HYBRID CAR – NEED OF DAY

                                                              ABSTRACT

            In this paper, a unique technology of HYBRID CAR is discussed which has high efficiency and hence is environment-friendly.

            In daily routine we come across different types of cars which are large in number. These are not called hybrid cars because they are running by single source of energy which may be petrol or diesel. In HYBRID CAR, two energy sources are used one is petrol / diesel / gas and another one is electric batteries. These two sources are stimulated by a unique device called as “Power Split Device” which is responsible for maximization of fuel economy.

            All plus points of these both sources are accumulated to get maximum efficiency which is nearly double than the other cars and tail-pipe emission is reduced by 90% approximately.

            These cars have unique place in automobile market because drawbacks of insufficient sunlight (in monsoon days) in case of solar car and frequent recharging of batteries in electrical cars (like REVA) are solved in this model.

1. INTRODUCTION

            Automobiles are inseparable part of our daily routine which consume fuel. This fuel is also a big question before human being as it is limited in stock. It also causes pollution which is responsible for drastic changes in biological clock.

            Hence, some research works are in process to make car run on non-conventional energy sources like sunlight. But yet, man has not succeeded to replace present technology.

            Hybrid cars use both electric batteries and fossil fuels for its working simultaneously which leads to somewhat complex technology where it makes use of advanced electronic and electrical circuit.

            TOYOTA has brought a practical solution in the form of “TOYOTA PRIUS” which can solve problem to some extent and alleviate pollution.

2. WHY SUCH COMPLEX TECHNOLOGY IS REQUIRED?

            Now a day advanced cars are available which are capable to accelerate to 100kmph within few seconds. Such cars are full of luxury but fuel efficiency is very low, more over they create pollution also.

            Now such situation is prevailing that fuel economy has to be maximized and pollution has to be minimized. In case of conventional cars, fuel economy is less and contribution to pollution is large. Some research works are going on to make car run on solar energy and electrical batteries but in this case one has to compromise over luxuries provided by other cars. Hence some unique technology is required which will give higher fuel economy, less pollution and no compromise over luxuries.

3. ENGINE STRUCTURE

            Two different types of structures are available in hybrid car technology.

One is parallel technology and the other is series technology.

Fig 3 . 1

In parallel structure, there is fuel tank to supply petrol but it also has set of batteries to supply power to electrical motors. Here, both sources are used for transmission at same time.

In series, petrol engine turns a generator, which either can charge batteries or provide power to the electric motor that performs the transmission.

 Fig.  3 . 2

4. ENGINE COMPONENTS

Various components used in this HYBRID CAR are as follows:-

4.1  HYBRID SYSTEM

It is a complex technology that runs on electricity at lower speeds when the engine is less efficient and switches to petrol only after it picks up speed.

4.2  BEAMS 

(BREAK through ENGINE with ADVANCED MECHANISM SYSTEM)

BEAMS powers hybrids system. It is highly efficient system that is     INZ-FXE-1500cc, 58bhp, four cylinders and petrol unit with VVT-T. The engine on a hybrid car will be smaller and will use advanced technologies to reduce emissions and increase efficiency.

4.3  MOTOR GENERATOR

This electric motor is very sophisticated. Advanced electrical technology allows it to act as motor as well as generator.

4.4  METAL HYDRIDE BATTERIES

These batteries are similar to those in conventional flashlights. They are placed behind the rear seat. They last for about 2,40,000 km before they need replacement and never have to stop for recharge.

4.5  FUEL TANK

The fuel tank in a hybrid car is the energy storage device for the petrol engine. Petrol has a much higher energy density than batteries do.

5. HOW TECHNOLOGY WORKS?

Petrol and electric cars have two things to be noticed:

·         Petrol engine gives optimum performance with minimum tail-pipe emission at moderate engine speed only, and

·         In electric car tail-pipe emission is zero as it runs on batteries but its speed range is very low.

This technology works on a HYBRID SYSTEM that is in communication with both petrol engine and batteries, and consists of generator, electric motor as transmission system.

6. WHAT MAKES SYSTEM EFFICIENT?

The efficiency of the hybrid technology depends on following factors:-

6.1 DIFFERENT SPEED RANGES

6.1.1 Speed range: - 0 kmph

This speed range indicates that a vehicle is just started. Petrol engine is used to start the car propulsion system, after several seconds, the engine warms up all the car system. The petrol engine shuts off, there by minimizing tail-pipe emission.

