Basic Introduction Of Composite Materials_apresentação

8/3/2019 Basic Introduction Of Composite Materials_apresentao

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Introduction to Composite Materials


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Composite materials Introduction

Definition: any combination of two or more different materials at the macroscopic level.

OR

Two inherently different materials that whencombined together produce a material withproperties that exceed the constituent materials.

R einforcement phase (e.g., Fibers)Binder phase (e.g., compliant matrix)

AdvantagesHigh strength and stiffnessLow weight ratioMaterial can be designed in addition to the structure


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Applications

Straw in clay construction by Egyptians Aerospace industry

Sporting goods AutomotiveConstruction


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Types of CompositesMatrixphase/Reinforcement Phase

Metal Ceramic Polymer

Metal Powder metallurgy parts combiningimmiscible metals

Cermets (ceramic-metal composite)

Brake pads

Ceramic Cermets, TiC, TiCNCemented carbides used in toolsFiber-reinforcedmetals

SiC reinforcedAl2O3Tool materials

Fiberglass

Polymer Kevlar fibers in anepoxy matrix

Elemental(Carbon,Boron, etc.)

Fiber reinforcedmetalsAuto partsaerospace

Rubber withcarbon (tires)Boron, Carbonreinforced plastics

MMCs CMCs PMCsMetal Matrix Composites Ceramic Matrix Comps. Polymer Matrix Comps


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D. Laminar Composites - 4

A lamina (laminae) is anyarrangement of unidirectionalor woven fibers in a matrix.Usually this arrangement isflat, although it may becurved, as in a shell.

A laminate is a stack of

lamina arranged with theirmain reinforcement in at least two different directions.


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E. Filled Composites

There are two types of filled composites. Inone, filler materials are added to a normalcomposite result in strengthening thecomposite and reducing weight. The secondtype of filled composite consists of a skeletal3-D matrix holding a second material. Themost widely used composites of this kind are

sandwich structures and honeycombs .


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Forms of R einforcement PhaseFibers

cross-section can be circular, square or hexagonalDiameters --> 0.0001 - 0.005

Lengths --> L/D ratio100 -- for chopped fibermuch longer for continuous fiber

Particulatesmall particles that impede dislocation movement (in metal composites) and strengthens the matrixFor sizes > 1 Q m, strength of particle is involves inload sharing with matrix

Flakesflat platelet form


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Fiber R einforcement

The typical composite consists of a matrix holdingreinforcing materials. The reinforcing materials, themost important is the fibers , supply the basicstrength of the composite. However, reinforcingmaterials can contribute much more than strength.They can conduct heat or resist chemical corrosion.They can resist or conduct electricity. They may bechosen for their stiffness (modulus of elasticity) or formany other properties.


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Types of Fibers

The fibers are divided into two main groups:Glass fibers: There are many different kinds of glass,ranging from ordinary bottle glass to high purity quartz

glass. All of these glasses can be made into fibers.Each offers its own set of properties. Advanced fibers: These materials offer high strengthand high stiffness at low weight. Boron, silicon, carbideand graphite fibers are in this category. So are thearamids, a group of plastic fibers of the polyamide(nylon) family.


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Fibers - Glass

Fiberglass properties vary somewhat according to the type of glassused. However, glass in general has several well knownproperties that contribute to its great usefulness as a reinforcingagent:

Tensile strengthChemical resistanceMoisture resistanceThermal propertiesElectrical properties

There are four main types of glass used in fiberglass: A glassC glassE glass

S glass


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Fibers - Glass

Most widely used fiberUses: piping, tanks, boats, sporting goods

Advantages

Low cost Corrosion resistanceLow cost relative to other composites:

DisadvantagesR elatively low strength

High elongationModerate strength and weight

Types:E-Glass - electrical, cheaperS-Glass - high strength


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Fibers - Aramid (kevlar, Twaron)

Uses:high performance replacement for glassfiber

Examples Armor, protective clothing, industrial,sporting goods

Advantages:higher strength and lighter than glassMore ductile than carbon


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Fibers - Carbon

2nd most widely used fiberExamples

aerospace, sporting goods Advantages

high stiffness and strengthLow densityIntermediate cost Properties:

Standard modulus: 207-240 GpaIntermediate modulus: 240-340 GPaHigh modulus: 340-960 GPaDiameter: 5-8 microns, smaller than human hair

