Hybrid Composite

Hybrid Composite

ABSTRACT The Role of Materials in the Development of the modern industry is getting overwhelming importance .This is because 40% of the total cost of product is used for material. As technology becomes more and more sophisticated, the material used should also be more efficient and is expected to have more performance efficiency and reliability. Composite materials, plastics and ceramics have been dominant emerging materials. The demand for new material for special engineering application is increasing due to recent advances in space crafts, structural, automobile, IT and a host of other industries. The Modern need focuses on cheaper and flexible materials which perform in stringent conditions of high temperature and pressure, in highly corrosive environment, with higher strength but low weight, with wear resistance and longer durability. This gives ample scope for fabrication of newer composites. The present study is focused on fabrication of polymer composites as Epoxy Resin blended with Glass and PET Woven fabric .In this project an attempt has been made to fabricate the composite laminates by Vacuum Bag Moulding technique , because it one of the most versatile method of preparation of laminates, almost all the laminates can be prepared by this method and it is also the most economical method of preparation of laminates, but it involves a lot of labour work. The laminates prepared by varying the weights of woven fabrics and Epoxy; resin content has varied from 35% to 50% and were subjected to experiments to determine mechanical properties and Non Destructive Evaluation. Data has been tabulated and analyzed.

The properties evaluated from these tests have been systematically analyzed to study the behavior and variation of properties with respect to its composition. This has enabled us to derive to certain conclusions. With this study, we can conclude that composites can successfully replace certain conventional metals in some structural and aerospace applications.

Hybrid Composite

CHAPTER 1

INTRODUCTION

CHAPTER 1 INTRODUCTION 1.1 COMPOSITE MATERIAL

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Composite materials are materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure. There are two categories of constituent’s materials: matrix and reinforcement. At least one portion (fraction) of each type is required. The matrix materials surround and support the reinforcement materials by maintaining their relative position. The reinforcement imparts special physical (mechanical and electrical) properties to enhance the matrix properties. A synergism produces material properties unavailable from naturally occurring materials. The advantages of composites are that they usually the best quality of their constituents and often some qualities that neither constituents possesses. The properties that can be improved by forming a composite material include: 1. Specific properties –high strength, and strength to density ratio ,high strength at high temperature. 2. High stiffness to density ratio ,toughness (impact and thermal shock) 3. Improved fatigue strength, , improved strength –rupture life. 4. Surface finish 5. Improved hardness with corrosion resistance and erosion resistance. 6. Improved Creep Strength.

7. Ability to tailor made specific properties. 8. Ability to use low cost tooling materials . 9. Composite can provide a specific tensile strength that is approximately 4 to 6 times greater than steel or aluminum. 10. Composites can provide a specific modulus i.e. 3.5 to 5 times greater than steel or aluminum. 11. Tougher composites can have impact energies significantly higher than metal alloys. 12. Design flexibility is greater and can allow for physical property and dimensionally in part where desired . 13. Composite material has good sound dampening nature. 14. The need for machinery is eliminated or significantly reduced.

Hybrid Composite

The production of composite material is booming all over the world, i.e. the output is increasing at a high rate every year. Although the cost of composite materials is higher than standard materials, this is offset by the substantial advantages their properties afford users such as light weight and resistance. These serviceable properties have allowed composite materials to break into major markets in automotive construction, aeronautics, and the building trade. The control of the product life cycle from design to recycling, and the improved characterization of the products and their performance are the requisites for considering the substantial development programs. The most primitive composite materials comprised straw and mud in the form of bricks for building construction. The most advanced examples perform routinely on spacecraft in demanding environments. The most visible application paves our roadways in the form of either steel and aggregate reinforced Portland cement or asphalt concrete. Those composite closest to our personal hygiene form our shower stalls and bath tubs made of fiberglass. Solid surface, imitation granite and cultured marble sinks and countertops are widely used. Designing materials for specific application is the underlying philosophy of composite materials. That is, composite materials are tailored for specific technological needs. Composite provide designer, fabricator, equipment manufacturer and consumer with sufficient flexibility to meet the demands presented by different environments and special requirements. Thus they often eliminate the crippling necessity face by the designers of restriction the requirements of design to traditional experience. The goal in creating the composite is to combine similar or dissimilar materials in order to develop specific properties that are related to desired characteristics. Since composite can be designed to provide and almost unlimited selection of characteristics, they are employed practically in all industries.

