COMPOSITE MATERIALS (PowerPoint) by yurtgc548

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									                          Composites
                           Full Lecture



   Dr. David R. Veazie
Southern Polytechnic State
        University




Manufacturing Processes
  Prof David Veazie
                                    Composites Lecture
                COMPOSITE MATERIALS
• Technology and Classification of Composite
  Materials
• Metal Matrix Composites
• Ceramic Matrix Composites
• Polymer Matrix Composites
• Guide to Processing Composite Materials




     Manufacturing Processes
       Prof David Veazie
                                Composites Lecture
              Composite Material Defined
A materials system composed of two or more physically
  distinct phases whose combination produces
  aggregate properties that are different from those of
  its constituents
• Examples:
     Cemented carbides (WC with Co binder)
     Plastic molding compounds containing fillers
     Rubber mixed with carbon black
     Wood (a natural composite as distinguished from
      a synthesized composite)


     Manufacturing Processes
       Prof David Veazie
                                  Composites Lecture
         Why Composites are Important
• Composites can be very strong and stiff, yet very light
  in weight, so ratios of strength-to-weight and
  stiffness-to-weight are several times greater than
  steel or aluminum
• Fatigue properties are generally better than for
  common engineering metals
• Toughness is often greater too
• Composites can be designed that do not corrode like
  steel
• Possible to achieve combinations of properties not
  attainable with metals, ceramics, or polymers alone

     Manufacturing Processes
       Prof David Veazie
                                  Composites Lecture
     Disadvantages and Limitations of
          Composite Materials
• Properties of many important composites are
  anisotropic - the properties differ depending on the
  direction in which they are measured – this may be
  an advantage or a disadvantage
• Many of the polymer-based composites are subject to
  attack by chemicals or solvents, just as the polymers
  themselves are susceptible to attack
• Composite materials are generally expensive
• Manufacturing methods for shaping composite
  materials are often slow and costly

     Manufacturing Processes
       Prof David Veazie
                                 Composites Lecture
           One Possible Classification of
               Composite Materials
1. Traditional composites – composite materials that
   occur in nature or have been produced by
   civilizations for many years
    Examples: wood, concrete, asphalt
2. Synthetic composites - modern material systems
   normally associated with the manufacturing
   industries, in which the components are first
   produced separately and then combined in a
   controlled way to achieve the desired structure,
   properties, and part geometry

     Manufacturing Processes
       Prof David Veazie
                                 Composites Lecture
    Components in a Composite Material
•   Nearly all composite materials consist of two
    phases:
    1. Primary phase - forms the matrix within which the
       secondary phase is imbedded
    2. Secondary phase - imbedded phase sometimes
       referred to as a reinforcing agent, because it
       usually serves to strengthen the composite
        The reinforcing phase may be in the form of
           fibers, particles, or various other geometries


      Manufacturing Processes
        Prof David Veazie
                                   Composites Lecture
           Our Classification Scheme for
               Composite Materials
1. Metal Matrix Composites (MMCs) - mixtures of
   ceramics and metals, such as cemented carbides
   and other cermets
2. Ceramic Matrix Composites (CMCs) - Al2O3 and SiC
   imbedded with fibers to improve properties,
   especially in high temperature applications
     The least common composite matrix
3. Polymer Matrix Composites (PMCs) - thermosetting
   resins are widely used in PMCs
     Examples: epoxy and polyester with fiber
      reinforcement, and phenolic with powders

     Manufacturing Processes
       Prof David Veazie
                               Composites Lecture
        Functions of the Matrix Material
               (Primary Phase)
• Provides the bulk form of the part or product made of
  the composite material
• Holds the imbedded phase in place, usually
  enclosing and often concealing it
• When a load is applied, the matrix shares the load
  with the secondary phase, in some cases deforming
  so that the stress is essentially born by the
  reinforcing agent



     Manufacturing Processes
       Prof David Veazie
                                  Composites Lecture
                       The Reinforcing Phase
                        (Secondary Phase)
• Function is to reinforce the primary phase
• Imbedded phase is most commonly one of the
  following shapes:
    Fibers
    Particles
    Flakes
• In addition, the secondary phase can take the form of
  an infiltrated phase in a skeletal or porous matrix
    Example: a powder metallurgy part infiltrated with
      polymer

     Manufacturing Processes
       Prof David Veazie
                                     Composites Lecture
Figure 9.1 - Possible physical shapes of imbedded phases in
    composite materials: (a) fiber, (b) particle, and (c) flake




