AE-681 Composite MaterialsInstructor:Dr. PM MohiteDrOffice: AE-11, Aerospace EngineeringEmail: [email protected]: 6024Course Credits: 4LTPD:3-0-0-0Course Content: Introduction,Introduction Definition,Definition classification,classification behaviors of unidirectional composites Analysis of lamina; constitutive classical laminate theory, thermal stresses, Design consideration, analysis of laminates after initial failure, interlaminarstresses,tf tfracturemechanics,h i jointsj i t andd experimentalit l characterization,ht i ti Micromechanics Factors influencing strength and stiffness failure modes, Performance under adverse environment Prediction of strength, stiffness

AE-681 Composite MaterialsReference Books/Material: Mechanics of Fibrous Composites, CT Herakovich. Analysis and Performance of Fibre Composites, BD Agarwal and LJ Broutman. Mechanics of Composite Materials, RM Christensen. Any other book on composite materials Research papersGrading Policy:Midsem I II:Assignments:Endsem:40%20%40%(Individual Group) Absolute 40% for passing. Relative grading after that. Assignments should be submitted on due date by 5.00 pm. Late submissionand copying will be heavily penalized ! Attendance will be monitored regularly.

About Fibrous Composites

Composite: Formal Definition and HistoryWhat is composite?Definition: A material which is composed of two or more materials at a microscopic scaleandd havehchemicallyh i ll distinctdi ti t phases.h Heterogeneous at a microscopic scale but statically homogeneous atmacroscopic scale. Constituent materials have significantly different properties.Classification of certain materials as a composite:1.22.3.Combination of materials should result in significant property changesContent of the constituents is generally more than 10%In general, property of one constituent is much greater ( 5) than the other

Composite: Formal DefinitionHistory: Oldest application/existence of composite material?4000 B.C. – laminated writing material from the papyrus plant1300 B.C. – Egyptians and Mesopotamian used straw bricks1200 A.D. - Mongols invented the first composite bow

Composite: Formal Definition and HistoryComposite Bow – dates back to 3000 BC (Angara Dating)Materials Used:Wood, Horn, Sinew (Tendon), Leather, Bambooand Antler (Deer horn)Horn and Antler: naturally flexible and resilientSinews: back tendons or hamstrings of cows and deerGlue: From bladder of fishStrings: Sinew, Horse hair, SilkOverall processing time was almost a year !Source:

Composite: Formal Definition and HistoryComposite Bow – dates back to 3000 BC (Angara Dating)

Evolution of MaterialsSource: MF Ashby. Phil. Trans R. Soc. London A 1987(332):393-407.

Composite: Examples from Day-to-Day LifeExamples:1. Straw-bricks2. Concrete3. Wood(cellulose lignin)4. Human body(muscles bones)5. Tyres6 Plywood6.7. Sports good

Evolution of MaterialsUse of Modern (Polymer) Composites:During World War II –Military applicationNon-metallic shielding of Radomes(to house electronic radar equipments)Glass Fibre Reinforced Plastics (GFRP)The first application of wood - composite laminates in Havilland Mosquito Fighter/Bomber of British Royal Air-Force

Evolution of MaterialsUse of Modern (Polymer) Composites:During World War II –Attack on Pearl Harbour by JapaneseTorpedo bomberSopwith CuckooSource: bomberFairey Swordfish

Composite: NecessicityWhy do you need composite materials?Enhanced desired properties !What are these desired properties? Strength Stiffness Toughness Corrosion resistance Wear resistance Reduced weight Fatigue life Thermal/Electrical insulation and conductivity Acoustic insulation Energy dissipation Attractiveness, cost, . Tailorable properties

Composite: NecessicityHigh Fatigue 40.0 §§§120.0§§100.0S (Ksi)§§§§§80.0ø60.0E-GI/Epθ§ 965. 827. 690. (MPa) 552.§§§414.§§øø ø ø§øø θ θ2024-T3 ALøø θ θ § §§ø ø θ276276.§S-GI/Epø θ 觧ø§§ø øθ θ θB/AL138.ø ø θ θ θB/Epθø øø øKevlar/Ep0.0C/Ep7 (10x cycles)θ θ40 040.0§ θθ§θθSource: Mechanics of Fibrous Composites, CT Herakovich, Wiley 1998.

Composite: NecessicityHigh Specific Strength and Modulus:18.0IM815.0Kevlar12.0T300 & AS4σ ult / ρS-2 Glass9.00BoronooSCS-6Sapphire6.00P 100NicalonFP AlMetals3.ρSource: Mechanics of Fibrous Composites, CT Herakovich, Wiley 1998.