Hybrid Composite

Fig 1.1 Stress strain curves for fiber matrix and composites •

Figure shows schematic representation of brittle fibre,ductile matrix and combined effect of composites to obtain the properties and advantages stated above.

1.2 OBJECTIVE The main objective of this Project Work undertaken is to manufacture a hybrid composite of optimum fiber resin composition by weight with high performance PET – GF as the reinforcement and Epoxy as the resin which is expected to give the following properties in both Longitudinal and Transverse directions. 1) High Mechanical Properties. 2) Outstanding Thermal Properties.

1.3 HISTORY Although composite materials had been known in various forms throughout the history of mankind, the history of modern composites probably began in 1937 when salesmen from the Owens Corning Fiberglass Company began to sell fiberglass to interested parties around the United States. Fiberglass had been made, almost by

Hybrid Composite

accident in 1930, when an engineer became intrigued by a fiber that was formed during the process of applying lettering to a glass milk bottle. The Owens Corning Fiberglass Company was formed in 1935 by OwensIllinois and Corning Glass Works to capitalize on this new fibrous material. A Japanese company (Nitto Boseki) had also made fiberglass and was attempting to market the fibers in Japan and the United States. The initial products for this finely drawn molten glass were used as insulation (glass wool) but structural products soon followed. The fiberglass salesmen realized that the aircraft industry was, in particular, a likely customer for this new type of material because the many small and vigorous aircraft companies seemed to be creating new aircraft designs and innovative concepts in manufacturing almost daily with many of these innovations requiring new materials. One company, Douglas Aircraft, bought the first roll of fiberglass shipped to the west coast because they believed that the fiberglass would help them solve a production problem. They had a bottleneck in the making of metal molds for their sheet metal forming process (called hydro press forming). Each changed aircraft design needed new molds and metal molds were expensive and had long lead times. Douglas engineers tried using cast plastic molds, but they could not withstand the forces of the forging process. Maybe if the plastic molds were reinforced with fiberglass they would be strong enough to allow at least a few parts to be made so that the new designs could be quickly verified. If the parts proved to be acceptable, then metal dies could be made for full production runs. In collaboration with Owens Corning Fiberglass, dies were made using the new fiberglass material and phenolic resin (the only resin available at the time). What a success! Reinforced plastic dies for prototype parts became the standard. Other applications in cooling for aircraft soon followed. Many of the tools (jigs and fixtures) for forming and holding aircraft sections and assemblies needed to be strong, thin and highly shaped, often with compound curves. Metals did not easily meet all of these criteria and so fiberglass reinforced phenolic tooling became the preferred material for many of these aircraft manufacturing applications. Not long afterward, unsaturated polyester resins became available (patented in 1936) and they eventually (although not immediately) became the preferred resin because of the relative ease in curing these resins compared to phenolics. Peroxide curing systems were already available with benzoyl peroxides being patented in 1927,

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lauroyl peroxide in 1937, and many other peroxides following not too long afterward. Higher performance resin systems also became available about this time with the invention of epoxies in 1938. The materials and the applications seemed to be converging at the same time.

