Presentation on theme: "Teaching of Composites"— Presentation transcript:
1Teaching of Composites Brent StrongBrigham Young University
2Course Details Title―Composites: Materials and Processes Level―Beginning graduate/advanced undergraduateCredit―3 hours (2 lectures and 1 lab/week)Prerequisites―General Engineering Materials (no organic chemistry)Text―Fundamentals of Composites Manufacturing, 2nd Edition by A. Brent Strong
3Curriculum Issues Required: Manufacturing students Option: Mechanical, chemical, civil engineering and occasionally othersGateway course: Engineering Materials or equivalentFocusThis course: Manufacturing methods including the chemistry (simplified) of crosslinkingTypical ME course: Laminate design
4Basic Composite Concepts Concept 1: Composite componentsComposites are made of two materials ―a continuous phase (matrix) and a discontinuous phase (reinforcement)In the most common composites, the matrix is a polymeric resin and the reinforcements are fibersThe resin must bond to the fibersThe properties of the components are synergistic
5Basic Composite Concepts Concept 2: Advantages and DisadvantagesComposites are not “super” materials without some drawbacks
6Composites: Advantages and Disadvantages LightweightHigh specific modulusTailored propertiesEasily moldablePart consolidationEasily bondableGood fatigue resistanceGood dampingCrash worthinessInternal energy storage/releaseLow thermal expansionLow electrical conductivityStealthThermal transport (carbon fibers only)Cost of materialsLack of well-proven rulesMetal and composite designs are seldom interchangeableLong development timeManufacturing difficultiesFastenersLow ductilitySolvent/moisture attackTemperature limitsDamage susceptibilityHidden damageEMI shielding sometimes required
7Basic Composite Concepts Concept 3: Advanced and EngineeringAdvanced composites optimize the relationship of mechanical properties and weight, or optimize thermal performance and weightUsually made from long, high performance fibers (carbon and aramid) and advanced resins“Specific properties” (accounting for density) are importantEngineering composites have good properties with a focus on costUsually made from fiberglass, often chopped, and engineering resinsSometimes termed “Fiberglass reinforced plastics (FRP)”
8Properties comparisons of metals and composites SteelCompositesThermal ExpansionSteelAlCompositesAlSteelCompositesSpecific StrengthWeightAlSteelCompositesSpecific StiffnessSteelAlCompositesFatigue Resistance
9U.S. Composites Shipments TransportOther 3%32%Aircraft 1%Appliance 5%Marine11%Construction20%ElectricalConsumer10%Corrosion7%11%Est. 3.9 Billion Lbs of ShipmentsSource: CFA (June 2000)
10Basic Composite Concepts Concept 4: StealthStealth properties come from controlling radiation detection
11Stealth Radiation Considerations RadarInfra-redVisual from groundVisual from above (satellite)Visual from other aircraftSoundCon-trailRadio transmissionsUltravioletX-ray
14Basic Composite Concepts Concept 5: Matrix-dominated propertiesPropertyMolecular Cause or AssociationThermal ResistanceChemical components and bondingResistance to Solvents or WaterPolarityPermeabilityCrystallinityFire ResistanceAromaticity or halogen contentElectrical PropertiesPolarity and filler contentWeather resistanceAliphatic content, additives and fillersToughnessAliphatic content, rubber toughenersWet-out of fibersMolecular weight, backbone stiffness
15Resin Choices (Most common) Unsaturated polyestersAdvantages: low cost, room or elevated temperature cureDisadvantages: water absorption, low thermal stability, relatively poor mechanical propertiesEpoxiesAdvantages: good adhesion, good thermal stability, good mechanical propertiesDisadvantages: requires heat curing to develop properties, cost
16Resin Choices (Common) PhenolicsAdvantages: Excellent flame retardance and low smoke emission, good adhesive, good thermal and electrical insulationDisadvantages: Brittle, difficult to cureVinyl estersAdvantages: Easy to cure, good resistance to water absorptionDisadvantages: More expensive than polyesters, fewer choices in types of resins available
17Metal, Ceramic and Polymeric Composites Metal and ceramic composites are for high temperatures
19Basic Composite Concepts Concept 6: Reinforcement-dominated propertiesIn advanced composites, the reinforcements typically carry over 90% of the loadComposites are non-isotropic materials (that is, they have directionality)Many composites are layered and are called “composite laminates”
20Resin RulesThese rules allow for easy understanding of resin propertiesThese rules require no previous knowledge of organic chemistry or plasticsThe rules allow prediction of trends in matrix-dominated properties
21Resin RulesResin Rule 1: Thermal Properties ― Thermal properties depend upon the difficulty with which polymer molecules separate from each other.The separation of molecules the atoms remain bonded together in long chains.The separation of atoms occurs at a much higher temperature than the temperatures at which molecules separate.
