COMPOSITE MATERIALS

WHY COMPOSITES?ADVANTAGES OVER TRADITIONAL MATERIALSCORROSION RESISTANCEHIGH STRENGTH TO WEIGHT RATIOLOW MAINTENANCEEXTENDED SERVICE LIFEDESIGN FLEXIBILITY

COMPOSITES DEFINITIONA combination of two or more materials (reinforcement, resin, filler, etc.), differing in form or composition on a macroscale. The constituents retain their identities, i.e.., they do not dissolve or merge into each other, although they act in concert. Normally, the components can be physically identified and exhibit an interface between each other.A judicious combination of two or more materials that produces a synergistic effect. A material system composed of two or more physically distinct phases whose combination produces aggregate properties that are different from those of its constituents

A composite material consists of two phases:PrimaryForms the matrix within which the secondary phase is imbeddedAny of three basic material types: polymers, metals, or ceramicsSecondaryReferred to as the imbedded phase or called the reinforcing agentServes to strengthen the composite. (fibers, particles, etc.)Can be one of the three basic materials or an element such as carbon or boronComposition / Phase

Classification of composite materialMetal Matrix Composites (MMCs)Include mixtures of ceramics and metals, such as cemented carbides and other cermets, as well as aluminum or magnesium reinforced by strong, high stiffness fibersCeramic Matrix Composites (CMCs)Least common composite matrix. Aluminum oxide and silicon carbide are materials that can be imbedded with fibers for improved properties, especially in high temperature applicationsPolymer Matrix Composites (PMCs)Thermosetting resins are the most widely used polymers in PMCs. Epoxy and polyester are commonly mixed with fiber reinforcement

METAL MATRIX COMPOSITESMatrix material serves several functions in the composite provides the bulk form of the part or productholds the imbedded phase in placeshares the load with the secondary phase

METAL MATRIX COMPOSITESCommon reinforcing phase includesParticles of ceramic (commonly called cermets)Fibers of various materials, including other metals, ceramics, carbon, and boronFRMMC combine the high tensile strength and modulus of elasticity of a fiber with metals of low density, thus achieving good strength-to-weight and modulus-to-weight ratios in the resulting composite material.

METAL MATRIX COMPOSITESCemented carbides are composed of one or moreCarbide compounds bonded in a metallic matrixCommon cemented carbides are based on:Tungsten carbide (WC)Titanium carbide (TiC)Chromium carbide (Cr3C2)Tantalum carbide (TaC)

METAL MATRIX COMPOSITESCarbide ceramics constitute the principal ingredient in cemented carbides, typically ranging in content from 80% to 95% of total weight.

Principle metallic binders are:Cobalt used for WCNickel - used TiC and Cr3C2

METAL MATRIX COMPOSITESCutting tools are the most common application of cemented carbides based on tungsten carbide

Titanium carbide cermets are used principally for high temperature applications. Nickel is the preferred binder; its oxidation resistance at high temperature is superior to that of cobalt. Used as a cutting tool material for machining steels.

CERAMIC MATRIX COMPOSITESAdvantageHigh stiffnessHardnessHot hardnessCompressive strength Relatively low density

DisadvantageLow toughness and bulk tensile strengthSusceptibility to thermal cracking

Ceramic matrix composites represent an attempt to retain the desirable properties of ceramics while compensating for their weakness.

CERAMIC MATRIX COMPOSITESCeramic materials used as matrices includes:AluminaBoron carbideBoron nitrideSilicon carbideSilicon nitrideTitanium carbide

POLYMER MATRIX COMPOSITESFiber Reinforced Polymer (FRP) Composites are defined as:

A matrix of polymeric material that is reinforced by fibers or other reinforcing material

COMPOSITES MARKETSTRANSPORTATIONCONSTRUCTIONMARINECORROSION-RESISTANTCONSUMERELECTRICAL/ELECTRONICAPPLIANCES/BUSINESSAIRCRAFT/DEFENSE

Infrastructure BenefitsHIGH STRENGTH/WEIGHT RATIOORIENTATED STRENGTHDESIGN FLEXIBILITYLIGHTWEIGHTCORROSION RESISTANCELOW MAINTENANCE/LONG-TERM DURABILITYLARGE PART SIZE POSSIBLETAILORED AESTHETIC APPEARANCEDIMENSIONAL STABILITYLOW THERMAL CONDUCTIVITYLOW INSTALLED COSTS

FRP COMPOSITE CONSTITUENTSRESINS (POLYMERS)

