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  • 1. COMPOSITE MATERIALS
    • Technology and Classification of Composite Materials
    • Metal Matrix Composites
    • Ceramic Matrix Composites
    • Polymer Matrix Composites
    • Guide to Processing Composite Materials
  • 2. Composite Material Defined
    • A materials system composed of two or more distinct phases whose combination produces aggregate properties different from those of its constituents
    • Examples:
      • Cemented carbides (WC with Co binder)
      • Plastic molding compounds with fillers
      • Rubber mixed with carbon black
      • Wood (a natural composite as distinguished from a synthesized composite)
  • 3. Why Composites are Important
    • Composites can be very strong and stiff, yet very light in weight
      • Strength‑to‑weight and stiffness‑to‑weight ratios are several times greater than steel or aluminum
    • Fatigue properties are generally better than for common engineering metals
    • Toughness is often greater
    • Possible to achieve combinations of properties not attainable with metals, ceramics, or polymers alone
  • 4. Disadvantages and Limitations
    • Properties of many important composites are anisotropic
      • May be an advantage or a disadvantage
    • Many polymer‑based composites are subject to attack by chemicals or solvents
      • Just as the polymers themselves are susceptible
    • Composite materials are generally expensive
    • Manufacturing methods for shaping composite materials are often slow and costly
  • 5. Possible Classification of Composites
    • Traditional composites – composite materials that occur in nature or have been produced by civilizations for many years
      • Examples: wood, concrete, asphalt
    • Synthetic composites - modern material systems normally associated with the manufacturing industries
      • Components are first produced separately and then combined to achieve the desired structure, properties, and part geometry
  • 6. Components in a Composite Material
    • Most composite materials consist of two phases:
    • Primary phase - forms the matrix within which the secondary phase is imbedded
    • Secondary phase - imbedded phase sometimes referred to as a reinforcing agent , because it usually strengthens the composite material
      • The reinforcing phase may be in the form of fibers, particles, or various other geometries
  • 7. Our Classification of Composite Materials
    • Metal Matrix Composites (MMCs) ‑ mixtures of ceramics and metals, such as cemented carbides and other cermets
    • Ceramic Matrix Composites (CMCs) ‑ Al 2 O 3 and SiC imbedded with fibers to improve properties
    • Polymer Matrix Composites (PMCs) ‑ polymer resins imbedded with filler or reinforcing agent
      • Examples: epoxy and polyester with fiber reinforcement, and phenolic with powders
  • 8. 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
  • 9. Reinforcing Phase
    • Function is to reinforce the primary phase
    • Reinforcing phase (imbedded in the matrix) is most commonly one of the following shapes: fibers, particles, or flakes
    • Also, secondary phase can take the form of an infiltrated phase in a skeletal or porous matrix
      • Example: a powder metallurgy part infiltrated with polymer
  • 10. Physical Shapes of Imbedded Phase
    • Possible physical shapes of imbedded phases in composite materials: (a) fiber, (b) particle, and (c) flake
  • 11. Fibers
    • Filaments of reinforcing material, usually circular in cross section
    • Diameters from ~ 0.0025 mm to about 0.13 mm
    • Filaments provide greatest opportunity for strength enhancement of composites
      • 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
  • 12. Continuous Fibers 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)
      • Whiskers = discontinuous fibers of hair-like single crystals with diameters down to about 0.001 mm (0.00004 in) and very high strength
  • 13. 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
  • 14. Fiber Orientation
    • 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
  • 15. 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 Al 2 O 3
      • Metals - steel
    • Most important commercial use of fibers is in polymer composites
  • 16. 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
    • Distribution of particles in the matrix is random
      • Strength and other properties of the composite material are usually isotropic
  • 17. Interface between Constituent Phases in Composite Material
    • For the composite to function, the phases must bond where they join at the interface
    • Direct bonding between primary and secondary phases
  • 18. Interphase
    • In some cases, a third ingredient must be added to bond primary and secondary phases
    • Called an interphase , it is like an adhesive
  • 19. Alternative Interphase Form
    • Formation of an interphase consisting of a solution of primary and secondary phases at their boundary
  • 20. Properties of Composite Materials
    • In selecting a composite material, an optimum combination of properties is often sought, rather than one particular property
      • Example: fuselage and wings of an aircraft must be lightweight, strong, stiff, and tough
        • Several fiber‑reinforced polymers possess these properties
      • Example: natural rubber alone is relatively weak
        • Adding carbon black increases its strength
  • 21. Three Factors that Determine Properties
    • Materials used as component phases in the composite
    • Geometric shapes of the constituents and resulting structure of the composite system
    • How the phases interact with one another
