11.1 CHAPTER ELEVEN FIBER-REINFORCED POLYMER (FRP)-WOOD HYBRID COMPOSITES Sheldon Q. Shi, Ph.D. Associate Scientist 11.1 INTRODUCTION Fiber-reinforced polymer (FRP)-wood hybrid composite materials are high- performance advanced engineered wood composites resulting from a combination of wood with fiber-reinforced polymers as reinforcements. The composites may have the advantages of both wood and FRP. Wood is a versatile structural material that can be processed into different forms of wood elements, such as lumber, ve- neers, flakes, strands, or fibers. These elements can then be combined with adhe- sives to form a variety of structural wood composites, including glued laminated timber (glulam), structure composite lumber (SCL), I-joists, and structural panel products. Wood has high performance-to-cost and strength-to-weight ratios. FRPs, sometimes called advanced fiber composites (AFCs), are also versatile materials consisting of both synthetic fibers and polymers. Because of FRP’s higher strength and stiffness properties compared to wood materials, they can be used as reinforce- ment of conventional wood composites. With a suitable design for the material configuration, the reinforced engineered wood composites exhibit better perform- ance and may show many potential advantages over traditional engineered wood composites. The following benefits are identified as possible enhancements to en- gineered wood composites that can be achieved by introducing FRP: • Increase strength and/or stiffness. • Reduce the variability in mechanical properties, which allows for higher design values. • Allow using lower-grade and/or fast-growing species in construction products. • Reduce the size and weight of the structural members. • Increase the product ductility, serviceability, and fatigue performance. • Enhance product durability and dimensional stability. 11.2 CHAPTER ELEVEN The reinforcement of structural wood products has been studied for more than 40 years. In the earlier stages of the research, the focus was mainly on using metallic reinforcement, including steel bars, prestressed stranded cables, and bonded steel and aluminum plates. 1–9 The major problem for the metallic reinforcement was the incompatibility between the wood and the reinforcing materials. For ex- ample, wood beams reinforced with bonded aluminum sheets had metal-wood bond delamination when the moisture content changed a few percent. 9 Metal is an elastic material, while wood is a viscoelastic material (a material exhibiting both viscous and elastic properties). Also, the hygro-expansion and stiffness behaviors between the wood and reinforcement materials are so different that separation at the glue line or tension failure in the wood near the glue line may occur. Unlike the traditional metallic reinforcement, fiber-reinforced polymers could be a better reinforced material for structural wood products. Both wood and FRP are viscoelastic materials. Also, there are some similarities in material processing (e.g., resin curing process) between the two materials. Therefore, the incompatibility problems between the wood and the reinforcing FRP are minimized if they are designed properly. Another advantage of FRP over metallic reinforcement is that the FRP materials can be more easily incorporated into the manufacturing process used to produce the wood composites. The development of FRP-reinforced wood composite materials may significantly increase the potential of expanding the use of engineered wood composites in build- ing construction, including residential, commercial, and nonbuilding construction application. For the FRP itself, it is also an excellent material for retrofitting dam- aged wood members, which will extend the service life of wood material. FRP- reinforced wood composites have a far greater strength-to-weight ratio than either concrete or steel. From the material and technology standpoint, FRP-reinforced wood composites show remarkable strength in terms of properties and performance. Considerable attention has been focused by the wood industry and different research institutions on this new class of engineered wood material. A state-of-the-art re- search center, the Advanced Engineered Wood Composites (AEWC) center, has been established at the University of Maine and is supported by several funding agencies and industries. The major research focuses of the AEWC center are on FRP-wood hybrid composites. A commercial FRP-wood composite product, FiRP glulam (using pultruded FRP as reinforcement), has been patented and an Evalua- tion Report (ER-5100) was issued by the International Conference of Building Officials (ICBO) in September of 1995 on this new reinforced wood product. 