REINFORCEMENTS

FILLERS

ADDITIVES

MATERIALS: RESINSPRIMARY FUNCTION: TO TRANSFER STRESS BETWEEN REINFORCING FIBERS AND TO PROTECT THEM FROM MECHANICAL AND ENVIRONMENTAL DAMAGE

TYPES:THERMOSETTHERMOPLASTIC

RESINSTHERMOSETPOLYESTERVINYL ESTEREPOXY PHENOLICPOLYURETHANE

RESINSTHERMOPLASTICACETALACRYRONITRILE BUTADIENE STYRENE (ABS)NYLONPOLYETHYLENE (PE)POLYPROPYLENE (PP)POLYETHYLENE TEREPHTHALATE (PET)

RESINSTHERMOSET ADVANTAGESTHERMAL STABILITYCHEMICAL RESISTANCEREDUCED CREEP AND STRESS RELAXATIONLOW VISCOSITY- EXCELLENT FOR FIBER ORIENTATIONCOMMON MATERIAL WITH FABRICATORS

RESINSTHERMOPLASTIC ADVANTAGESROOM TEMPERATURE MATERIAL STORAGERAPID, LOW COST FORMINGREFORMABLEFORMING PRESSURES AND TEMPERATURES

POLYESTERSLOW COSTEXTREME PROCESSING VERSATILITYLONG HISTORY OF PERFORMANCEMAJOR USES:Transportation Construction Marine

VINYL ESTERSIMILAR TO POLYESTER

EXCELLENT MECHANICAL & FATIGUE PROPERTIES

EXCELLENT CHEMICAL RESISTANCE

MAJOR USES:Corrosion Applications - Pipes, Tanks, & Ducts

EPOXYEXCELLENT MECHANICAL PROPERTIESGOOD FATIGUE RESISTANCELOW SHRINKAGEGOOD HEAT AND CHEMICAL RESISTANCEMAJOR USES:FRP Strengthening SystemsFRP RebarsFRP Stay-in-Place Forms

PHENOLICSEXCELLENT FIRE RETARDANCELOW SMOKE & TOXICITY EMISSIONSHIGH STRENGTH AT HIGH TEMPERATURESMAJOR USES:Mass Transit - Fire Resistance & High TemperatureDucting

POLYURETHANETOUGH

GOOD IMPACT RESISTANCE

GOOD SURFACE QUALITY

MAJOR USES:Bumper Beams, Automotive Panels

SUMMARY: POLYMERSWIDE VARIETY AVAILABLESELECTION BASED ON:PHYSICAL AND MECHANICAL PROPERTIES OF PRODUCTFABRICATION PROCESS REQUIREMENTS

MATERIAL: FIBERREINFORCEMENTSPRIMARY FUNCTION: CARRY LOAD ALONG THE LENGTH OF THE FIBER, PROVIDES STRENGTH AND OR STIFFNESS IN ONE DIRECTION

CAN BE ORIENTED TO PROVIDE PROPERTIES IN DIRECTIONS OF PRIMARY LOADS

REINFORCEMENTSNATURAL

MAN-MADE

MANY VARIETIES COMMERCIALLY AVAILABLE

MAN-MADE FIBERSARAMIDBORONCARBON/GRAPHITEGLASSNYLONPOLYESTERPOLYETHYLENEPOLYPROPYLENE

FIBER PROPERTIESDENSITY (g/cm3)

FIBER REINFORCEMENTGLASS (E-GLASS)MOST COMMON FIBER USEDHIGH STRENGTHGOOD WATER RESISTANCEGOOD ELECTRIC INSULATING PROPERTIESLOW STIFFNESS

FIBER REINFORCEMENTARAMID (KEVLAR)SUPERIOR RESISTANCE TO DAMAGE (ENERGY ABSORBER)GOOD IN TENSION APPLICATIONS (CABLES, TENDONS)MODERATE STIFFNESSMORE EXPENSIVE THAN GLASS

FIBER REINFORCEMENTCARBONGOOD MODULUS AT HIGH TEMPERATURESEXCELLENT STIFFNESSMORE EXPENSIVE THAN GLASSBRITTLELOW ELECTRIC INSULATING PROPERTIES

FIBER ORIENTATIONANISOTROPICUNIDIRECTIONALBIAS - TAILORED DIRECTION0O - flexural strengthening90O - column wraps+ /- 45O - shear strengtheningANGLE VARIES BY APPLICATION

