Applications & Mechanical Properties of FRP

Alexandria University- Faculty of Engineering 1st Year Naval Architecture and Marine Engineering Department Second Semester- Academic Year 2009/2010

Applications & Mechanical Properties of FRP

Group Members: 1) Ahmed Hassan Mahmoud [Type the abstract of the document here. The abstract is typically a short summary of the Khamis contents of the document. Type the abstract of the document 2) Abdelrahman here. The abstract is typically a short summary of the contents of the document.] 3) Hesham Atef Mohamed

Presented to:

Dr. Mona El-Salamaw

[Type the company name]

Contents Summary………………………………………………………..………1 1.1 Naval applications of FRP composites………………………..…..2 1.2 Leisure, sports, and commercial FRP composite craft……..….8 1.3 Offshore applications of FRP composites……………….……10 2. Testing the mechanical prosperities of FRP………………………12 2.1 Weak-direction (beam) Bending test………………………...12 2.1.1 Specimen description………………………………………12 2.1.2 Test setup and instrumentation ………………………..…...13 2.1.3 Experimental procedure and results …………………….....14 2.1.4 Service load tests……………………………………….…..14 2.1.5 Crack initiation and failure tests ……………………….….16 3. Typical properties of currently available products …………...….19 4. Test methods for mechanical properties …………………...……..22 4.1 Tension test methods…………………………………………22 4.2 Compression test methods ……………………………….….22 4.3 Shear test methods ………………………………………..….22 4.4 Flexural test methods ……………………………………..…22 4.5 Bond test methods for internal FRP reinforcement………….23 4.6 pullout tests…………………………………………………...23 4.7 Flexural bond tests …………………………………………..23 4.8 Direct axial tension test……………………………………...24 4.9 Bond test methods for externally bonded FRP reinforcement...24

Applications & Mechanical Properties of FRP

4.10 Shear bond type tests ……………………………………….25 4.11 Tension-type bond tests……………………………………...26 4.12 Mixed-mode bond tests........................................................….26 4.13 Tensile fatigue testing methods ………………….……………26 4.14 Concrete prism tensile fatigue test method ……………….….27 4.15 Direct fatigue tests……………………………………………27 4.16 Creep test methods ……………………………………....…..28

Applications & Mechanical Properties of FRP

Summary: The first marine application of fiber-reinforced polymer (FRP) composite materials was in the construction of boats shortly after World War II. This was about the time that composites were first used for other applications, such as in aircraft, electrical devices, and building materials. Boat builders began to use FRP composites instead of timber, which was traditionally used in small maritime craft, because wood was becoming increasingly scarce and expensive. Timber was also losing favor with many boat builders and owners, because wooden boat hulls are degraded by seawater and marine organisms and therefore require ongoing maintenance and repairs that can be expensive. The earliest attempt to fabricate boat hulls with FRP composites was in 1947 when twelve small surfboats were made for the United States Navy. At the time, little was known about the design and construction of composite boats, the fabrication technologies were underdeveloped, and the materials had low strength and poor durability in seawater. This combination of factors led to the construction of composite boats that were not seaworthy, and many had to be scrapped. The early history of the development and application of composites to marine craft has been reported. The design techniques, processing technology, fiber reinforcements, and resins improved rapidly after the early problems, and composites were used successfully during the 1950s in small leisure craft, yachts, and naval boats as well as in ship and submarine structures, such as radomes, sonar domes, and casings. Knowledge and confidence in composites grew with these applications, and this further expanded the number and types of maritime craft made of composites. For example, by the mid-1960s, over 3000 boats had been built of composite materials for the United States Navy, including over 800 motor whaleboats, 330 utility boats, 250 landing craft, 220 personnel boats, and 120 patrol boats. Since the 1970s, composites have also been used in niche applications on offshore oil drilling platforms and, as with maritime craft, the use of FRP materials is expanding into new platform applications. Most maritime craft are built using glass-reinforced polyester (GRP) composites, although sandwich composites and advanced FRP materials containing carbon or aramid fibers with vinyl ester or epoxy-resin matrices are commonly used for high-performance structural applications. Composites are now used in a wide variety of craft, ranging in size from canoes, dinghies, and yachts to racing maxis, hovercraft, patrol boats, naval minehunting ships, and corvettes. Composites are also used in lightweight structures on warships, such as advanced mast systems and superstructure sections. The application of composites to leisure craft, yachts, boats, ships, submarines, and offshore structures has been extensively reviewed. The purpose of this article is to briefly outline current and potential applications of composites for maritime craft and offshore drilling platforms. The key benefits gained from using FRP materials together with an examination of the drawbacks and major issues impeding the more widespread use of composites in marine structures are given. The discussion includes the standard tests required to evaluate this material.

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1.1 Naval Applications of FRP Composites: The application of FRP composites to maritime craft was initially driven by a need for lightweight, strong, corrosion resistant, and durable naval boats. The United States Navy sponsored most of the early design, research, and development work that led to the production of composite boats. Initially, the navy funded the production of small personnel boats, although this was followed in the 1950s by support for a variety of other craft, including patrol boats, landing craft, and minesweeping boats. The United States Navy was also the first to use composites on large ships for deckhouses, pipes, and fuel and water tanks, as well as on submarines for fairwaters and mast shrouds. From the 1950s, other navies, most notably the British, French, and Swedish Navies, began to use composites on their vessels, which further expanded the marine applications of FRP materials. The expansion in the use of composites on naval ships and submarines during the 1950s and 1960s was dramatic, and by the mid-1960s the number of applications was extremely diverse, as shown in Table 1. Most of these early applications were driven by the need to overcome corrosion problems experienced with steel or aluminum alloys or environmental degradation suffered by wood. Another reason for using composites was to reduce weight, particularly the topside weight of ships. The high acoustic transparency of composites also resulted in their use in radomes on ships and sonar domes on submarines.

