The Composites Institute identifies eight market segments (plus a ninth - miscellaneous) for composite applications. The are: transportation construction marine corrosion-resistant consumer electrical/electronic appliance/business aircraft/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 80 0 C 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.
Urethane’s 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.
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.
STRENGTHENINGSTRUCTURES USING FRPCOMPOSITE MATERIALSDAMIAN I. KACHLAKEV, Ph.D., P.E.California Polytechnic State UniversitySan Luis Obispo
WHY COMPOSITES?• ADVANTAGES OVER TRADITIONALMATERIALS• CORROSION RESISTANCE• HIGH STRENGTH TO WEIGHT RATIO• LOW MAINTENANCE• EXTENDED SERVICE LIFE• DESIGN FLEXIBILITY
COMPOSITES DEFINITION• A combination of two or more materials (reinforcement,resin, filler, etc.), differing in form or composition on amacroscale. The constituents retain their identities, i.e..,they do not dissolve or merge into each other, althoughthey act in concert. Normally, the components can bephysically identified and exhibit an interface betweeneach other.
DEFINITIONFiber Reinforced Polymer (FRP) Compositesare defined as:“A matrix of polymeric material that isreinforced by fibers or other reinforcingmaterial”
RESINS• THERMOSET ADVANTAGES– THERMAL STABILITY– CHEMICAL RESISTANCE– REDUCED CREEP AND STRESS RELAXATION– LOW VISCOSITY- EXCELLENT FOR FIBERORIENTATION– COMMON MATERIAL WITH FABRICATORS
RESINS• THERMOPLASTIC ADVANTAGES– ROOM TEMPERATURE MATERIAL STORAGE– RAPID, LOW COST FORMING– REFORMABLE– FORMING PRESSURES AND TEMPERATURES
POLYESTERS• LOW COST• EXTREME PROCESSING VERSATILITY• LONG HISTORY OF PERFORMANCE• MAJOR USES:–Transportation– Construction– Marine
VINYL ESTER• SIMILAR TO POLYESTER• EXCELLENT MECHANICAL & FATIGUEPROPERTIES• EXCELLENT CHEMICAL RESISTANCE• MAJOR USES:–Corrosion Applications - Pipes, Tanks, &Ducts
EPOXY• EXCELLENT MECHANICAL PROPERTIES• GOOD FATIGUE RESISTANCE• LOW SHRINKAGE• GOOD HEAT AND CHEMICAL RESISTANCE• MAJOR USES:–FRP Strengthening Systems–FRP Rebars–FRP Stay-in-Place Forms
PHENOLICS• EXCELLENT FIRE RETARDANCE• LOW SMOKE & TOXICITY EMISSIONS• HIGH STRENGTH AT HIGH TEMPERATURES• MAJOR USES:–Mass Transit - Fire Resistance & HighTemperature–Ducting
POLYURETHANE• TOUGH• GOOD IMPACT RESISTANCE• GOOD SURFACE QUALITY• MAJOR USES:–Bumper Beams, Automotive Panels
SUMMARY: POLYMERS• WIDE VARIETY AVAILABLE• SELECTION BASED ON:– PHYSICAL AND MECHANICAL PROPERTIESOF PRODUCT– FABRICATION PROCESS REQUIREMENTS
Physical Properties of ThermosettingResins Used in StructuralCompositesResinTypeDensity(kg/m3)TensileStr.(MPa)Elong.(%)E-Mod.(GPa)Long.Termt ,(C)Polyester 1.2 50-65 2-3 3 120VinylEster1.15 70-80 4-6 3.5 140Epoxy 1.1-1.4 50-90 2-8 3 120-200Phenolic 1.2 40-50 1-2 3 120-150
