CHAPTER BACKGROUND INTRODUCTION TO COMPOSITES FIBRE REINFORCED COMPOSITES AND ITS CONSTITUENTS 6

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1 1 CHAPTER 1 INTRODUCTION 1.1 BACKGROUND INTRODUCTION TO COMPOSITES FIBRE REINFORCED COMPOSITES AND ITS CONSTITUENTS SIGNIFICANT AND IMPORTANT FUNCTIONS OF FIBRES AND MATRIX Functions of fibres Functions of Matrix SALIENT FEATURES OF COMPOSITES FABRICATION OF POLYMER COMPOSITE PRODUCTS FIBRE REINFORCEMENTS Glass fibre E-Glass fibre Carbon fibre AUTOMOTIVE APPLICATIONS OF LAMINATED COMPOSITES 13 BIBLIOGRAPHY 15

2 2 CHAPTER 1 INTRODUCTION 1.1 BACKGROUND A composite material is composed of reinforcement (fibres, particles, flakes, and/or fillers) embedded in a cured resin also known as a matrix (polymers, metals, or ceramics). The matrix holds the reinforcement together to form the desired shape while the reinforcement improves the overall mechanical properties of the matrix. When designed properly, the new combined material exhibits improved strength compared with each individual material. A fibre-reinforced composite is a material system made primarily of varying amounts of fibre reinforcement embedded in a protective material called a matrix, with a coupling agent applied to the fibre to improve the adhesion of the Fibre to the matrix material. FRP composites unlike steel or aluminum are anisotropic (properties are different in different direction) whereas steel or aluminum is isotropic (uniform properties in all directions, independent of applied load). Therefore, FRP composite properties are directional, meaning that the best mechanical properties are in the direction of the Fibre placement. The field of application for such composites depends on their physical and mechanical properties. These properties can be evaluated from standard ASTM procedures. Modern Composite Structures are employed today in a broad range of aeronautical, space, marine, automotive, and civil structural applications. The advantages of combining two or more materials with suitable matrix are to provide a light, strong, and stiff structural element. This configuration further allows much versatility in the design, manufacturing, and use of the advanced panel as an integrated system. One aspect of this design flexibility is the ability to incorporate

3 3 different fibre system to evaluate mechanical properties and ascertain the best composite system for a particular application. Further, these composite structural elements are subjected to various types of loading system during in-service conditions. In this work, composite specimens subjected to flexural & shear load is tested and hence their properties are evaluated experimentally and these are compared with automotive components. 1.2 INTRODUCTION TO COMPOSITES The commercial application of composite materials in large scale production started in the early 1940s and before 1950s during the period of the Second World War with the marine applications in the military. Today presently the composite materials are the integral part of the many products including the aerospace, automotive, and marine, consumer goods, sporting goods, and infrastructure and in many more applications. The recent developments in the area of the polymer composite manufacturing technology have enhanced the use of composites in wider prospects. The high volume production techniques such as Sheet Moulded Components have gained higher maturity level and are routinely used in the automotive, consumer and in many industries in a large scale. The advancement in the newer material invention in the field of composite materials and the drop in the price of the manufacturing process has enhanced its usage in all most all the industrial sectors. Composites happens to be material of choice for the automotive and transportation, aerospace, marine engineers for various reasons like styling detail possibilities, high strength to volume ratio, high surface finish quality attainable, simple processing etc. With the introduction of the polymeric based composites the polymer composite materials captured the attention of the industry and its application in various industries including automotive components, sporting goods aero space

4 4 parts, consumer goods, marine applications and structural applications increased. The growth in the field of composite usage is also because of the increased awareness regarding product performance and increased competition in the global market for lightweight components. Composite materials have the ability to replace the widely used steel and aluminium and many a times can provide a better performance. Steel materials replaced with composite materials can reduce 60-80% in component weight and 20-50% weight by replacing aluminium parts. A composite material happens to be the choice of today s industries for many applications. Traditionally materials are of three basic types metals, ceramics, and polymers. Materials from these different categories or even different materials from the same category combine to achieve properties and performance that are unique. Such materials are called composites. In the most basic manner all materials except elements are composites. For example an alloy a binary mixture of two elements is considered a composite structure of atomic scale. At the microstructure level a larger scale than the atomic level definition, composites are composed of crystals, phases and compounds. With the micro structure definition, steel, a suspension of carbon in iron, is a composite, But brass a single- phase alloy is not a composite. By considering one more level on the size scale, one can find that there are macro structural composites. Macro structural composite material is composed of fibres, matrices, and particulates. Fibres, matrices and particulates form materials systems. The highest level of structural classification gives the definition of composites [1]. Hence a composite is a material brought about by combining materials differing in composition or form on a macro scale for the purpose of obtaining specific characteristics and properties.