Table 1 Early naval applications of FRP composites (1945–1965) Minesweeper (15.5 m, or 51 ft, long) Landing craft (15.2 m, or 50 ft) Personnel boat (7.9 m, or 26 ft) Sheathing of wood hulls Submarine sonar dome Submarine fins Masts and mast shrouds Rudders Tanks (fuel, lube oil, water) Torpedo tubes Hatch covers Landing craft reconnaissance (15.8 m, or 52 ft) River patrol boat (9.5m, or 31 ft) Pilot boat Submarine fairwater Submarine nonpressure hull casing Deckhouses for small ships Radomes Antenna trunks Piping Crew shelters Rope guards

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Up to the 1960s, however, the only naval boats built entirely of composites were under 20 m (66 ft) in length. It was not safe to build larger warships with composites, because they would not have adequate hull girder stiffness due to the low Young's modulus of FRP materials. Low hull girder stiffness would cause excessive hogging and sagging of a composite ship in heavy seas. Such large hull deflections cause fatigue- induced failures of the hull, bulkheads, and joints and also cause serviceability problems, such as shaft misalignment and loss of sealing to watertight hatches. The problem of low hull girder stiffness for small warships (less than ~50 m, or 165 ft, long) was overcome in the early 1970s with the construction of the Royal Navy minesweeper HMS Wilton. This ship was 46.6 m (153 ft) long with a full-load displacement of 450 tons, making it the largest all-composite ship at the time. High hull girder stiffness was achieved by building the ship with an innovative composite hull known as the framed single-skin design. The hull basically consisted of a thin FRP laminate shell stiffened with longitudinal and transverse frames, mostly of “top hat” cross-section sandwich composite construction. Not only did the hull have adequate stiffness, but it also had excellent impact and underwater blast damage resistance that is essential for naval ships. Since the mid-1970s, hundreds of patrol boats and minehunter ships in the 50 to 60 m (165 to 200 ft) length range have been built using composites. While the framed single-skin hull remains popular, two other hull forms have been developed for composite ships up to about 70 m (230 ft). These forms are monocoque construction, which basically consists of the thick laminate hull, and sandwich construction, which consists of thin FRP face skins over a thick core of medium-density polyvinyl chloride foam or polyurethane foam or end-grain balsa. 1 shows examples of naval ships with the framed single-skin, monocoque, and sandwich hull types. Increasingly, naval patrol boats are being built with an all-composite design or a composite hull fitted with an aluminum superstructure. The growing popularity of FRP patrol boats is due mainly to their excellent corrosion resistance, which reduces maintenance costs, and light weight, which can result in higher speeds and better fuel economy. It is estimated that composite patrol boats are usually approximately 10% lighter than an aluminum boat and over 35% lighter than a steel boat of the same size. However, the fabrication cost of a composite patrol boat is estimated to be about 30% higher than for a steel boat, which is a major impediment to their construction. An example of a modern composite patrol boat is the Skjø ld class operated by the Royal Norwegian Navy, as shown in Fig. 2. The Skjø ld is 46.8 m (154 ft) long with a fullload displacement of 270 tons and is made of a sandwich composite material. The core of the sandwich composite is polyvinyl chloride foam, and the face skins consist of glass- and carbon-fiber polymer laminates. Carbon-fiber composites are rarely used on naval vessels because of their high cost, however it is used in the Skjø ld for structures requiring high stiffness, such as the mast, beam frames, and the support base to the gun.

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(a)

(b)

(c)

Fig. 1 Composite naval ships: (a) Sandown class minehunter ship with a framed single-skin single skin hull form. (b) Huon class minehunter ship with a monocoque hull form. (c) Bay class minehunter ship with a sandwich composite hull form

Fig. 2 The Skjøld class patrol boat

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The other type of naval vessel that is commonly built of composites is minehunting ships. Nearly 250 minehunter ships have been built since the mid-1970s mid 1970s using composite materials. A wide variety of minehunter ships made of single single-skin or sandwich composites are in service, and three types are shown in Fig. 1. The main reasons for building minehunting ships with composite are they are nonma nonmagnetic and corrosion resistant. As a general design rule, the structural performance of ships less than approximately 50 to 60 m (165 to 200 ft) long, such as patrol boats and minehunters, is determined by the response of local structures, such as bulkheads and decks. On the other hand, the performance of ships longer than about 60 m (200 ft) is dominated by the hull girder stiffness. Because se of the relatively low stiffness of most glass-reinforced glass reinforced polymer materials, almost all composite ships are under 60 m (200 ft) long. The only composite naval vessel built to date above this size is the 72 m (236 ft) long Visby class corvette for the Royal al Swedish Navy, Navy, which is shown in Fig. 3. The Visby uses a sandwich composite incorporating a polyvinyl chloride foam core and carbon-fiber/vinyl fiber/vinyl ester laminate skins manufactured using a resin-infusion resin infusion laminating method. The use of carbon-fiber carbon composite osite reflects the increased demand on hull girder stiffness from a vessel of this length. The composite design also affords a high level of strength and durability, good shock resistance, a low magnetic signature, and a lightweight structure, as necessary for a ship designed for a multimission capability. The ship is undergoing sea trials and evaluation, and five more corvettes will be built.