10 The American Society for Testing and Materials (ASTM) is drafting a standard for establishing and monitoring structure capacities of fiber-reinforced glulam. The American Institute of Timber Construction (AITC) has established a task committee to develop a reinforcement supplement to the American National Standard Institute (ANSI) glulam standard A190.1. FRP-reinforced wood composites promise to rev- olutionize the structural wood and wood composites industry. The objectives of this chapter are: (1) to introduce background information on the fiber-reinforced polymers and their fabrication processes; (2) to discuss the techniques of creating advanced FRP-wood hybrid composites; and (3) to show examples of how FRP-wood hybrid composites have been used in construction applications. 11.2 FIBER-REINFORCED POLYMERS Fiber-reinforced polymers encompass a wide variety of composite materials with a polymer resin matrix that is reinforced (combined) with fibers in one or more FIBER-REINFORCED POLYMER 11.3 directions. FRP composite properties are directional with the best mechanical prop- erties in the direction of fiber placement. Compared to wood, FRPs have a much higher tensile strength and stiffness. With their high strength and stiffness, the fibers carry the loads imposed on the composite, while the resin matrix distributes the load across all the fibers in the structure. The combination of reinforced fibers and resin matrix is more useful than the individual components. By aligning fibers in one direction in a thin plate or shell, called lamina, layer, or ply, the maximum strength and stiffness of the unidirectional lamina can be obtained. If the fibers are randomly oriented, the same properties in every direction on the plane of the lamina are achieved. The properties of the FRP material are not just predicted by simply summing the properties of its components. The combination of the fibers and resin matrix is the complementary nature of the components. Most polymer resins are weak in tensile strength but are extremely tough and malleable, while the thin fibers have high tensile strength but are susceptible to damage. The following sections detail the comparisons of the different reinforcement fibers and resin matrices that are commonly used in the FRP processing. The different FRP fabrication processes are also discussed. 11.2.1 Reinforcement Fibers When a material is shaped into a form of fiber, its strength and stiffness are usually much higher than that of the bulk because of the preferential orientation of mole- cules along the fiber direction and reduced number of defects presented in a fiber. For example, the tensile strength of bulk E-glass is only 0.22–0.84 ϫ 10 6 psi (1.5– 5.8 GPa) vs. 10.48 ϫ 10 6 psi (72.3 GPa) for those in fiber form. 11 The reinforcement fibers are typically 3–20 ␮ m(1 ␮ m ϭ 0.00004 in.) in di- ameter, similar to human hair. They can be in the form of continuous filaments or discontinuous fibers (chopped fibers). Continuous fibers are long fibers that usually attain maximum strength and stiffness due to their controlled anisotropy and low number and size of surface defects with the load carried mostly by the fibers ori- ented along the load direction. Continuous filaments are supplied in bundles, such as strands, rovings, or yarns. A strand is a bundle of more than one continuous filament. A roving is a collection of parallel continuous strands forming a cylin- drical element. A yarn is a collection of filaments or strands that are twisted to- gether. Rovings are the most common forms of fibers that can be chopped, woven, or processed to create secondary fiber forms for composite manufacturing, such as woven fabrics, knitted fabrics, braided fabrics, and mats. Mats formed either by chopped strand or continuous strand are nonwoven fabrics that provide equal strength in all directions. Continuous-strand mats are formed by swirling continuous strands of fiber onto a moving belt and are finished with a chemical binder that holds the fiber in place. Discontinuous fibers (short or chopped fibers) are cut from rovings into about 1.5–2.5 in. (2.81–6.35 cm). The length-to-diameter ratio (L/D) is called the aspect ratio or slenderness ratio. The aspect ratio of the discontinuous fiber significantly affects the properties of the short fiber reinforced composites. Chopped strand mats contain randomly distributed discontinuous fibers and held together with a resin. FRP composites made with these chopped fibers arranged randomly have nearly isotropic properties in the plane of the laminate. Short fiber composites usually have lower strength than continuous fiber composites and do not reduce the creep of polymer matrices as effectively as continuous reinforcement. However, short fiber composites find their good application in molded products where the short fibers can be adapted to the product contours more easily. 11.4 CHAPTER ELEVEN There are three main types of fiber reinforcements used in polymer matrix: glass fibers, carbon/graphite fibers, and synthetic polymer fibers (such as kevlar and aramid). The majority of the fibers used in the composites industry are glass. The basic building blocks for these fibers are carbon, silicon, oxygen, and nitrogen, each of which is characterized by strong covalent interatomic bonds, low density, thermal stability, and relative abundance in nature. Depending on the fiber type, filament diameter, sizing chemistry, and fiber form, a wide range of properties and perform- ance can be achieved. Table 11.1 shows the major properties of some commonly used reinforced fibers. 