6.1.2 Speed range: - 0 – 20 kmph

At this speed range, petrol engine is completely shut off and the drive is powered by batteries at slow speed. Thus at this speed range, tail-pipe emission is zero.

If we compare the same speed range of petrol engine, we can see that the tail-pipe emissions are maximum as specific fuel consumption is high.

6.1.3 Speed range: - 20-60 kmph (moderate speed)

At moderate speed, the petrol engine takes over the charge and car runs only on petrol propulsion system. But again, tail pipe emissions are minimum as the engine is running at a speed of about 3000 to 3500 rpm.

6.1.4 Speed range: - Above 60 kmph

At very high speeds, additional power is required which is supplied by the electric motor, which gets it power from battery. In this case, also the petrol engine is still running at moderate speed at 3000 to 3500 rpm. And tail-pipe emission to lowest possible value.           

6.2 POWER SPLIT DEVICE

    Decision of which energy source is to be used is taken by a unique device called as power split device. This allows engine to stay in its most efficient mode and speed range most of the time.

PSD has a clever gear box that hooks the petrol engine, generator and electric motor together.

6.3 RECOVERY OF ENERGY AND STORAGE IN THE BATTERY

            Whenever breaks are applied to moving car, actually energy is removed from the brake. Faster the car is moving, the more kinetic energy it has. The brakes of a car remove this energy and dissipate it in the form of heat. A HYBRID CAR can capture some of this energy and store it in the batteries to use it later. It does this by using “regenerative braking”. Instead of just using the brake to stop the car, the electric motor that drives the hybrid can also slow the car. In this mode, the electric motor acts as a generator and charges the batteries while the car is slowing down.

7. SPECIAL FEATURES

7.1  Recharging of batteries during deceleration and braking:- The problem of recharging the batteries is completely eliminated in this system. Here batteries are charged by generator during gradual deceleration period.

7.2  At signals and short stops:- If this system has to stop at signals its exhaust emission are zero and when traffic crawls, car is powered by electric motor only. This feature is very suitable for roads in India.

7.3  Control on air fuel ratio:- In conventional fuel engine, air-fuel ratio varies according to load on it. When this is rich in percentage of fuel is more in air fuel mixture that causes higher tail pipe emission. Hence in this system air fuel ratio is kept constant.

7.4  During acceleration:- When the speed of car increase above 120 kmph the engine works in tandem with the electric motor – it kicks in like a super charger to gain optimal power with optimum fuel economy at a continuous speed.

8. ADVANTAGES OF USING HYBRID SYSTEM

8.1  Environment friendliness: - The car equipped with hybrid system emits only half the CO2 of a regular 1.5 ltr. Engine and reduces other tail pipe emissions by 90%. In this way it reduces the problem of air pollution to a large extent and protects nature

8.2  Recharging facilities of the battery:- Unlike electric car batteries are not required to be charged at regular interval as the hybrid system. It self generates the supply of kinetic energy from braking that is converted into electricity, which keeps them recharged.

8.3  Less noise: - The hybrid system uses the quite engine and electric motor which makes no noise during the operation reducing the sound pollution as well.

8.4  Optimum fuel efficiency :- This system results in the ultra efficient fuel consumption level which is nearly, twice the fuel efficiency of conventional petrol engine cars.

8.5  Economical aspects: - Initial cost of this technology is high but process of mass production will certainly reduce its initial cost to such a level that it will even beat the conventional fuel cars.

Again its working cost is nearly half than that of the conventional cost.   Thus, it will be greatly economical.

9. CONCLUSION

                        As discussed in the earlier pages, the conventional fuel cars are the main source of environmental pollution, about 60% of the air pollution is done by automobiles and they also have large contribution in sound pollution. Electric cars are invented to overcome air and sound pollution but due to some inherent limitations of electric cars (like recharging of batteries etc.) their use is limited.

                        Hybrid propulsion system may not be a complete solution to reduce pollution as it uses fuel, but the overall concept is most significant than other ones. In other words, car running on the hybrid system are most successful “ENVIRONMENT - FRIENDLY” in the world of automobiles.

GEOTHERMAL ENERGY

                                                                          INTRODUCTION

WHAT IS GEOTHERMAL ENERGY?

"Geothermal" comes from the Greek words geo (earth) and thermal (heat). So, geothermal means earth heat. The thermal energy contained in the interior of the earth is called geothermal energy. Geothermal heat originates from earth’s fiery consolidation of dust and gas over four billion years ago. The geothermal energy is enormous and will last for several millions of years and is therefore called renewable.     