  Manufacturing Processes
    Prof David Veazie
                                     Composites Lecture
                                Fibers
Filaments of reinforcing material, usually circular in
   cross-section
• Diameters range from less than 0.0025 mm to about
   0.13 mm, depending on material
• Filaments provide greatest opportunity for strength
   enhancement of composites
     The filament form of most materials is significantly
      stronger than the bulk form
     As diameter is reduced, the material becomes
      oriented in the fiber axis direction and probability
      of defects in the structure decreases significantly

      Manufacturing Processes
        Prof David Veazie
                                         Composites Lecture
   Continuous vs. Discontinuous Fibers
• Continuous fibers - very long; in theory, they offer a
  continuous path by which a load can be carried by
  the composite part
• Discontinuous fibers (chopped sections of continuous
  fibers) - short lengths (L/D = roughly 100)
    Important type of discontinuous fiber are
     whiskers - hair-like single crystals with diameters
     down to about 0.001 mm (0.00004 in.) with very
     high strength


     Manufacturing Processes
       Prof David Veazie
                                  Composites Lecture
       Fiber Orientation – Three Cases
• One-dimensional reinforcement, in which maximum
  strength and stiffness are obtained in the direction of
  the fiber
• Planar reinforcement, in some cases in the form of a
  two-dimensional woven fabric
• Random or three-dimensional in which the composite
  material tends to possess isotropic properties




     Manufacturing Processes
       Prof David Veazie
                                   Composites Lecture
          Figure 9.3 - Fiber orientation in composite materials:
(a) one-dimensional, continuous fibers; (b) planar, continuous fibers in
     the form of a woven fabric; and (c) random, discontinuous fibers




       Manufacturing Processes
         Prof David Veazie
                                           Composites Lecture
                               Materials for Fibers
• Fiber materials in fiber-reinforced composites:
    Glass – most widely used filament
    Carbon – high elastic modulus
    Boron – very high elastic modulus
    Polymers - Kevlar
    Ceramics – SiC and Al2O3
    Metals - steel
• The most important commercial use of fibers is in
  polymer composites

     Manufacturing Processes
       Prof David Veazie
                                             Composites Lecture
                                Particles and Flakes
• A second common shape of imbedded phase is
  particulate, ranging in size from microscopic to
  macroscopic
• Flakes are basically two-dimensional particles - small
  flat platelets
• The distribution of particles in the composite matrix is
  random, and therefore strength and other properties
  of the composite material are usually isotropic
• Strengthening mechanism depends on particle size


      Manufacturing Processes
        Prof David Veazie
                                              Composites Lecture
                                The Interface
• There is always an interface between constituent
  phases in a composite material
• For the composite to operate effectively, the phases
  must bond where they join at the interface




 Figure 9.4 - Interfaces between phases in a composite material:
 (a) direct bonding between primary and secondary phases

      Manufacturing Processes
        Prof David Veazie
                                           Composites Lecture
                                Interphase
• In some cases, a third ingredient must be added to
  achieve bonding of primary and secondary phases
• Called an interphase, this third ingredient can be
  thought of as an adhesive




 Figure 9.4 - Interfaces between phases: (b) addition of a third
 ingredient to bond the primary phases and form an interphase


      Manufacturing Processes
        Prof David Veazie
                                         Composites Lecture
                                Another Interphase
  Interphase consisting of a solution of primary and
  secondary phases




Figure 9.4 - Interfaces and interphases between phases in a
   composite material: (c) formation of an interphase by solution of
   the primary and secondary phases at their boundary


      Manufacturing Processes
        Prof David Veazie
                                             Composites Lecture
     Properties of Composite Materials
• In selecting a composite material, an optimum
  combination of properties is usually sought, rather
  than one particular property
    Example: fuselage and wings of an aircraft must
     be lightweight and be strong, stiff, and tough
       Several fiber-reinforced polymers possess this
        combination of properties
    Example: natural rubber alone is relatively weak
       Adding significant amounts of carbon black to
        NR increases its strength dramatically

     Manufacturing Processes
       Prof David Veazie
                                 Composites Lecture
            Properties are Determined by
                   Three Factors:
1. The materials used as component phases in the
   composite
2. The geometric shapes of the constituents and
   resulting structure of the composite system
3. The manner in which the phases interact with one
   another




     Manufacturing Processes
       Prof David Veazie
                                 Composites Lecture
Figure 9.5 - (a) Model of a fiber-reinforced composite material
   showing direction in which elastic modulus is being estimated by
   the rule of mixtures (b) Stress-strain relationships for the
   composite material and its constituents. The fiber is stiff but
   brittle, while the matrix (commonly a polymer) is soft but ductile.