MATERIAL: FIBERREINFORCEMENTS• PRIMARY FUNCTION:“CARRY LOAD ALONG THE LENGTH OF THEFIBER, PROVIDES STRENGTH AND OR STIFFNESSIN ONE DIRECTION”• CAN BE ORIENTED TO PROVIDE PROPERTIES INDIRECTIONS OF PRIMARY LOADS
REINFORCEMENTS• NATURAL• MAN-MADE• MANY VARIETIES COMMERCIALLYAVAILABLE
DESIGN VARIABLESFOR COMPOSITES• TYPE OF FIBER• PERCENTAGE OF FIBER or FIBER VOLUME• ORIENTATION OF FIBER– 0o, 90o, +45o, -45o• TYPE OF POLYMER (RESIN)• COST• VOLUME OF PRODUCT - MANUFACTURINGMETHOD
TAILORING COMPOSITEPROPERTIES• MAJOR FEATURE• PLACE MATERIALS WHERE NEEDED -ORIENTED STRENGTH– LONGITUDINAL– TRANSVERSE– or between• STRENGTH• STIFFNESS• FIRE RETARDANCY
STRUCTURAL DESIGNAPPROACH FOR COMPOSITESS t r u c t u r a l D e s ig n W it h F R P C o m p o s it e sM a t r ix , F ib e r sM ic r o m e c h a n ic sL a m in a , L a m in a t eM a c r o m e c h a n ic sS t r u c t u r a l A n a ly s isS t r e n g t h e n in g D e s ig nS T R U C T U R EF R P R e p a ir
FLOW CHART FOR DESIGN OFFRP COMPOSITES[ E ] x , yT r a n s fo r m e d E n g . C o n s t a n t s[ Q ] x , yT r a n s fo r m e d M a t h . C o n s t a n t s[ Q ] 1 , 2M a t h e m a t ic a l C o n s t a n t s[ F ib e r O r ie n t a t io n ][ E ] x , yT r a n s fo r m e d E n g . C o n s t a n t s[ S ] x , yT r a n s fo r m e d M a t h . C o n s t a n t s[ S ] 1 , 2M a t h e m a t ic a l C o n s t a n t s[ E ] 1 , 2E n g in e e r in g C o n s t a n t s
MATERIAL PROPERTIES• PROPERTIES OF FRP COMPOSITES VARYDEPENDING ON:– TYPE OF FIBER & RESIN SELECTED– FIBER CONTENT– FIBER ORIENTATION– MANUFACTURING PROCESS
REPAIR• HYBRIDS (SUPER COMPOSITES): TRADITIONALMATERIALS ARE JOINED WITH FRPCOMPOSITES– WOOD– STEEL– CONCRETE– ALUMINUM
BENEFITS - SUMMARY• LIGHT WEIGHT• HIGH STRENGTH to WEIGHT RATIO• COMPLEX PART GEOMETRY• COMPOUND SURFACE SHAPE• PARTS CONSOLIDATION• DESIGN FLEXIBILITY• LOW SPECIFIC GRAVITY• LOW THERMAL CONDUCTIVITY• HIGH DIELECTRIC STRENGTH
LIFE CYCLE ECONOMICS• PLANNING/DESIGN/DEVELOPMENTCOST• PURCHASE COST• INSTALLATION COST• MAINTENANCE COST• LOSS/WEAR COST• LIABILITY/INSURANCE COSTS• DOWNTIME/LOST BUSINESS COST• REPLACEMENT/DISPOSAL/RECYCLINGCOST
LIFE CYCLE ECONOMICS(Examples)• IBACH BRIDGE (SWITZERLAND)– CFRP LAMINATES- 50 TIMES MOREEXPENSIVE THAN STEEL PER KILOGRAM– CFRP LAMINATES- 9 TIMES MOREEXPENSIVE THAN STEEL BY VOLUME– REPAIR WORK REQUIREMENTS-175 KGSTEEL OR 6.2 KG CFRP– MATERIAL COST-20 % OF THE TOTALPROJECT COST
CONCLUSIONS• ECONOMICS ARE MORE THAN THE BASICELEMENTS OF MATERIALS, LABOR,EQUIPMENT, OVERHEAD, ETC.• ENTIRE LIFE CYCLE ECONOMICS MUST BECONSIDERED AND COMPARED TO THAT OFTRADITIONAL MATERIALS TO DETERMINE THEBENEFITS OF COMPOSITES IN A GIVENAPPLICATION
EXTERNAL REINFORCEMENT OFRC BEAMS USING FRP• BACKGROUND• DESIGN MODELS– LACK OF DUCTILITY– FLEXURAL STRENGTHENING– SHEAR STRENGTHENING– PRESTRESSED FRP APPLICATION• DESIGN METHODOLOGY ANDANALYSIS• OTHER ISSUES– FATIGUE, CREEP, LOW TEMPERATURE FRPPERFORMANCE• DESIGN EXAMPLES