EARTH’S HEAT AND VOLCANIC REGIONS

It is almost 6,500 kilometers (4,000 miles) from the surface to the center of the Earth, and the deeper you go, the hotter it gets. The outer layer, the crust, is three to 35 miles thick and insulates us from the hot interior.

From the surface down through the crust the normal temperature gradient (the increase of temperature with the increase of depth) in the Earth’s crust is 17 - 30°C per kilometer of depth (50-87°F per mile). Below the crust is the mantle, made of highly viscous, partially molten rock with temperatures between 650 and 1,250°C (1,200-2,280°F). At Earth's core, which consists of a liquid outer core and a solid inner core, temperatures may reach 4,000-7,000°C (7,200 to 12,600°F).

Since heat always moves from hotter regions to colder regions, the Earth’s heat flows from its interior toward the surface. This outward flow of heat from Earth’s interior drives convective motion in the mantle rock which in turn drives plate tectonics -- the "drift" of Earth's crustal plates that occurs at 1 to 5 cm per year (about the rate our fingernails grow). Where plates move apart, magma rises up into the rift, forming new crust. Where plates collide, one plate is generally forced (subducted) beneath the other. As a subducted plate slides slowly downward into regions of ever-increasing heat, it can reach conditions of pressure, temperature and water content that cause melting, forming magma. Plumes of magma ascend by buoyancy and force themselves up into (intrude) the crust, bringing up vast quantities of heat.

HOW DOES GEOTHERMAL HEAT GET UP TO EARTH'S SURFACE?

The heat from the earth's core continuously flows outward. It transfers (conducts) to the surrounding layer of rock, the mantle. When temperatures and pressures become high enough, some mantle rock melts, becoming magma. Then, because it is lighter (less dense) than the surrounding rock, the magma rises (convects), moving slowly up toward the earth's crust, carrying the heat from below.

GEOTHERMAL RESOURCES

Understanding geothermal energy begins with an understanding of the source of this energy—the earth’s internal heat. The Earth’s temperature increases with depth, with the temperature at the center reaching more than 4200 °C (7600 °F). A portion of this heat is a relic of the planet’s formation about 4.5 billion years ago, and a portion is generated by the continuing decay of radioactive isotopes. Heat naturally moves from hotter to cooler regions, so Earth’s heat flows from its interior toward the surface.

Because the geologic processes known as plate tectonics, the Earth’s crust has been broken into 12 huge plates that move apart or push together at a rate of millimeters per year. Where two plates collide, one plate can thrust below the other, producing extraordinary phenomena such as ocean trenches or strong earthquakes. At great depth, just above the down going plate, temperatures become high enough to melt rock, forming magma.3 Because magma is less dense than surrounding rocks, it moves up toward the earth’s crust and carries heat from below. Sometimes magma rises to the surface through thin or fractured crust as lava.

However, most magma remains below earth’s crust and heats the surrounding rocks and subterranean water. Some of this water comes all the way up to the surface through faults and cracks in the earth as hot springs or geysers. When this rising hot water and steam is trapped in permeable rocks under a layer of impermeable rocks, it is called a geothermal reservoir. These reservoirs are sources of geothermal energy that can potentially be tapped for electricity generation or direct use. Figure 1 is a schematic of a typical geothermal power plant showing the location of magma and a geothermal reservoir.4 Here, the production well withdraws heated geothermal fluid, and the injection well returns cooled fluids to the reservoir.

RESOURCE IDENTIFICATION

Geological, hydrogeological, geophysical, and geochemical techniques are used to identify and quantify geothermal resources. Geological and hydrogeological studies involve mapping any hot springs or other surface thermal features and the identification of favorable geological structures. These studies are used to recommend where production wells can be drilled with the highest probability of tapping into the geothermal resource. Geophysical surveys are implemented to figure the shape, size, depth and other important characteristics of the deep geological structures by using the following parameters: temperature (thermal survey), electrical conductivity (electrical and electromagnetic methods), propagation velocity of elastic waves (seismic survey), density (gravity survey), and magnetic susceptibility (magnetic survey).5 Geochemical surveys (including isotope geochemistry) are a useful means of determining whether the geothermal system is water or vapor-dominated, of estimating the minimum temperature expected at depth, of estimating the homogeneity of the water supply and, of determining the source of recharge water.