1.3.1 Developments during World War II The pace of composite development, already fast, was accelerated during World War II. Not only were even more aircraft being developed and, therefore, composites more widely used in tooling, but the use of composites for structural and semistructural parts was being explored and then adopted. For instance, in the frantic days of the war, among the last parts on an aircraft to be designed were the ducts. Since all the other systems were already fixed, the ducts were required to go around the other systems, often resulting in ducts that were convoluted, twisting, turning, and placed in the most difficult to access locations. Metal ducts just couldn’t easily be made in these “horrible” shapes. Composites seemed to be the answer. The composites were hand layup on plaster mandrels which were made in the required shape. Then, after the resin had cured, the plaster mandrels were broken out of the composite parts. Literally thousands of such ducts were made in numerous manufacturing plants clustered around the aircraft manufacturing/assembly facilities. Other early WWII applications included engine nacelles, which lightened the A20 airplane and radomes (domes to protect aircraft radar antennas) which gave both structural strength and radar transparency. Phenolic-reinforced paper was used to make a structural wing box beam for the PT-19 airplane at about this time. Plastic airplane seats using combed and carded cotton fibers impregnated with urea and polyester were also made on an Air Force contract during the early war years. Non-aircraft applications included cotton-phenolic ship bearings, asbestos4 phenolic switchgears, cotton/asbestos-phenolic brake linings, cotton-acetate bayonet scabbards, and thousands of others. The early war period also marked the first production of a fiberglass reinforced boat molded by Basons Industries. However, when molding the boat, no mold release or parting agent was used and the part could not be extracted from the mold. After all attempts to separate the part from the mold had failed, the entire assembly was rolled into the Bronx River.

Hybrid Composite

At about this time (1942), the government became concerned that supplies of metals for aircraft may not be available and so they instructed the engineers at Wright Patterson Air Force Base to survey all of the manufacturers of composite parts in the United States and try to determine the current best practices in composite manufacture. Wright Patterson personnel were also to remote the use of composites by developing design rules, by encouraging the development of new composite materials and applications, and by using their own expertise for the development of new and bold composite applications. Perhaps the boldest applications of all were the development of aircraft wings for the AT-6 and the BT-15, two training airplanes. A total of six wing sets were made, installed on aircraft, and successfully flown. In spite of the success of this project, aircraft structural parts were not made again for 50 years. Even more amazing, after the 50 year hiatus, the method of making the parts was nearly identical to the method employed at Wright Patterson Air Force Base in 1942. Many other composite improvements were developed during WWII including some Innovative manufacturing methods such as filament winding and spray-up. Sandwich structures using a cellular core, fire resistant composites, and prepared materials were also developed during this time of development opportunity.

1.3.2 Post World War II Developments When the war effort came to a sudden halt, the many companies who had been active in making war materials were faced with an acute problem. They needed to quickly identify new markets and new products which utilized the expertise they had developed. Companies like Goldsworthy Engineering were trying to make any composite part they could think of and were receiving support from the companies who manufactured fiberglass who would “sponsor” some of the projects. For instance, the fiberglass manufacturers would pay for the tooling for a new application just to reduce the development cost. Some of the war-oriented applications were converted directly to commercial applications such as fiberglass reinforced polyester boats. By 1948 several thousand commercial boats had been made. Almost everyone agreed that the pent-up demand for automobiles was a logical application for composites. By 1947 a fully composite body automobile had been made

Hybrid Composite

and tested. This car was reasonably successful and led to the development of the Corvette in 1953 which was made using fiberglass performs which were impregnated with resin and molded in matched metal dies. Eventually the dominant molding method for automobile parts was compression molding of sheet molding compound (SMC) or bulk molding compound (BMC). Premix materials of these types were developed as early as 1948 by the Galstic Corporation. One automotive innovation that deserves special mention is the auto/plane development led by Convair Aircraft Company. Convair reasoned that the many returning wartime pilots would like to continue with their flying, but would also like to combine it with family vacations. Hence, Convair made an automobile with an all-composite body (for weight savings) that would allow a special wing assembly to be attached. The wings would be available for rent at various airports, thus permitting the driver to rent a wing assembly at one airport, fly to the vacation site, turn in the wing assembly, and drive away. Prototypes were made and successfully demonstrated. What a boon they would be today in Los Angeles, although the skies might be more hazardous than the roads! Some of the products made during the post-war era have now emerged as major markets for composite materials. These include tubs and shower assemblies, noncorrosive pipes, appliance parts, trays, storage containers, and furniture. Other composite products have also been successful, although not quite as well known or spectacular. For instance, sets for entertainment groups and stage productions, especially those that travelled like the Ice Follies, were made of composites. In the movie “Captain from Castile” the armor and helmets of the Spanish soldiers were made of composites and painted to resemble metal. The headdresses of the Aztecs were also molded composites. Several innovative manufacturing methods were also developed in the late 1940's and early 1950's including pultrusion (by Goldsworthy), vacuum bag molding, and large-scale filament winding.

