STRENGTHENING STRUCTURES USING FRP COMPOSITE MATERIALSDAMIAN I. KACHLAKEV, Ph.D., P.E.California Polytechnic State UniversitySan Luis Obispo

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.

DEFINITIONFiber 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

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

transportationconstructionmarinecorrosion-resistantconsumerelectrical/electronicappliance/businessaircraft/defense

U.S. COMPOSITES SHIPMENTS - 1996 MARKET SHARESEMI-ANNUAL STATISTICAL REPORT - AUGUST 26, 1996Includes reinforced thermoset and thermoplasticresin composites, reinforcements andfillers.SOURCE: SPI Composites InstituteTransportation 30.6%Other- 3.4%Aircraft/Aerospace 0.7%Appliance/Business Equipment - 5.3% Construction 20%ConsumerProducts - 6%Marine - 11.6%Electrical/Electronic - 10%Corrosion-ResistantEquipment - 12.4%

Sheet:

Market Share

NEW

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

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.

FRP COMPOSITE CONSTITUENTSRESINS (POLYMERS)

REINFORCEMENTS

FILLERS

ADDITIVES

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.

MATERIALS: RESINSPRIMARY FUNCTION:

TO TRANSFER STRESS BETWEEN REINFORCING FIBERS AND TO PROTECT THEM FROM MECHANICAL AND ENVIRONMENTAL DAMAGE

TYPES:THERMOSETTHERMOPLASTIC

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.

RESINSTHERMOSETPOLYESTERVINYL ESTEREPOXY PHENOLICPOLYURETHANE

Thermosetting polymers are used for the major portion of the composites industry.

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

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 ESTERSIMILAR TO POLYESTER

EXCELLENT MECHANICAL & FATIGUE PROPERTIES

EXCELLENT CHEMICAL RESISTANCE

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

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.

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

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.

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

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.

POLYURETHANETOUGH

GOOD IMPACT RESISTANCE

GOOD SURFACE QUALITY

MAJOR USES:Bumper Beams, Automotive Panels

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.

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

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.

Physical Properties of Thermosetting Resins Used in Structural Composites

Resin

Type

Density

(kg/m3)

Tensile

Str. (MPa)

Elong.

(%)

E-Mod.

(GPa)

Long.Term

t ,(C)

Polyester

1.2

50-65

2-3

3

120

Vinyl

Ester

1.15

70-80

4-6

3.5

140

Epoxy

1.1-1.4

50-90

2-8

3

120-200

Phenolic

1.2

40-50

1-2

3

120-150

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

There are many reinforcing fibers commercially available for use in composites. They are of both natural and synthetic or man-made origin.

MAN-MADE FIBERSARAMIDBORONCARBON/GRAPHITEGLASSNYLONPOLYESTERPOLYETHYLENEPOLYPROPYLENE

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.

FIBER PROPERTIESDENSITY (g/cm3)

FIBER PROPERTIESTENSILE STRENGTHx103 psi

FIBER PROPERTIESSTRAIN TO FAILURE(%)

Glass has very good impact resistance due to their high strain to failure, when compared to other fibers.

Aramid also has excellent impact resistance, particularly to ballistic impact.

Not shown on this chart is steels ability to have a strain to failure up to 20%. The value shown is the strain at yield.

FIBER PROPERTIESTENSILE MODULUS106 psi

I want to point out that in this graph, carbon can be shown with several different modulus. For example, 12K carbon fibers are available with standard or low (33-35 MSI), intermediate (40-50 MSI), high (50-70 MSI), and ultra high (70-140 MSI) modulus. The higher you go, the more expensive it gets. The higher modulus is more suitable for aircraft and spacecraft where performance is the main objective, not cost.

FIBER PROPERTIESCTE - Longitudinalx10-6/0C

Sheet:

Aramid

Carbon

S-Glass

E-Glass

Steel

Alum

East

West

North

Carbon and aramid fibers can have small or negative coefficients of thermal expansion. It should be noted that the matrix has a much higher CTE than the reinforcement.

