Reading Assignment Composites And Engineering Of Materials", 4th Carbon .
Reading assignmentComposites andcarbon fibersTopic 2 Askeland and Phule, “The Science andEngineering of Materials”, 4th Edition,Ch. 16. Shakelford, “Introduction to MaterialsScience for Engineers”, 6th Edition, Ch.14. Chung, “Composite Materials”, Ch. 2. Chung, “Carbon Fiber Composites”,Ch. 1, 2 and 3.Hull made of a sandwich compositeExterior: Kevlar fiber epoxy-matrix compositeInterior: Polyvinyl chloride foam 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. (a) A hexagonal cell honeycomb core, (b) can bejoined to two face sheets by means of adhesivesheets, (c) producing an exceptionally lightweightyet stiff, strong honeycomb sandwich structure.Aramid-aluminum laminate(layers joined by adhesives)Lightning strikeresistanceFatigue resistance 2003 Brooks/Cole, a division of Thomson Learning, Inc.Glass fibersThomson Learning is a trademark used herein under license.1
Glass fiber polymerpolymer-matrix compositeA carbonfiber tow 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. A three-dimensional weave for fiberreinforced ctionTransversedirection 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. (a) Tapes containing aligned fibers can be joined toproduce a multi -layered different orientations toproduce a quasi -isotropic composite. In this case, a0 / 45 /90 composite is formed.Throughthicknessdirection2
2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein underlicense.Effect of fiber orientation on the tensilestrength of E-glass fiber -reinforcedepoxy composites.Size distribution of particles used asreinforcementSingle fiber tensilestrength Carbon fiber Kevlar fiber E-glass fiber Steel3.5 GPa3.6 GPa3.4 GPa1.3 GPaSpecific strength Carbon fiberKevlar fiberE-glass fiberSteel2.00 GPa2.50 GPa1.31 GPa0.17 GPa3
Single fiber tensilemodulus230 GPa60 GPa22 GPa210 GPa 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. Carbon fiber Kevlar fiber E-glass fiber Steel Comparison of the specific strength and specificmodulus of fibers versus metals and polymers. 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. The structure of KevlarTM. The fibers are joined bysecondary bonds between oxygen and hydrogenatoms on adjoining chains.Some examples of composite materials: (a) plywood is a laminarcomposite of layers of wood veneer, (b) fiberglass is a fiber reinforced composite containing stiff, strong glass fibers in asofter polymer matrix ( 175), and (c) concrete is a particulatecomposite containing coarse sand or gravel in a cement matrix(reduced 50%).4
2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. The effect of clay on the properties ofpolyethylene. 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. The influence of volume percent boron-coated SiC(Borsic) fibers on the properties of Borsic-reinforcedaluminum parallel to the fibers 2003 Brooks/Cole, a division of Thomson Learning, Inc.Tensile stressThomson Learning is a trademark used herein under license.Critical stressfor fiber failureShort fiber 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. Increasing the length of chopped E-glass fibers in anepoxy matrix increases the strength of thecomposite. In this example, the volume fraction ofglass fibers is about 0.5.Long fiber5
Thomson Learning is a trademark used herein under license. 2003 Brooks/Cole, a division of Thomson Learning, Inc. 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. The specific strength versus temperature forseveral composites and metals. 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license.A comparison of the specific modulus and specificstrength of several composite materials with thoseof metals and polymers.Methods of fabricatingpolymer-matrix compositesA comparison of the specific strength of variouscarbon-carbon composites with that of other hightemperature materials relative to temperature. 2003 Brooks/Cole, a division of Thomson Learning, Inc. 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license.Thomson Learning is a trademark used herein under license. Producing composite shapes by filament winding.Producing composite shapes by pultrusion.6