5 5 An understanding of the basic component materials is essentially required to understand and use the composites for various applications. A composite material is essentially made up of two or more elements combined together to create a material whose properties are much more superior to the properties of the elements it self. The concept of composites are not man derived it is available in nature it self as natural composites the example of natural composites are wood, which is a composite of cellulose fibre in matrix of natural glue called lignin. The shell of invertebrates is another example of composite; these shells are much stronger and harder than the man made composites. A composite material will have a unique combination of properties. The above logic of combination of materials is applicable to metal alloys, plastic co-polymers, minerals, wood, etc., the fibre reinforced polymers are different from the above materials as that the constituent materials are different at the molecular level and are mechanically separable. The fibre reinforced polymer in its bulk form will have the constituent materials work together but remain in their original form and the final property of the composite materials will be better than constituent material properties. The important significant property of composite is that it contains matrix materials. The composite material is formed by reinforcing fibres, particulates, or whiskers and the matrix materials can be metals, plastics, or ceramics. The reinforcing material can be a polymer, ceramic and metals. The fibres used for reinforcement can be continuous, long, or short. Composites made with polymer matrix have become more common in present day application in industries. The polymer based resins can be of two type s thermo set or thermoplastic resins. The reinforcing material can be in the form of a fibre or fabric this reinforcing material will provide strength and stiffness to the composite, where as the polymer matrix used will provide rigidity and

6 6 environmental resistance to the composite. The reinforcing fibre material is found in different forms, like long continuous fibre, woven fabric, short chopped fibres and mat. Every combination of fibre reinforcement with the matrix will result in different configuration of property. The property of a polymer composite will strongly depend on the way the fibres are arranged in the composite. Many permutation and combination of arrangement of fibres can be tried to attain at the required property of the composite. The most important fact to be noticed in the composite is that the fibre (reinforcing element) carries the load and its strength is greatest along the axis of the fibre. Long continuous fibres in the direction of the load result in a composite with properties far exceeding the material resin itself. The same material chopped in to short lengths yields lower properties than continuous fibres or long fibres. Depending on the type of application (Structural or non-structural) and manufacturing method used the fibre form (long, short or woven) is selected. In case of the structural application generally long fibre reinforcement is adopted and in case of non structural applications short fibre reinforcement can be adopted. 1.3 FIBRE REINFORCED COMPOSITES AND IT S CONSTITUENTS: A polymer composite made of fibre reinforced polymer differs from the other types of composites as it is distinctly and macroscopically separable or mechanically separable between the fibres and the matrix. Composite in its basic constituents retains its identity such that it can be physically identified; the composites exhibit an interface between one another. The concept of basic constituents of composites is illustrated in figure 1.1. A fibre reinforced composites generally consists of two basic elements, the matrix which forms the bulk of the material and the reinforcing materials which are added generally to increase the strength and stiffness of the composite material.

7 7 In general the reinforcement will be in the fibre form. In the present day application we come across three basic types of composites in use [2]. (1) Metal matrix composites (2) Ceramic matrix composites & (3) Polymer matrix composites/fibre reinforced polymers. A polymer matrix composite primarily consists of a base material which is called as the matrix and the commonly used matrix is the polymer based resin. The reinforcing material will be in the form of fibres and the reinforcement is provided to enhance the strength and stiffness of the composite, the commonly used reinforcing fibres are glass fibres, boron fibres, graphite fibres, carbon fibres, aramid fibres etc., The matrix materials like epoxy resin, polyesters etc., can not be used for any kind of structural applications on their own as they do not processes the adequate required mechanical properties as compared with metals. To over come this barrier the matrix material is reinforced with the fibres such as glass, aramid, graphite boron etc., which provide the required mechanical strength. But the fibres alone can not attain the desired solid shape, but when combined with the matrix material the fibres can provide the required strength to the composite. The fibres alone will exhibit excellent tensile properties like rope. The materials like glass, boron, carbon and aramid in the solid form can not give the required strength as much they provide in the fibre form. In the solid form these materials will have surface flaws which cause the material to fail much below the theoretical breaking point. In the fibre form even though the same number of random flaws are existing they are restricted to small number in fibres and these fibres exhibit more strength compared to its solid form. Hence a bundle of fibres provides a optimum strength and performance.