22Thermal PropertiesThermal transitions and thermal stability are linkedThermal stability is the temperature at which a polymer can be used and still have acceptable propertiesFailure to perform is usually associated with molecular motion and so the same concepts associated with thermal transitions apply to thermal stability
24Resin RulesResin Rule 2: Mechanical Properties ― Mechanical properties depend upon the difficulty with which polymer molecules separate from each other.
25Resin Rules Impediment 1: Entanglement (molecular weight) Increases in molecular weight (length of the polymer chain) result in increases in thermal and most mechanical propertiesAnalogy: spaghetti
26Measuring factors related to chain length As chain length increases, viscosity increasesConsider pouring liquids from a cupLow viscosity fluidHigh viscosity fluid
27The Great Dilemma in Polymers Polymers must have good propertiesGood properties are favored by high molecular weightPolymers must have good processingGood processing is favored by low molecular weight
28The Great Dilemma In Polymers Thermoplastics meet the dilemma by compromiseHigh enough molecular weight to get adequate propertiesLow enough molecular weight to process OKThermosets meet the dilemma by crosslinkingLow molecular weight initially (for wetout and processing) followed by curing to increase molecular weightNo compromise is required
29Resin RulesImpediment 2: CrosslinksFormed during curing
30Covalent bond (shared electrons) Polymeric moleculesCovalent bond (shared electrons)Crosslink bonds
32Viscosity curves for typical thermoplastic and thermosets Gel PointSolidsLiquid-Solid LineViscosityRegion ARegion BLiquidsThermosetthinning due totemperatureThermoplasticThermosetcrosslinkingTime/TemperatureThermosetcombination(What is seen)
33Thermoplastics Thermoplastics are not crosslinked and so they melt Thermoplastics are molded as molten liquidsThermoplastics are cooled to solidifyThermoplastics can be re-melted repeatedlyKitchen example:candyThermoplastics are tough rather than brittleExamples of thermoplastics: polyethylene, polystyrene, nylon, polycarbonate, acrylic, Teflon®, PET (thermoplastic polyester)
34Thermosets Thermosets are crosslinked and do not melt Crosslinking is sometimes called curingThermosets are processed as room temperature liquidsThermosets are heated to solidifyKitchen example:cakeThermosets are often brittleExamples of thermosets: polyesters, vinyl esters, epoxies, phenolics, polyimides
35Polyester polymerization MonomersAcids A (di-acids)-Two types: unsaturated and saturated-(In polyesters crosslinking occurs at unsaturation sites)AGAGlycols G (di-alcohols)GAGAPolyester polymerGA
36Polyesters − specific molecules AcidAcidAcidAcidAcidAcidAcidCrosslinking occurs at the carbon-carbon double bondsthe number of which can be increased when the polymer is made
37Epoxies Crosslinking occurs only at the epoxy rings CH3│CH2―CH―CH2―O―(―CH2―C―CH2――O―)nCH2―CH―CH2│CH3OOCrosslinking occurs only at the epoxy ringsCH3H2C―CH―CH2―CH2CH2―CH2―CH―CH2│N――CH2―C―CH2――NOO│H2C―CH―CH2―CH2CH2―CH2―CH―CH2CH3OOThe tetra-functional epoxy has much greater crosslinking
38Thermoplastics and Thermosets Melting vs. decompositionMeltedDecomposed
39Resin Rules Impediment 3: Crystallinity Formed when polymers pack tightly together
40Covalent Bond (shared electrons) Polymeric MoleculesCovalent Bond (shared electrons)Amorphous RegionCrystalline Region
41Amorphous and Crystalline RegionsAmorphous(random entanglement)Semi-Crystalline or Crystalline(regular packing)
42Three-dimensional representation of a crystalline polymer Amorphous regionCrystalline region
44Comparison of advanced and engineering thermoplastics and thermosets Advanced ThermosetAdvanced ThermoplasticsEngineering ThermosetEngineering ThermoplasticHigh temperature capabilitiesHigh CostHigh strengthHigh modulusGood fiber wet-outBrittleHigh costSolvent resistanceHigh toughnessPoor wet-outLow costExcellent fiber wet-outModerate strengthStandard TP mfgShort fibersGood toughness
45Resin Rules Impediment 4: Polarity Occurs when F, O, N, and Cl are present
46Polarity N S S N S N S N Polyester d+ d- d+ d- d+ d- d+ d- Attacked by water molecules
47Bonding between fiberglass and resin − A highly polar moleculed+Sizing (alkylsilane)− Mixed polar/non-polard-d+Nonpolar regions (weak attraction)d-d+Polyester− Largely non-polar region
48Weight gain in water of polyester and vinyl ester resins 6―Polyester resin5―4―●●●Weight gain (%)3―2―●Vinyl ester resin□1―□□□●□│││││50100150200250Exposure time (hours)
49Resin Rules Impediment 5: Aromaticity Presence of aromatic groups (containing benzene molecule or similar group)Aromatic rings are hard, flat objectsAromatic objects increase stiffness of the polymer, especially as they are integrated into the backbone or into a network