Fibers grouped into tows or yarns of 2-12k fibers


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Fibers -- Carbon (2)

Types of carbon fibervary in strength with processingTrade-off between strength and modulus

Intermediate modulusPAN (Polyacrylonitrile)

fiber precursor heated and stretched to align structureand remove non-carbon material

High modulusmade from petroleum pitch precursor at lowercost much lower strength


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Fibers - Others

BoronHigh stiffness, very high cost Large diameter - 200 micronsGood compressive strength

Polyethylene - trade name: Spectra fiberTextile industry

High strengthExtremely light weight Low range of temperature usage


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Fibers -- Others (2)

Ceramic Fibers (and matrices) Very high temperature applications (e.g.

engine components)Silicon carbide fiber - in whisker form.Ceramic matrix so temperature resistanceis not compromisedInfrequent use


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Fiber Material Properties

Steel: density (Fe) = 7.87 g/cc; TS=0.380 GPa; Modulus=207 GPaAl: density=2.71 g/cc; TS=0.035 GPa; Modulus=69 GPa


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Fiber Strength


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Matrix Materials

Functions of the matrixTransmit force between fibersarrest cracks from spreading between fibers

do not carry most of the loadhold fibers in proper orientationprotect fibers from environment

mechanical forces can cause cracks that allowenvironment to affect fibers

Demands on matrixInterlaminar shear strengthToughnessMoisture/environmental resistanceTemperature properties

Cost


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EpoxyEpoxies have improved strength and stiffness propertiesover polyesters. Epoxies offer excellent corrosion

resistance and resistance to solvents and alkalis. Curecycles are usually longer than polyesters, however noby-products are produced.

Flexibility and improved performance is also achievedby the utilization of additives and fillers.

Matrices - Thermosets


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Matrices - Thermoplastics

Formed by heating to elevated temperatureat which softening occurs

R eversible reaction

Can be reformed and/or repaired - not commonLimited in temperature range to 150C

ExamplesPolypropylene

with nylon or glasscan be injected-- inexpensive

Soften layers of combined fiber and resin andplace in a mold -- higher costs


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Matrices - Others

Metal Matrix Composites - highertemperature

e.g., Aluminum with boron or carbon fibersCeramic matrix materials - very hightemperature

Fiber is used to add toughness, not necessarily higher in strength and stiffness


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Important Note

Composite properties are less thanthat of the fiber because of dilution

by the matrix and the need to orient fibers in different directions.


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MANUFACTUR ING PR OCESSESOF COMPOSITES

Composite materials have succeeded remarkably in theirrelatively short history. But for continued growth,especially in structural uses, certain obstacles must beovercome. A major one is the tendency of designers torely on traditional materials such as steel and aluminumunless composites can be produced at lower cost .

Cost concerns have led to several changes in thecomposites industry. There is a general movement toward the use of less expensive fibers. For example,graphite and aramid fibers have largely supplanted themore costly boron in advanced fiber composites. Asimportant as savings on materials may be, the real keyto cutting composite costs lies in the area of processing .


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The processing of fiber reinforced laminates can bedivided into two main steps:

Lay upCuring

Curing is the drying and hardening (or polymerization) of the resin matrix of a finished composite. This may bedone unaided or by applying heat and/or pressure.

Lay up basically is the process of arranging fiberreinforced layers (laminae) in a laminate and shapingthe laminate to make the part desired. (The term lay upis also used to refer to the laminate itself before curing.)Unless prepregs are used, lay up includes the actualcreation of laminae by applying resins to fiberreinforcements.


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Laminate lay up operations fall into three maingroups:

A. Winding and laying operationsB. Molding operationsC. Continuous lamination

Continuous lamination is relatively unimportant compared with quality parameters as not good as wrt other two processes. In this process, layers of fabric ormat are passed through a resin dip and brought together between cellophane covering sheets.

Laminate thickness and resin content are controlled bysqueegee rolls. The lay up is passed through a heat zone to cure the resin.


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A. Winding Operation

The most important operation in this category is filament winding . Fibers are passed through liquid resin, and thenwound onto a mandrel. After lay up is completed, the

composite is cured on the mandrel. The mandrel is thenremoved by melting, dissolving, breaking out or someother method.


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B. Molding OperationsMolding operations are used in making a large number of common composite products. There are two types of processes:

A. Open mold(1) Hand lay up(2) Spray up(3) Vacuum bag molding

(4) Pressure bag molding(5) Thermal expansion molding(6) Autoclave molding(7) Centrifugal casting

(8) Continuous pultrusion and pulforming.