8 8 When the matrix material is combined with the reinforcing materials the exceptional properties of both matrix can be brought out. In general the properties of a composite is dependent on (1) Fibre and its properties (long/short). (2) Matrix (Resin) and its properties. (3) Composition of fibre and matrix (Volume Fraction). (4) The geometric orientation of fibres. Fig.1.1: Schematic illustrations of composite constituents. The body constituent gives the composite its bulk form, and it is called the matrix. The other component is a structural constituent, it is called the reinforcement. Reinforcement determines the internal structure of the composite. The region that exists between the body and the structural constituents is called the interface. Interface properties play a very important role in determining the ultimate properties of the bulk composite. Interface is the region where mechanical stresses are transferred between the matrix and the reinforcement. The interface plays a important and critical role in the long term stability of composite. It is always assumed that a interface is present in a composite even though the thickness of the interface is only an atomic dimension.

9 9 The constituents of the chemical composition of the composite and the interface can not be limited to any material class. There are many composites which has relevant industrial applications such as metal-matrix, ceramic-matrix and polymer matrix composites. Reinforcement in important commercially available composites are made of materials such as steel, E-glass, graphite, carbon, and Kevlar. In most of the applications a bonding agent is added to the fibres prior to the compounding to enhance the interface between the reinforcement and the matrix and to attain the required chemistry. 1.4 SIGNIFICANT AND IMPORTANT FUNCTIONS OF FIBRES AND MATRIX To thoroughly know the behaviour of the composites it is very much required to have fairly good knowledge about the roles of fibres and matrix materials in a polymer composite. The significant and important functions of reinforcing fibres and matrix materials are Functions of fibres: The fibres carry the load to an extent of 65% to 90% in case of structural composites. Reinforced fibres provide stiffness, strength and thermal stability to the composite. Reinforced fibres may provide the electrical insulation and conductivity depending on the fibre type used Functions of Matrix: Matrix provides rigidity and shape to the composite structure. Matrix binds the fibres together and transfers the load to the reinforcing fibres.

10 10 Matrix helps to isolate the fibres allowing the individual fibres to act independently. Isolation of reinforced fibres decreases the crack propagation rate. Matrix provides the net shape or the near net shape of the parts. Matrix gives surface finish to the composite. Matrix protects the reinforcing fibres and avoids any kind of chemical attack and mechanical abrasion. Matrix material influences the performance characteristics such as ductility, brittleness, impact strength and resistance to fatigue. Matrix material as a significant influence on the failure mode. 1.5 SALIENT FEATURES OF COMPOSITES: Composites offers several advantages over the traditional engineering materials, composites are employed for high performance and light weight applications A single composite component can replace several metallic components, that is the composite materials have the capability of part integration. In case of polymer composites it is possible to embed the sensor into a composite structure which can be used to perform on line monitoring of the composite material, these kinds of applications are used in air craft and marine applications. Polymer Composite materials provide greater strength and greater stiffness along with lighter weight. Polymer Composite materials posses better fatigue strength than metals. Polymer Composite materials posses corrosion resistant properties and also have high chemical resistance properties.

11 11 A great amount of design flexibility can be achieved in the polymer composite materials. Net shape or near net shape can be produced in polymer composite materials. Several manufacturing steps like cutting, machining, joining, assembling can be eliminated and a single manufacturing process can be used in the manufacture of the polymer composite materials. Parts with special contours, complex parts, and intricate details can be easily manufactured in case of polymer composite materials. Polymer composites offer good impact properties which is a desired property in automotive applications. Polymer composites offer better resistance to noise and vibration. Polymer composites dampen the vibrations at a very fast rate. 1.6 FABRICATION OF POLYMER COMPOSITE PRODUCTS Polymer composites are manufactured by transforming the raw materials into finished products using one of the manufacturing processes discussed. 1. Forming: In this process by the application of heat and pressure, feed stock is changed into the finished product. 2. Machining: The undesired excess material is removed by performing the various machining operations such as turning, drilling, milling etc., machining of polymer composites requires different tools and operating conditions are also different when compared with metals. 3. Joining and Assembling: Polymer composite materials are joined and assembled by various methods such as adhesive bonding, fusion bonding and mechanical fastening. Generally the joining and assembling process are

