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INTRODUCTION TO ADVANCED COMPOSITE MATERIALS. Dr. ZAFFAR M. KHAN. Fabrication. Introduction. Processing/NDT. INDUSTRIAL COMPOSITES. Industrial Application. Design Analysis. Historical background, nature and advantages of composites Types of matrices Fibers and their characterization
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INTRODUCTION TO ADVANCEDCOMPOSITE MATERIALS Dr. ZAFFAR M. KHAN
Fabrication Introduction Processing/NDT INDUSTRIAL COMPOSITES Industrial Application Design Analysis
Historical background, nature and advantages of composites Types of matrices Fibers and their characterization Physical and mechanical properties of composites Application in aircraft, sports goods, medical, civil engineering and automobile industries Scope
Relative importance of Engineering Materials with respect to time period
Composite Materials • Composite materials are macroscopic combination of two or more materials each having distinct properties. It is composed of: • Matrix (Black) • Reinforcement (White) • Iinterphase
Advantages of Composite Materials • Significant weight saving which increases payload and/or range along with fuel saving. • Maximum specific strength and stiffness make them lighter than aluminum, stronger than steel. • Permits aero-elastic tailoring of structural components. • Flexibility of Design • Integrated structures diminishes application of rivets. • Enhanced fatigue life. • Absence of corrosion. Reduced operational, manufacturing and maintenance cost.
Aero-elastic Composite Structure • The composite structure is tailored to meet varying aerodynamic requirements in aircrafts, cars wind and rotor blades. It reduces drag and enhances energy conservation.
Influence of Vibrations on Composites • The vibration damping characteristics • of composites are far superior as • Compared to metals for following • reasons; • Matrix visco-elastic effects and • micro-cracking • Blunting of crack by in fibers • transverse direction • Debonding and sliding of fibers • in axial direction.
Integrated Structure • Integrated composite structure reduces rivets and associated weight which leads to integrated structure of aircraft, automobiles and other engineering systems.
Roles: Binds and holds reinforcemaent together Determines composite shape and geometry Transfers stresses to reinforcement Types: Ceramic (Temp < 6000°F) Metallic (Temp < 4000°F) Polymeric (Temp < 600°F) Determine: Environmental resistance Shelf Life Compressive & transverse mechanical properties of composite Matrix Constituent
Manufacturing Process: Cast from slurries or processed into shape with organic binder and then fired/ sintered/ cured at very high temperature. Examples: Silicon carbide filament in Silicate matrix Boron carbide in Alumina matrix Aluminum oxide in Alumina matrix Metal particles in ceramic matrix CERMETS Applications: Rocket nose cone and Nozzle Combustion Chamber Skin of space plane/ spacecraft Problem Areas: Interface problem Ceramic MatrixOxides, carbides, nitrides, borides and silicates characterizes high degree of thermal and dimensional stability.
Relatively lower densities of aluminum, titanium and magnesium are reinforced by high strength/ stiffness fibers. Organic fibers are not used due to high processing temperatures. Most common fibers are; Metal fibers of beryllium, molybdenum, steel and tungsten Boron, silicon carbide, silicon boride coated fine wires Whiskers of aluminum oxide, boron carbide or silicon carbide Manufacturing Process: Metal matrix may be coated onto fibers by electro deposition, vapor deposition or plasma spray followed by hot pressing Fibers can be infiltrated with liquid metal under high process Fiber pressed between metal foils and sintered with powder metals Examples: Aluminum, titanium alloys, silver, magnesium, cobalt and copper matrices Applications: Space shuttle, piston ring, connecting rods, suspension components Metal Matrix
Thermoplastics: Softens when heated and hardens when cooled. Can be recycled. Relatively tough Low dimensional stability. Styrenes, Vinyls, Acrylics, Thermosets: Hardens when heated. Composed of long molecular cross links. Cannot be recycled. Relatively brittle. Relatively greater dimensional tolerance. Epoxies, urathanes, phenolics. Polymeric Matrix Composed of long chains of hydro carbons
Comparison of Thermoset Versus Thermoplastic PROPERTY THERMOSET THERMOPLASTIC (FIBERITE 931 EPOXY) (ICI APC-2 PEEK) Melt Viscosity Low High Fiber Impregnation Easy Difficult Prepreg Tack Good None Prepreg Drape Good Poor Prepreg Stability at 0° F 6 mos. -1 yr. Indefinite Processing Cycle 1-6 Hrs 15 sec 6 hr Processing Temperature 350° F 700° F Mechanical Properties Good Good Environmental Durability Good Exceptional Damage Tolerance Average Good Database Large Average
Temperature Response of Ceramic, Metallic & Polymeric Composites • Polymeric composites have maximum specific strength but has poor strength at elevated temperatures. Metal and ceramic composites retain their lower mechanical properties at elevated temperature. Selection of composites is determined by environmental temperatures.