REINFORCEMENTSSUMMARYTAILORING MECHANICAL PROPERTIESTYPE OF FIBERPERCENTAGE OF FIBERORIENTATION OF FIBER

DESIGN VARIABLESFOR COMPOSITESTYPE OF FIBERPERCENTAGE OF FIBER or FIBER VOLUMEORIENTATION OF FIBER0o, 90o, +45o, -45oTYPE OF POLYMER (RESIN)COSTVOLUME OF PRODUCT - MANUFACTURING METHOD

DESIGN VARIABLESFOR COMPOSITESPHYSICAL: tensile strengthcompression strengthstiffnessweight, etc.ENVIRONMENTAL:FireUVCorrosion Resistance

TAILORING COMPOSITE PROPERTIESMAJOR FEATUREPLACE MATERIALS WHERE NEEDED - ORIENTED STRENGTHLONGITUDINALTRANSVERSEor betweenSTRENGTHSTIFFNESSFIRE RETARDANCY

MANUFACTURING PROCESSESHand Lay-up/Spray-upResin Transfer Molding (RTM)Compression MoldingInjection MoldingReinforced Reaction Injection Molding (RRIM)PultrusionFilament WindingVacuum Assisted RTM (Va-RTM)Centrifugal Casting

PROCESS CHARACTERISTICSHand Lay-up/Spray-upMAX SIZE:UnlimitedPART GEOMETRY:Simple - ComplexPRODUCTION VOLUME:Low - MedCYCLE TIME:SlowSURFACE FINISH:Good - ExcellentTOOLING COST:LowEQUIPMENT COST:Low

PRODUCT CHARACTERISTICSPultrusion

CONSTANT CROSS SECTIONCONTINUOUS LENGTHHIGH ORIENTED STRENGTHSCOMPLEX PROFILES POSSIBLEHYBRID REINFORCEMENTS

MATERIAL PROPERTIESPROPERTIES OF FRP COMPOSITES VARY DEPENDING ON:TYPE OF FIBER & RESIN SELECTEDFIBER CONTENTFIBER ORIENTATIONMANUFACTURING PROCESS

REPAIRHYBRIDS (SUPER COMPOSITES): TRADITIONAL MATERIALS ARE JOINED WITH FRP COMPOSITESWOODSTEELCONCRETEALUMINUM

BENEFITS - SUMMARYLIGHT WEIGHTHIGH STRENGTH to WEIGHT RATIOCOMPLEX PART GEOMETRYCOMPOUND SURFACE SHAPEPARTS CONSOLIDATIONDESIGN FLEXIBILITYLOW SPECIFIC GRAVITYLOW THERMAL CONDUCTIVITYHIGH DIELECTRIC STRENGTH

STRUCTURAL DESIGN WITH FRP COMPOSITES

*****The Composites Institute identifies eight market segments (plus a ninth - miscellaneous) for composite applications. The are:

transportationconstructionmarinecorrosion-resistantconsumerelectrical/electronicappliance/businessaircraft/defense*Composites can provide infrastructure applications with many benefits as listed here.

Infrastructure can have all these benefits an more when the proper materials and manufacturing process is selected.

But I believe that in order to achieve these goals, the engineer must specifically know the performance of his product. This includes the physical, mechanical, installation, cost, and quality that identifies the minimum performance specifications. *Composites are composed of polymers, reinforcing fibers, fillers, and other additives. Each of these ingredients play an important role in the processing and final performance of the end product.

In general terms, you could say that:

The polymer is the glue that holds the composite and influence the physical properties of the composite end product.

The reinforcement provides the mechanical strength properties to the end product.

The fillers and additives are processing aids and also impart special properties to the end product.

Other materials that we will cover include core materials. Depending on you application, core materials provide stiffness while being lightweight.*Polymers are generally petrochemical or natural gas derivatives and can be either thermoplastic or thermosetting. Both types of polymers are used in composites and can benefit when combined with reinforcing fibers.

However, the major volume of thermoplastic polymers are not used in composite form.

In contrast to thermoplastics, thermosetting polymers generally require reinforcing fibers of high filler loading in order to be used.

Properties required are usually dominated by strength, stiffness, toughness, and durability. The end-user must take into account the type of application, service temperature, environment, method of fabrication, and the mechanical propeties needed.

Proper curing of the resin is essential for obtaining optimum mechanical properties, preventing heat softening, limiting creep, and reducing moisture impact.*Thermosetting polymers are used for the major portion of the composites industry.****Unsaturated polyester have the dominant share of this market because of their relatively low cost, fabrication flexibility and good performance.

These polyesters are different than the thermoplastic polyesters used for textile fibers.

Polyesters are available in many different varieties based on their special attributes or processing characteristics.