Geothermal exploration addresses at least nine objectives:6

• Identification of geothermal phenomena
• Ascertaining that a useful geothermal production field exists
• Estimation of the size of the resource
• Classification of the geothermal field
• Location of productive zones
• Determination of the heat content of the fluids that will be discharged by the wells in the geothermal field
• Compilation of a body of data against which the results of future monitoring can be viewed
• Assessment of the pre-exploitation values of environmentally sensitive parameters
• Determination of any characteristics that might cause problems during field development

DRILLING

Once potential geothermal resources have been identified, exploratory drilling is carried out to further quantify the resource. Because of the high temperature and corrosive nature of geothermal fluids, as well as the hard and abrasive nature of reservoir rocks found in geothermal environments, geothermal drilling is much more difficult and expensive than conventional petroleum drilling. Each geothermal well costs $1–4 million to drill, and a geothermal field may consist of 10–100 wells. Drilling can account for 30–50% of a geothermal project’s total cost.

 Typically, geothermal wells are drilled to depths ranging rom 200 to 1,500 meters depth for low- and medium-temperature systems, and from 700 to 3,000 meters depth for high-temperature systems. Wells can be drilled vertically or at an angle. Wells are drilled in a series of stages, with each stage being of smaller diameter than the previous stage, and each being secured by steel casings, which are cemented in place before drilling the subsequent stage. The final production sections of the well use an uncemented perforated liner, allowing the geothermal fluid to pass into the pipe. The objectives of this phase are to prove the existence of an exploitable resource and to delineate the extent and the characteristics of the resource. An exploratory drilling program may include shallow temperature-gradient wells, “slim-hole” exploration wells, and production-sized exploration/production wells. Temperature-gradient wells are often drilled from 2–200 meters in depth with diameters of 50–150 mm. Slim-hole exploration wells are usually drilled from 200 to 3000 meters in depth with bottom-hole diameters of 100 to 220 mm. The size and objective of the development will determine the number and type of wells to be included in exploratory drilling programs

APPLICATIONS OF GEOTHERMAL ENERGY:

1. POWER GENERATION:

Utility-scale geothermal power production employs three main technologies. These are known as dry steam, flash steam and binary cycle systems. The technology employed depends on the temperature and pressure of the geothermal reservoir. Unlike solar, wind, and hydro-based renewable power, geothermal power plant operation is independent of fluctuations in daily and seasonal weather.

DRY STEAM:

Dry steam power plants use very hot (>455 °F, or >235 °C) steam and little water from the geothermal reservoir.12 The steam goes directly through a pipe to a turbine to spin a generator that produces electricity. This type of geothermal power plant is the oldest, first being used at Lardarello, Italy, in 1904.13 Figure 2 is a schematic of a typical dry steam power plant.14

 
Figure 1. Dry Steam Power Plant Schematic  
Source: National Renewable Energy Laboratory (NREL)

FLASH STEAM 

Flash steam power plants use hot water (>360 ºF, or >182 ºC) from the geothermal reservoir.15 When the water is pumped to the generator, it is released from the pressure of the deep reservoir. The sudden drop in pressure causes some of the water to vaporize to steam, which spins a turbine to generate electricity. Both dry steam and flash steam power plants emit small amounts of carbon dioxide, nitric oxide, and sulfur, but generally 50 times less than traditional fossil-fuel power plants.16 Hot water not flashed into steam is returned to the geothermal reservoir through injection wells. Figure 3 is a schematic of a typical flash steam power plant.17

Figure 2. Flash Steam Power Plant Schematic

BINARY-CYCLE

Binary-cycle power plants use moderate-temperature water (225 ºF–360 ºF, or 107 ºC–182 ºC) from the geothermal reservoir. In binary systems, hot geothermal fluids are passed through one side of a heat exchanger to heat a working fluid in a separate adjacent pipe. The working fluid, usually an organic compound with a low boiling point such as Iso-butane or Iso-pentane, is vaporized and passed through a turbine to generate electricity. An ammonia-water working fluid is also used in what is known as the Kalina Cycle. Makers claim that the Kalina Cycle system boosts geothermal plant efficiency by 20–40 percent and reduces plant construction costs by 20–30 percent, thereby lowering the cost of geothermal power generation.

