INTRODUCTION Historical Backgrounds The existence of composite is not new. The word composite has become very popular in recent four-five decades due to the use of modern composite materials in various applications. The composites have existed from 10000 BC. For example, one can see the article by Ashby [1]. The evolution of materials and their relative importance over the years have been depicted. The common composite was straw bricks, used as construction material. Then the next composite material can be seen from Egypt around 4000 BC where fibrous composite materials were used for preparing the writing material. These were the laminated writing materials fabricated from the papyrus plant. Further, Egyptians made containers from coarse fibers that were drawn from heat softened glass.

One more important application of composites can be seen around 1200 BC from Mongols. Mongols invented the so called modern composite bow. The history shows that the earliest proof of existence of composite bows dates back to 3000 BC - as predicted by Angara Dating. The bow used various materials like wood, horn, sinew (tendon), leather, bamboo and antler. The horn and antler were used to make the main body of the bow as it is very flexible and resilient. Sinews were used to join and cover the horn and antler together. Glue was prepared from the bladder of fish which is used to glue all the things in place. The string of the bow was made from sinew, horse hair and silk. The composite bow so prepared used to take almost a year for fabrication. The bows were so powerful that one could shoot the arrows almost 1.5 km away. Until the discovery of gun-powder the composite bow used to be a very lethal weapon as it was a short and handy weapon.

As said, Need is the mother of all inventions, the modern composites, that is, polymer composites came into existence during the Second World War. During the Second World War due to constraint impositions on various nations for crossing boundaries as well as importing and exporting the materials, there was scarcity of materials, especially in the military applications. During this period the fighter planes were the most advanced instruments of war. The light weight yet strong materials were in high demand. Further, applications like housing of electronic radar equipments require non-metallic materials. Hence, the Glass Fiber Reinforced Plastics (GFRP) were first used in these applications. Phenolic resins were used as the matrix material. The first use of composite laminates can be seen in the Havilland Mosquito Bomber of the British Royal Air Force.

The composites exist in day to day life applications as well. The most common existence is in the form of concrete. Concrete is a composite made from gravel, sand and cement. Further, when it is used along with steel to form structural components in construction, it forms one further form of composite. The other material is wood which is a composite made from cellulose and lignin. The advanced forms of wood composites can be ply-woods. These can be particle bonded composites or mixture of wooden planks/blocks with some binding agent. Now days, these are widely used to make furniture and as construction materials.

WHY A COMPOSITE? Over the last thirty years composite materials, plastics and ceramics have been the dominant emerging materials. The volume and number of applications of composite

materials have grown steadily, penetrating and conquering new markets relentlessly. Modern composite materials constitute a significant proportion of the engineered materials market ranging from everyday products to sophisticated niche applications.

While composites have already proven their worth as weight-saving materials, the current challenge is to make them cost effective. The efforts to produce economically attractive composite components have resulted in several innovative manufacturing techniques currently being used in the composites industry. It is obvious, especially for composites, that the improvement in manufacturing technology alone is not enough to overcome the cost hurdle. It is essential that there be an integrated effort in design, material, process, tooling, quality assurance, manufacturing, and even program management for composites to become competitive with metals.

The composites industry has begun to recognize that the commercial applications of composites promise to offer much larger business opportunities than the aerospace sector due to the sheer size of transportation industry. Thus the shift of composite applications from aircraft to other commercial uses has become prominent in recent years.

Further, the need of composite for lighter construction materials and more seismic resistant structures has placed high emphasis on the use of new and advanced materials that not only decreases dead weight but also absorbs the shock & vibration through tailored microstructures. Composites are now extensively being used for rehabilitation/ strengthening of pre-existing structures that have to be retrofitted to make them seismic resistant, or to repair damage caused by seismic activity.