The thermal expansion of the composite depends not only on the type of reinforcement and the type of matrix, but also the geometry of the reinforcement, its volume fraction, and the amount and type of filler used.

FIBER PROPERTIESTHERMAL CONDUCTIVITYx10-6/0CBTU-in/hr-ft2 - 0F

Sheet:

Aramid

Carbon

S-Glass

FRP

Steel

Alum

Concrete

East

West

North

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

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.

GLASS TYPESE-GLASSS-GLASSC-GLASSECR-GLASSAR-GLASS

E-Glass is electrical resistant glass providing good overall strength at low cost. It accounts for about 90% of all glass fiber reinforcements. It has good electrical resistance, and it is used in radomes and antennas because of its radio frequency transparency. It is also used in computer circuit boards to provide stiffness and electrical resistance.S-Glass is a high strength, high stiffness glass with good performance in high temperature and corrosive environments. This type of glass is stronger and stiffer than E-Glass and is used in more demanding applications were their extra cost can be justified. This type of glass is referred to R-Glass in Europe and T-Glass in Japan. A lower cost version, S-2 glass is approximately 40-70% stronger than E-Glass. S-2 Glass is used in golf club shafts because is provides flexibility and accuracy for long ball hitting, and it is less expensive than carbon.C-Glass is a calcium borosilicate glass providing good resistance to corrosive acid environments such as hydrochloric and sulfuric acid. It is also noted that E-Glass and S-2 Glass have a much better resistance to basic solutions such as sodium carbonate, compared to C-Glass. C-Glass has poor high-temperature performance, therefore either E-Glass or S-Glass is used.ECR-Glass , used in Europe is an alternative to E-Glass in a corrosive environment. They have similar properties to E-Glass, very resistant to chemical attack and are boron free.AR-Glass is a alkali resistant glass formulated for use in cement substrates and concrete.

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

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.

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

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.

TYPICAL PROPERTIES OF STRUCTURAL FIBERS

Fiber Type

Density

(kg/m3)

E-Modulus

(GPa)

Tensile Strength

(GPa)

Elong.

(%)

E-Glass

2.54

72.5

1.72-3.45

2.5

S-Glass

2.49

87

2.53-4.48

2.9

Kevlar 29

1.45

85

2.27-3.80

2.8

Kevlar 49

1.45

117

2.27-3.80

1.8

Carbon (HS)

1.80

227

2.80-5.10

1.1

Carbon (HM)

1.80-1.86

370

1.80

0.5

Carbon (UHM)