Elastic modulus (slope of stress-strain curve)Hand lay-upPressure bagmoldingUnidirectional compositeMatched die molding 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license.IsostrainconditionPc Pm Pfσ c Ac σ m Am σ f A fFor isostrain condition (ε c ε m ε f )Longitudinal directionE cε c Ac Emε m Am E f ε f A fEc EmAAm Ef fAcAcE c ν m Em ν f E f 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. The stress-strain curve for a fiber -reinforcedcomposite. At low stresses (region l), the modulus ofelasticity is given by the rule of mixtures. At higherstresses (region ll), the matrix deforms and the ruleof mixtures is no longer obeyed. 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license.7
Fraction of load carried by fibersX c ν m X m ν f X fPfRule of Mixtures (ROM)PcIsostresscondition σ f Afσ c Ac E f ε f AfEc ε c Ac EfEcνfIsostress conditionσc σm σ f Lc Lm L fTransversedirection Lc Lm L f LcLcLc Lc Am Lm A f L f LcLmLfε c ν mε m ν f ε fL m Am LcL f A f LcFor isostress condition (σ Ecε c Em ε m E f ε f ),sσσ ν m ν fEcEmEf1 νm ν f Ec Em E fEc Em E fν m E f ν f Em8
Xc XmX fν m X f ν f X mEcn ν t Eln ν h Ehnn 1 Isostrainn -1 IsostressRule of Mixtures (ROM)Fiber-matrix debonding Silver-copper alloy matrix Carbon fiber reinforcement Fracture surface observation(fractography)9
Fiber-matrix debonding Polymer matrix Glass fiber reinforcementFailure mechanisms Failure in fibers (ductile -matrixcomposites, e.g., polymer-matrix and metalmatrix composites), so a high interfacialstrength is desired. Failure in matrix (brittle -matrixcomposites, e.g., ceramic-matrix and carbonmatrix composites), so a low interfacialstrength is desired (to allow cracks to deflectalong fiber-matrix interface, thereby allowingfibers to pull out for the purpose ofincreasing the toughness)Poor bondingMatrixFiberGood bondingFiber pull-out Two failure modes in ceramic-ceramic composites:(a) Extensive pull-out of SiC fibers in a glass matrixprovides good composite toughness (x20). (b)Bridging of some fibers across a crack enhances thetoughness of a ceramic-matrix composite (unknownmagnification).10
Fracture toughnessIncreased by reinforcementReasons for fiber-matrixinterface engineering To control fiber-matrix bondstrength (shear bond strength) To improve wetting of matrixprecursor on fiber To improve fiber dispersionMethods offiber surface treatment Chemical treatment fiber Coating of fiberSpecific strength strength/densityMethods for fiber-matrixinterface engineering Fiber surface treatment Dispersant as an additive to thematrixTable 2.2 Effects of various surface treatments on properties of high-modulus carbon fibers and their epoxymatrix composites. All liquid treatments at reflux temperature.Fiber propertiesFiber treatmentComposite propertiesWt. loss(%)Tensile strengthloss (%)Flexural strengthloss (%)ILSS gain (%)400ºC in air (30 min)00018500ºC in air (30 min)0.461250600ºC in air (30 min)4.550Too weak to test-60% HNO 3 (15 min)0.208115.25% NaOCl (30 min)0.41.553010-15% NaOCl (15 min)0.208615% HClO4 (15 min)0.201205% KMnO 4/10% NaOH (15 min)0.4015195% KMnO 4/10% H2S O4 (15 min)6.0( )17139510% H2O2/20% H 2SO 4 (15 min)0.151442% HNO 3/30% H2S O4 (15 min)0.104( )010% NaClO3/15% NaOH (15 min)0.20121210% NaClO3/25% H2 SO4 (15 min)0.225( )9115% NaClO3/40% H2 SO4 (15 min)0.741510810% Na 2Cr2O7/25% H2S O4 (15 min)0.3815( )1815% Na 2Cr2O7/40% H2S O4 (15 min)1.7273118011
Types ofpolymer-matrix composites Thermoplastic-matrix composites Thermoset-matrix compositesBetter performance ofthermoplastic-matrix composites high toughness (damage tolerance) good hot/wet properties high environmental toleranceAttractive properties of carbon fiberpolymer-matrix composites low density (40% lower than aluminum) high strength (as strong as high-strengthsteels) high stiffness (stiffer than titanium, yetmuch lower in density) good fatigue resistance (a virtuallyunlimited life under fatigue loading) good creep resistanceLower manufacturing cost ofthermoplastic-matrix composites no cureunlimited shelf-lifereprocessing possible (for repair and recycling)less health risks due to chemicals during processinglow moisture contentthermal shaping possibleweldability (fusion bonding possible)Disadvantages ofthermoplastic-matrix composites limitations in processing methodshigh processing temperatureshigh viscositiesprepreg (collection of continuous fibersaligned to form a sheet which has beenimpregnated with the polymer or polymerprecursor) being stiff and dry when solvent isnot used (i.e., not drapeable or tacky) fiber surface treatments less developedAttractive properties of carbonfiber polymer-matrix composites low friction coefficient and good wear resistance (a40 wt.