Figure 4. Binary Cycle Power Plant Schematic
Source: National Renewable Energy Laboratory (NREL)

The advantages of binary cycle systems are that the working fluid boils at a lower temperature than water does, so electricity can be generated from reservoirs with lower temperature, and the binary cycle system is self-contained and therefore, produces virtually no emissions. For these reasons, some geothermal experts believe binary cycle systems could be the dominant geothermal power plants of the future. Figure 4 is a schematic of a typical binary cycle power plant.18

2. GEOTHERMAL HEAT PUMPS:

The shallow ground, the upper 10 feet of the Earth, maintains a nearly constant temperature between 50° and 60°F (10°–16°C). Like a cave, this ground temperature is warmer than the air above it in the winter and cooler than the air in the summer. Geothermal heat pumps take advantage of this resource to heat and cool buildings.              

Geothermal heat pump systems consist of basically three parts: the ground heat exchanger, the heat pump unit, and the air delivery system (ductwork). The heat exchanger is basically a system of pipes called a loop, which is buried in the shallow ground near the building. A fluid (usually water or a mixture of water and antifreeze) circulates through the pipes to absorb or relinquish heat within the ground.

    

In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to heat water, providing a free source of hot water.

Geothermal heat pumps offer unmatched benefits over traditional heating and cooling systems, including:

• Lower operating costs: A geothermal system can cut utility bills by 30 to 50 percent compared to conventional heating and cooling systems.
• Environmental impact: Ground-source heat is naturally renewable and non-polluting.
• Lower maintenance costs: All equipment is protected indoors or underground.
• Life span: A geothermal system can have a life expectancy of up to 30 years; ground loops are often warranted for up to 50 years.
• Single system: Geothermal equipment provides both heating and cooling in one system.
• Indoor comfort: Geothermal systems eliminate the drafts common with conventional forced-air systems.
• Design flexibility: Geothermal systems can be easily and inexpensively subdivided or expanded to fit building remodeling or additions.
• Energy efficiency: A geothermal heat pump can move more than three units of heat energy for every one unit of electrical energy used to power the system.
• Safety: No dangers of gas leaks or carbon monoxide poisoning.

 3. DIRECT USE APPLICATIONS

Geothermal reservoirs within the low to moderate temperature range can provide heat for residential, industrial, and commercial use.  The Energy Efficiency and Renewable Energy (EERE) division of the U.S. Department of Energy reports that savings can be as much as 80% over the use of fossil fuels.  This form of energy is also very clean, with far fewer air pollutants emitted when compared to fossil fuels. 

The employment of direct use geothermal energy requires that a certain infrastructure be established for proper handling of this resource.  First, a production facility, usually a well, will bring the hot water to the ground surface.  Second, a mechanical system to deliver the heat to a space or process must be developed.  This means the piping, heat exchanger, and control infrastructure for heat extraction. Third, there must be a disposal system, such as an injection well or storage pond, that can receive the cooled geothermal fluid.

Direct use applications for geothermally heated waters is quite extensive.  A number of operations use low-temperature geothermal resources for district and space heating, greenhouses, and aquaculture facilities. District systems distribute naturally heated water from one or more geothermal wells through a series of pipes to several houses and buildings, or blocks of buildings.  Space heating uses one well per structure.  In both of these systems, the geothermal heat is replacing fossil fuel burning as the heat source for the traditional heating system.  District heating systems can save consumers 30% to 50% of the cost of natural gas heating.  

Numerous other industrial and commercial uses are also possible.  Industrial applications can include food dehydration, cement and aggregate drying, concrete block curing, milk pasteurizing, spas, and others

ADVANTAGES OF USING GEOTHERMAL ENERGY

• Clean.

Geothermal power plants, like wind and solar power plants, do not have to burn fuels to manufacture steam to turn the turbines. Generating electricity with geothermal energy helps to conserve nonrenewable fossil fuels, and by decreasing the use of these fuels, we reduce emissions that harm our atmosphere. There is no smoky air around geothermal power plants -- in fact some are built in the middle of farm crops and forests, and share land with cattle and local wildlife.

• Easy on the land.

 The land area required for geothermal power plants is smaller per megawatt than for almost every other type of power plant. Geothermal installations don't require damming of rivers or harvesting of forests -- and there are no mine shafts, tunnels, open pits, waste heaps or oil spills.

• Reliable.

Geothermal power plants are designed to run 24 hours a day, all year. A geothermal power plant sits right on top of its fuel source. It is resistant to interruptions of power generation due to weather, natural disasters or political rifts that can interrupt transportation of fuels.

• Flexible.

Geothermal power plants can have modular designs, with additional units installed in increments when needed to fit growing demand for electricity.