1.86-2.10

350-520

1.00-1.75

0.2

ADVANTAGES AND DISADVANTAGES OF REINFORCING FIBERS

Fiber Type

Advantages

Disadvantages

E-Glass, S-Glass

High Strength, Low Cost

Low Stiffness, Fatigue

Aramid

High Strength, Low Density

Low Compr. Str., High Moisture Absorption

HS Carbon

High Strength and Stiffness

High Cost

UHM Carbon

Very High Stiffness

Low Strength, High Cost

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

NEW

DEGREE OF ANISOTROPY OF FRP COMPOSITES

FRP Composite

E1/E2

E1/G12

F1/F2t

Steel

1.00

2.58

1.00

Vinyl Ester

1.00

0.94

1.00

S-Glass/Epoxy

2.44

5.06

28

E-Glass/Epoxy

4.42

8.76

17.7

Carbon/Epoxy

13.64

19.1

41.4

UHM/Epoxy

40

70

90

Kevlar/Epoxy

15.3

27.8

260

PROPERTIES OF UNIDIRECTIONAL COMPOSITES

Property

E-Glass/

Epoxy

S-Glass/

Epoxy

Aramid/

Epoxy

Carbon/

Epoxy

Fiber Volume

0.55

0.50

0.60

0.63

Longitudinal Modulus GPa

39

43

87

142

Transverse .Modulus,

GPa

8.6

8.9

5.5

10.3

Shear Modulus,

GPa

3.8

4.5

2.2

7.2

Poissons

Ratio

0.28

0.27

0.34

0.27

Long.Tensile Strength

MPa

1080

1280

1280

2280

Compressive Strength,

MPa

620

690

335

1440

ELASTIC AND SHEAR MODULI OF FRP COMPOSITES

Material

E1

E2

G12

G13

G23

Aluminum

10.40

10.40

3.38

3.38

3.38

Steel

29

29

11.24

11.24

11.24

Carbon/Epoxy

20

1.30

1.03

1.03

0.90

Glass/Epoxy

7.80

2.60

1.25

1.25

0.50

REINFORCEMENTSSUMMARYTAILORING MECHANICAL PROPERTIESTYPE OF FIBERPERCENTAGE OF FIBERORIENTATION OF FIBER

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.

COMPARISON OF AXIAL AND FLEXURAL EFFICIENCY OF FRP SYSTEMS

AXIAL EFFICIENCY

FLEXURAL EFFICIENCY

Material

E/(

Rank

E1/2/(

Rank

Carbon/Epoxy

113.1

1

8.4

1

Kevlar/Epoxy

52.1

2

6.0

2

E-Glass/Epoxy

21.4

4

3.5

3

Mild Steel

25.6

3

1.8

4

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

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.

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

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.

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

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.

STRUCTURAL DESIGN APPROACH FOR COMPOSITES

40.bin

SPECIFIC MODULUS AND STRENGTH OF FRP COMPOSITE

FLOW CHART FOR DESIGN OF FRP COMPOSITES

42.bin

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

We will discuss the various types of manufacturing processes. They include.....

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

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.

PRODUCT CHARACTERISTICSPultrusion

CONSTANT CROSS SECTIONCONTINUOUS LENGTHHIGH ORIENTED STRENGTHSCOMPLEX PROFILES POSSIBLEHYBRID REINFORCEMENTS

- 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.

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

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.

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

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.

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

LIFE CYCLE ECONOMICSPLANNING/DESIGN/DEVELOPMENT COSTPURCHASE COSTINSTALLATION COSTMAINTENANCE COSTLOSS/WEAR COSTLIABILITY/INSURANCE COSTSDOWNTIME/LOST BUSINESS COSTREPLACEMENT/DISPOSAL/RECYCLING COST

LIFE CYCLE ECONOMICS (Examples)IBACH BRIDGE (SWITZERLAND)CFRP LAMINATES- 50 TIMES MORE EXPENSIVE THAN STEEL PER KILOGRAMCFRP LAMINATES- 9 TIMES MORE EXPENSIVE THAN STEEL BY VOLUMEREPAIR WORK REQUIREMENTS-175 KG STEEL OR 6.2 KG CFRPMATERIAL COST-20 % OF THE TOTAL PROJECT COST

LIFE CYCLE ECONOMICS (Examples)HORSETAIL CREEK BRIDGE (OREGON)CONVENTIONAL REPAIR (SHEAR ONLY-ONE BEAM)-$69,000FRP REPAIR (GFRP SHEAR ONLY-ONE BEAM)-$1850FRP REPAIR [SHEAR (GFRP)+ FLEXURE(CFRP), ONE BEAM]- $9850

CONCLUSIONSECONOMICS ARE MORE THAN THE BASIC ELEMENTS OF MATERIALS, LABOR, EQUIPMENT, OVERHEAD, ETC.ENTIRE LIFE CYCLE ECONOMICS MUST BE CONSIDERED AND COMPARED TO THAT OF TRADITIONAL MATERIALS TO DETERMINE THE BENEFITS OF COMPOSITES IN A GIVEN APPLICATION