Composite: NecessicityStress strain curve for fibres:3750.5171.946500.σ ( ksi NicalonFP AlS 0ε ((%))Source: Mechanics of Fibrous Composites, CT Herakovich, Wiley 1998.

Composite: ConstituentsWhat are the constituents in a composite material?1. Reinforcement:discontinuousstrongerharder2. Matrix:ContinuousWhat are the functions of a reinforcement?1. Contribute desired properties2. Load carrying3. Transfer the strength to matrix

Composite: ConstituentsWhat are the functions of a matrix? the fibres togetherProtects the fibres from environmentProtects the fibres from abrasion (with each other)Helps to maintain the distribution of fibresDistributes the loads evenly between fibresEnhances some of the properties of the resulting material and structuralcomponent (that fibre alone is not able to impart). These properties aresuch as:transverse strength of a laminaImpact resistanceProvides better finish to final product

Classification of CompositesBased on the type of matrix material

Classification of CompositesBased on the form of reinforcement Fibre - a filament with L/D very high (of the order 1000) A composite with fibre-reinforcement is called Fibrous Composite Particle – non fibrous with no long dimension A composite with particles as reinforcement is called Particulate Composite Whiskers – nearly perfect single crystal fibre Short, discontinuous, polygonal cross-section

Classification of CompositesBased on theform of reinforcementInterest of this course !

Classification of CompositesBased on the form of reinforcement

Fibres as a ReinforcementFibre reinforced composites is the interest of this course !Why do you make fibre reinforcements of a thin diameter?1. As the diameter decreases the inherent flaws in the materialalso decreases and the strength increases.E De Lamotte, AJ Perry. Fibre Science and Technology, 1970;3(2):157-166.

Fibres as a Reinforcement22. For better load transfer from matrix to fibre composites require largersurface area of the fibre matrix interface.Fibre matrixFibt i interfacei t farea: A N π D L(N – No. of fibres, D – fibre diameter, L – length of fibres)Replace D by d (smaller diameter fibres)For same Fibre Volume FractionFraction*::n N(D/d)2New fibre matrix interface area: A N π D2 L/d 4 * Volume of fibres / dThus, for a given fibre volume fraction, the area of the fibre-matrix interface isinversely proportional to the diameter of the fibre.* Fibre Volume Fraction (Vf) Volume of fibres/Volume of compositeMatrix Volume Fraction (Vm) Volume of matrix/Volume of compositeVf Vm 1

Fibres as a Reinforcement33. The fibres should be flexible/pliant so that they can be bend easily withoutbreaking. For example, woven fibre composites needs flexible fibres.Fl ibilit isFlexibilityi definedd fi d as inverseioff bendingb di stiffness.tiffConsider a fibre as beam under pure bending, thenEI – Bending stiffness or Flexural rigidityFlexibility α 1/EIwhere, I π d4/64Flexibility α 1/Ed4Thus, flexibility of a fibre is inversely proportional to 4th power of the fibrediameter.

Types of Fibres11.Advanced Fibres:Fibres possessing high specific stiffness [E/ρ] and specific strength [σ/ρ])a) Glassb) Carbonc) Organicd) Ceramic

Types of Fibres22.Natural Fibres:a) Animal fibresi) Silkiv) Sinewb) Vegetable fibresi) Cottoniv) Sisalvii) Sugarcanex) Kapokxii) Kenafc) Mineral fibresi) Asbestosiii) Mineral woolii) Woolv) Camel hairiii) Spider silkvi)ii) Jutev) Mazeviii) Bananaxi) Coirxiv) Flaxiii) Bamboovi) Hempix) Ramiexii) Abacaxv) Raffia palm .ii) Basaltiv) Glass wool

Types of FibresUsed for Advanced fibresConventional Metals

Advanced FibresGlass fibres: ancient Egyptians made containers from coarse fibres drawn from heatsoftened glass producedd d byb extrudingt di moltenlt glasslatt 1200ºC passed through spinnerets of 1-2 mm diameter then drawing the filaments to produce fibres of diameter between 1-5 μm individual filament is small in diameter, isotropic in behaviour and veryflexible variety of forms:E glass: high strength and high resistivityS2 glass: high strength, modulus and stability under extremetemperature,e pe u e, cocorrosiveos ve eenvironmentv o eR glass: enhanced mechanical propertiesC glass: resists corrosion in an acid environmentD glass: dielectric properties In general, glass fibres are isotropic in nature

Advanced FibresCarbon fibres: carbon- carbon covalent bond is the strongest in natureGuess who made the first carbon fibre?Thomas Edison made carbon fibre from bamboo whenexperimenting for light bulb !What is the difference between carbon and graphite fibres?- Carbon fibre contains 80-95 % of carbon and graphite fibre containsmore than 99% carbon- carbon fibre is produced at 1300ºC while graphite fibre is producedin excess of 1900ºCCaution ! - In general term carbon fibre is used for both fibresMade from two types of precursor materials:1) Polyacrylonitrile (PAN)(PAN Based)2) Rayon Pitch - residue of petroleum refining (Pitch Based)