Fig. 3 Artist drawing of the all--composite Visby class corvette

An all-composite patrol boat/corvette, known as the NGPV class, is being designed for the Royal Singapore Navy and is expected to be 80 m (260 ft) long with a full fullload displacement of 1016 tons. The United States Navy is also considering building their next-generation generation corvettes with composite materials. Navy ships longer onger than about 100 m (330 ft), such as frigates, destroyers, and aircraft carriers, are not likely to be constructed entirely with composites because it is much cheaper to build large ships with welded steel construction. construc At this stage in the development of large composite ships, it is glass-fiber-reinforced glass reinforced structures that have the longest service history. However, as carbon-reinforced carbon reinforced ships, such as the Visby corvette, enter service Applications & Mechanical Properties of FRP

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and as the price of carbon--fiber material continues to drop, larger carbon carbon-reinforced ship structures may become practical. While it is not feasible to build large naval ships using composites, these materials are now used in a wide variety of topside structures and internal equipment on frigates, destroyers, and aircraft carriers. Composites are used in the superstructures on some naval ships to eliminate corrosion and fatigue cracking, lower topside weight, and reduce the radar cross section. The first large naval ship built with a compo composite superstructure was the La Fayette class frigate, which is shown in Fig. 4. Sandwich composite is used in the aft section of the superstructure, which includes a helicopter hangar and funnels. The aft section is 38 m (125 ft) long, 15 m (50 ft) wide, 66.5 to 8.5 m (21 to 28 ft) high from the main deck, and weighs 85 tons, which makes it the largest and heaviest composite superstructure on a naval ship. The forward section of the superstructure, which includes the bridge and combat and telecommunications centers, is built of steel because it was considered that a composite structure would not provide adequate protection against a high-pressure high pressure air blast. It is estimated that composite superstructures are 30 to 40% lighter than a steel structure, which resu results in better ship stability and fuel savings. Composite superstructures are also more resistant to corrosion and fatigue, and therefore require less maintenance and fewer repairs. However, composite superstructures are estimated to be 35 to 50% more expensive sive to build, and for this reason, most naval ships will continue to be built with steel or aluminum superstructures for at least the next ten years. However, the United States, British, and Norwegian Navies are considering fitting composite superstructuree sections and helicopter hangars to some of their next nextgeneration warships.

Fig. 4 La Fayatte frigate with the composite superstructure section shown within the circled region

Another major composite topside structure being developed for future use on large naval ships is masts. The feasibility of fabricating advanced communication and surveillance masts using composites is being explored because of numerous problems with conventional tional steel truss masts. The major problems with steel masts are that they corrode, increase the radar signature of the ship, and interfere with the ships own radar and communications systems because of their open structure. In 1997, the advanced enclosed mast/sensor (AEM/S) system was installed on the Spruance class destroyer USS Arthur W. Radford as a technology demonstrator. The entire mast is Applications & Mechanical Properties of FRP

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made of sandwich composite material and is 28 m (92 ft) tall and up to 10.7 m (35 ft) wide, as shown in Fig. 5. A major reason for building the AEM/S system with composites is that these materials enable the passage of radar and communications signals with very little interference or attenuation, unlike metals. This, then, allows all the antennas, sensors, and other other sensitive electronic equipment to be enclosed within the mast structure and thereby protected from the weather. Other benefits of the AEM/S system are that it is lighter and more corrosion resistant than steel truss masts; however, composite masts are much much more expensive to build. The AEM/S system has performed beyond the expectations of the United States Navy, and consideration is currently being given to installing advanced composite masts on future amphibious ships, destroyers, and sea--lift vessels. A composite mast structure similar to the AEM/S system is also being developed in the United Kingdom for next next-generation warships. Smaller composite masts have been fitted to some naval submarines to lower weight, reduce corrosion, and dampen vibrations.

Fig. 5 Advanced enclosed mast/sensor (AEM/S) composite mast on the USS Arthur W. Radford

The feasibility of using composites in a wide variety of secondary structures and equipment on warships and submarines is under investigation. For example, a major effort is being given to the development of composite propellers, propulsors, and propulsion shafts. Composites are expected to offer a number of important benefits over metals when used in propulsion systems, including lower costs, reduced weight, lower magnetic signature, better noisenoise damping properties, and superior corrosion resistance. It iss anticipated that propulsion shafts made of composites will be 25 to 80% lighter than a steel shaft of the same size and will reduce life-cycle life cycle costs by at least 25% because of fewer problems associated with corrosion and fatigue. Despite the projected benefits, nefits, the use of composites in propulsion systems has been limited. Applications & Mechanical Properties of FRP

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Composite propellers have only been used on torpedoes and one minehunter ship, composite propeller shafts have only been installed on a small number of patrol boats, including the Skjø ld, whereas composite propulsors have not yet been used. However, within the next ten years the use of composites in these applications is expected to increase, albeit at a slow rate. Composites are also being evaluated for use in rudders for ships and control surfaces for submarines. Other potential applications include funnels, bulkheads, decks, watertight doors, machinery foundations, pipes, ventilation ducts, and components for diesel engines, pumps, and heat exchangers on large warships.

1.2 Leisure, Sporting, and Commercial FRP Composite Craft: The diverse application of composite materials to naval vessels is matched by their wide- ranging use in leisure, sporting, and commercial vessels and small submersibles. Composites were first used in leisure craft and yachts in the 1950s and in commercial craft, such as fishing trawlers and pilot boats as well as submersibles, in the late 1960s. The use of composites in these vessels was due to the successful application of FRP materials to naval boats during the 1950s and 1960s. It is interesting to note, however, that the experience and knowledge gained from using composites in leisure and commercial craft later facilitated the wider use of these materials in naval ships. Since the 1970s, the use of composites in the hulls of marine craft has increased dramatically, and currently most vessels under a length of 15 to 20 m (50 to 65 ft) are built with FRP materials. The types of craft in this size range that are made of composites include kayaks, canoes, dinghies, jet skis, lifeboats, yachts, and powerboats. Vessels longer than approximately 20 m (50 ft) are usually made of steel or aluminum alloy, although the use of composites is increasing as their fabrication cost continues to fall and as boat operators become aware of the reduced through-life costs. Among the largest commercial vessels that are built using composites are luxury cruisers, passenger ferries, hovercraft, and fishing trawlers. Several years ago, between 50 and 60% of all fishing boats under 60 m (200 ft) were made of GRP, and the proportion of trawlers built of composites is expected to continue to rise. Composites are often used because the lightweight construction allows a heavier fishing haul to be carried, the fish holds are easier to clean than wooden holds, and the hulls are easier to maintain and repair. Composites have also been used in propellers of fishing trawlers as well as powerboats to overcome corrosion and noise problems that can be experienced with metal propellers. Composites are also being used increasingly in high-speed ferries capable of carrying 350 to 400 passengers. The ferries are usually built with a composite hull and an aluminum superstructure. Ferries are rarely built with a composite superstructure because of the poor fire resistance. The hoisting decks and bow gates on car ferries have also been made of sandwich composite material. As with naval ships, the composite material most commonly used in leisure and commercial craft is GRP in the form of a thick laminate or a sandwich composite. Over 95% of all composite marine craft are built with GRP because of its low cost, which is similar to the cost of steel and aluminum alloy. There are, however, a number of other reasons for the popularity of GRP composites in marine craft, and these include:

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    

Ability to easily and inexpensively mold GRP to the near near-net shape, even for marine structures with a complex shape, such as boat hulls, thus making it suitable for mass production Excellent corrosion resistance Light weight, resulting result in reduced fuel consumption Simple to repair Good ability to absorb noise and dampen vibrations, which makes for a more comfortable ride on motor-powered motor boats

High-performance performance yachts competing in the world's most prestigious races, such as the America's Cup and Admiral's Cup, are built with aerospace-quality aerospace quality comp composite materials rather than GRP. Advanced composites are also used in the construction of racing powerboats and skiff sailing hulls. A state-of-the-art art International America's Cup Class (IACC) yacht and a racing powerboat that have been built using advanced composites are shown in Fig. 6. Racing yachts and boats such as these are built using ultralight sandwich composite materials that have thin laminate skins containing carbon, glass and/or and aramid (Kevlar, DuPont) fibers and a core of polyvinyl chloride foam or Kevlar honeycomb. Advanced fabrication processes, such as resin transfer molding, resin film infusion, or autoclaving, are used in the construction of the hull and decks to produce composites that are defect-free, free, excellent dimensional tolerance, and a high fiber content for maximum stiffness, strength, and fatigue resistance.

Fig. 6 Boats built almost entirely from aerospace-grade aerospace composite materials. (a) 2000 Team New Zealand IACC yacht. (b) F-2 series race boat

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The main advantages of using advanced composites are optimal weight distribution, good fatigue resistance, vibration damping, and most importantly, high stiffness-toweight and strength-to-weight ratios. The use of advanced composites with high stiffness- and strength-to- weight ratios allows lighter hull structures to be built with stiffness and strength equivalent to much thicker GRP hulls. This is desirable for planing craft, such as powerboats and sailing hulls, for reducing hydrodynamic resistance. Similarly, for displacement craft such as yachts, a reduction in hull structure weight allows increased ballast to be used for a given displacement. Appendages such as centreboards and rudders on high-performance sailing hulls, trim tabs on powerboats, and rudders on high-performance yachts are also commonly constructed using advanced sandwich materials. This is beneficial for hydrodynamic performance because the overall weight is minimized, higher appendage stiffness is obtained, and a reduction in the weight of the rudder contributes to lower hullpitching moments. Composites are also commonly used for spars (mast, boom, and spinnaker poles), fittings, and fitting reinforcements on sailing boats and yachts. Mast tips, which are about the top one- third of the mast, on sailing boats are made of glass- or carbonreinforced composite to obtain desired flexibility for optimal gust response. Carbonfiber composite is also used in masts for IACC and other high-performance-class yachts. Composite masts are 40 to 50% lighter than similar masts made of aluminum alloy, which results in a reduced heeling moment and therefore, improved performance. The high stiffness obtained with carbon-fiber composite spars is also beneficial for maintaining sail shape under high rig loads. Similarly, the use of highperformance composites in hull structures is beneficial for maintaining high rig loads with minimal hull distortion and added hydrodynamic resistance.

1.3 Offshore Applications of FRP Composites: FRP composites have been used in offshore drilling platforms for many years, although the oil industry has only used these materials in niche applications and not in major structural elements. Steel is the primary structural material used in drilling platforms and is expected to remain so for the foreseeable future, because it has many benefits that other materials, including composites, cannot match. The benefits include low materials cost, the ability to fabricate large structures at low cost, good flame resistance, well-established design rules, and a long service history for using steel in offshore platforms. However, steel has a number of drawbacks that have allowed composites to be used to a limited extent. The greatest problem with using steel in an offshore structure is the poor corrosion resistance against seawater and other highly corrosive agents, such as hydrogen sulfide and hydrogen chloride, that occur during drilling. It is estimated that the oil industry spends several billion dollars each year in maintaining, repairing, and replacing corroded steel structures. Composites offer the potential to reduce these costs because of their outstanding corrosion resistance against most types of chemicals. Composites also offer the possibility of reducing the topside weight of offshore platforms when used in such applications as accommodation modules, helicopter landing pads, and decks. It is estimated that composites provide a weight saving of 30 to 50% compared to steel for many non-structural components. The increased use of composites in topside structures is expected to make the transportation and installation of platforms easier, reduce the weight of tethers, foundations, and piles

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needed to anchor platforms, and allow drilling in deeper waters than is currently possible with heavier steel platforms. Composites are used in a variety of structures and components on offshore platforms because of their better corrosion resistance and lighter weight compared with steel. The most common types of composites used are GRP and phenolic composites, with the latter being used because of good fire resistance. Advanced composites containing carbon fibers, Kevlar fibers, or epoxy resins are used sparingly because of their high cost. Some of the current applications of FRP materials are:  Low pressure pipes  Diesel storage tanks, lube tanks, and utility tanks  Walkway gratings, stair steps, and handrails  Cable ladders and trays  Fire protection panels and sections of accommodation modules  Buoys and floats  Strengthening of primary steel structures  Helicopter landing decks It is worth noting that not all offshore platforms use composites, and in most applications, composite components have been used to replace corroded steel sections. New platforms are rarely built with significant amounts of composite, although this may change as the oil industry assesses the feasibility of using FRP materials for new applications. Potential applications include:  High-pressure (firewater) pipes  Drill pipes, tubing, and risers  Mooring tendons for tension leg platforms and semisubmersible platforms  Walls and floors to provide protection against blast and fire The use of composites is expected to grow as some of these new applications are realized, however, there remain many economic and technical issues that must be resolved before FRP materials are more widely used in offshore platforms. The higher cost of fabricating offshore structures with composites compared with welded steel is a concern to the oil industry. However, there is growing recognition that significant through-life cost savings can be gained with composites due to reduced maintenance and replacement of corroded structures. There is also concern about the lack of design codes and well-established oilfield standards in the use of composites. An important safety concern is that most FRP materials have poor fire- resistant properties, such as short ignition times and high rates of heat release, smoke production, and flame spread. While it is generally recognized that composites have much lower thermal conductivity than metallic materials, these factors make it difficult for composites to meet the stringent fire safety requirements applied to offshore oil and gas platforms.