1.3.4 AEROSPACE The push for aerospace dominance that began in the 1950's and really picked up speed in the 1960's was a new impetus for composite development. Richard Young of the W. M. Kellogg Company began using filament winding for making small rocket motors. This technology was purchased by Hercules and was the basis for the largescale rocket motor business which was at the heart of the space race. By 1962 the need

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for highly accurate filament winding machines became apparent to Larry Ashton, an engineer at Hercules, who founded Engineering Technology to produce these machines. (Engineering Technology was started from an initial stake of money the founders obtained from selling their blood to a blood bank. That’s giving it all for the company!) In 1961 a patent was issued to A. Shindo for experimentally producing the first carbon (graphite) fiber but Courtalds Limited of the United Kingdom was the first to produce commercially viable carbon fibers several years later. With these fibers, part stiffness to weight was improved and even more applications in aerospace were introduced. Perhaps the crowning jewel of this period (1978) was the development of the first fully filament wound aircraft fuselage, the Beech Starship, by Ashton. The plane was successfully flown, but was not commercialized using the filament wound technology. Many people still believe that the filament winding technology is the best method to produce small aircraft fuselages.

1.3.5 Leading Up To the Present New fibers were also introduced with boron filaments becoming available in 1965 and aramid fibers (Kevlar®) offered commercially by DuPont in 1971. Fibers made from ultra high molecular weight polyethylene were made in the early 1970's. These advanced performances fibers, along with fiberglass and carbon fibers, have led to tremendous developments in aerospace, armor (structural and personal), sports equipment, medical devices, and many other high performance applications. The development of new and improved resins has also contributed to the expansion of the composites market, especially into higher temperature applications and applications where high corrosion resistance is needed. Today, the composites marketplace is widespread. As reported recently by the SPI Composites Institute, the largest market is still in transportation (31%), but construction (19.7%), marine (12.4%), electrical/electronic equipment (9.9%), consumer (5.8%), and appliance/business equipment are also large markets. The aircraft/aerospace market represents only 0.8% which is uprising in light its importance in the origins of composites. Of course, the aerospace products are fewer in number but are much higher in value. Most of the markets continue to grow. Composites have found their place in the world and seem to be gaining market share, especially in

Hybrid Composite

products where performance is critical. Some of these products are very new, but isn’t it interesting that construction is still a major market for composites, just as it was in 1500 B.C. when the Egyptians and Israelites were using straw to reinforce mud bricks.

1.4

Classification of composites 1.4.1 Based on Micro Structure The microstructure of the composite provides a basis for classifying them for

purpose of study, processing and analysis. Two materials can be combined only by two ways: By inserting one material into other 1. By bonding them layer by layer The former type of composition is called multiphase composition and other type is multi-layered composition .The phase composition is generally at microscopic level and the layered composition at macroscopic level.