% short carbon fiber nylon-matrixcomposite has a friction coefficient nearly as lowas Teflon and unlubricated wear propertiesapproaching those of lubricated steel) toughness and damage tolerance (can be designedby using laminate orientation to be tougher andmuch more damage tolerant than metals) chemical resistance (chemical resistance controlledby the polymer matrix) corrosion resistance (impervious to corrosion)12
Attractive properties of carbon fiberpolymer-matrix composites dimensional stability (can be designed forzero coefficient of thermal expansion) vibration damping ability (excellentstructural damping when compared withmetals) low electrical resistivity high electromagnetic interference (EMI)shielding effectiveness high thermal conductivityLimitation of polymermatrix compositesInability to resisthigh temperaturesCarbon-carbon (C/C)compositesCarbon-matrix compositesAbility to resist hightemperaturesCarbon matrixprecursors Pitch Resins Carbonaceous gases Carbon fiber Carbon matrix Carbon matrix made from pitchor polymerConversion of carbon matrixprecursor to carbon Pyrolysis (also calledcarbonization) Heating at around 1000 C in theabsence of oxygen to causedecomposition, like charring13
Bonding in graphitewIn-plane:covalent and metallic bondingwOut-of-plane:van der Waals bondingProperties of graphitew Anisotropicw Easy shear between carbon layerslimiting the strengthw High electrical and thermalconductivity and high modulus in theplane of the carbon layersFiber microstructureFiber texture, i.e.,preferred crystallographicorientation with thecarbon layers along thefiber axis.14
Carbonw Non-crystalline, turbostraticw Metastable form– graphitizes upon heating above2000 C.Conversion ofcarbon to graphite Graphitization (i.e., crystallization) Heating at 2000 C or above in theabsence of oxygen to cause theturbostratic carbon to be convertedto graphite ion (oxidation)wCarbonization (pyrolysis)wGraphitizationGrades of carbon fiberPAN polyacrylonitrile 2003 Brooks/Cole, a division of Thomson Learning, Inc. High-strength carbon fiber(without graphization) High-modulus carbon fiber(with graphitization)Thomson Learning is a trademark used herein under license.15
Thomson Learning is a trademark used herein under license.Properties of carboncompared to graphite 2003 Brooks/Cole, a division of Thomson Learning, Inc.w Less conductivew Lower in modulusw Higher in strengthw Lower in oxidation resistancew Cannot be intercalatedFiber vs. nanofiberw Fiber (diameter 1 micron or above,typically around 10 microns)w Nanofiber (also called filament,diameter below 1 micron, typically0.1 micron or less)Types ofcarbon nanofiberw Nanofiber with fish-bone morphologyw Multi-walled nanotube (concentriccylinders in shell)w Single-walled nanotube (chirality)Carbon nanotubeHybrid of graphite andfullerene16
Crystal forms of carbonwGraphitewDiamondwFullerene17
Nanofiber groupmorphologywIntertwinedwParallelFabrication ofcarbon nanofiberswCatalytic growth fromcarbonaceous gaswArc dischargewLaser evaporationCatalytic methodw Carbonaceous gases: acetylene,ethylene, methane, natural gas,benzene, etc.w Catalyst: iron, nickel, etc.(particles typically 10 nm, fromsalts or organometallics)w Reducing gases: CO, hydrogen18
