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INTRODUCTION TO ADVANCEDINTRODUCTION TO ADVANCEDCOMPOSITE MATERIALSCOMPOSITE MATERIALS
Dr. ZAFFAR M. KHAN
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INDUSTRIALCOMPOSITES
Fabrication
Introduction
Design AnalysisIndustrial Application
Processing/NDT
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Scope
Historical background, nature and advantages of compositesTypes of matrices Fibers and their characterizationPhysical and mechanical properties of compositesApplication in aircraft, sports goods, medical, civil engineering and automobile industries
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First Composite Solo Flight
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Relative importance of Engineering Materials with respect to time period
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Trends of Carbon Fiber Composite Growth
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Carbon Composites for Defence Systems
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Composite Materials
Composite materials are macroscopic combination of two or more materials each having distinct properties. It is composed of:
1. Matrix (Black)
2. Reinforcement (White)
3. Iinterphase
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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 DesignIntegrated structures diminishes application of rivets.Enhanced fatigue life.Absence of corrosion.
Reduced operational, manufacturing and maintenance cost.
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Comparison of Composites with Metals
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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.
Flexibility of Composite Design
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The vibration damping characteristicsof composites are far superior asCompared to metals for followingreasons;1. Matrix visco-elastic effects and
micro-cracking2. Blunting of crack by in fibers
transverse direction3. Debonding and sliding of fibers
in axial direction.
Influence of Vibrations on Composites
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Integrated Structure
Integrated composite structure reduces rivets and associated weight which leads to integrated structure of aircraft, automobiles and other engineering systems.
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Matrix Constituent
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 resistanceShelf LifeCompressive & transverse mechanical properties of composite
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Ceramic MatrixOxides, carbides, nitrides, borides and silicates characterizes high degree
of thermal and dimensional stability.
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 matrixBoron carbide in Alumina matrixAluminum oxide in Alumina matrixMetal particles in ceramic matrix CERMETS
Applications:Rocket nose cone and NozzleCombustion ChamberSkin of space plane/ spacecraft
Problem Areas:Interface problem
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Metal Matrix
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 tungstenBoron, silicon carbide, silicon boride coated fine wiresWhiskers 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 pressingFibers can be infiltrated with liquid metal under high processFiber 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
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Polymeric Matrix
Thermoplastics:Softens when heated and hardens when cooled.Can be recycled.Relatively toughLow 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.
Composed of long chains of hydro carbons
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Comparison of Thermoset Versus Thermoplastic
PROPERTY THERMOSET THERMOPLASTIC(FIBERITE 931 EPOXY) (ICI APC-2 PEEK)
Melt Viscosity Low HighFiber Impregnation Easy DifficultPrepreg Tack Good NonePrepreg Drape Good PoorPrepreg Stability at 0° F 6 mos. -1 yr. IndefiniteProcessing Cycle 1-6 Hrs 15 sec 6 hrProcessing Temperature 350° F 700° FMechanical Properties Good GoodEnvironmental Durability Good ExceptionalDamage Tolerance Average GoodDatabase Large Average
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Structural Performance Ranking of Materials
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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.
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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 basePOLYESTER (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.
Properties of Polymeric Matrices
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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 resistanceEasily 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” structuresReinforced with carbon fiber Ejection seatsPEEK (THERMOPLASTIC)Tough, high impact resistance, high fracture toughness Excellent abrasion resistanceExcellent solvent resistanceLow moisture absorption Very high costNew, not much data availableRequires 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.
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Thermoset Composites
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Thermoplastic Composites
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Thermoplastic Composites
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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.
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Reinforcement Constituent
1. Particulate: Good compression strength but poor tensile properties, and particles in cement.
2. Flakes: Effective solvent resistant but difficult fabrication.
3. Whiskers: High degree of strength but poor crack stopping properties.
4. Fibers: Better structural properties, crack stopping properties, flexibility of design requirement by changing orientation of fibers 0°, +45°, 90°Stacking sequenceTypes of fibers i.e. glass, carbon, kevlar & carbon
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Milled Carbon Fibers
Chopped Carbon Fibers
Carbon Fiber Pellets
Carbon Fiber Mat
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Micrographs of Carbon, Kevlar and Glass Fibers
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Properties of High Performance Synthetic Fibers
CARBON
(2-Dimension)
KEVLAR
(1 Dimension)
GLASS
(3 Dimension)
ADVANTAGES Max specific strength
Max specific modulus
High temp resistance
Tough
Light weight
No galvanic corrosion
High temp resistance
No galvanic corrosion
Low notch sensitivity
DISADVANTAGES Expensive
Low impact resistance
Promotes oxidation
Difficult machining
Poor compression
Absorbs moisture
Difficult machining
Poor coupling to resin
High density
Low stiffness
APPLICATIONS Rocket motors
Aircrafts members
Leading edges, ropes
Ballistic protection
Water tank, bathroom accessories, shelters
COST INDEX High (6-7) Intermediate (3) Low (1-2)
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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.
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Fabrication of Carbon Fiber
Carbonization:
200-250°FOxidation:
1000°C Graphitization:
2500-3000°C Etching of fiber surface
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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).
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Variation of Mechanical Properties of Carbon Fiber With Respect to Temperature
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Chemical Kinetics of during Curing of CFRP
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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.
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Properties of Kevlar Fibers
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Glass Fibers
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Weave Architecture
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Through Thickness Stitching
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Fiber Architecture
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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.
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Unidirectional and Fabric Prepreg
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Composite Materials Summary
Composite Materials
Matrix Interphase Reinforcment
Ceramic Metalic Polymers
Thermoset Thermoplastic
Phenolics Polyester Epoxy Acrylics PEEK Carbonates
Particulate Flakes Fibers
Carbon Kevlar Glass
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THANK YOUTHANK YOU
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