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2. Testing ting the mechanical prosperities of FRP: In this section, we will talk about testing the mechanical properties of the FRP. We will use, as example, the testing of FRP deck bridges. The results taken from these tests can be adopted for further investigation in marine field. Generally, FRP decks are made as wide and as long as is practical to transport. Because of the size limitations, manufacturers typically provide FRP decks in modular panel forms and almost all decks are joined in the field by panel panel-to-panel connections to create a seamless final installation. Panel-to-panel panel connections are designed to efficiently transfer bending moments and shear forces between joined modular panels; to ensure deformation compatibility due to thermal effects; and to simplify on-site on installation. Several techniques have been developed for panel-to-panel panel connections, including adhesively bonded splicing tongue-groove groove connection and shear key or clip-joint clip joint mechanical fixing connection. Recent research has focused on panel-to-panel panel panel connections to ensure their satisfactory performance ance in field applications.

2.1 Weak-direction direction (beam) Bending Test: At the test, a full-length, length, simplified adhesively-bonded adhesively bonded tongue and groove panel panel-topanel connection was tested under a weak-direction weak direction (beam) bending configuration configuration, shown in Fig.7.

Fig. 7 Evolution of panel-to-panel connections, Adhesively-bonded bonded connection.

2.1.1Specimen Specimen description: description Deck panels, The specimens were fabricated with off-the-shelf off shelf pultruded Strongwell FRP 4 in. x 4 in. x 1/4 in. pultruded square tubes and 3/8 in .The tubes were first bonded together with an epoxy adhesive and then the top and bottom plates were bonded to the tubes using the same epoxy adhesive. A uniform pressure of 10 10-14 psi was applied by sealing the deck panel within a vacuum bag to ensure contact until curing was complete. Applications & Mechanical Properties of FRP

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2.1.2Test Test setup and instrumentation: Test setup, Six specimens were used in this test; referred as Deck #1 to Deck #6. All those six specimens were tested under three-point three bending with 6-ft ft clear span between the supports, shown in Fig.8.The orientation of the connection relative to the supports was rotated ninety degrees, in comparison to the in-site in site orientation, so that the specimen could be bent in the weak direction and the desired strain along the adhesive seam am could be obtained. Because of this fact, testing of the adhesive connection was strain-controlled, controlled, rather than load-controlled. load

Fig.8 Setup of three-point point bending test.

Instrumentation, All six specimens were instrumented with a load cell in the testing frame, six wire pots on the bottom of the deck and one linear variable differential transducer (LVDT) across the th bottom adhesive seam. Table 2 shows all the instruments used in each specimen during the test. The strain gauge locations used in the six decks varied. Decks #1 and #2 used four strain gauges on the bottom of the deck, denoted “SG#1 to #4”. Two additional strain gauges were set up on the top of the deck to locate the neutral axis. SG#5 was located above SG#2, and S SG#6 was located above SG#4. Deck #3 used more strain gauges (10 strain gauges on the bottom of the deck, denoted “SG#1 to SG#10”) in order to collect detailed stress data from the bottom near the adhesive seam. Decks #4 to #6 used six strain gauges on the bottom of the deck, denoted “SG#1 to #6.” No strain gauges were set up on the top of Decks #3 to #6. All instrumentation was attached to the bottom of the deck. Since the deck specimen was much stiffer in the direction transverse to that of major bending, a Applications & Mechanical Properties of FRP

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slight variation in the transverse placement of the gauges was not considered to be problematic.

Table 2 Instrumentation used in each deck Wire pot displacement transducer Strain gauges on the top of the deck Strain gauges on the bottom of the deck LVDTs Load Cell

Deck #1

Deck#2

Deck#3

Deck#4

Deck#5

Deck#6

6

6

6

6

6

6

2

2

0

0

0

0

4

4

10

6

6

6

1 1

1 1

1 1

1 1

1 1

1 1

2.1.3Experimental procedure and results: Testing of the adhesive joints under a weak-direction (beam) bending configuration was strain-controlled. The strain data with normalized values and nomenclature presented in Table 3. The “F” indicates the gauges that were on the external face of the deck, the “E” or “W” indicates which span (east or west, respectively) the gauges were located in, and the “T” indicates the orientation of the gauges with respect to the span direction of the tubes (transverse). All strains listed in Table 3 are transverse strains recorded directly under the load patch during single span tests in the lab. Although the average strain from the field test of 341 με is much smaller, the average strain of 501 με based on lab testing column was used as a conservative service strain for this testing. Each specimen was loaded to this service strain. If the adhesively bonded connection had no initiation of crack below service strain, the connection was judged to be safe under service load. Each specimen was also loaded until failure and an ultimate factor of safety (ultimate strain with respect to the service strain) was calculated to evaluate the performance of the adhesive connection.