• Keeps Dollars at Home

Money does not have to be exported to import fuel for geothermal power plants. Geothermal "fuel'" - like the sun and the wind - is always where the power plant is; economic benefits remain in the region and there are no fuel price shocks.

FUTURE PROSPECTS IN INDIA.

In a global tectonic context, India is not particularly well placed as far as geothermal energy is concerned. However, due to anomalous nature of some segments of its lithosphere, it does contain a number of geothermal areas with temperature in the range of 30 degrees celsius to 100 degrees celsius. Most of them are intermediate temperature type and occur along certain tectonic boundaries.

The most promising geothermal areas include-(I) Puga-Chhumathang, Manikaran and Tapoban in New Himalayas, (2) Konkan, Cambay and Bombay Offshore, (3) Taptapani (Orissa), (4) Gondwanic grabens, and (5) Volcanic areas of Andaman-Nocobar chain.

Power deficient India is planning to use geothermal energy to produce 10,600 megawatts of power, five times more than the combined output from all non-conventional energy sources.

The first such plant is being set up in the Ladakh region of Jammu and Kashmir. Officials say this renewable energy would come at a throwaway cost, less than one third of hydropower. China on the other side of the border has already set up a geo-thermal plant.

                  Officials associated with the project say that they have already completed preliminary investigations in Ladakh. A five-member team led by Dr D.Chandrasekharam, head of the Earth Sciences Department at the Indian Institute of Technology, that visited the region recently is submitting a blue print to the government. According to Chandrasekharam, India has the capacity to produce 10,600 megawatts of geo-thermal power.

CONCLUSION:

Today is the era of non-conventional sources of energy. Till now India has tapped the potential of wind, tidal, solar and nuclear energy only. But geothermal technology is still to appear in India. The Indian government has taken few modest steps in this regard. Considering the potential applications of geothermal energy and the present Indian power scenario, it is high time that India exploits this source of energy to the fullest and makes a mark in the field of power production.

Carbon fiber reinforced plastic Composites

ABSTRACT

            Composites are the 21^st century material to meet the stringent demands of light weight, high strength, corrosion resistance & near-net shapes. Carbon Fiber Reinforced Plastic Composite is new class of materials has recently emerged as a leading contender for numerous application in automobile, aerospace, electronic and wear industries. in brake disks of aircraft or Formula 1 / Indy race cars. These type of composite can operate at temperatures up to approx. 900ºC or higher. Useful properties of carbon fibres are their durability, resistance to fatigue and that they are chemically inert and still exhibit high  strength at high temperatures.Although they were know to mankind since prehistoric times, the concept and technology have undergone a sea change with better understanding of the basics like the bonding mechanism between the matrix and fiber. Technologically composites are artificially produced multiphase materials having desirable combination of best properties of the constituent phases. Since carbon is a high performance fiber material that is most commonly used reinforcement in advanced Polymer- matrix composites known as CFRP.

Keywords: - CFRP, Carbon fiber, PMC.

INTRODUCTION

             Many of our modern technologies require material with unusual combination of properties that can not be met by the conventional metal alloys, ceramics & polymeric materials. Composites are one of the most widely used material because of their adaptability to different situations & the relative ease of combination with other material to serve specific purposes & exhibit desire properties. “A composite material is a combination of two or more chemically distinct & insoluble phases.” Its properties & structural performance are superior to those of the constituents acting independently. The plastic posses mechanical properties that are generally inferior to those of metal & alloys-in particular low strength, stiffness & creep resistance. These properties can be improved by imbedding reinforcement of various types (such as glass or graphite fibers) to produce reinforced plastic.

Many composite materials are composed of just two phases ; one is termed the matrix, which is continuous & surrounds the other phase often called dispersed phase another is discontinuous phase & termed as fiber. The properties of composites are a function of the properties of the constituent phase, their relative amounts, & the geometry of fibers.

FIBERS:-

In a continuous fiber reinforced composite, the fibers provide virtually all of the load carrying characteristics of the composites, the most important of which are strength and stiffness. The multiple fibers in a composite make it a very redundant material because the failure of even several fibers results in the redistribution of load on to other fibers rather than a catastrophic failure of the part.

On the basis of diameter & character, fibers are grouped into three different classifications; whiskers, fibers, & wires.