Table 2.1 on page 13 of the handbook provides a handy selection guide that relates these characteristics to composite performance properties and typical end product uses.*Vinyl esters are epoxy/polyester hybrids that combine some of the better characteristics of each system.

They have good structural performance and dynamic properties.

Vinyl esters should be considered for higher performance applications than isophthalic polyesters because they have superior chemical and water resistant properties, better retention of strength and stiffness at elevated temperatures and greater toughness.

They process like polyesters. Their higher cost is offset by performance improvements.*Epoxy polymers have higher mechanical properties, particularly dynamic and fatigue resistant properties, and water resistance than polyesters,. They exhibit low shrinkage during cure. They also have excellent adhesion characteristics. They have good heat and chemical resistance, good electrical properties. Epoxies generally have a slower cure.

Epoxy resins should be considered where higher shear strength than is available with polyesters, and the application requires good mechanical properties at elevated temperatures or durability.

Epoxies are used automated manufacturing such as pultrusion, filament winding, resin transfer molding, and compression molding.

Some epoxies have low ultra-violet resistance and may need special surface protection.*Phenolics are experiencing a resurgence of interest in composites because of their fire resistance. They have low creep and good dimensional stability.Phenolic resins should be considered when the goal is performance under heat, retention of properties under fire conditions or low emission of toxic fumes. Characteristics of phenolics include low flammability, low spread of flame and little smoke. Mechanical properties are comparable to orthophthalic polyesters. Low shrinkage compared with polyesters is as characteristic of this resin.

Phenolics are available in liquid form or as molding compounds. Cure at room temperature is possible, however an elevated post cure above 800C is needed ot obtain dimensionally stable materials.

Development efforts by the resin producers have resulted in liquid systems for filament winding, pultrusion, and spray-up. This has greatly broadened the market opportunity for phenolics in the composites industry.Their excellent ablative characteristics have been used in rocket nozzle applications.*Urethanes are available as either thermoplastic or thermosets.

Broad compounding capability cover the range from flexible to rigid systems.

Both foams and solid forms are in use.

They process rapidly, and although higher in cost, are gaining in usage based on cost/performance. Polyurethanes are used primarily in Reinforced Reaction Injection Molding, for items such as automotive bumpers and fascia.*To summarize the discussion on polymers:

A wide variety of polymers are available that can satisfy virtually every conceivable end use application.

Proper selection requires knowledge of the physical and mechanical properties of the application and the fabrication process to be used to produce the end products.**There are many reinforcing fibers commercially available for use in composites. They are of both natural and synthetic or man-made origin.*The most prominent reinforcing fibers in terms of both quantity consumed and product sales value would be aramid, boron, carbon/graphite, glass, nylon, polyester, and polyethylene.

Of these, glass fiber represents the predominant reinforcement because of its relatively low cost, good balance of properties, and a 40 year experience base.

Materials such as boron are very expensive and only used in the most demanding performance applications.**As shown in the video, many raw materials are used to produce glass. silica sand is the primary ingredient, accounting for more than 50 percent of the raw materials. Additional materials that may be used include limestone, flourspar, boric acid, and clay, in addition to a variety of metal oxides. The combination and amounts depends on which type of glass is being produced.Glass is generally the most impact resistant fiber but also weighs more than carbon or aramid. Glass fibers have excellent strength characteristics, equal and higher than steel in certain forms. The lower modulus requires special design treatment in applications where stiffness is critical.Processing characteristics required of glass fibers include: choppability, low static buildup, good fiber matrix adhesion.Glass fibers are insulators of both electricity and heat and thus their composites exhibit very good electrical and thermal insulation properties. They are transparent to radio frequency radiation, therefore they are used extensively in radar antenna applications.Glass filaments are extremely fragile, and are supplied in bundles called strands, rovings or yarns. Strands are a collection of continuous filaments. A roving refers to a collection of untwisted strands or yarns. Yarns are collections of filaments or strands that are twisted together.*Aramid fiber, is an aromatic polyimide, organic man made fiber. There are three major commercial suppliers: DuPont produces a product called Kevlar, Akzo produces a product called Twaron, and Teijin produces a product called Technora.Kevlar is produced in two distinct types of aramid fibe: Kevlar 29 and and a higher modulus Kevlar 49. Both types have a tensile stress/strain curve which is essentially linear to failure.Aramid fibers offer good mechanical properties at a low density with the added advantage of toughness or damage resistance. They are characterized as having reasonably high tensile strength, a medium modulus, and a very low density. There is a significant cost difference compare with glass fibers. Since aramids are lightweight, they have an advantage in their strength/weight and stiffness to weight ratios. It should be noted that they have relatively low compressive strengths.Aramid fibers are insulators of both electricity and heat. They are resistant to organic solvents, fuels, and lubricants. Fibers without resin are tough and used as cables or ropes because they do not behave in a brittle manner as do both carbon and arramid.