Unlike conventional materials (e.g., steel), the properties of the composite material can be designed considering the structural aspects. The design of a structural component using composites involves both material and structural design. Composite properties (e.g. stiffness, thermal expansion etc.) can be varied continuously over a broad range of values under the control of the designer. Careful selection of reinforcement type enables finished product characteristics to be tailored to almost any specific engineering requirement

Whilst the use of composites will be a clear choice in many instances, material selection in others will depend on factors such as working lifetime requirements, number of items to be produced (run length), complexity of product shape, possible savings in assembly costs and on the experience & skills the designer in tapping the optimum potential of composites. In some instances, best results may be achieved through the use of composites in conjunction with traditional materials.

1.1 DEFINITION OF COMPOSITE The most widely used meaning is the following one, which has been stated by Jartiz [1] Composites are multifunctional material systems that provide characteristics not obtainable from any discrete material. They are cohesive structures made by physically combining two or more compatible materials, different in composition and characteristics and sometimes in form

The weakness of this definition resided in the fact that it allows one to classify among the composites any mixture of materials without indicating either its specificity or the laws which should give it which distinguishes it from other very banal, meaningless mixtures.

Kelly [2] very clearly stresses that the composites should not be regarded simple as a combination of two materials. In the broader significance; the combination has its own distinctive properties. In terms of strength to resistance to heat or some other desirable quality, it is better than either of the components alone or radically different from either of them.

Beghezan [3] defines as The composites are compound materials which differ from alloys by the fact that the individual components retain their characteristics but are so incorporated into the composite as to take advantage only of their attributes and not of their short comings, in order to obtain improved materials

Van Suchetclan [4] explains composite materials as heterogeneous materials consisting of two or more solid phases, which are in intimate contact with each other on a microscopic scale. They can be also considered as homogeneous materials on a microscopic scale in the sense that any portion of it will have the same physical property.

1.2 PROPERTIES OF COMPOSITE Composites are extremely versatile products - their benefits being:

High Strength to Weight Ratio:

Fiber composites are extremely strong for their weight. By refining the laminate many characteristics can be enhanced. A common laminate of say 3 mm Chopped strand mat, is quite flexible compared to say a 3 mm ply. However it will bend a long way more than the ply before yielding. Stiffness should not be confused with Strength. A carbon fiber laminate on the other hand, will have a stiffness of many times that of mild steel of the same thickness, increased ultimate strength.

Light weight:

A standard Fiber glass laminate has a specific gravity in the region of 1.5, compared to Alloy of 2.7 or steel of 7.8. When you then start looking at Carbon laminates, strengths can be many times that of steel, but only a fraction of the weight. A DVD case lid was produced using carbon fiber to reduce the case's overall weight so that it could be carried as cabin baggage whilst travelling, and for improved security. It was used by support crew for the All Blacks during their 1999 Rugby World Cup campaign.

Fire Resistance:

The ability for composites to withstand fire has been steadily improving over the years. There is two types of systems to be considered:- Fire Retardent - are self-extinguishing laminates, usually made with chlorinated resins and additives such as Antimony trioxide. These release CO2 when burning so when the flame source is removed, the self-extinguish.

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Fire Resistant - More difficult and made with the likes of Phenolic Resins. These are difficult to use, are cured with formaldehyde, and require a high degree of post curing to achieve true fire resistance. Other materials are also becoming more readily available to be used as intumescent layers, which expand and blanket the surface, preventing spread of flame. There is a paint on coating usually applied to the back of the product laminate, plus a thin fiber film to go under the Gel coat.

Electrical:

Fiber glass Developments Ltd produced the Insulator Support straps for the Tranz Rail main trunk electrification. The straps, although only 4mm thick, meet the required loads of 22kN, as well as easily meeting insulation requirements

Chemical:

Weathering Resistance Composite products have good weathering properties and resist the attack of a wide range of chemicals. This depends almost entirely on the resin used in manufacture, but by careful selection resistance to all but the most extreme conditions can be achieved. Because of this, composites are used in the manufacture of chemical storage tanks, pipes, chimneys and ducts, boat hulls and vehicle bodies.