Fig.  Common forms of fiber reinforcement

Matrices:-

The purpose of the matrix is to bind the reinforcements together by virtue of its cohesive and adhesive characteristics, to transfer load to and between reinforcements, and to protect the reinforcements from environments and handling. The matrix also provides a solid form to the composite, which aids handling during manufacture and is typically required in a finished part. This is particularly necessary in discontinuously reinforced composites, because the reinforcements are not of sufficient length to provide a handle able form. Because the reinforcements are typically stronger and stiffer, the matrix is often the “weak link” in the composite, from a structural perspective. As a continuous phase, the matrix therefore controls the transverse properties, interlaminar strength, and elevated-temperature strength of the composite. However, the matrix allows the strength of the reinforcements to be used to their full potential by providing effective load transfer from external forces to the reinforcement.

                                                             Fig: Types of matrices
 

CARBON FIBER RAINFORCED PLASTIC (CFRP)

In this type of composite carbon/graphite fiber is embedded in polymer matrix. Carbon is a high performance fiber material that is most common in used reinforcement in advanced (i.e. non-fiber glass) polymer- matrix composites. The reason for this is as follows:

1. Carbon fibers have the highest specific modulus & specific strength of all reinforcing fiber materials.
2. They retain their high tensile modulus & high strength at elevated temperatures: high temp. Oxidation however may be a problem.
3. At room temp. Carbon fibers are not affected by moisture or a wide variety of solvents, acids, bases.
4. These fibers exhibit a diversity of physical & mechanical characteristics, allowing composites in corporating these fibers to have specific engineered properties.
5. Fiber & composite manufacturing processes have been developed that are relatively inexpensive & cost effective.

CARBON FIBERS

Classification of Carbon Fibers:-

Carbon fibers are classified by the tensile modulus of the fiber. Tensile modulus is a measure of how much pulling force a certain diameter fiber can exert without breaking. Carbon fibers classified as "low modulus" have a tensile modulus below 240 million kPa. Other classifications, in ascending order of tensile modulus, include "standard modulus," "intermediate modulus," "high modulus," and "ultrahigh modulus." Ultrahigh modulus carbon fibers have a tensile modulus of 500 million-1.0 billion kPa. As a comparison, steel has a tensile modulus of about 200 million kPa. Thus, the strongest carbon fiber is about five times stronger than steel.  The term graphite fiber refers to certain ultrahigh modulus fibers made from petroleum pitch. These fibers have an internal structure that closely approximates the three-dimensional crystal alignment that is characteristic of a pure form of carbon known as graphite.

Raw Materials

The raw material used to make carbon fiber is called the precursor. About 90% of the carbon fibers produced are made from polyacrylonitrile. The remaining 10% are made from rayon or petroleum pitch. All of these materials are organic polymers, characterized by long strings of molecules bound together by carbon atoms. The exact composition of each precursor varies from one company to another and is generally considered a trade secret. During the manufacturing process, a variety of gases and liquids are used. Some of these materials are designed to react with the fiber to achieve a specific effect. Other materials are designed not to react or to prevent certain reactions with the fiber. As with the precursors, the exact compositions of many of these process materials are considered trade secrets.

MANUFACTURING PROCESS

           The manufacturing process for producing carbon fibers involved highly controlled steps of heat treatment and tension to form the appropriately ordered carbon structure. Rayon, Pitch has been largely supplanted as a precursor by Polyacrylonitrile (PAN). Polyacrylonitrile precursors produce much more economical fibers because the carbon yield is higher and because PAN-based fibers do not intrinsically require a final high-temperature “graphitization” step. Polyacrylonitrile-based fibers having intermediate- modulus values of about 240 to 310 GPa (35 to 45 _ 106 psi), combined with strengths ranging from 3515 to 6380 MPa (510 to 925 ksi), are now commercially available. Because carbon fibers display linear stress-strain behavior to failure, the increase in strength also means an increase in the elongation-to-failure. The commercial fibers thus display elongations of up to 2.2%, which means that they exceed the strain capabilities of conventional organic matrices. The diameter of carbon fibers typically ranges from 8 to 10 lm (0.3 to 0.4 mils).

              The process for making carbon fibers is part chemical and part mechanical Plastics are drown into long strands or fibers and then heated to a very high temperature without allowing it to come in contact with oxygen. Without oxygen, the fiber cannot burn. Instead, the high temperature causes the atoms in the fiber to vibrate violently until most of the non-carbon atoms are expelled. This process is called carbonization and leaves a fiber composed of long, tightly.

Fig: Manufacturing of carbon fibers.