Properties of Polymeric Matrices • EPOXY (THERMOSET) • Most widely used matrix in hi-tech applications • Outstanding adhesion • Low shrinkage during cure • Easy to process forgiving • Strong, tough • Extensive, reliable data base • POLYESTER (THERMOSET) • Most widely used matrix for less demanding applications • High shrinkage during cure • Poorer adhesion than epoxy • Very easy to process ; lower pressures and temperatures and shorter cure cycles than epoxy. • Lower cost than epoxy • In general, poorer properties than epoxy (and less expensive) • POLYIMIDE (THERMOSET) • Primarily for service at high temperature i.e. 600 F • Higher cost than epoxy • More difficult to process than epoxy ; more complex cure cycles, requires higher temperatures are pressures • Dark colours only • High brittleness • Propreg does not drape well ( tends to be a little shiff) • BISMALEIMIDE (THERMOSET) • Proposed to fill the gap between polyimide and high temperature epoxies i.e. 450 – 500 degrees F • Better strength than epoxy at high temperature • It has relatively simple are cycles more like epoxy than polyimide (Thus it is relatively easy to process • Application in X-wing vertical take off/landing sibors by Aircraft /copter.
PHENOLIC (THERMOSET) • Expensive and difficult to process; requires high cure pressure • Good electrical resistance • Self extinguishing and not toxic, thus it has received interest for aircraft interiors (for example : • graphite fabric reinforced phenolic facings for honeycomb floor panels ) • URETHANE (THERMOPLASTIC) • Good toughness and abrasion resistance • Easily foamed and low heat transfer (thus, a common use is insulation ) • Limited in service temperature • Commonly used in Reuction Injection Molding (RIM) to produce strong, stiff, light weight “Self-skinned” structures • Reinforced with carbon fiber Ejection seats • PEEK (THERMOPLASTIC) • Tough, high impact resistance, high fracture toughness • Excellent abrasion resistance • Excellent solvent resistance • Low moisture absorption • Very high cost • New, not much data available • Requires very high processing temperature (600 degrees F) which complicates manufacturing • Prepregs are stiff (no drape); thus, flat laminates must first be made, then laminates must be formed to shape with high temp and pressure. Manufacturing with prepregs is still in development stage.
Evolution of Epoxy Resin • Poly functional epoxy resin contains more than two epoxide group • FIRST GENERATION EPOXIES: • Example: NARMCO 5208, CIBA GEIGY – 914 • Better dimensional stabile but inherently brittle. • Composed of: • Tetra Glycidyl Derivative (Wt Fraction : 38.2 %) • Triglycidyl Ether (33.4%) • Dicyandiamide (5.0%) • Poly Ether Sul Phone (23.4) • SECOND GENERATION EPOXIES: • Example:NARMCO 5245, CIBA GEIGY-924 • Addition of CTBN to original formulation • Better damage tolerance, reduced hot /wet performance. • Lead to phase separation which imparts desired toughness.
Reinforcement Constituent • Particulate: Good compression strength but poor tensile properties, and particles in cement. • Flakes: Effective solvent resistant but difficult fabrication. • Whiskers: High degree of strength but poor crack stopping properties. • Fibers: Better structural properties, crack stopping properties, flexibility of design requirement by changing orientation of fibers 0°, +45°, 90° Stacking sequence Types of fibers i.e. glass, carbon, kevlar & carbon
Milled Carbon Fibers Carbon Fiber Pellets Chopped Carbon Fibers Carbon Fiber Mat
Microstructure of Carbon Fibers • The covalently bonded aromatic chains of carbon fiber in the axial direction are held together by weak Wander wall bonds in transverse direction. The alignment of chains in axial direction determines their outstanding strength.
Fabrication of Carbon Fiber • Carbonization: 200-250°F • Oxidation: 1000°C • Graphitization: 2500-3000°C Etching of fiber surface
Processing Temperature • The higher degree of temperature and tension during graphitization process leads to greater alignment of carbon chains and superior mechanical properties of carbon fibers, T-300 (Boeing-727, 737, 747 and Airbus-310) and T-800 (Boeing-777, Airbus-380, Osprey V22 and JSF).
Variation of Mechanical Properties of Carbon Fiber With Respect to Temperature
Kevlar Fibers • Kevlar: Aromatic carbon chains are held together by amide group (-CH-NH-). • Concentrated solution in strong mineral acid is processed through spinnerets into neutralizing bath. The fibers are washed, dried and heated in nitrogen at high temperature under tension.
Prepreg Prepreg: The resin is impregnated in fibers by passing fibers through resin bath, oven and driers. The resin is advanced from A to B stage. The ready to mold material is stored for application.