11,12 Glass Fibers. Glass fibers were commercialized in the 1930s. The basis of nearly all the commercial glasses is formed by silica, SiO 2 (about 55–72%). Other con- stituents of the glass compositions include aluminum oxide, Al 2 O 3 and magnesium oxide, MgO. Silica does not melt, but begins to decompose at a temperature of 3,632 ЊF (2,000ЊC). Using silica as a glass is perfectly suitable for many industrial applications. Glass fibers exhibit many advantages including hardness, corrosion resistance, inertness, light weight, flexibility, and inexpensiveness. However, it needs a high temperature for processing. All glass fibers have similar stiffness but different strength values and different resistance to environmental degradation. The commonly used glass fibers are E-glass (E for electrical), S-glass (S for strength), and C-glass (C for corrosion). Other types of glass fibers include D-glass (D for dielectric) and A-glass or AR-glass (AR for alkaline resistant). E-glass is the most commonly used glass fiber because it is the most economical for composites, of- fering sufficient strength at a low cost. E-glass is an excellent electrical insulator and is designed for better resistance to water and mild chemical concentrations. S- glass has the highest strength for uses in high-performance applications, such as the aerospace industry, where high specific strength and stiffness are important. However, S-glass cost three to four times more than E-glass, which limits its ap- plication. C-glass is usually used for corrosion-resistant applications since it has a much-improved durability upon exposure to acid and alkalis compared to E-glass. D-glass is used for electrical applications such as the core reinforcement of high voltage ceramic insulators. A-glass is used only in a few minor applications. Carbon/Graphite Fibers. Carbon fibers, also called graphite fibers, are strong, lightweight, and chemically resistant. The beginning of the modern carbon fiber production was in the 1960s. Generally, carbon fibers are produced using the fol- lowing three types of raw materials or precursors: polyacrylonitrile (PAN), pitch, and rayon (C 6 H 10 O 5 ) n . Carbon fibers can be produced in three different ways: from gas, liquid, or solid raw materials. Gas-produced carbon fibers use hydrocarbons or organic compounds of transition metals; liquid produced fibers are asphaltic, high- viscosity pitches or bitumens; and solid-formed fibers use polymer fibers such as PAN and rayon. For the three major types of carbon fibers, rayon has the lowest yield (about 25%) and lowest initial modulus. However, the major advantage of rayon fibers is that they possess superior qualities when used as the reinforcement in metal matrix composites. They are slightly dense compared to PAN and pitched fibers. Carbon fibers made from PAN precursors are much stronger than those made from rayon. They also have a better electrical conductivity. There are two major advantages to use pitch as a precursor for carbon fibers: higher yield and faster production rates. However, pitched fibers are more brittle than those from PAN, and they have a higher density, causing lower specific properties. Pitch fibers are less expensive but have lower strength than PAN fiber. The maximum operating 11.5 TABLE 11.1 Properties of the Commonly Used Fibers in FRP Fibers Diameter ( ␮ m) Density (g/cm 3 ) Tensile modulus (GPa) Tensile strength (GPa) Elongation (%) Coefficient of thermal expansion (10 Ϫ 6 /ЊC) Thermal conductivity (W/m/ЊC) Specific heat (J/kg/K) E-glass 8 to 14 2.54 72.4 3.45 1.8 to 3.2 5.0 1.3 840 C-glass – 2.49 68.9 3.16 4.8 7.2 – 780 S-glass 10 2.49 85.5 4.59 5.7 5.6 – 940 D-glass – 2.14 55.0 2.50 4.7 3.1 – – PAN carbon 7 to 10 1.67 to 1.90 228 to 517 1.72 to 2.93 0.3 to 1.0 Ϫ0.1 to Ϫ1.0 20 to 140 925 to 950 Pitch carbon 10 to 11 2.02 345 1.72 0.4 to 0.9 Ϫ0.9 to Ϫ1.6 – – Rayon carbon 6.5 1.53 to 1.66 41 to 393 0.62 to 2.20 1.5 to 2.5 – 38 – Kevlar-29 12 1.44 62 2.76 3 to 4 Ϫ2–– Kevlar-49 12 1.48 131 2.80 to 3.79 2.2 to 2.8 Ϫ2 0.04 to 0.5 1,420 Kevlar-149 – 1.47 179 3.62 1.9 – – – Spectra 900 38 0.97 117 2.58 4 to 5 – – – Note: The values in this table are only for general products. The properties for special formulated or treated fibers can have different property values. 11.6 CHAPTER ELEVEN temperature of carbon fibers can be from 600–1000ЊF (315–537ЊC). Carbon fibers are much stronger and stiffer than glass fibers. The stress corrosion (static fatigue) phenomenon is less marked. Carbon fibers are also good electrical conductors. The major limitation factor for the application of carbon fibers is the cost. To be com- petitive, with the advanced composites moving into new application areas, the cost of carbon fibers is decreasing while the demand for them is increasing. The material suppliers are optimistic that the cost of carbon fiber composites can be reduced over the next 10 years. 