       Manufacturing Processes
         Prof David Veazie
                                           Composites Lecture
Figure 9.6 - Variation in elastic modulus and tensile strength as a
   function of direction of measurement relative to longitudinal axis
   of carbon fiber-reinforced epoxy composite


      Manufacturing Processes
        Prof David Veazie
                                          Composites Lecture
           Fibers Illustrate Importance of
                 Geometric Shape
• Most materials have tensile strengths several times
  greater as fibers than in bulk
• By imbedding the fibers in a polymer matrix, a
  composite material is obtained that avoids the
  problems of fibers but utilizes their strengths
    The matrix provides the bulk shape to protect the
     fiber surfaces and resist buckling
    When a load is applied, the low-strength matrix
     deforms and distributes the stress to the
     high-strength fibers

     Manufacturing Processes
       Prof David Veazie
                                  Composites Lecture
              Other Composite Structures
• Laminar composite structure – conventional
• Sandwich structure
• Honeycomb sandwich structure




     Manufacturing Processes
       Prof David Veazie
                                Composites Lecture
            Laminar Composite Structure
Two or more layers bonded together in an integral piece
• Example: plywood in which layers are the same
  wood, but grains are oriented differently to increase
  overall strength of the laminated piece




                               Figure 9.7 - Laminar composite
                               structures: (a) conventional laminar
                               structure



     Manufacturing Processes
       Prof David Veazie
                                         Composites Lecture
      Sandwich Structure – Foam Core
Consists of a relatively thick core of low density foam
  bonded on both faces to thin sheets of a different
  material




                                Figure 9.7 - Laminar
                                composite structures: (b)
                                sandwich structure using foam
                                core


      Manufacturing Processes
        Prof David Veazie
                                      Composites Lecture
 Sandwich Structure – Honeycomb Core
• An alternative to foam core
• Either foam or honeycomb achieves high
  strength-to-weight and stiffness-to-weight ratios




                                Figure 9.7 - Laminar
                                composite structures: (c)
                                sandwich structure using
                                honeycomb core


     Manufacturing Processes
       Prof David Veazie
                                   Composites Lecture
   Other Laminar Composite Structures
• Automotive tires - consists of multiple layers bonded
  together
• FRPs - multi-layered fiber-reinforced plastic panels
  for aircraft, automobile body panels, boat hulls
• Printed circuit boards - layers of reinforced plastic
  and copper for electrical conductivity and insulation
• Snow skis - composite structures consisting of layers
  of metals, particle board, and phenolic plastic
• Windshield glass - two layers of glass on either side
  of a sheet of tough plastic


     Manufacturing Processes
       Prof David Veazie
                                  Composites Lecture
     Metal Matrix Composites (MMCs)
A metal matrix reinforced by a second phase
• Reinforcing phases:
   1. Particles of ceramic (these MMCs are commonly
      called cermets)
   2. Fibers of various materials: other metals,
      ceramics, carbon, and boron




     Manufacturing Processes
       Prof David Veazie
                               Composites Lecture
                               Cermets
MMC with ceramic contained in a metallic matrix
• The ceramic often dominates the mixture,
  sometimes up to 96% by volume
• Bonding can be enhanced by slight solubility
  between phases at elevated temperatures used in
  processing
• Cermets can be subdivided into
  1. Cemented carbides – most common
  2. Oxide-based cermets – less common


     Manufacturing Processes
       Prof David Veazie
                                         Composites Lecture
                               Cemented Carbides
One or more carbide compounds bonded in a metallic
  matrix
• The term cermet is not used for all of these materials,
  even though it is technically correct
• Common cemented carbides are based on tungsten
  carbide (WC), titanium carbide (TiC), and chromium
  carbide (Cr3C2)
• Tantalum carbide (TaC) and others are less common
• Metallic binders: usually cobalt (Co) or nickel (Ni)



     Manufacturing Processes
       Prof David Veazie
                                           Composites Lecture
Figure 9.8 - Photomicrograph (about 1500X) of cemented carbide
   with 85% WC and 15% Co (photo courtesy of Kennametal Inc.)


     Manufacturing Processes
       Prof David Veazie
                                     Composites Lecture
Figure 9.9 - Typical plot of hardness and transverse rupture
            strength as a function of cobalt content

  Manufacturing Processes
    Prof David Veazie
                                     Composites Lecture
    Applications of Cemented Carbides
• Tungsten carbide cermets (Co binder) - cutting tools
  are most common; other: wire drawing dies, rock
  drilling bits and other mining tools, dies for powder
  metallurgy, indenters for hardness testers
• Titanium carbide cermets (Ni binder) - high
  temperature applications such as gas-turbine nozzle
  vanes, valve seats, thermocouple protection tubes,
  torch tips, cutting tools for steels
• Chromium carbides cermets (Ni binder) - gage
  blocks, valve liners, spray nozzles, bearing seal rings