50Aromatic molecules b) Polystyrene (pendant aromatic) Hb) Polystyrene (pendantaromatic)a) Aromatic group (benzene)c) Epoxy (aromatic backbone)Aromatic moleculesd) Phenolic (aromatic network)
51Super high thermal stability An imide-based epoxyOCH3OO―CC―OC│CCCNNCCCCOOC―C―C―O――CC――O―C―C―COOC―C―C―OO―C―C―COOSuper high thermal stability
52AromaticityAromatic content increases the flame resistance of the polymerAromatic content decreases the weathering resistance of the polymerMaterials with little aromatic character are called aliphatic
53Flammability Flame Spread Index Specific Optical Density Vinyl Ester EpoxyEpoxyFR PolyesterFR PolyesterPhenolicPhenolic10203040100200300400500600(ASTM E-162 for thermosetcomposites)(ASTM E-662 for thermosetcomposites)
58Reinforcement RulesReinforcement rule 1: Fiberglass is the least expensive of the major types of reinforcement and is often about the same strength as other major reinforcement types.Fiberglass composites are often called FRP (for fiberglass reinforced plastics)Fiberglass is used in most composite applications
59Effects of fiber content on properties of nylon Expansion, ppm/oF (ppm/oC)Coefficient of ThermalIzod Impact, ft-lb/in (J/mm )Flex Modulus (ksi)Elongation (%)Strength (ksi)TensileCTEFlex ModulusIzod ImpactElongationTensile StrengthScales for each property0% 10% 20% 30% 40% 50%
60Reinforcement RulesReinforcement rule 2: Carbon/graphite is the stiffest of the common fiber reinforcements and generally has the best specific strength and specific stiffness.
61Reinforcement RulesReinforcement rule 3: Aramid is the toughest of the major types of composite reinforcements.
62Reinforcement RulesReinforcement rule 4: Reinforcement forms can be of several types depending on the type of manufacturing process that is used.
63Reinforcement Forms Tow (or roving if Mat fiberglass) Prepreg Cloth fabricPreform
64Manufacturing RulesManufacturing rule 1: Put the fibers where the loads are going to be.
78SummaryComposites have succeeded in current products from automobiles to bathtubs
79SummaryComposites have great promise for the future
80Space PlaneCircling radius for landingXSpaceport
81Summary Category Concept/Rule Composites ― general 1 Composites are mixtures of two materials in which both materials retain some of their individual properties but also combine in such a way that the combined materials have some properties that are superior to either of the materials individually.Composites ― general 2While composites are certainly unique among structural materials, they are not super materials that have no disadvantages.Composites ― general 3Composites can be conveniently divided into two categories―advanced and engineering.Composites ― general 4Stealth properties come from controlling radiation detection.Composites ― general 5Some properties of the composite are dominated by the matrix.Composites ― general 6Some properties of the composite are dominated by the reinforcement.Resin ― Thermal propertiesThermal properties depend upon the difficulty with which polymer molecules separate from each other.Resin ― MechanicalMechanical properties depend upon the difficulty with which polymer molecules separate from each other (impediments).Resin ― Mechanical ― Impediment 1Molecular weight increases entanglementResin ― Mechanical ― Impediment 2Crosslinks inhibit molecular motions.Resin ― Mechanical ― Impediment 3Crystallinity restricts molecular movement.Resin ― Mechanical ― Impediment 4Polarity restricts molecular motion.Resin ― Mechanical ― Impediment 5Aromatic groups reduce molecular flexibility.Resin ― FlammabilityMaterials containing halogen atoms (F, Cl, Br, I) have good fire retardance properties.
82Summary Category Concept/Rule Reinforcement 1 Fiberglass is the least expensive of the major types of reinforcement and is often about the same strength as other major reinforcement types.Reinforcement 2Carbon/graphite is the stiffest of the common fiber reinforcements and generally has the best specific strength and specific stiffness.Reinforcement 3Aramid is the toughest of the major types of composite reinforcements.Reinforcement 4Reinforcement forms can be of several types depending on the type of manufacturing process that is used.Manufacturing 1Put the fibers where the loads are going to be.Manufacturing 2Control the temperature, viscosity, and crosslinking reaction.Manufacturing 3Compact the composite during cure to ensure that the layers are properly adhering and that the air bubbles are reduced.Manufacturing 4Composites are often part of assemblies and great care must be used to properly finish the structure.
83Composites are dynamic! Thank YouComposites are dynamic!