1.4.2 Based on methods of Manufacturing Natural composite These are composite materials, which exist in nature .wood, bone, muscle, skin, shell powder of the beetle nut and coconut, wheat rice coconut, wheat rice coffee and fibers of sisal, coir, jute, etc are the examples of natural composites. The nature fibers such as sisal, jute, coir etc provide strength to the composite through high transfer efficiency between the matrix and the fiber. These natural fibers generally used as reinforcement and they improve the toughness and flexural strength of the composite

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materials also they have a cellular structure and they can impart sound dampening properties to the composite. Another advantage of reinforcing these lingo cellulose materials in polymer matrix is that these composites have a wood like texture and can be used as substitute for wood. Man made composite These composites are the new family of composites created by man. Man made composite offer considerable freedom in the design and hence, they are of greater use. More than 200 families of composites have been made by man for his use. Man made composites can be further classified into two groups 1. Those in which the constituents are separately made and then combined into composites. 2. Those in which the insert in the form of fiber are grown within the matrix.

The eutectic metallic composite and self-reinforced polymer is examples of latter category of composites.

1.5 Importance of composite Composites have several properties and characteristics feature that make them stand above all other conventional material both in performance efficiency and in the manufacturing adaptability. Some of the attributes are given below. 1. Composites are multi-functional materials. The fact that several

functional requirements can be obtained by one single material make the designs easy and the product functionally efficient. 2. Composite are generally energy efficient because of their lightness,

they require less energy for transportation, erection and operation. 3. Composite generally can be made corrosion and weather resistant. As

a result, they are durable and require less maintenance 4. Composites can be designed to give properties for specific design conditions 5. By proper orientation of fibers, directional properties can be obtained.

Products of complex shapes can be molded without any material wastage part consolidation and close tolerances can also be maintained.

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1.6 Fiber reinforced composite material Major constituents in a fiber-reinforced composite material are the reinforcing fibers and a matrix, which acts as a binder for the fibers. Other constituents that may also be found are coupling agents, coatings and fillers. Coupling agents and coatings are applied on the fibers to improve their wetting with the matrix as well as to promote bonding across the fiber/matrix interface. Both in turn promote a better load transfer between the fibers and reduce cost and improve their dimensional stability. In general, fibers are the principal load-carrying members. While the surrounding matrix keeps them in the desired in the desired location and orientation, acts as a load transfer medium between them, and protects them from environmental damages due to elevated temperatures and humidity for example.

1.6.1 Fibers The fiber is an important constituent in composites. A great deal of research and development has been done with the fibers on the fibers on the effects in the types, volume fraction, architecture and orientation. The fiber generally occupies 30%-70% of the matrix volume in the composites. The fibers can be chopped, woven, stitched and/or braided. They are usually treated with sizing such as starch, gelatin, oil, or wax to improve the bond as well as binders to improve the handling .The most common types of fibers used in advanced composites for structural applications are the fiberglass, aramid and carbon. The fiberglass is the least expensive and carbon being the most expensive. The cost of aramid fibers is about the same as the lower grades of the carbon fiber. Other high strength, high modulus fibers such as boron are at present time considered to be economically prohibitive.

1.6.2 Resins The use of particular resin will determine the properties and range of conditions over which the Fiber reinforced polymer materials can be used. Resins are commercially available in a variety of forms, as powder, flakes, granules, water emulsions and latexes, solutions in organic solvents and in liquid form covering a wide range of viscosities.

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Properties of resins vary greatly and determine the conditions under which fabricating or molding a particular mixture can be done. For example, many resins generate volatiles during curing. As such, high molding pressures are necessary to prevent by-products from forming gas pockets in the product.Resins that can be used at low pressures are most often preferred for FRP molding. Molding equipment at low pressure is less costly and simpler in design.

CHAPTER 2 LITERATURE SURVEY

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CHAPTER 2 LITERATURE SURVEY Johns Manville's Engineered Products Group in Denver has introduced Comfil-G, a family of commingled yarns consisting of continuous glass and PET filaments. Another Comfil-G product with glass and polypropylene filaments will be introduced this year. • Johns Manville says the glass/PET product can be used to produce lightweight

plastic molds with improved tensile strength • It can also be used for pultrusion, hot-press forming, winding, and braiding. • Glass/PET yarn resists temperatures up to 120 C (248 F). It also reportedly

provides good paintability and adhesive bonding.