13 For carbon fibers used as reinforcement in composite materials, the fibers must go through several processing steps to ensure compatibility with matrix resin sys- tem. The first step involves oxidation or chemical treatment of the fiber surface to introduce functional groups (OH, NH 2 , COOH, etc.) capable of interacting with matrix resin. The second step involves sizing or coating the oxidized fiber with a coupling agent, and/or resin precursor. Polymer Fibers. Polymer fibers, sometimes called organic fibers, are made by a process of aligning the polymer chains along the axis of the fiber. They can also exhibit very high strength and stiffness, good chemical resistance, and low density if a suitable process is used. The best-known polymer fibers are the aramid fibers, first commercialized by DuPont in 1971 under the trade name Kevlar. Kevlar fiber is an aromatic polyamide called poly(paraphenylene terephthalamide) in which the aromatic rings make the fiber fairly rigid. The Kevlar fibers usually exhibit high specific strength and stiffness or high specific toughness. They also have a high thermal stability, low creep, and good chemical resistance. Kevlar fibers have been successfully used in different structural applications, including advanced compos- ites, rubber reinforcement, ballistic protection, friction products, and ropes/cables. Spectra is another polymer fiber made from oriented polyethylene. The advantage for the Spectra fibers is that they have a good chemical resistance and low density. However, their maximum operating temperature is relatively low (212 ЊF, or 100ЊC). There are some other polymeric fibers including aromatic co-polyesters and aro- matic heterocyclic polymers that have very limited commercial applications. Other Fibers. Some other fibers, such as boron fibers and silicon carbide (SiC) fibers, can also be used in fiber-reinforced polymer composites. Boron fibers, pro- duced by chemical vapor deposition on a tungsten wire, commonly have high stiff- ness, high strength, and low density. Because of the low production rate, boron fibers are among the most costly of the fibers presently made. SiC fibers, charac- terized by high stiffness, high strength, and higher temperature capacity, are also as high-cost as boron fibers. They have been used as reinforcement in both metal and polymeric resin matrices. SiC fibers also exhibit high stiffness and strength as well as high temperature capability. 11.2.2 Polymer Matrices The polymer matrix generally accounts for 30–40% of a FRP composite material. The purposes of the matrix material are to hold the fibers together and maintain the fiber orientation, transfer the load between fibers during the FRP composite application, and carry transverse and interlaminar shear stresses within the FRP composites. The polymer matrix also protects the fibers from the environment and mechanical abrasion. The FRP creep property is controlled by the polymer matrix. The rationale for choosing the polymer matrix will depend on the cost, properties, FIBER-REINFORCED POLYMER 11.7 and processing. A polymer matrix falls into two categories: thermoplastics and thermosets. Raw thermoplastic resins can be heated and cooled repeatedly to change their state from liquid to solid and vice versa, while a thermoset resin cannot return to its original state. Each type of resin offers benefits for particular applications. Thermoplastics will not undergo polymerization during the storage and therefore have an unlimited shelf life. They are easy to handle, easy to repair by welding, solvent bonding, etc., and recyclable (post-formable). However, thermoplastics usually have poor melt flow characteristics, which make them more difficult to process. They are also prone to creep. Thermosets have a low resin viscosity, which will be of benefit to the fiber wet-out during the processing. They have excellent thermal stability after polym- erization and are chemical-resistant and creep-resistant. The disadvantages of ther- mosets are that they are nonrecyclable via standard techniques, brittle, and not post- formable. Thermoplastics such as polyethylene, polystyrene, polypropylene, and thermo- plastic polyesters have been used in the manufacture of wood fiber/polymer com- posites (WPCs), also called plastic lumber. This product uses wood cellulosic fibers as reinforcements, with the thermoplastics as the matrix. The majority of resins used in the fiber-reinforced polymer processing are thermosets because of their low melting viscosity, good fiber impregnation, fairly low processing temperatures, and low cost. In this chapter, the main focus is on the commonly used thermosets used in the FRP applications. The most common thermosets are polyester, vinyl ester, epoxy, and phenolic resins. The general property information of these thermosetting resins is outlined in Table 11.2. 