FDL manufactured architectural panels for the construction of the Auckland Marine Rescue Centre. Composite panels were chosen because of their ability to withstand salty sea side condition without corrosion

Color:

Almost any shade of any color can be incorporated into the product during manufacture by pigmenting the gel coat used. Costs are therefore reduced by no further finishing or painting. Soluble dyes can be used if a translucent product is desired. We do not however, recommend dark colors. These produce excessive heat on the surface which can lead to the surface deteriorating and showing print through, where the Resin matrix cures more and shrinks, bringing the fibers to the surface. In extreme cases delamination can occur.

Translucency:

Polyester resins are widely used to manufacture translucent mouldings and sheets. Light transmission of up to 85% can be achieved.

Design flexibility:

Because of the versatility of composites, product design is only limited by your imagination.

Low thermal conductivity:

Fiberglass Developments has been involved in the development and production of specialized meat containers which maintain prime cuts of chilled meat at the correct temperature for Export markets. They are manufactured using the RTM process, with special reinforcing and foam inserts.

Manufacturing Economy:

Fiberglass Developments produces several models of fuel pump covers for Fuel quip. Fiberglass is an ideal material for producing items of this type for many reasons, including being very economical. Because of its versatile properties, fiberglass can be used in many varied applications.

1.3 CLASSIFICATION

Composite materials can be classified in different ways [5]. Classification based on the geometry of a representative unit of reinforcement is convenient since it is the geometry of the reinforcement which is responsible for the mechanical properties and high performance of the composites. A typical classification is presented in table1.1. The two broad classes of composites are (1) Particulate composites and (2) Fibrous composites. 1.3.1 Particulate Composites

As the name itself indicates, the reinforcement is of particle nature (platelets are also included in this class). It may be spherical, cubic, tetragonal, a platelet, or of other regular or irregular shape, but it is approximately equiaxed. In general, particles are not very effective in improving fracture resistance but they enhance the stiffness of the composite to a limited extent. Particle fillers are widely used to improve the properties of matrix materials such as to modify the thermal and electrical conductivities, improve performance at elevated temperatures, reduce friction, increase wear and abrasion resistance, improve machinability, increase surface hardness and reduce shrinkage.

1.3.2 Fibrous composites

A fiber is characterized by its length being much greater compared to its cross- sectional dimensions. The dimensions of the reinforcement determine its capability of contributing its properties to the composite. Fibers are very effective in improving the fracture resistance of the matrix since a reinforcement having a long dimension discourages the growth of incipient cracks normal to the reinforcement that might otherwise lead to failure, particularly with brittle matrices. Man-made filaments or fibers of non-polymeric materials exhibit much higher strength along their length since large flaws, which may be present in the bulk material, are minimized because of the small cross-sectional dimensions of the fiber. In the case of polymeric materials, orientation of the molecular structure is responsible for high strength and stiffness.

Fibers, because of their small cross- sectional dimensions, are not directly usable in engineering applications. They are, therefore, embedded in matrix materials to form fibrous composites. The matrix serves to bind the fibers together, transfer loads to the fibers, and protect them against environmental attack and damage due to handling. In discontinuous fiber reinforced composites, the load transfer function of the matrix is more critical than in continuous fiber composites.

1.4 COMPONENTS OF A COMPOSITE MATERIAL

In its most basic form a composite material is one, which is composed of at least two elements working together to produce material properties that are different to the properties of those elements on their own. In practice, most composites consist of a bulk material (the matrix), and a reinforcement of some kind, added primarily to increase the strength and stiffness of the matrix.

1.4.1 Role of matrix in a composite

Many materials when they are in a fibrous form exhibit very good strength property but to achieve these properties the fibers should be bonded by a suitable matrix. The matrix isolates the fibers from one another in order to prevent abrasion and formation of new surface flaws and acts as a bridge to hold the fibers in place. A good matrix should possess ability to deform easily under applied load, transfer the load onto the fibers and evenly distributive stress concentration. 1.4.2 Materials used as matrices in composites

In its most basic form a composite material is one, which is composed of at least two elements working together to produce material properties that are different to the properties of those elements on their own. In practice, most composites consist of a bulk material (the matrix) and a reinforcement of some kind, added primarily to increase the strength and stiffness of the matrix.