Advanced FibresCarbon fibres: Precursor fiber is carbonized rather then melting Filaments are made by controlled pyrolysis (chemical deposition by heat) of aprecursor materialt i l ini fiberfib formfb heatbyh t treatmentt tt att temperaturett1000 3000º C1000-3000º Different fibers have different morphology, origin, size and shape. Themorphology is very dependent on the manufacturing process. The size of individual filament ranges from 3 to 14 µm. Hence, very flexible. Maximum temperature of use of the fibers ranges from 250 ºC to 2000 ºC.Properties changes with temperature at higher temperature. The maximum temperature of use of a composite is controlled by the usetemperature of the matrix Modulus and strength is controlled by the process-thermal decomposition of theorganic precursor under well controlled conditions of temperature and stress Heterogeneous microstructure consisting of numerous lamellar ribbons Thus,, carbon fibers are anisotropicp in nature

Advanced FibresOrganic fibres: Aramid fibres Aromatic polyamide – family of nylons. Polyamide 6 nylon 6, Polyamide 6.6 nylon 6.6 Melt-spun from a liquid solution Morphology – radially arranged crystalline sheets resulting into anisotropicproperties Filament diameter about 12 µm and partially flexible High tensile strength Intermediate modulus Very low elongation up to breaking point Significantly lower strength in compression DuD PontP t developedd l d thesethfibfibersunderd theth tradet d name Kevlar.K lFFrompolyl (p(Phenylene terephthalamide (PPTA) polymer 5 grades of Kevlar with varying engineering properties are availablekevlar-29, Kevlar-49, Kevlar-100, Kevlar-119, Kevlar-129

Advanced FibresCeramic Fibres: BoronIt was the first advanced fibre developed for structural application (Talley 1959) Ceramic monofilament fiber Manufactured by CVD on to a tungsten core of 12 µm diameterTungstenBoron Fiber itself is a composite Circular cross section Fiber diameter ranges between 33 -400µm and typical diameter is 140µm Boron is brittle hence large diameter results in lower flexibilityCP Talley. J. Appl. Phys. 1959, Vol. 30, pp 1114.

Advanced FibresCeramic Fibres: Boron Thermal coefficient mismatch between boron and tungsten results in thermalresidualid l stressestd i fabricationduringf b i ti cooll downdt room temperaturetott When coated with Sic or B4C can be used to reinforce light alloys Strong in both tension and compression Exhibit linear axial stress-strain relationship up to 650ºC High cost of production

Advanced FibresCeramic fibres: Alumina (Al2O3) These are ceramics fabricated by spinning a slurry mix of alumina particles andadditivesdditit formtofa yarn whichhi h isi thenth subjectedbj t d tot controlledt ll d heating.h ti Fibers retain strength at high temperature

Advanced FibresCeramic fibres: Silicon Carbide (SiC)First method: CVD on tungsten or carbon- Carbon – pyrolytic graphite coated carbon core SCS-6- This fiber is similar in size and microstructure to boron- Relativity stiff, size of 140 µmSecond method: (Nicalon by Japan)- Controlled pyrolysis (chemical deposition by heat) of a polymericprecursor- filament is similar to carbon fiber in size.- SizeSi 14 µm- more flexible SiC shows high structural stability and strength retention even at temperatureabove 1000ºC

Cross Sectional Shapes of FibresShapeExamplesCircular:Glass, Carbon, Organic fibres,Alumina, Silicon CarbideElliptical:Alumina, MulliteTriangular:Silk, Silicon Carbide whiskers

Cross Sectional Shapes of FibresShapeExamplesHexagonal:Sapphire (Al2O3) whiskersgRounded Trianagular:Sapphire (Al2O3) single crystal fibreKideney bean:CarbonTrilobal:Carbon, Rayon

Types of Matrix MaterialsPolymers:Thermoplastic: Soften upon heating and can be reshaped with heat &pressureThThermosetting:ttibbecomecross linkedli k d duringd i fabricationf b i ti & dod nottsoften upon reheatingMetals:Ceramics:Carbon and Graphite:

Types of Matrix MaterialsThermoplastics:polypropylene,polyvinyl chloride (PVC),nylon,polyurethane,poly-ether-ether ketone (PEEK),polyphenylene sulfide (PPS),polysulpone higher toughness high volume low- cost processing Temperature range 225ºC

Types of Matrix MaterialsThermoplasti