11,12,14 Polyester. Polyesters are the most widely used class of thermosets in the construc- tion market. They have a relatively low price, ease of handling, and a good balance of mechanical, electrical, and chemical properties. The unsaturated polyester resin has a low viscosity and can be dissolved in a reactive monomer, such as styrene, divinyle benzene, or methyl methacrylate. These diluents are usually used during the impregnation to reduce the viscosity and increase the degree of cross-linking after cure. Cross-linking reaction between the unsaturated polymer and unsaturated monomer can occur by the addition of heat and a free radical initiator (e.g., organic peroxide), and the low-viscosity solution is converted into a three-dimensional ther- mosetting polymer. Cross-linking can also be obtained using peroxides and suitable activators at room temperature. The ratio of saturated to unsaturated components controls the degree of cross-linking and thus rigidity of the product. Polyester can be used in several fabrication processes, including hand lay-up, compression molding, resin transfer molding, and injection molding. Glass fibers are the most common reinforcements for polyester matrices. Polyester can be for- mulated for use in many outdoor applications (UV resistance, durability, color re- tention, and resistance to fiber erosion) since it has some degree of resistance to burning, improves impact and abrasion resistance and surface appearance of the final product, and has resistance to chemical attack. Vinyl Ester. Vinyl ester offers a transition in mechanical properties and cost be- tween the easily processed polyesters and higher-performance epoxy resins which are described in the following paragraph. Vinyl esters are synthesized from an unsaturated carboxylic acid (usually methacrylic acid) and an epoxy resin. Typical commercial resins have only terminal unsaturation (rather than inside the chain), pendant hydroxyl groups, and no carboxyl or hydroxyl end groups, so they are less susceptible to chemical attack. Compared to polyesters, vinyl ester resins shrink 11.8 TABLE 11.2 Properties of the Commonly Used Resin Matrices in FRP Resin matrix Density (g/cm 3 ) Tensile modulus (GPa) Tensile strength (MPa) Compressive strength (MPa) Elongation (%) Coefficient of thermal expansion (10 Ϫ 6 /ЊC) Thermal conductivity (W/m/ ЊC) Shrinkage on curing (%) Specific heat (J/kg/K) Glass transition temperature T g (ЊC) Polyester 1.10 to 1.50 1.2 to 4.5 40 to 90 90 to 250 2 to 5 60 to 200 0.2 4 to 12 – 50 to 110 Vinyl ester 1.15 3.0 to 4.0 65 to 90 127 1 to 5 53 – 1 to 6 – 100 to 150 Epoxy 1.1 to 1.4 2 to 6 35 to 130 100 to 200 1 to 8.5 45 to 70 0.1 to 0.2 1.5 1250 to 1800 50 to 250 Phenolic 1.25 to 1.4 – 55 – 1.8 – – 1.1 – – Note: The values in this table are only for general products. The properties of special formulated resin matrix can have different property values. FIBER-REINFORCED POLYMER 11.9 less and absorb less water and are more chemically resistant. Different vinyl ester resins are available for applications. Epoxy. Epoxy resins, first developed in the 1940s, are widely used in applications such as honeycomb structures, airframe and missile application, and tooling because of their versatility, high mechanical properties, high corrosion and chemical resis- tance, and good dimensional stability. Many epoxy resins are based upon the re- action of phenols with epichlorohydrin having an oxirane ring as their reactive moiety. Compared to polyester, epoxy resins shrink less and have higher strength/ stiffness at moderate temperatures. They also cure slowly and are quite brittle after they are fully cured. However, they can be toughened with additives, including the addition of thermoplastics or multifunctional epoxides. Epoxy resins typically are twice the cost of vinyl esters. Phenolics. Phenolic resins are the predominately used adhesive system for the wood composite industry. Therefore, as a reinforcement of wood composites, FRPs manufactured using phenolic resin should be more compatible with the wood com- posite materials. Phenolic resins are usually dimensionally stable to temperature. They have excellent physical and mechanical durability. They also have a good adhesive property, low smoke production, and low flammability. Phenolic resins are usually used in sheet molded compound (SMC), pultrusion, and filament winding. Processing phenolics is more complicated than processing other thermosets because of water being released during the curing process. Phenolic resins are usually mod- ified using an elastomer or resorcinol. Phenol-resorcinol formaldehyde (PRF) resins are very popular as a resin matrix for FRP and as a binder in many other appli- cations. Polyurethane. Polyurethanes appear in a variety of forms used as coating, elas- tomer, foam, or adhesive. However, they are all based on the exothermic reaction of an organic polyisocyanate with a polyol. As a coating material in exterior or interior finishes, polyurethanes are tough, flexible, chemical-resistant, and fast- curing. As an adhesive, polyurethane bond usually has good impact resistance, fast curing, and good bond to different surfaces. One formulation of polyurethane ad- hesive, polymeric diphenylemethane diisocyanate (PMDI), has been widely used in the wood structural panel industry. Similar to phenolic resin, polyurethane is also dimensionally stable and has excellent physical and mechanical durability. 