     Manufacturing Processes
       Prof David Veazie
                                   Composites Lecture
    Ceramic Matrix Composites (CMCs)
A ceramic primary phase imbedded with a secondary
  phase, which usually consists of fibers
• Attractive properties of ceramics: high stiffness,
  hardness, hot hardness, and compressive strength;
  and relatively low density
• Weaknesses of ceramics: low toughness and bulk
  tensile strength, susceptibility to thermal cracking
• CMCs represent an attempt to retain the desirable
  properties of ceramics while compensating for their
  weaknesses

     Manufacturing Processes
       Prof David Veazie
                                  Composites Lecture
   Polymer Matrix Composites (PMCs)
A polymer primary phase in which a secondary phase is
  imbedded as fibers, particles, or flakes
• Commercially, PMCs are more important than MMCs
  or CMCs
• Examples: most plastic molding compounds, rubber
  reinforced with carbon black, and fiber-reinforced
  polymers (FRPs)
• FRPs are most closely identified with the term
  composite


     Manufacturing Processes
       Prof David Veazie
                                Composites Lecture
    Fiber-Reinforced Polymers (FRPs)
A PMC consisting of a polymer matrix imbedded with
  high-strength fibers
• Polymer matrix materials:
    Usually a thermosetting (TS) plastic such as
     unsaturated polyester or epoxy
    Can also be thermoplastic (TP), such as nylons
     (polyamides), polycarbonate, polystyrene, and
     polyvinylchloride
    Fiber reinforcement is widely used in rubber
     products such as tires and conveyor belts

     Manufacturing Processes
       Prof David Veazie
                                 Composites Lecture
                               Fibers in PMCs
• Various forms: discontinuous (chopped), continuous,
  or woven as a fabric
• Principal fiber materials in FRPs are glass, carbon,
  and Kevlar 49
• Less common fibers include boron, SiC, and Al2O3,
  and steel
• Glass (in particular E-glass) is the most common fiber
  material in today's FRPs; its use to reinforce plastics
  dates from around 1920


     Manufacturing Processes
       Prof David Veazie
                                          Composites Lecture
                     Common FRP Structure
• Most widely used form of FRP is a laminar structure,
  made by stacking and bonding thin layers of fiber and
  polymer until desired thickness is obtained
• By varying fiber orientation among layers, a specified
  level of anisotropy in properties can be achieved in
  the laminate
• Applications: parts of thin cross-section, such as
  aircraft wing and fuselage sections, automobile and
  truck body panels, and boat hulls


     Manufacturing Processes
       Prof David Veazie
                                  Composites Lecture
                               FRP Properties
• High strength-to-weight and modulus-to-weight ratios
• Low specific gravity - a typical FRP weighs only
  about 1/5 as much as steel; yet, strength and
  modulus are comparable in fiber direction
• Good fatigue strength
• Good corrosion resistance, although polymers are
  soluble in various chemicals
• Low thermal expansion - for many FRPs, leading to
  good dimensional stability
• Significant anisotropy in properties

     Manufacturing Processes
       Prof David Veazie
                                          Composites Lecture
                               FRP Applications
• Aerospace – much of the structural weight of todays
  airplanes and helicopters consist of advanced FRPs
• Automotive – somebody panels for cars and truck
  cabs
    Continued use of low-carbon sheet steel in cars is
     evidence of its low cost and ease of processing
• Sports and recreation
    Fiberglass reinforced plastic has been used for
     boat hulls since the 1940s
    Fishing rods, tennis rackets, golf club shafts,
     helmets, skis, bows and arrows.
     Manufacturing Processes
       Prof David Veazie
                                           Composites Lecture
 Figure 9.11 - Composite materials in the Boeing 757
   (courtesy of Boeing Commercial Airplane Group)

Manufacturing Processes
  Prof David Veazie
                                 Composites Lecture
     Other Polymer Matrix Composites
• In addition to FRPs, other PMCs contain particles,
  flakes, and short fibers as the secondary phase
• Called fillers when used in molding compounds
• Two categories:
   1. Reinforcing fillers – used to strengthen or
      otherwise improve mechanical properties
       Examples: wood flour in phenolic and amino
         resins; and carbon black in rubber
   2. Extenders – used to increase bulk and reduce
      cost per unit weight, but little or no effect on
      mechanical properties

     Manufacturing Processes
       Prof David Veazie
                                   Composites Lecture
Guide to Processing Composite Materials
• The two phases are typically produced separately
  before being combined into the composite part
• Processing techniques to fabricate MMC and CMC
  components are similar to those used for powdered
  metals and ceramics
• Molding processes are commonly used for PMCs
  with particles and chopped fibers
• Specialized processes have been developed for
  FRPs


     Manufacturing Processes
       Prof David Veazie
                                Composites Lecture

								
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