(a) BULK PHASES (1) Metal Matrices Metal matrix composites possess some attractive properties, when compared with organic matrices. These include (i) strength retention at higher temperatures, (ii) higher transverse strength, (iii) better electrical conductivity, (iv) superior thermal conductivity, (v) higher erosion resistance etc. However, the major disadvantage of metal matrix composites is their higher densities and consequently lower specific mechanical properties compared to polymer matrix composites. Another notable difficulty is the high-energy requirement for fabrication of such composites (2) Polymer Matrices

A very large number of polymeric materials, both thermosetting and thermoplastic, are used as matrix materials for the composites. Generally speaking, the resinous binders (polymer matrices) are selected on the basis of adhesive strength, fatigue resistance, heat resistance, chemical and moisture resistance etc. The resin must have mechanical strength commensurate with that of the reinforcement. It must be easy to use in the fabrication process selected and also stand up to the service conditions. Apart from these properties, the resin matrix must be capable of wetting and penetrating into the bundles of fibers which provide the reinforcement, replacing the dead air spaces therein and offering those physical characteristics capable of enhancing the performance of fibers.

(3) Ceramic Matrices

Ceramic fibers, such as alumina and SiC (Silicon Carbide) are advantageous in very high

temperature applications, and also where environment attack is an issue. Since ceramics have poor properties in tension and shear, most applications as reinforcement are in the particulate form (e.g. zinc and calcium phosphate). Ceramic Matrix Composites (CMCs) used in very high temperature environments, these materials use a ceramic as the matrix and reinforce it with short fibers, or whiskers such as those made from silicon carbide and boron nitride.

(b) REINFORCEMENT

The role of the reinforcement in a composite material is fundamentally one of increasing the mechanical properties of the neat resin system. All of the different fibers used in composites have different properties and so affect the properties of the composite in different ways. For most of the applications, the fibers need to be arranged into some form of sheet, known as a fabric, to make handling possible. Different ways for assembling fibers into sheets and the variety of fiber orientations possible to achieve different characteristics.

(c) INTERFACE

It has characteristics that are not depicted by any of the component in isolation. The interface is a bounding surface or zone where a discontinuity occurs, whether physical, mechanical, chemical etc. The matrix material must wet the fiber. Coupling agents are frequently used to improve wet ability. Well wetted fibers increase the interface surfaces area. To obtain desirable properties in a composite, the applied load should be effectively transferred from the matrix to the fibers via the interface. This means that the interface must be large and exhibit strong adhesion between fibers and matrix. Failure at the interface (called deboning) may or may not be desirable.

TYPES OF COMPOSITE MATERIALS

The composite materials are broadly classified into the following categories shown in

Figure 1.1

1. Fiber-reinforced composites Reinforced-composites are popularly being used in many industrial applications because of their inherent high specific strength and stiffness. Due to their excellent structural performance, the composites are gaining potential also in tribological applications. Fiber reinforced composites materials consists of fiber of high strength and modulus bonded in to a matrix with distinct interfaces (boundary) between them [4,5]. In this form both fibers and matrix retain their physical and chemical identities. Yet they produce a combination of properties that cannot be achieved with either of the constituents acting alone. In general, fibers are the principal load carrying candidates, while the surrounding matrix keeps them in the desired location and orientation [6, 7]. A Fibrous composite can be classified into two broad groups: continuous (long) fiber composite and discontinuous (short) fiber composite.

2. Continuous or long fiber composite Continuous or long fiber composite consists of a matrix reinforced by a dispersed phase in the form of continuous fibers. A continuous fiber is geometrically characterized as having a very high length-to- diameter ratio. They are generally stronger and stiffer than bulk material. Based on the manner in which fibers are packed within the matrix, it is again subdivided in to two categories: (a) unidirectional reinforcement and (b) bidirectional reinforcement. In unidirectional reinforcement, the fibers are oriented in one direction only where as in bidirectional reinforcement the fibers are oriented in two directions either at right angle to one another (cross-ply), or at some desired angle (angle-ply). When fibers are large and continuous, they impart certain degree of anisotropy to the properties of the composites particularly when they are oriented. Multi-axially oriented continuous fiber composites are also display near isotropic properties.