11.2.3 Fillers and Additives Filler is the least expensive major ingredient in FRP components. The major pur- poses of adding fillers are to reduce the cost and improve the performance. By using the fillers properly, the properties of the FRP, including dimensional stability, water resistance, weathering, surface smoothness, stiffness, flame/smoke suppres- sion, and temperature resistance, can be improved. The inorganic fillers are being used increasingly. The most common inorganic fillers are calcium carbonate, kaolin, alumina trihydrate, and calcium sulfate. Other commonly used fillers used in FRP are silica, talc, and mica. Additives are also used in FRP process. The additives may increase the material cost, but they can enhance the FRP processability by modifying the properties and performance of the materials. It has been shown that the additives can enhance the fire resistance, emission control, air-release capability, viscosity control, electrical 11.10 CHAPTER ELEVEN conductivity, and toughness. For example, antioxidants can help to inhibit polymer oxidation and degradation. Plasticizers help to improve processing characteristics and give a wider range of physical and mechanical properties. Heat or ultraviolet (UV) stabilizers are used to prevent either polymer degradation or surface and physical property changes due to UV radiation. Colorants are often used in the FRP manufacturing to provide color to the products. In the polyester processing, an organic peroxide such as methylethylketone peroxide (MEKP) is typically used as a catalyst or initiator for room temperature-cured process, and benzoyl peroxide is used for heat-cured molding. 11.2.4 Fabrication of FRP FRP processing methods can be separated into two groups: opened-mold processes and closed-mold processes. In the opened-mold processes, open-contact molding for forming a new product is in one-sided molds. Wet lay-up (or hand lay-up) and open-mold spray-up are usually used in the opened-mold processes. Closed-mold processes are to transfer the liquid resin from an external source into a dry preform that has been placed in a two-sided matched closed mold. Closed-mold processes include filament winding, pultrusion, compression molding, vacuum bag molding, resin transfer molding, and extrusion. The choice of processing type depends on the type of matrix and fibers used in the FRP manufacturing, the temperature re- quired for forming the products and curing the resin matrix, production rate, quality and performance of the final products, and cost-effectiveness of the process. For example, continuous fibers are primarily used in compression molding, resin trans- fer molding, and pultrusion application. Chopped strand mat is usually used in the hand lay-up process, continuous laminating, and some closed-molding applications. Following are brief discussions of each processing method. Hand Lay-up. Hand lay-up, also called wet lay-up, is the simplest, lowest-cost, and most widely used process of FRP manufacturing. Figure 11.1 illustrates the hand lay-up process. In this process, the mold is first treated with the mold release, such as wax, polyvinyl alcohol, silicones, and release papers. The choice of release agent depends on the type of material to be molded. After the release agent is cured, a gel coat, such as polyester, mineral-filled, and pigmented layer, is then applied to the mold before the reinforcement to produce a good surface appearance of the FRP products. Precut continuous strand fiber in the forms of mat, woven roving, or fabric is manually placed in the mold. Catalyzed resin with a viscosity of 1000–1500 centerpoise is applied to the mat. Serrated hand rollers are used to compact the material against the mold for removing the entrapped air. Curing is usually accomplished at room temperature, and the final molded part is removed by pulling the molded product from the mold. The hand lay-up can be partially automated by the spray-up process. The viscosity of the resin in the spray-up pro- cess is in the range from 500–1000 centerpoise. Simple wet-preg machines can also be used to introduce resin in controlled amount into the woven fabrics which are then laid on the mold. Typical fiber volume is 15% with the spray-up and 25% with the hand lay-up. The advantages of the hand lay-up and spray-up processes are (1) minimal equipment investment, (2) easy operation, (3) design flexibility allowing larger parts and complex items to be produced, and (4) low void content of the composites. The disadvantages of these processes are (1) labor intensive, (2) low production rate, (3) high emission of volatile organic compounds (VOCs), (4) [...]