STRUCTURAL DESIGN WITH FRP COMPOSITES

EXTERNAL REINFORCEMENT OF RC BEAMS USING FRPBACKGROUNDDESIGN MODELSLACK OF DUCTILITY FLEXURAL STRENGTHENINGSHEAR STRENGTHENINGPRESTRESSED FRP APPLICATIONDESIGN METHODOLOGY AND ANALYSISOTHER ISSUESFATIGUE, CREEP, LOW TEMPERATURE FRP PERFORMANCEDESIGN EXAMPLES

FRP STRENGTHENED BEAMSBACKGROUNDFRP VS. EXTERNALLY STEEL BONDED PLATESCORROSION AT THE EPOXY-STEEL INTERFACESTEEL PLATES DO NOT INCREASE STRENGTH, JUST STIFFNESSHIGH TEMPERATURES PERFORMANCE DIFFICULTIES DUE TO HEAVY WEIGHT OF THE STEEL PLATESSTRENGTHENING DESIGN BASED ON MATERIAL WEIGHT, NOT STRUCTURAL NEEDSCONSTRUCTION DIFFICULTIESTIME CONSUMING, HEAVY EQUIPMENT NEEDED

FRP STRENGTHENED BEAMSLACK OF DUCTILITYLINEAR STRESS-STRAIN PROFILEDEFINITION OF DUCTILITYDEFLECTION AT ULTIMATE/DEFLECTION AT YIELD- NOT APPLICABLE FOR FRP MATERIALSTRAIN-ENERGY ABSORPTION, I.E., AREA UNDER LOAD-DEFLECTION CURVE- OK FOR FRP COMPOSITESIN GENERAL- THE HIGHER THE FRP FRACTION AREA, THE LOWER THE ENERGY ABSORPTION OF THE STRENGTHENED CONCRETE BEAM

FRP STRENGTHENED BEAMS

TYPICAL LOAD-DEFLECTION CURVE

FRP REINFORCED BEAMS- FAILURE MODES

FRP REINFORCEMENT OF RC COLUMNSAdvantages of Strengthening Columns with FRP JacketsIncreased DuctilityIncreased StrengthLow Dead WeightReduced Construction TimeLow Maintenance

FRP REINFORCEMENT OF RC COLUMNSFactors Influencing the Behavior of FRP-Retrofitted ColumnsColumn compositionColumn geometryCurrent conditionType of loadingEnvironmental conditions

DESIGN OF FRP RETROFIT OF RC COLUMNSShear StrengtheningFlexural Hinge ConfinementLap Splice Clamping

LOAD-DISPLACEMENT CURVE(Before Strengthening)

LOAD-DISPLACEMENT CURVE(After Strengthening)

COLUMN DUCTILITY

FRP REINFORCEMENT OF RC COLUMNSAdvantages of Strengthening Columns with FRP JacketsIncreased DuctilityIncreased StrengthLow Dead WeightReduced Construction TimeLow Maintenance

FRP REINFORCEMENT OF RC COLUMNSFactors Influencing the Behavior of FRP-Retrofitted ColumnsColumn compositionColumn geometryCurrent conditionType of loadingEnvironmental conditions

LOAD-DISPLACEMENT CURVE(Before Strengthening)

LOAD-DISPLACEMENT CURVE(After Strengthening)

COLUMN DUCTILITY

CONSTRUCTION PROCESSPreparation of the Concrete SurfaceMixing Epoxy, Putty, etc.Preparation of the FRP Composite System Application of the FRP Strengthening SystemAnchorage (if recommended)Curing the FRP MaterialApplication of Finish System

CONCRETE SURFACE PREPARATIONRepair of the existing concrete in accordance to:ACI 546R-96 Concrete Repair GuideICRI Guideline No. 03370 Guide for Surface Preparation for the Repair of Deteriorated Concrete...Bond Between Concrete and FRP Materials Should satisfy ICRI Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces

CONCRETE SURFACE PREPARATIONRepair Cracks 0.010 inches or WiderEpoxy pressure injectedTo satisfy Section 3.2 of the ACI 224.1R-93 Causes, Evaluation and Repair of CracksConcrete Surface Unevenness to be Less than 1 mmConcrete Corners- Minimum Radius of 30 mm