Methods of making carboncarbon composites Carbonization, followed by impregnation of pitchor resin, and repeating the carbonizationimpregnation process again and again untilsufficient density has been attained. Chemical vapor infiltration (CVI) using acarbonaceous gas, i.e., CVD under atemperature/pressure gradient so as to preventcrust formation, thereby allowing completeinfiltration; CVI can be an extra step that followscarbonization-impregnation for the purpose offilling the pores.Table 2.3 Pitch properties.Grades of pitch Isotropic pitch Mesophase pitch(liquid crystal formcalled the mesophase)Carbon yield (%)Pitch Molecular 0.1 MPa 10 MPaweightA72645.285.9B78254.486.4C93184.589.8Main problem withcarbon-carbon compositesOxidation at high temperaturesin the presence of oxygenMethods for oxidation protection ofcarbon-carbon compositesup to 1700 C1.2.3.4.SiC conversion coatingOxidation inhibitorsGlassy sealantDense SiC or Si3 N4 overlayer onglassy sealant or SiC conversioncoating19
SiC conversion coatingmethodSiC coating (known as SiCconversion coating, due tograded composition from pureSiC at the surface to purecarbon inside)Pack cementationPacking the composite in amixture of SiC and Sipowders and heat up to1600 CChemical conversion of the outermost surfaceof the composite to SiCMethods of applyingSiC conversion coating- Pack cementation,- Reaction sintering,- Silicone resinimpregnation/pyrolysis, or- Chemical vapor deposition(CVD) to the outer surface ofthe composite.Pack cementationSi(l) C SiCSi(g) C SiCSiO(g) 2C SiC CO(g)Problem with entrapped siliconvaporising.SiC coating thickness typically 0.3-0.7 mm.Reaction sinteringDipping C/C composite into asuspension of Si powder (10µm) in an alcohol solution andthen sintering at 1600 C for 4hours in argon.Silicone resinimpregnation/pyrolysisVacuum impregnation and coldisostatic pressing (30,000 psi or200 MPa) a silicone resin into thematrix of a C/C composite andsubsequent pyrolysis at 1600 C for2 hours in argon.Note: Silicone is a polymer with siliconatoms as a part of the backbone.20
Prior deposition of carbon film(10 µm) by CVD Prior to pack cementation, reactionsintering or resin impregnation To improve homogeneity of C/Csurface To ease the reaction with SiChemical vapor deposition (CVD)by thermal decompositionof a volatile silicon compoundHeat/H2CH3SiCl3 (g) SiC 3HCl(g)Temperature: 1125 CAdvantages of SiC or Si3N4 Thermal expansion compatibility withC/C Low oxidation rate Thin amorphous SiO2 scale that growshas low oxygen diffusion coefficient.Dense SiC or Si3N4 overlayers SiC overlayer is more dense thanthe SiC conversion coating. As oxygen barrier To control venting of reactionproducts to the outside Made by chemical vapordeposition (CVD)SiSiC overlayer CVD overlayer contains a smallpercentage of unreacted silicondispersed in the SiC, The excess Si upon oxidationbecomes SiO2, which has a verylow oxygen diffusion coefficient.SiC or ineffectiveabove 1800 C Reactions at the interface betweenSiO2 and SiC or Si3N4 Reduction of SiO2 by carbon toform CO gas.21
Oxygen inhibitors Oxygen getters Glass formersTo provide additional oxidation protectionfrom within by migrating to the outersurface and sealing cracks and voidsduring oxidation.Examples of inhibitors Elemental Si, Ti and B SiC, Ti 5Si3 and TiB2 Alloys such asSi2TiB14 Organoborosilazanepolymer solutionOxidation of the elemental Si, Ti or Bwithin the carbon matrix forms aviscous glass, which serves as asealant that flows into the microcracksof the SiC coating.Boron asan oxidation inhibitor Boron is oxidized to form B 2O3. B2O3 blocks active sites, suchas the edge carbon atoms. B2O3 forms a mobile diffusionbarrier for oxygen.Oxidation rateRate of weight lossMethod of introducing oxidationinhibitors to the carbon matrixInhibition factorRatio of oxidation rate ofuntreated carbon to thatof the treated carbonIncorporating particulatefillers in the resin or pitch(i) prior to prepregging.during lay-up and(ii) during densification cycles.22