FRP STRENGTHENED BEAMSBACKGROUND• FRP VS. EXTERNALLY STEEL BONDEDPLATES– CORROSION AT THE EPOXY-STEEL INTERFACE– STEEL PLATES DO NOT INCREASE STRENGTH,JUST STIFFNESS– HIGH TEMPERATURES PERFORMANCEDIFFICULTIES DUE TO HEAVY WEIGHT OF THESTEEL PLATES– STRENGTHENING DESIGN BASED ON MATERIALWEIGHT, NOT STRUCTURAL NEEDS– CONSTRUCTION DIFFICULTIES– TIME CONSUMING, HEAVY EQUIPMENT NEEDED
FRP STRENGTHENED BEAMSLACK OF DUCTILITY• LINEAR STRESS-STRAIN PROFILE• DEFINITION OF DUCTILITY– DEFLECTION AT ULTIMATE/DEFLECTION ATYIELD- NOT APPLICABLE FOR FRP MATERIAL– STRAIN-ENERGY ABSORPTION, I.E., AREA UNDERLOAD-DEFLECTION CURVE- OK FOR FRPCOMPOSITES– IN GENERAL- THE HIGHER THE FRP FRACTIONAREA, THE LOWER THE ENERGY ABSORPTION OFTHE STRENGTHENED CONCRETE BEAM
CONSTRUCTION PROCESS• Preparation of the Concrete Surface• Mixing Epoxy, Putty, etc.• Preparation of the FRP Composite System• Application of the FRP Strengthening System• Anchorage (if recommended)• Curing the FRP Material• Application of Finish System
CONCRETE SURFACEPREPARATION• Repair of the existing concrete in accordance to:– ACI 546R-96 “Concrete Repair Guide”– ICRI Guideline No. 03370 “Guide for SurfacePreparation for the Repair of DeterioratedConcrete...”• Bond Between Concrete and FRP Materials– Should satisfy ICRI “Guide for Selecting andSpecifying Materials for Repair of ConcreteSurfaces”
CONCRETE SURFACEPREPARATION• Repair Cracks 0.010 inches or Wider– Epoxy pressure injected– To satisfy Section 3.2 of the ACI 224.1R-93“Causes, Evaluation and Repair of Cracks…”• Concrete Surface Unevenness to be Less than 1mm• Concrete Corners- Minimum Radius of 30 mm
APPLICATION OF THE FRPCOMPOSITE• In Accordance to Manufacturer’s and DesignersSpecifications– Priming– Putty Application– Under-coating with Epoxy Resin– Application of the FRP Laminate/ FRP Fiber Sheet– Over-coating with Epoxy Resin
CURING OF THE FRPCOMPOSITES• In Accordance to Manufacturer’s Specifications– Temperature ranges and Curing Time- varies fromfew hours to 15 days for different FRP systems• Cured FRP Composite– Uniform thickness and density– Lack of porosity
CONSTRUCTION PROCESS• Typical RC Beam inNeed for Repair– corroded steel– spalling concrete
CONSTRUCTION PROCESS• Deteriorated Column /Beam Connection
CONSTRUCTION PROCESS• Concrete SurfacePreparation– Smooth, free of dust andforeign objects, oil, etc.– Application of primerand putty (if required bythe manufacturer)
CONSTRUCTION PROCESS• Preparation of the FRPComposites forApplication– Followmanufacturer’srecommendations
CONSTRUCTION PROCESS• Priming of the ConcreteSurface• Application of theUndercoating epoxyLayer (adhesive whenFRP pultruded laminatesare used)
CONSTRUCTION PROCESS• Application of CFRPFiber Sheet on a Beam-Wet Lay-Up Process• Similar for Applicationof Pultruded Laminates
CONSTRUCTION PROCESS• Column Wrapping withAutomated FRPApplication device
CONSTRUCTION PROCESS• Robo Wrapper by XxsysTechnologies