APPLICATION OF THE FRP COMPOSITEIn Accordance to Manufacturers and Designer's SpecificationsPrimingPutty ApplicationUnder-coating with Epoxy ResinApplication of the FRP Laminate/ FRP Fiber SheetOver-coating with Epoxy Resin

CURING OF THE FRP COMPOSITESIn Accordance to Manufacturers SpecificationsTemperature ranges and Curing Time- varies from few hours to 15 days for different FRP systemsCured FRP CompositeUniform thickness and densityLack of porosity

CONSTRUCTION PROCESSTypical RC Beam in Need for Repaircorroded steelspalling concrete

CONSTRUCTION PROCESSDeteriorated Column / Beam Connection

CONSTRUCTION PROCESSConcrete Surface PreparationSmooth, free of dust and foreign objects, oil, etc.Application of primer and putty (if required by the manufacturer)

CONSTRUCTION PROCESSPreparation of the FRP Composites for ApplicationFollow manufacturers recommendations

CONSTRUCTION PROCESSPriming of the Concrete SurfaceApplication of the Undercoating epoxy Layer (adhesive when FRP pultruded laminates are used)

CONSTRUCTION PROCESSApplication of CFRP Fiber Sheet on a Beam- Wet Lay-Up ProcessSimilar for Application of Pultruded Laminates

CONSTRUCTION PROCESSColumn Wrapping with Automated FRP Application device

CONSTRUCTION PROCESSRobo Wrapper by Xxsys Technologies

CONSTRUCTION PROCESSColumn Wrapping Device

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

transportationconstructionmarinecorrosion-resistantconsumerelectrical/electronicappliance/businessaircraft/defenseNEWComposites 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.

Glass has very good impact resistance due to their high strain to failure, when compared to other fibers.

Aramid also has excellent impact resistance, particularly to ballistic impact.

Not shown on this chart is steels ability to have a strain to failure up to 20%. The value shown is the strain at yield.I want to point out that in this graph, carbon can be shown with several different modulus. For example, 12K carbon fibers are available with standard or low (33-35 MSI), intermediate (40-50 MSI), high (50-70 MSI), and ultra high (70-140 MSI) modulus. The higher you go, the more expensive it gets. The higher modulus is more suitable for aircraft and spacecraft where performance is the main objective, not cost.Carbon and aramid fibers can have small or negative coefficients of thermal expansion. It should be noted that the matrix has a much higher CTE than the reinforcement.

The thermal expansion of the composite depends not only on the type of reinforcement and the type of matrix, but also the geometry of the reinforcement, its volume fraction, and the amount and type of filler used.

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.E-Glass is electrical resistant glass providing good overall strength at low cost. It accounts for about 90% of all glass fiber reinforcements. It has good electrical resistance, and it is used in radomes and antennas because of its radio frequency transparency. It is also used in computer circuit boards to provide stiffness and electrical resistance.S-Glass is a high strength, high stiffness glass with good performance in high temperature and corrosive environments. This type of glass is stronger and stiffer than E-Glass and is used in more demanding applications were their extra cost can be justified. This type of glass is referred to R-Glass in Europe and T-Glass in Japan. A lower cost version, S-2 glass is approximately 40-70% stronger than E-Glass. S-2 Glass is used in golf club shafts because is provides flexibility and accuracy for long ball hitting, and it is less expensive than carbon.C-Glass is a calcium borosilicate glass providing good resistance to corrosive acid environments such as hydrochloric and sulfuric acid. It is also noted that E-Glass and S-2 Glass have a much better resistance to basic solutions such as sodium carbonate, compared to C-Glass. C-Glass has poor high-temperature performance, therefore either E-Glass or S-Glass is used.ECR-Glass , used in Europe is an alternative to E-Glass in a corrosive environment. They have similar properties to E-Glass, very resistant to chemical attack and are boron free.AR-Glass is a alkali resistant glass formulated for use in cement substrates and concrete.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.