3. Discontinuous or short fiber composite Short-fiber reinforced composites consist of a matrix reinforced by a dispersed phase in form of discontinuous fibers (length < 100* diameter). The low cost, ease of fabricating complex parts, and isotropic nature are enough to make the short fiber composites the material of choice for large-scale production. Consequently, the short-fiber reinforced composites have successfully established its place in lightly loaded component manufacturing. Further the discontinuous fiber reinforced composite divided into: (a) biased or preferred oriented fiber composite and (b) random oriented fiber composite. In the former, the fibers are oriented in predetermined directions, whereas in the latter type, fibers remain randomly. The orientation of short fibers can be done by sprinkling of fiber on to given plane or addition of matrix in liquid or solid state before or after the fiber deposition. The discontinuities can produce a material response that is anisotropic, but the random reinforcement produces nearly isotropic properties.

4. Laminate Composites

Laminate Composites are composed of layers of materials held together by matrix. Generally, these layers are arranged alternatively for the better bonding between reinforcement and the matrix. These laminates can have uni-directional or bi-directional orientation of the fiber reinforcement according to the end use of the composite. The different types of composite laminates are: unidirectional, angle-ply, cross-ply and symmetric laminates. A hybrid laminate can also be fabricated by the use of different constituent materials or of the same material with different reinforcing pattern. In most of the applications of laminate composites, man-made fibers are used due to their good combination of physico-mechanical and thermal behavior.

5. Particulate Composite Particulate composite consists of the composite material in which the filler materials are roughly round. An example of this type of composite would be the unreinforced concrete where the cement is the matrix and the sand serves as the filler. Lead particles in copper matrix is another example where both the matrix and the filler are metals. Cermet is a metal matrix with ceramic filler. Particulate composites offer isotropic properties of composite

along with increase in toughness. Particulate composites are used with all three types of matrix materials metals, polymers and ceramics.

6. Flake composites Flakes are often used in place of fibers as can be densely packed. Metal flakes that are in close contact with each other in polymer matrices can conduct electricity or heat, while mica flakes and glass can resist both. Flakes are not expensive to produce and usually cost less than fibers. But they fall short of expectations in aspects like control of size, shapeand show defects in the end product. Glass flakes tend to have notches orcracks around the edges, which weaken the final product. They are also resistant to be lined up parallel to each other in a matrix, causing uneven strength.

Continuous fiber composites Particulate composites Flake composites

Random fiber composites Laminate composites

Figure-1.1 Schematic diagram of different types of Composite

APPLICATIONS OF COMPOSITES Composites are one of the most widely used materials because of their adaptability to different situations and the relative ease of combination with other materials to serve specific purposes and exhibit desirable properties.

In surface transportation, reinforced plastics are the kind of composites used because of their huge size. They provide ample scope and receptiveness to design changes, materials and

processes. The strength-weight ratio is higher than other materials. Their stiffness and cost effectiveness offered, apart from easy availability of raw materials, make them the obvious choice for applications in surface transportation.

In heavy transport vehicles, the composites are used in processing of component parts with cost-effectiveness. Good reproductivity and resilience handling by semi-skilled workers are the basic requirements of a good composite material. While the costs of achieving advanced composites may not justify the savings obtained in terms of weight vis-a-vis vehicle production, carbon fibers reinforced epoxies have been used in racing cars and recently for the safety of cars.

Polyester resin with suitable fillers and reinforcements were the first applications of composites in road transportation. The choice was dictated by properties like low cost, ease in designing and production of functional parts etc. Using a variety of reinforcements, polyester has continued to be used in improving the system and other applications.

Most of the thermoplastics are combined with reinforcing fibers in various proportions. Several methods are used to produce vehicle parts from thermo plastics. Selection of the material is made from the final nature of the component, the volume required, apart from cost-effectiveness and mechanical strength.

Components that need conventional paint finishing are generally made with thermosetting resins, while thermoplastics are used to build parts that are moulded and can be pigmented. Press moulded reinforced polyester possess the capability to produce large parts in considerable volume with cost-effectiveness.

