                          UHS
      Tensile Strength (ksi)




                                                                                           SiC
                               600
                                                             HS
                               500                                                               PAN
                                                                    IM        HM      UHM
                               400            Aramid

                               300
                                          Glass
                               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
                                                                                                            Page 18
Composite forms:
   Prepreg Tape
     Fibers are „pre-impregnated‟ into matrix which is partially cured but
      tacky
     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




                                                                          Page 19
     What is a Prepreg?




From “PrePreg Technology”, Hexcel Composites
                                               Page 20
Weave Styles




               Page 21
3D Woven / Braided Forms




                           Page 22
Composite Fabrication:


    Batch
               Lay up    Bagging
  acceptance




  Assembly     Inspect    Cure




                                   Page 23
Voight Model
                                                       
  Iso-strain
  A = B = 
  Av.  = VA  A + VB B
  Av. E = Av.  /  = VA A /  + VB  B / 

  Ecomposite = VA EA + VB EB                   A   B




                                                       Page 24
Reuss Model
                                          
 Iso-stress
                                      A
 A = B =                           B
 Av.  = VA  A + VB B
 Av.    = VA A   + VB B  


 1 / Ecomposite = VA / EA + VB / EB




                                          Page 25

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:9
posted:11/12/2011
language:English
pages:25