... potential ways to reinforce engineered wood and wood composites using FRP materials The potential benefits for the FRP-reinforced engineered wood composites were described in the Introduction to this chapter Research and trial evaluations are ongoing looking for the best ways to incorporate FRP reinforcement into wood composites Questions that need to be answered are: 1 What engineered wood products are... a GFRP Stress-Laminated Deck Located in Milbridge, Maine, Research Report No AEWC 00-02, Advanced Engineered Wood Composites Center, University of Maine, 2000 25 American Plywood Association (APA) , Basic Panel Properties Plywood Overlaid with Fiberglass-Reinforced Plastic, Research Report 119, Part 1, APA, Tacoma, WA, 1972 26 Bulleit, W M., ‘‘Elastic Analysis of Surface Reinforced Particleboard,’’... FIBER-REINFORCED POLYMER 11.23 Figures 11.12 and 11 .13 show an example of the use of FRP-reinforced glulam used in a commercial building application Figure 11.12 is a close-up showing the FRP material positioned between the outmost and second lamination on the tension side Typically the percentage of FRP used in this type of application is between 0.5% and 1.5% Figure 11 .13 shows the FRP-reinforced glulam in the... Most of these panel applications require good flexural properties such as high moment capacity and stiffness (EI ) Their bending strength and stiffness can be improved by overlaying layers of FRP sheets on the surfaces of structural panels Figure 11.14 shows a reinforcement configuration in a research report published by APA in 1972.25 This is a sandwich panel combining fiberglassreinforced polymer and plywood... Wood I-joists are highly engineered wood components used extensively in the floor framing of residential construction and in roof and commercial building applications The failure modes of I-joists subjected to bending could be tension on the bottom flange, compression on the top flange, shear on the web or web-web joints, web-flange joints, or web buckling Because they are highly engineered, the failure... tensile material, with a 25% increase in design capacity.28 In I-joist applications, high nailing strength of the top flanges is usually required in order to achieve composite structural action with the wood structural panel flooring system Therefore, applying a FRP layer on the surface of the I-joist top flange may offer the potential of increasing the nailing capacity and thus improving the structural performance... acceptance 11.26 CHAPTER ELEVEN LVL flange OSB web FRP reinforcements FIGURE 11.15 A design configuration of FRP-reinforced I-joist 11.4.4 Reinforcement for Other Engineered Wood Products FRP reinforcements could also apply to many other engineered wood products to improve the performance during their applications Some research work has been conducted on the reinforcement of sawn lumber using FRP materials... patented and many new technologies on the FRP-reinforced engineered wood composites have been released Following is a discussion of the different potentials and technologies of FRP-reinforced wood composites 11.4.1 Reinforcement for Glued Laminated Timber (Glulam) FRP reinforcement of glulam may have a significant impact on the glulam industry Glulam is an engineered wood composite manufactured by bonding... C Lowry, ‘‘FRP Reinforced LVL and Structural I-Joists,’’ First International Conference on Advanced Engineered Wood Composites, Bar Harbor, ME, July 5–8, 1999 28 Tingley, D., ‘‘High-Strength Fiber Reinforced Plastic as Reinforcement for Wood Flange I-Beams,’’ First International Conference on Advanced Engineered Wood Composites, Bar Harbor, ME, July 5–8, 1999 11.30 CHAPTER ELEVEN 29 Plevris, N., and... reinforcement cost, it may be more effective to apply the FRP reinforcing material to the structural panels during the end-use application For example, in shear wall applications, since high fastener capacity around the edge of the panel is required in order to provide maximum shear resistance, it may be feasible to put FRP reinforcement around the edge of the panels to increase the fastener / panel . the material configuration, the reinforced engineered wood composites exhibit better perform- ance and may show many potential advantages over traditional engineered wood composites. The following. and different research institutions on this new class of engineered wood material. A state-of-the-art re- search center, the Advanced Engineered Wood Composites (AEWC) center, has been established. COMPOSITES There are many potential ways to reinforce engineered wood and wood composites using FRP materials. The potential benefits for the FRP-reinforced engineered wood composites were described in