2.1.4 Service load tests: In service load tests, each specimen was loaded slowly to around 501 με three times. The test was controlled by whichever strain gauge read the highest value (since there was some variation as to where the maximum strain was located). Each deck was then loaded until its collapse. For all tests, the instrumentation was zeroed before the loading ram was extended to touch the deck. A special loading patch, which consisted of a quarter tire filled with silicone rubber, was used to mimic the cushioning effect of a pneumatic tire. This was done to minimize local stress concentrations of a standard rectangular steel patch. All six specimens exhibited approximately linear behavior up to service load. Every specimen deflected linearly, emitted very little noise, and supported the service load without any indication of cracking or other behavior indicative of structural deterioration. Applications & Mechanical Properties of FRP

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Fig.9 is a representative plot of load versus maximum strain recorded during the test and illustrates this linear behavior.

Table 3 Strain train Values

Fig.9 Representative plots of loads vs. strain in services load test (Deck#3)

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In all specimens except Deck #3, SG#3 reported the maximum strain values measured during testing. In Deck #3, SG#9 recorded the maximum strain value, but this value is only 10 με larger than the corresponding value recorded by SG#3, as shown in Figure 2.8. In Figure 2.8, strain values shift as the loading values still equal zero. The reason is that the weight of the loading ram acted on the deck before the loading ram began to compress the load cell and thus the load cell showed load values.

2.1.5 Crack Initiation and Failure Tests: Tests After being ng tested at service load level, each specimen was then loaded until failure. Audio indications ications helped to capture the appearance of initial cracks in the connection during test. A sudden popping sound was heard and a sudden drop in strain values was simultaneously observed by the monitoring computer at the time of the first crack. However, noo crack could be seen with the naked eye. In all the tests, initial cracking was noticed by these two means. Data analysis after the test also provided evidence of crack initiation. The evidence of cracking in Deck #1 (shown ( in Fig.10)) is typical of what was as seen in all the specimens: a sudden drop of strain with a slight decrease of load. The data from the LVDT also showed the first crack point. As seen in Fig.11 Fig.11, a small disturbance of displacement with a sudden drop of strain values shows the first crack point of Deck #1. After crack initiation, all decks were continuously loaded to 200 με above the strain at first crack point then unloaded and reloaded reloaded until failure (shown in Fig.10 Fig.10). Data indicated no significant stiffness loss occurred after crack initiation until the deck approached ultimate failure. As seen in Fig.10, Fig.10, there was no significant slope change in the load vs. strain plots after the first crack, until near the ultimate failure. The comparison among the six specimens during the failure testing testing is presented in Table 4.

Fig.10 Representative plots of load vs. strain in failure test (Deck#1)

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Fig.11 Representative plots of LVDTs vs. SG#3 Strain in failure test (Deck#1)

Table 4 shows both the maximum strain sustained before cracking initiated and the maximum strain the specimen sustained at any point during the failure testing. T The initiation of crack occurred at load levels varying from 121% to 260% above the target strain. Deck #5 was able to sustain the highest strain level before crack initiation (1300με), followed by Deck #1 (802με). Deck #6 was by far the weakest of the six, supporting 607 με before crack initiated.

Table 4 Behavior Comparison during Failure Stage

This variability in performance may be a direct result of the bond quality. Understandably, the amount of adhesive used to make the joint and the quality of its application have a large influence on the performance of the joint. Since the bottom side of the seam is in tension, any undulation or anomaly in the adhesive can serve as an initiator of a crack. Deck #6 was the first specimen fabricated. Due Due to lack of experience and human error, not enough adhesive was applied, and the excess adhesive was not squeezed out from the bottom side of the seam. A black “line” can be seen along the joint where the adhesive receded and formed a depression along th the seam, approximately as deep as half the depth of the bottom plate. The recess on Deck #6 is essentially a built-in in crack former. The deck capacities reflected these differences, with Deck #6 being the weakest one. Applications & Mechanical Properties of FRP

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The failure modes were different. As seen see in Table 4,, four specimens (Decks #1, #4, #5 and #6) failed at Bond A, which is a factory made epoxy resin connection. Two decks, #2 and #3 failed at Bond B, which is a polyurethane adhesive connection. Two kinds of failure types were observed in this test. test. Progressive failure only happened on Deck #1, and all other specimens were brittle failure. Fig. 12 shows a progressive failure of Deck #1. The crack initiation started at the bottom butt joint of Bond A. After crack initiation, the stresses were redis redistributed and the connection continued to resist load. It seemed that adhesive bonding was stronger than the bottom plate of the tube near the seam. Final failure mode was a tensile failure in the bottom plate of the tube, rather than adhesive or adhesive iinterface failure, which showed the success of this adhesive joint. All other specimens showed brittle failures in the failure test. The crack initiation started inside the seam, at either Bond A or Bond B. No crack could be seen along the seam with the naked ed eye, but a sudden popping sound and a sudden drop in strain values could be observed at the time of crack initiation. After crack initiation, the stresses were redistributed and the connection continued to accept load until another crack formed. While cracks racks developed inside the seam, popping and creaking noises were audible, but no cracks could be seen with the naked eye. When the load reached ultimate, a sudden popping sound was heard and the specimen totally separated, as seen in Fig. 13.

Fig. 12 Progressive failure of Deck#1

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Fig. 13 The groove shape after brittle failure

3. Typical properties of currently available products: Advances in FRP technology, increased use of FRP systems in the construction industry, and steadily decreasing costs of FRP materials have led to the development of a wide range of available FRP products for a variety of specific applications. The properties of currently available FRP systems vary significantly depending on their specific formulation, rmulation, constituents, and manufacturing method. method Off-axis axis properties are typically significantly different than those in the fiber direction. In the fiber direction, the products typically display linear elastic behavior to failure (Fig. 14), but hybrid combinations, such as carbon and glass or carbon, display monotonic stress-strain strain behavior (Fig. 14) similar to that of steel steel. Tables 5 and 6 present overviews of the properties of some typical FRP products for internal reinforcement and external strengthening, respectively, of reinforced concrete structures. Included in the tables is information on FRP bars, rods, sheets, plates, and tapes. Specific information on the potential applications of each of these systems can be obtained by contacting the the FRP manufacturers (also included in the tables). These tables should not be considered as endorsements for a particular FRP product

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T

Fig. 14 Typical stress-strain strain curves for FRP products

Table 5 selected properties of typical currently available FRP reinforced products

*specified yield strength.