The Fracture Behavior of Glass Fiber/Recycled PET Composites. W. J. Cantwell Department of Engineering, University of Liverpool, Liverpool L69 3BX, United Kingdom. They Investigated potential offered by glass fiber reinforced composite materials based on a recycled PET matrix has been investigated. Laminates containing both woven glass fabrics and chopped strand mats have been manufactured and tested under both quasi-static and impact conditions. Polished sections from a number of laminates have highlighted the high degree of fiber wetting and the low level of voiding in the laminates. Three point bend tests and Charpy impact tests on simple beam-like samples have shown that recycled polymer composites offer a range of mechanical properties similar to those associated with corresponding laminates based on virgin polymer matrices. A series of interlaminar fracture tests on the woven fiber composites

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have shown that the delamination resistance of these materials is comparable to that exhibited by relatively tough systems such as carbon fiber reinforced PEEK.

Glass fibre recycled poly(ethylene terephthalate) composites: mechanical and thermal properties by A.L.F. de M. Giraldi, Department of Polymer Technology, College of Chemical Engineering, State University of Campinas, SP, Brazil. Their Investigations of thermal and mechanical properties of recycled poly(ethylene terephthalate) (PET) reinforced with glass fibre have been carried out, focusing on the influence of two variables involved in the extrusion process: screw speed and torque. A Factorial Experimental Design of the processing conditions during extrusion (screw speed and torque) was done to get the best thermomechanical properties versus processing conditions. Mechanical properties such as Young's Modulus and Impact Resistance increased after the addition of glass fibre in recycled PET matrix.

Interlaminar fracture of commingled-fabric-based GF/PET composites L. Ye and K. Friedrich Department of Mechanical and Mechatronic Engineering at the University of Sydney, NSW 2006, Australia,Institute for Composite Materials Ltd, University of Kaiserslautern, Germany. A 45:55 weight% mixture of commingled glass/polyethylene terephthalate (PET) fabric was selected to study the relationships between material microstructure, Mode I and Mode II interlaminar fracture toughnesses and failure mechanisms. Composite laminates subjected to different cooling histories were manufactured within a steel mould using a laboratory heat press. Mode I and Mode II interlaminar fracture tests were performed using double cantilever beam and end-notched flexure specimens. PET matrix morphology appeared to be sensitive to the thermal histories, although this occurred on a subspherulitic scale (in contrast to observations made with polypropylene-based composites). The spherulitic textures were generally very fine and no evidence of interspherulitic fracture paths could be identified. When the composites were subjected to low cooling rates or an isothermal crystallization process, many small matrix cracks developed between fibres within the reinforcing bundles. The lower the cooling rate, the higher the density of matrix cracks per unit volume of material. The

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interlaminar fracture toughness in the laminates with slow cooling rates was much lower than in the case where a quasi-quenched condition was applied. Characterization of thermoplastic poly(ethyleneterephthalate)-glass fibre composites, crystallization study By Catherine Gauthier , Laboratoire d'Etudes des Matériaux Plastiques et des Biomatériaux, Université Claude Bernard,France. They investigated the influence of glass fibers on crystallization kinetics and on matrix morphology for poly(ethylene terephthalate) (PET)/glass fibre composites. The following parameters are also considered: fusion-crystallization conditions, thermal stability and the addition of nucleating agents in the matrix (talc or sodium benzoate). It clearly appears that the influence of those additives on the crystallization of PET is predominant compared to the effect of stiffening fibres. Moreover, the application of shear stresses at the PET/glass fiber interface promotes the growth of a different crystalline superstructure.