  • 22. Example: Fiber Reinforced Polymer
    • Model of fiber‑reinforced composite material showing direction in which elastic modulus is being estimated by the rule of mixtures
  • 23. Example: Fiber Reinforced Polymer (continued)
    • 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
  • 24. Variations in Strength and Stiffness
    • Variation in elastic modulus and tensile strength as a function of direction relative to longitudinal axis of carbon fiber‑reinforced epoxy composite
  • 25. Importance of Geometric Shape: Fibers
    • Most materials have tensile strengths several times greater as fibers than as bulk materials
    • By imbedding the fibers in a polymer matrix, a composite material is obtained that avoids the problems of fibers but utilizes their strengths
      • 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
  • 26. Other Composite Structures
    • Laminar composite structure – conventional
    • Sandwich structure
    • Honeycomb sandwich structure
  • 27. Laminar Composite Structure
    • Conventional laminar structure - two or more layers bonded together in an integral piece
    • Example: plywood, in which layers are the same wood, but grains oriented differently to increase overall strength
  • 28. Sandwich Structure: Foam Core
    • Relatively thick core of low density foam bonded on both faces to thin sheets of a different material
  • 29. Sandwich Structure: Honeycomb Core
    • Alternative to foam core
    • Foam or honeycomb achieve high ratios of strength‑to‑weight and stiffness‑to‑weight
  • 30. Other Laminar Composite Structures
    • FRPs - multi‑layered, fiber‑reinforced plastic panels for aircraft, boat hulls, other products
    • Printed circuit boards - layers of reinforced copper and plastic for electrical conductivity and insulation, respectively
    • Snow skis - layers of metals, particle board, and phenolic plastic
    • Windshield glass - two layers of glass on either side of a sheet of tough plastic
  • 31. Metal Matrix Composites (MMCs)
    • Metal matrix reinforced by a second phase
    • Reinforcing phases:
      • Particles of ceramic
        • These MMCs are commonly called cermets
      • Fibers of various materials
        • Other metals, ceramics, carbon, and boron
  • 32. 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
      • Cemented carbides – most common
      • Oxide‑based cermets – less common
  • 33. Cemented Carbides
    • One or more carbide compounds bonded in a metallic matrix
    • Common cemented carbides are based on tungsten carbide (WC), titanium carbide (TiC), and chromium carbide (Cr 3 C 2 )
      • Tantalum carbide (TaC) and others are less common
    • Metallic binders: usually cobalt (Co) or nickel (Ni)
  • 34.
    • Photomicrograph (about 1500X) of cemented carbide with 85% WC and 15% Co (photo courtesty of Kennametal Inc.)
    Cemented Carbide
  • 35.
    • Typical plot of hardness and transverse rupture strength as a function of cobalt content
    Cemented Carbide Properties
  • 36. Applications of Cemented Carbides
    • Tungsten carbide cermets (Co binder)
      • Cutting tools, wire drawing dies, rock drilling bits, powder metal dies, indenters for hardness testers
    • Titanium carbide cermets (Ni binder)
      • Cutting tools; high temperature applications such as gas‑turbine nozzle vanes
    • Chromium carbide cermets (Ni binder)
      • Gage blocks, valve liners, spray nozzles
  • 37. Ceramic Matrix Composites (CMCs)
    • Ceramic primary phase imbedded with a secondary phase, usually consisting 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
  • 38. Ceramic Matrix Composite
    • Photomicrograph (about 3000X) of fracture surface of SiC whisker reinforced Al 2 O 3 (photo courtesy of Greenleaf Corp.)
  • 39. Polymer Matrix Composites (PMCs)
    • 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)
  • 40. Fiber‑Reinforced Polymers (FRPs)
    • PMC consisting of a polymer matrix imbedded with high‑strength fibers
    • Polymer matrix materials:
      • Usually a thermosetting plastic such as unsaturated polyester or epoxy
      • Can also be thermoplastic, such as nylons (polyamides), polycarbonate, polystyrene, and polyvinylchloride
      • Fiber reinforcement is widely used in rubber products such as tires and conveyor belts
  • 41. 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 Al 2 O 3 , 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
  • 42. Common FRP Structures
    • 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: boat hulls, aircraft wing and fuselage sections, automobile and truck body panels
  • 43. FRP Properties
    • High strength‑to‑weight and modulus‑to‑weight ratios
      • 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
  • 44. FRP Applications
    • Aerospace – much of the structural weight of today’s airplanes and helicopters consist of advanced FRPs
      • Example: Boeing 787
    • Automotive – some body panels for cars and truck cabs
      • Low-carbon sheet steel still widely used due to its low cost and ease of processing
    • Sports and recreation
      • FRPs used for boat hulls since 1940s
      • Fishing rods, tennis rackets, golf club shafts, helmets, skis, bows and arrows
  • 45. Other Polymer Matrix Composites
    • Other PMCs contain particles, flakes, and short fibers
    • Called fillers when used in molding compounds
    • Two categories:
      • Reinforcing fillers – used to strengthen or otherwise improve mechanical properties
      • Extenders – used to increase bulk and reduce cost per unit weight, with little or no effect on mechanical properties
  • 46. 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