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Table 6 selected properties of typical current available FRP strengthened systems

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4. Test methods for mechanical properties: The basic mechanical properties of FRP materials can be determined by applying tensile, compressive, and shear loadings. Flexural testing is also used in some cases. Static material properties are usually of primary interest. Test methods to evaluate mechanical properties include: tension test methods, compression test methods, shear test methods, flexure test methods, and bond test methods.

4.1Tension test methods: Axial tension testing of high-strength unidirectional composites is often a challenge because load must be transmitted from the testing apparatus to the specimen via shear, and the shear strength of a unidirectional composite is typically much lower than its axial tensile strength. Further, shear gripping will load the external fibers more than the internal ones causing shear lag and progressive fiber failure. To distribute gripping forces and to protect the composite from surface damage and premature failure, end tabs are required when testing flat laminates. Special anchors are required for testing of FRP rods and bars by inserting their ends into steel cylinders that are subsequently filled with mortar that may be a polymer resin or a cement-based grout. The bond area of the tabs or the anchor tubes must be large enough such that the applied force can be transmitted without shear failure of the adhesive or grout. For grid-type FRP reinforcements, linear test specimens can be prepared by cutting away extraneous material in such a way as not to affect the performance of the part to be tested. It is recommended leaving a minimum 2 mm projection of crossbars.

4.2Compression test methods: It has been said that there is no true axial compression test for composites. The mode of failure is buckling, ranging from buckling of the entire specimen cross section or local micro buckling of individual fibers. Thus, the greater resistance to buckling the test fixture provides, the higher the compressive strength values obtained. For flat laminate FRP composites, many axial compression test methods in current use are some variation of the Celanese compression test. This test uses a thin, straight-sided specimen that looks very much like an axial tension specimen except that the distance between tabs is much smaller. For FRP rods, tests can be carried out.

4.3Shear test methods: Several ASTM (American Society for Testing and Materials) standards are available for determining the shear properties of composite materials. For flat FRP laminates, direct in-plane shear test methods include the Iosipescu shear test, the two-rail and three-rail shear tests and the 45-degree laminate tensile shear test. For FRP rods, shear test devices have been constructed so that a rod-shaped test specimen is sheared on two planes.

4.4Flexural test methods: Flexural tests are relatively easy to perform; thus, they are fairly popular. The difficulty is that flexural testing does not directly provide information on basic material properties. The stress state on the loaded side of the specimen is compression, on the other side is tension, and at the neutral axis is pure shear. Usually, the shear component is minimized by making the test specimen long relative to its thickness (a ratio of about 32:1 is commonly used).Although flexural tests do not directly provide basic design data, their use is often justified on the basis that the material is subjected to flexural loading in service. Applications & Mechanical Properties of FRP

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4.5Bond Bond test methods for internal FRP reinforcement: reinforcement Bond characteristics influence the mechanism of load transfer between FRP reinforcement and concrete, and therefore control the concrete crack spacing, crack width, required concrete cover to the reinforcement, and the reinforcement development length. The behavior of reinforced concrete structures thus depends on the integrity of the bond. Many test methods have been developed and carried out to determine the bond strength of FRP bars and rods in concrete.

4.6Pullout tests: The concentric pullout test is a popular test method adopted by researchers for comparative bond assessment for FRP reinforcement. In this method, an FRP bar specimen is embedded in a concrete block, the embedded length of the FRP rod typically being five times the rod diameter, and the bar is pulled in tension as shown in Fig.15. The average bond stress and bond stress versus slip at the loaded end can thus be obtained. The pullout test is used for comparative tests, but is not considered a valid test to determine the development that is needed for the design embedment length for flexural ural beam design The ring testis carried out as a pullout test, where the specimen is a concrete cylinder with the studied reinforcing bar embedded along the centre axis of the cylinder. This test allows for determination of the splitting tendency of the bar ar in all stages of loading up to bond failure by determination of the angle between bond forces and the bar axis. The bond length corresponds to the height of the cylinder, which is chosen to be three diameters of the bar, so the bond stress along the bondd length becomes practically evenly distributed. The cylinder is cast in a thin steel tube (the ring), which becomes a part of the test specimen.

Fig. 15 Pullout test specimen

4.7Flexural Flexural bond tests: tests Pullout tests, while extremely useful in many circumstances, are not representative of stress field conditions in an FRP reinforced concrete beam. Flexural beam tests such as the beam-end end test solve some of the stress field discrepancies that are present in pullout tests, and thus offer the advantages advantages of representing the beam stress field more closely. In this method, a bar is embedded in a concrete block, and a tensile load is introduced into the bar using a special test setup as shown schematically in Fig. 16 16. This test setup has the advantages advantages of simulating the stress field condition in a reinforced concrete member in flexure.

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Fig.16 Beam-end end test method

4.8Direct Direct axial tension test: test Two types of direct axial tension tests have been used with a concrete specimen having a continuous bar embedded in its center. In the first type, load is directly applied to the bar protruding from the concrete ends. In the second type, load is applied to the concrete. A concrete specimen is cast with an FRP bar embedded at its center and a notch otch at midlength to allow for the formation of the first crack at a preset location (Fig. 17). Bond strength is studied indirectly through the observation of crack spacing and width in the concrete block. These tests can also be performed with flat (doublee concrete cover) concrete specimens reinforced with one or more bars. Equal tensile load is applied on all or some of the bars. The length of the specimen should allow for at least five cracks to form. Crack spacing and width is studied, and from these, tension ension stiffening and bond can be quantified. Also, staggering of reinforcement can be studied.