2.1 Scope of Present Study A probe by accident into the field of thermosetting polymers has brought about a quantum growth in its basic as well as technological aspects .The synthetic thermosetting polymers with the combinational properties of the existing conventional high strength polymers and glass fibers with a variety of filler materials have altogher offered a new field of research. The review work presented here reveals that bulk of the effort has gone into the

understanding of the mechanical ,thermal and physical properties of

thermosets .A thorough literature search reveals that there are no systematic studies on mechanical properties of thermosetting composites .There is ample scope for fabrication of newer composites with different weight fractions of glass fiber and PET in polymers and there characterization for physical ,mechanical and thermal properties .In

this thesis ,a wealth of data on

properties of polymer glass PET composites has been generated .These data are useful for material technologists and A probe by accident into the field of thermosetting polymers has brought about a quantum growth in its basic as well as technological aspects .The synthetic thermosetting polymers with the combinational properties of the existing conventional high strength polymers and glass fibers with a variety of filler materials have altogher offered a new field of research. The review work presented here reveals that bulk of the effort has gone into

Hybrid Composite

the

understanding of the mechanical and thermal properties of thermosets .A

thorough literature search reveals that there are no systematic studies on mechanical properties of thermosetting composites .There is ample scope for fabrication of newer composites with different weight fractions of glass fiber and fillers in polymers and there characterization for physical ,mechanical and thermal properties .In

this thesis ,a wealth of data on mechanical properties of polymer

glass filler composites has been generated .These data are useful for material technologists ,mechanical engineers and defence engineering ,who can make use of this database for the generation of new materials for specific application. In that respect it has been used GF and virgin PET fibers in the form of woven mat and epoxy as matrix .Laminates are obtained from vacuum bag moulding technique . Tests carried out to evaluate Physico-Mechanical and thermal properties according to ASTM standards.

Hybrid Composite

CHAPTER 3 MATERIALS USED

CHAPTER 3 MATERIALS USED 3.1 Glass fiber

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The most common and inexpensive fiber used is glass fiber, usually for the reinforcement of polymer matrices. Typical composition of glass fibers is 50-60% SiO2, and other oxides of Al, Ca, Mg, Na, etc.Glass fibers are produced by melting the raw materials in a reservoir and feeding into a series of platinum bushings. Each of which has several hundred holes in its base. The glass flows under gravity and line filaments are drawn mechanically downwards as the glass extrudes from the holes. The fibers are wound onto a drum at speeds of several thousand meters per minute. Control of the fiber diameter is achieved by adjusting the head of the glass in the tank, the viscosity of the glass (dependent on composition and temperature), the diameter of the holes and the winding speed . Properties

Values

Specific gravity

2.54-2.56

Tensile strength

260-360 KN/m *10

Modulus of elasticity

7.0-7-3 KN/m *10

Index of refraction

1.547

Softening point

1555F

Table 3.1 .Typical properties of E-glass fibre . Typical compositions of three types of glass popular for composites are given. The most commonly used E-glass (E for electrical), draws well and has good strength, stiffness, electrical and weathering properties. In some cases, C-glass (C for corrosion) is preferred, having better resistance to corrosion than E-glass, but lower strength. Finally, S-glass (S for strength) is more expensive than E-glass, but has a higher strength, Young’s modulus and temperature resistance. The strength and modulus are determined primarily by the atomic structure. Silica-based glasses consist primarily of covalently bonded tetrahedron, with silicon at the centre and oxygen at the corners.

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Addition of alkali and alkaline earth metals such as K, Na and Ca tends to lower the stiffness and strength, but improves the formability. The strength depends on processing conditions and test environment. Freshly drawn E-glass fibers, provided they are handled very carefully to avoid surface damage, have strength of 3.5 GPa and the variation in strength is almost zero. The strength falls in humid air, owing to the adsorption of water on the surface. A major factor determining the strength is the damage which fibers sustain when they rub against each other during processing operation. To minimize this damage, glass fibers are usually treated with a size at an early stage in manufacture. This is a thin coating applied to the fibers by spraying with water containing an emulsified polymer. Glass fibers are available as a) Chopped Strands b) Continuous Yarn c) Roving d) Fabric Sheets

constitue

E glass

nts Sio2

54

S

C

glass

glass

64

65

Al2o3

15

25

4

Cao

17