In manufacturing of automobile parts, glass and sisal fibers usually find the maximum use. Sisal costs very less and this alone has prompted extensive research to come up with applications in which sisal is the dominant reinforcing material in filled polyester resin, in parts where specific mechanical properties are required and appearance is not very important. Heater housings, which find uses for sisal, are produced by compression moulding. Since a variety of glass fibers are available, it is used as reinforcement for a large range of parts of different types. Rovings, non-woven mats are the commonly used low cost versions. Woven cloth is applied in special cases, where particular properties are required as cloth is not known to be amenable to large quantity production methods.

A reinforced-plastic composite is likely to cost more than sheet steel, when considered on the basis of cost and performance. In such a case, other qualities must necessarily justify the high expenditure. Mechanical properties of the parts, which affect the thickness and weight, must offer enough savings to render them more effective than steel. It however shows a higher machining waste than reinforced plastics.

REFERENCES

1. Jartiz, A.E., Design 1965, p.18.

2. Kelly, A. Sci. American 217, (B), (1967): p. 161.

3. Berghezan,A.Nucleus,8(5),1966,(Nucleus A Editeur,1,rhe,Chalgrin,Paris, 16(e).

4. Suchetclan Van, Philips Res. Repts. Volume 27, (1972): p. 28.

5. Agarwal B.D. and Broutman L.J., Analysis and performance of fiber composites John Wiley & Sons, New York, (1980): p. 3-12.

6. Chand N., Rohatgi P.K., Natural fibers and their composites, Publishers, Periodical Experts, Delhi, (1994).

7. Chand N., Dwivedi U.K., Effect of coupling agent on high stress abrasive wear of chopped jute/PP composites, Journal of Wear, Volume 261, (2006): p. 1057.

8. Tong J., Ren L., Li J., Chen B., Abrasive wear behaviour of bamboo, Tribol. Int., volume 28, No. 5, (1995): p. 323-327.

9. Jain S., Kumar R., Jindal U.C., Mechanical behaviour of bamboo and bamboo composites. J. Mat. Sci., Volume 27, (1992): p. 4598-4604.

10. Elsunni M. M., and Collier J. R. Processing of Sugar Cane Rind into Nonwoven Fibers. Journal of American Society of Sugar Cane Technologists, Volume 16, (1996): p. 94 110.

11. Paturau J.M., By-Products of Sugar Cane Industry, 3rd Edition, Elsevier, Amsterdam (1989).

12. Mohanty A.K, Misra MDrzal LT 92001). Compos Interfaces, Vol 8: p.313.

13. Rowell RM, Young RA, Rowell JK (1997) Paper and composites from agro-based resources. CRC Lewis Publishers, Boca Raton RL.

14. Alvarez VA, Ruscekaite RA, Vazquez A. Journal of Composite Material, Volume 37, No.17, (2003): p.1575.

15. Frederick TW, Norman W (2004) Natural fibers plastics and composites. Kluwer Academic Publishers, New York.

16. Dhingra A.K., metal replacement by composite, JOM, Volume 38, No. 03, (1986): p. 17.

17. Mehrabian R., Riek R.G. and Flemings M.C., Preparation and casting of Metal- Particulate Non-Metal Composites, Metall Trans, Volume 5A, (1974): p. 1899 1905.

PLAN OF STUDY & LITERATURE SURVEY

On

TRIBOLOGICAL BEHAVIOUR OF COMPOSITE MATERIALS Submitted By

DEEPAK KUMAR BEHERA [Roll No: 214ME1283]

Under the Guidance of

Dr. Samir Kumar Acharya

Sp-Machine Design & Analysis

Mechanical Engineering Department National Institute of Technology, Rourkela

Rourkela-769008

Table of Contents

1. Historical Backgrounds.

2. Why a composite. 3. Definition of Composite. 4. Properties of Composite material. 5. Classification of Composite. 6. Component of Composite material. 7. Types of Composite materials.

8. Application of composite.