Fir.17 Direct axial tension test

4.9Bond Bond test methods for externally bonded FRP reinforcement reinforcement: Flexural and shear strengthening techniques of bonding FRP plates or sheets to reinforced concrete elements is now a method of choice for structural rehabilitation. Failure of these bonded systems before their achieving their FRP capacity. The behavior of the FRP-adhesive adhesive-concrete interface region, which ch must include the region of cover concrete adjacent to the interface, is collectively interpreted as bond behavior. Transfer of stresses through the cover concrete, for instance, can lead to failures through the cover concrete that are nonetheless affected affected by the properties of the bonding adhesive. Complicating interface region behavior is the mixed mode behavior of the deboning process and the heterogeneous material properties in this region. Bond behavior is a critical parameter in strengthening a concrete concrete structure through externally bonded FRP, and numerous test methods have been presented for Applications & Mechanical Properties of FRP

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externally bonded FRP materials for concrete. Test methods can be broadly classified into three types: shear bond, tension, or mixed mode. Recent research has fo focused largely on mixed mode bond test methods in an effort to accurately characterize the FRP-concrete concrete bond, which in practice experiences a combination of shear and normal stresses.

4.10 Shear bond type tests: tests Because externally bonded FRP materials are most most often used in configurations where stress transfer across the interface is dominated by shear stresses, various shear bond test methods are available in the literature. The various methods can be used to study the local interfacial shear bond behaviors by studying the bond strain distribution. Schematics showing the configurations of various types of shear bond tests are given in Fig. 18, including: (a) the single-lap single shear bond test, (b) The push-apart, apart, (c) the pull-apart double-lap lap shear bond test , (d) ( the bending-type type shear bond test , and (e) the inserted-type type shear bond test.

Fig.18 Various shear-bond bond test method configuration: (a) singe-lap singe lap shear bond test; (b) push push-apart; (c) pull-apart double-lap lap shear bond test; (d) bending-type bending shear bond test; and (e) inserted-type type shear bond test

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4.11Tension-type type bond tests: tests At least three test methods are available in the literature to evaluate the strength of the FRP-concrete concrete bond subject to pure normal stresses. Fig. 19 shows a schem schematic of the direct tension pulloff off test method. In this method, a special testing rig is used to pull a circular disc of bonded FRP away from the surface of the concrete in direct tension. The circular area is typically created using a core drill, drill, and an adhesion disc is used, with an appropriate adhesive, to apply an increasing tensile load to the disc until bond failure occurs. For well-bonded bonded FRP materials, the failure surface is in (and thus limited by) the substrate concrete. An alternate shear test arrangement uses a similar test setup, but twists the adhesion disc off of the substrate; this is referred to as torsion pull off test.

Fig.19 Direct tension pulloff test method

4.12Mixed-mode mode bond tests: tests Mixed mode bond test methods are more representative of the interface bond behavior for concrete structures retrofitted with FRP sheets. Mixed-mode mode testing methods include the variable angle peel test, the beam beam-type and slab-type type dowel tests, the single contoured cantilever beam test, the double cantilever beam test, and the modified double cantilever ca beam test.. These bond test methods are considerably more complex and difficult to perform than those discussed previously, and they are typically used to study the fracture fr behavior of FRP-concrete concrete interfaces.

4.13Tensile Tensile fatigue testing methods: methods Fatigue tests on FRPs can be carried out using several specimen configurations, including direct tests on rods using various kinds of gripping mechanisms, and tests on concretee beam specimens reinforced with FRP reinforcements. In the case of performing direct tests on rods, problems are often encountered in gripping the rod, because some grips perform poorly when used for cyclic tests, and failure may occur in the anchoring zone. ne. When performing fatigue tests on concrete beam specimens, the rod is continuously in contact with concrete, which may affect the fatigue behavior of the FRP rod through fretting or friction heating.

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4.14Concrete Concrete prism tensile fatigue test method: method Because of the relatively low modulus of elasticity of FRP reinforcement combined with its high strength, it is very difficult to develop high levels of stress in FRP rods used as tensile reinforcement in concrete beams. A reinforced concrete prism specimen en for tensile fatigue testing has been developed. Fig.20 Fig. shows the details of the specimen, where top and bottom blocks of concrete serve as anchors for the FRP rod while the middle block provides the concrete environment for the FRP rod at the part where the failure is expected. The middle block is separated from the end blocks by a bond breaker during casting. This specimen is loaded in tension by collars at the shoulders of the end blocks, and can be tested under any stress amplitude and with the maximum m stress almost equal to the tensile strength of the FRP rod. To avoid stress concentrations near the rod and splitting of concrete end blocks during the test, a bond breaker is included, as shown, of approximately five bar diameters, and the end blocks aree recompressed near the constriction with a steel compression ring (not shown in the figure).

Fig.20 schematic view of test specimen

4.15 Direct fatigue tests: tests Fatigue tests can also be conducted directly on FRP specimens. These specimens can be rods, flat laminates, or sections of FRP grids. To perform compression fatigue tests directly on flat FRP specimens, a compression compression fatigue test can be used. To overcome the problem of buckling, either short specimens or ant buckling guides should be used. Applications & Mechanical Properties of FRP

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4.16Creep test methods: Unlike steel bars or prestressing tendons, FRP materials may fail by creep at strengths below the maximum static strength when subjected to a significant sustained stress for long periods. This creep-rupture strength varies according to the type of FRP, and so the creep-rupture strength must be evaluated when determining the allowable level of sustained tension in FRP used as reinforcement. Traditional methods of performing creep tests, including direct gravity loading, compressed spring loading, or gravity loading using a lever arm (so called creep frame) to permit greater loads, have all been adapted for testing FRP materials.

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References - ASM Handbook Volume 21, Composites, by ASM International, December 2001. - Report on Fiber-Reinforced Polymer (FRP) Reinforcement for Concrete Structures, by ACI Committee 440. - Testing and Analysis of a Fiber-Reinforced Polymer (FRP) Bridge Deck, by Zihong Liu, dissertation submitted to the Faculty of Virginia Polytechnic Institute and State University in partial fulfillment for the requirements for the degree of Doctor of Philosophy in Civil Engineering.

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