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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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