Glassy sealants Glazes comprising mainly silicates (SiOx)and borates (B 2O3). Glaze can be filled with SiC particles Particularly important if the SiC conversioncoating is porous Glaze fills microcracks in the denseoverlayerApplication of a glassy sealant on top ofthe SiC conversion coating mainly byslurry brush-on, so that the sealants melt,fill voids and stop oxygen diffusion, and, insome cases, act as oxygen getters.Effectiveness of borate sealantsModified borate sealants Borates wet C and SiC quite well Borates cannot be used above 1200 Cdue to volatilization Borates have poor moisture resistancedue to hydrolysis, which results inswelling and crumbling Borate has a tendency to galvanicallycorrode SiC coatings at hightemperatures The problems of borate can bealleviated by using multicomponentsystems such as 10TiO2.20SiO2.70B2O3 . TiO2 has a high solubility in B2O3 and isused to prevent the volatilization ofB2O3 and increase the viscosity. SiO2 acts to increase the moistureresistance, reduce B2O3 volatility,increase viscosity and preventcorrosion of SiC by B2O3.Dense SiC or Si3N4 overlayerMethod of oxidation protectionof C/C above 1700 C Applied by CVD. On top of glassy sealant or on top ofSiC conversion coating To control and inhibit transfer ofoxygen to the substrate To control the venting of reactionproducts to the outsideFour-layer coating scheme:(1) Refractory oxide (e.g., ZrO2, HfO2, Y 2O3,ThO2) as the outer layer for erosion protection.(2) SiO2 glass inner layer as and oxygen barrierand sealant.(3) Another refractory oxide layer for isolationof the SiO2 from the carbide layer underneath.(4) Refractory carbide layer (e.g., TaC, TiC,HfC, ZrC) to interface with the C/C substrate andto provide a carbon diffusion barrier23
Fundamental approaches foroxidation protection of carbonsHfC 3O 2 HfO 2 CO2Carbon matrix precursors Pitch (preferred for oxidation protection) Chemical vapor infiltration (CVI) carbon(preferred for oxidation protection) Resins (not preferred for oxidationprotection) Prevention of catalysisRetardation of gas access to the carbonInhibition of carbon-gas reactionsImprovement in the carbon crystallinestructureEffects of carbon fiberon oxidation protection Alignment of the matrix molecules near thefibers Microstructure of fiber affecting that ofmatrix Microstructure of matrix affecting amountof accessible porosity in the matrixMetal-matrix compositesDisadvantage ofcoatings on C/CDegrade room temperaturemechanical properties of C/C Better temperature resistance thanpolymer-matrix composites Lower temperature resistance thanceramic-matrix composites High fabrication cost compared topolymer-matrix composites Low fabrication cost compared toceramic-matrix composites24
Methods of fabricatingmetal-matrix composites Liquid metal infiltration Hot pressing above thesolidus of the matrix metal Powder metallurgy (diffusionbonding) Plasma spraying Slurry castingAdvantages ofliquid metal infiltration Near-net shape Fast 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license. The steps in producing a silver -tungsten electricalcomposite: (a) Tungsten powders are pressed, (b) a lowdensity compact is produced, (c) sintering joins thetungsten powders, and (d) liquid silver is infiltrated into thepores between the particles.Liquid metal infiltration(squeeze casting)Difficulty inliquid metal infiltationLiquid metal does notwet ceramic or carbonparticles/fibers well.25
Reaction between metal andreinforcement Helps wetting Degrades reinforcement Reaction product (e.g., acarbide) lining the metalreinforcement interface may bebrittleCoating of TiB 2 on carbon fiberby CVD TiCl 4 and BCl 3 gases, which arereduced by zinc vapor Coating particularly good for liquidaluminumMethods of wettingenhancement Coat reinforcement with ametal (e.g., Ni, Cu, Ag) byplating Coat reinforcement with aceramic (e.g., TiC, SiC, B 4C,TiB 2, TiN, K 2ZrF6, ZrO2) by CVD,solution coating, etc.Solution coating method Dip in organometallic solution(e.g., alkoxides, which are M(OR)x,where M is the metal, and R is ahydrocarbon group, such asmethyl, ethyl, etc.) Hydrolysis or pyrolysis toorganometallic compoundsPyrolysis of organometallic compoundHydrolysis of organometallic compoundM(OR) x Si(OC2 H5 )4 SiO 2 2C2 H5OH 2C2 H4xH 2 O MO x/2 xROH2Si(OC2 H5 )4 2H2O SiO 2 4C2 H5OH26
Two methods ofpowder metallurgyPowder metallurgy Near-net shape Size limited by the pressurerequirementThomson Learning is a trademark used herein under license.Yieldstrength 2003 Brooks/Cole, a division of Thomson Learning, Inc.Production of fiber tapes byencasing fibers betweenmetal cover sheets bydiffusion bonding Mixture of matrix powder andreinforcement particles/fibers Matrix coated reinforcementparticles/fibers 2003 Brooks/Cole, a division of Thomson Learning, Inc.Aluminum alloysParticulate aluminummatrix compositeThomson Learning is a trademark used herein under license.Electron micrograph of TD -nickel. The dispersed ThO2particles have a diameter of 300 nm or less ( 2000).(From Oxide Dispersion Strengthening, p. 714,Gordon and Breach, 1968. AIME.)Microstructure of tungsten carbide—20% cobaltcemented carbide (1300). (From Metals Handbook,Vol. 7, 8th Ed., American Society for Metals, 1972.)27