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1. Hand Lay-up

Hand lay up , or contact molding, is the oldest andsimplest way of making fiberglass resin composites.

Applications are standard wind turbine blades, boats,

etc.)


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2. Spray-up

In Spray up process, chopped fibers and resins aresprayed simultaneously into or onto the mold. Applicationsare lightly loaded structural panels, e.g. caravan bodies,

truck fairings, bathtubes, small boats, etc.


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3. Vacuum-Bag Molding

The vacuum bag process was developed for makinga variety of components, including relatively largeparts with complex shapes. Applications are large

cruising boats, racecar components, etc.


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5. Thermal Expansion Molding

In Thermal Expansion Molding process, prepreg layersare wrapped around rubber blocks, and then placed ina metal mold. As the entire assembly is heated, therubber expands more than the metal, putting pressureon the laminate. Complex shapes can be madereducing the need for later joining and fasteningoperations.


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6. Autoclave Molding

Autoclave molding is similar to both vacuum bag andpressure bag molding. Applications are lighter, fasterand more agile fighter aircraft, motor sport vehicles.


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Continuous pultrusionis the compositecounterpart of metal

extrusion. Complexparts can be made.

7. Centrifugal Casting

Centrifugal Casting is used to form round objects such aspipes .

8. Continuous Pultrusion and Pulforming


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Pulforming is similar to pultrusion in many ways.However, pultrusion is capable only of making straight products that have the same volume all along theirlengths. Pulformed products, on the other hand, can be

either straight or curved, with changing shapes andvolumes. A typical pulformed product is a curvedreinforced plastic car spring . (shown in figure.)


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B. Closed mold(1) Matched die molding : As the namesuggests, a matched die mold consistsof closely matched male and femaledies (shown in figure). Applications arespacecraft parts, toys, etc.(2) Injection molding : The injectionprocess begins with a thermosetting(or sometimes thermoplastic) materialoutside the mold. The plastic maycontain reinforcements or not. It is first

softened by heating and/or mechanicalworking with an extrusion type screw.It is then forced, under high pressurefrom a ram or screw, into the coolmold. Applications are auto parts,vanes, engine cowling defrosters andaircraft radomes.


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Material Forms and Manufacturing

Objectives of material productionassemble fibers

impregnate resinshape product cure resin


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Sheet Molding Compound (SMC)

Chopped glass fiber added to polyesterresin mixture

Question: Is SMC isotropic or anisotropic?


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Manufacturing - Filament Winding

Highly automatedlow manufacturing

costs if highthroughput e.g., Glass fiber pipe,sailboard masts


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Manufacturing - Layups

compressionmolding

vacuum bagging


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Material Forms

Textile formsBraiding or weaving

Tubular braided formcan be flattened and cut for non-tubularproducts


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Fabric Structures

W oven: Series of Interlaced yarns at 90 to each other

K nit: Series of Interlooped Yarns

Braided: Series of Intertwined, Spiral Yarns

Nonwoven: Oriented fibers either mechanically,chemically, or thermally bonded


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Woven Fabrics

Basic woven fabrics consists of twosystems of yarns interlaced at right

angles to create a single layer withisotropic or biaxial properties.


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Physical Properties

Construction (ends & picks)Weight

ThicknessWeave Type


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Components of a Woven Fabric


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Basic Weave Types

Plain Weave


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Basic Weave TypesS atin 5H S


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Basic Weave Types

2 x 2 Twill


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Basic Weave TypesN on-Crimp


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Braiding

A braid consists of two sets of yarns, which are helicallyintertwined.

The resulting structure is oriented to the longitudinal axisof the braid.

This structure is imparted with a high level of

conformability, relative low cost and ease of manufacture.


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Braid Structure


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Types of Braids


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Fabric effects on material properties


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R esin transfer molding ( R TM)

Dry-fiber preform placed in a closedmold, resin injected into mold, thencured


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Material Forms

PultrusionFiber and matrix are pulled through a

die, like extrusion of metals --assembles fibers, impregnates theresin, shapes the product, and curesthe resin in one step.Example. Fishing rods


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Pultrusion


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Manufacturing

Tube rolling - tubular productsExamples

fishing rods

golf clubsoars

Prepreg tape typically used wrapped in 2directions or spiral wrapped

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