hybrids of the two fibers may be used in specific applications such as high performance boats.*

Carbon/graphite fibers combine high modulus with low density and make them very attractive for aircraft and other applications where weight saved can be directly translated to cost savings and, therefore, justify their higher material cost.Carbon fiber is created using polyacrylonitrile (PAN), pitch or rayon fiber precursors. PAN based fibers offer good strength and modulus values up to 85-90 Msi. They also offer excellent compression strength for structural applications. Pitch fibers are made from petroleum or coal tar pitch. Their extremely high modulus values (up to 140 Msi) and favorable CTE make them the material used in spacecraft applications.It should be noted that Carbon fiber composites are more brittle than glass or aramid and can show galvanic corrosion when used next to metal. A barrier material, such as glass, and sometimes epoxy, must be used. *NEW*To summarize the discussion about reinforcements, one should remember that with composites, the mechanical strength properties are dependent on the type, amount, and orientation of the reinforcement that is selected for the particular product.

With the variety and many different forms of reinforcements that are commercially available, an almost limitless number of composite systems are available to meet the strength requirements of any applications.

Additionally, the ability to orient the composite strength characteristics to the specific performance requirements of the application, provides a unique advantage for composites that translates to weight and cost advantage as compared to traditional homogeneous structural materials.*Reinforcing fibers contribute to the mechanical strength characteristics of the composite. The strength is dependent on:- the type or species of fiber- the amount of fiber- the orientation of the fiber- the fiber surface treatment- and its compatibility with the matrix polymer.

By varying these parameters, a broad range of mechanical properties are possible.

For example, a composite which has all the fibers aligned in one direction, it is stiff and strong in that direction, but in the transverse direction, it will have a lower modulus and low strength. Also, the fiber volume fraction heavily depends on the method of manufacture. Generally, The higher the fiber content the stronger the composite.*These same parameters allow the tailoring of the mechanical properties of the composite to the specific property requirements of the end product application.

This is a major feature of composite materials that allows their efficient use in highly stressed applications.*By carefully selecting the fiber, resin and manufacturing process, designers can tailor composites to meet final product requirements that could not be achieved using other materials.

Fiber orientation can maximize strength in one or more directions. This allows wall thickness variations, complex-contoured parts, and various degrees of stiffness or strengths.

Composite laminates may be designed to be isotropic (uniform properties in all directions, independent of applied load) or anisotropic (properties only apparent in the direction of the applied load), balanced or unbalanced, symmetric or asymmetric depending on the forces from the application.

Understanding layered or laminate structures behavior is very important in designing effective composite parts or structures.*We will discuss the various types of manufacturing processes. They include.....*Both processes are characterized by relatively low equipment and tooling costs, low to medium production volumes, high level of worker dependence, and the requirement for emissions control techniques because of the styrene fumes that come from the polyester resins that are typically used.*- Pultruded parts naturally have a high degree of reinforcement orientation in the continuous direction.- Cross direction reinforcement is achieved by woven tapes or mats, or process attachments that wind reinforcements around the reinforcing system.- The process, once operating, uses very low labor. Long continuous runs can be economically produced.- Tooling and capital equipment costs are moderate and depend on the size and complexity of the profiles to be produced.- Long production runs with minimum number of profile changes provide the best economics.- Very large, complex profiles have been produced. Hollow and encapsulated core structures are routinely produced. Hybrid reinforcing systems are easily incorporated into a pultruded product to maximize the strength of a particular profile.*To summarize, FRP composites material properties vary depending on the type of fiber and resin selected, the fiber content, the fiber orientation, and the manufacturing process.

This is very important in order for composites to be used in the proper applications. *Repair of the infrastructure using FRP composites promises to have a huge impact for the civil engineer. FRP composites, used in conjunction with traditional construction materials such as wood, steel, concrete, and aluminum, will create SUPER COMPOSITES, where both materials complement each other in the performance of a structure.

For example, both glass and aramid have demonstrated major benefits when applied in wood glulam beams. A thin layer of FRP composites used on the tensile face of glulam beams nearly doubles the length of that beam without increasing the depth of the beam.

Some of you may be familiar with the use of carbon and glass FRP composites to repair, strengthen, and seismically upgrade reinforced concrete structures, particularly in California. *