12 12 avoided as it is a time consuming process only at occasions where it is essentially required it is carried out. 4. Finishing: Finishing operations are done to avoid environmental degradation to improve appearance by providing wear resistant coating, metal coating to make component resemble metal and coatings to improve external appearance and look. 1.7 FIBRE REINFORCEMENTS: The most commonly used materials for reinforcement in case of polymer composites are glass, carbon, graphite, aramid and boron fibres. Reinforcement forms the important constituents in polymer composite materials as it provides the necessary strength and stiffness to the component, further the reinforcing material is the load bearing component in the composite additionally the reinforcing element will have wear resistance, corrosion resistance, impact strength, &damping properties, reinforcement imparts special mechanical property to the composite [3]. The reinforcing materials are thin rod like structures used to support the structures in composites. These reinforced fibres are available in various diameters ranging from 2µm to 25µm, as these are thin they are flexible and easily conform to required shapes. Generally fibres are made into strands for weaving and winding purposes. For easy delivery the fibre are wound around a bobbin and is called a roving. In polymer composites the fibres are used in many forms, such as continuous fibres, to discontinuous fibres, long fibres short fibres, organic and inorganic fibres. The widely used fibre material in fibre reinforced polymer composites are glass, boron, carbon and aramid. Glass is the cheapest and easily available in abundance, these glass fibres are of three types E-Glass, S-Glass, & S2- Glass. The concept of particulate reinforcement was introduced to avoid the whisker damage [4].

13 13 Combination of many properties like weight to high strength ratio, weight to stiffness, weight to modulus, improved fatigue resistance, thermal expansion, in combination with several other properties like resistance to wear enhanced fracture toughness [5]. The use of reinforcement becomes more with increase in the high temperature applications [6]. Ceramic matrix composites are the obvious choice for the high temperature applications [7].Several components of race cars and body parts are made of reinforcement fibres /fibre reinforced polymers [8] Glass fibre: Most commonly used reinforcing material. These have high tensile strength but low modulus when compared with other types of fibres [9] E-Glass Fibre: E- Glass fibre Occupies 90% of glass fibre market, E- signifies electrical and is intended to indicate low electrical conductivity. E-Glass is the cheapest variety hence is the most preferred for general purpose applications [10] Carbon fibre: Carbon fibre is considered as the reinforcement material for advanced composites. Carbon fibres exhibit excellent fatigue resistance, moisture resistant has excellent bonding characteristics between the fibre and the matrix. Carbon fibres are the derivative of poly acrylonitrile [11]. 1.8 AUTOMOTIVE APPLICATIONS OF LAMINATED COMPOSITES: Polymer laminated composites are used in various automotive applications, in recent days polymer composites is considered as the material of choice, because of its high quality, excellent surface finish styling details and simple processing options, low cost. In present day composite body panels are exhaustively used ranging from the sports cars to passengers cars.

14 14 Some of the applications of the laminated composites in the automotive components are as follows; Body panel Bumper Structural member Engine Noise cover Floor sheet panel Ceiling sheet panel Bonnet Cover Floor mats Complete Body (Body In white) Luggage carriers in bus/ Air bus Sheet panel beneath the vehicle Body Front Cover Panel Dickey bottom and top panel Inside side panels of the door Dash Board Interior components Mud Guards Wheel disk Covers.

15 15 BIBLIOGRAPHY [1] Carl Zweben, Composite Materials and Mechanical Design, Mechanical Engineer's Handbook, 2nd ed., Myer Kutz, Ed., John Wiley & Sons, Inc., New York, [2] Autar Kaw, Ed, Introduction to composite materials, Chapter 1, CRC Press [3] A.P.Divecha, S.G.Fishman, and S.D.Karmarkar, Silicon Carbide Reinforced Aluminum A Formable Composite, JOM, Vol 33 (No. 9), 1981, p [4] S. G. Fishman, Office of Naval Research, private communication, [5] Bryan Harris- Engineering Composite Materials, The Institute Of Materials, London [6] Kelly.A.C Zweben and T.W.Dyne Comprehensive Composite Materials volume Metal matrix composites UK: Pergamon, [7] K K Chawla, Ceramic Matrix Composites, Chapman & Hall, London, 1993 [8] D Hull & T W Clyne, An introduction to composite materials, 2nd Ed, Cambridge University press, [9] Hibbard.W.R., Fibre Glass Composite Materials, American Society for Metals,Metals Park, Ohio Vol. 1,1964, pp [10] D.M. Miller, Glass Fibers, Composites, Vol 1, Engineered Materials Handbook, ASM International, 1987, p [11] K. Shariq, E. Anderson, and M. Yamaki, Carbon Fibers,, Chemical Economics Handbook Market Research Report, SRI International, Menlo Park, CA, July 1999.