Superconductingcomposite Microstructure of an aluminum casting alloyreinforced with silicon carbide particles. In this case,the reinforcing particles have segregated tointerdendritic regions of the casting( 125). 2003 Brooks/Cole, a division of Thomson Learning, Inc.Thomson Learning is a trademark used herein under license.Laminar compositesCeramic-matrix compositesExplosiveRollbondingbondingCoextrusion 2003 Brooks/Cole, a division of Thomson Learning, Inc.Brazing Ceramic-ceramic composites(ceramic-fiber ceramic-matrixcomposites) Better oxidation resistance thancarbon-carbon composites Technology less matured thancarbon-carbon compositetechnologyThomson Learning is a trademark used herein under license.Examples of ceramic matrices Silicon carbide Silicon nitride Alumina (aluminum oxideAl2O3) Mullite (Al2O3-SiO2) Glasses28
1 Composites and carbon fibers Topic 2 Reading assignment Askeland and Phule, "The Science and Engineering of Materials", 4th Edition, Ch. 16. Shakelford, "Introduction to Materials Science for Engineers", 6th Edition, Ch. 14. Chung, "Composite Materials ", Ch. 2. Chung, "Carbon Fiber Composites", Ch. 1, 2 and 3.
5 NATURAL FIbRE-SYNThETIC poLYMER CoMpoSITES 28 5.1 Wood Plastic Composites 29 5.2 Natural Fibre Injection Moulding Compounds 30 5.3 Non-Woven Natural Fibre Mat Composites 32 5.4 Aligned Natural Fibre-Reinforced Composites 33 6 FULLY bIo-bASEd CoMpoSITES 34 6.1 Natural Fibre-Bio-based Polymer .
The following tutorial aims at guiding you when you open the CATIA Composites Design workbench for the first time. It provides 3 step-by-step tasks for: Entering the Composites Design Workbench Defining the Composites Parameters This tutorial should take about 5 minutes t
GEOG 1303 World Regional Geography World Regional Geography Signature Assignment . Course Assignment Title Assignment ID (to be assigned) Outcomes/Rubrics to be Assessed by the Assignment Assignment Description For this assignment students must analyze an issue related to world regional geography. Students will research the issue using .
All About the Alphabet Reading Alphabet Fun: A Reading Alphabet Fun: B Reading Alphabet Fun: C Reading Alphabet Fun: D Reading Alphabet Fun: E Reading Alphabet Fun: F Reading Alphabet Fun: G Reading Alphabet Fun: H Reading Alphabet Fun: I Reading Alphabet Fun: J Reading Alphabet Fun: K Reading Alphabet Fu
Week 8: March 1 st-5 th Dictation Assignment 6/Singing Assignment 6/Rhythmic Assignment 6 due by 11pm on Friday, March 5 th Week 9 : March 8 th-12 th Sight Singing and Rhythmic Sigh t-Reading Test 2 Week 10: March 15 th - 19 th Dictation Assignment 7/Singing Assignment 7/Rhythmic Assignment 7 due by 11pm on Friday, March 19 th Week 11: March 22 .
(MS, Aerospace Engineering, 2013) This two-part series will detail the role that composites can play in Finite Element Analysis. Running on consecutive Wednesday afternoons, this series will show the use and value of composites in two separate Finite Element Modelers. The first week, we will show the analysis of composites in FEMAP.
Assignment 3A: Fractals Assignment by Chris Gregg, based on an assignment by Marty Stepp and Victoria Kirst. Originally based on a problem by Julie Zelenski and Jerry Cain. JULY 12, 2017 Outline and Problem Description Note: because of the reduced time for this assignment, the Recursive Tree part of the assignment is optional.
Additif très dangereux E249 : Nitrite de potassium . Conservateur chimique. Risques : essoufflements, vertiges, maux de tête, chez les nourrissons les nitrites peuvent provoquer la mort par asphyxie car ils empêchent les globules rouges de transporter l'oxygène, cancérigène. Très répandu dans les charcuteries, les salaisons, le foie gras et le bacon traité, MÊME DANS LES .