PYROLYSIS PROCESS:-

Fig:Pyrolysis processes for PAN precursors

Pyrolysis is the processes of inducing chemical changes by heat-for a instance, by burning a length of yarn & causing the material to carbonize & become black in color. The temperature of carbonizing range up to about 1500°C; for graphitizing to 3000°C,    Here is a typical sequence of operations used to form carbon fibers from polyacrylonitrile.

Spinning:-

1.  Acrylonitrile plastic powder is mixed with another plastic, like methyl acrylate or methyl methacrylate, and is reacted with a catalyst in a conventional suspension or solution polymerization process to form a polyacrylonitrile plastic.
2.  The plastic is then spun into fibers using one of several different methods. In some methods, the plastic is mixed with certain chemicals and pumped through tiny jets into a chemical bath or quench chamber where the plastic coagulates and solidifies into fibers. This is similar to the process used to form polycyclic textile fibers. In other methods, the plastic mixture is heated and pumped through tiny jets into a chamber where the solvents evaporate, leaving a solid fiber. The spinning step is important because the internal atomic structure of the fiber is formed during this process.
3.  The fibers are then washed and stretched to the desired fiber diameter. The stretching helps align the molecules within the fiber and provide the basis for the formation of the tightly bonded carbon crystals after carbonization.

Stabilizing:-

4.  Before the fibers are carbonized, they need to be chemically altered to convert their linear atomic bonding to a more thermally stable ladder bonding. This is accomplished by heating the fibers in air to about 390-590° F (200-300° C) for 30-120 minutes. This causes the fibers to pick up oxygen molecules from the air and rearrange their atomic bonding pattern. The stabilizing chemical reactions are complex and involve several steps, some of which occur simultaneously. They also generate their own heat, which must be controlled to avoid overheating the fibers. Commercially, the stabilization process uses a variety of equipment and techniques. In some processes, the fibers are drawn through a series of heated chambers. In others, the fibers pass over hot rollers and through beds of loose materials held in suspension by a flow of hot air. Some processes use heated air mixed with certain gases that chemically accelerate the stabilization.

Carbonizing:-

5.  Once the fibers are stabilized, they are heated to a temperature of about 1,830-5,500° F (1,000-3,000° C) for several minutes in a furnace filled with a gas mixture that does not contain oxygen. The lack of oxygen prevents the fibers from burning in the very high temperatures. The gas pressure inside the furnace is kept higher than the outside air pressure and the points where the fibers enter and exit the furnace are sealed to keep oxygen from entering. As the fibers are heated, they begin to lose their non-carbon atoms, plus a few carbon atoms, in the form of various gases including water vapor, ammonia, carbon monoxide, carbon dioxide, hydrogen, nitrogen, and others. As the non-carbon atoms are expelled, the remaining carbon atoms form tightly bonded carbon crystals that are aligned more or less parallel to the long axis of the fiber. In some processes, two furnaces operating at two different temperatures are used to better control the rate de heating during carbonization.

Treating the surface:-

6.  After carbonizing, the fibers have a surface that does not bond well with the epoxies and other materials used in composite materials. To give the fibers better bonding properties, their surface is slightly oxidized. The addition of oxygen atoms to the surface provides better chemical bonding properties and also etches and roughens the surface for better mechanical bonding properties. Oxidation can be achieved by immersing the fibers in various gases such as air, carbon dioxide, or ozone; or in various liquids such as sodium hypochlorite or nitric acid. The fibers can also be coated electrolytically by making the fibers the positive terminal in a bath filled with various electrically conductive materials. The surface treatment process must be carefully controlled to avoid forming tiny surface defects, such as pits, which could cause fiber failure.

Sizing:-

7.  After the surface treatment, the fibers are coated to protect them from damage during winding or weaving. This process is called sizing. Coating materials are chosen to be compatible with the adhesive used to form composite materials. Typical coating materials include epoxy, polyester, nylon, urethane, and others.
8.  The coated fibers are wound onto cylinders called bobbins. The bobbins are loaded into a spinning machine and the fibers are twisted into yarns of various sizes.

Fig: sizing

. Capabilities:-

• Excellent air flow uniformity
• Easy internal access to facilitate maintenance
• Electric or gas fired
• Optimal temperature uniformity
• Operator isolation from effluent

Features

• Multiple temperature control zones
• Proven alternating cross flow design
• Adjustable louvers and diffuser plates for precise temperature adjustment
• Excellent float end seals for positive sealing, minimized infiltration of ambient atmosphere and improved temperature uniformity
• Aluminized steel construction
• Plug fans to facilitate maintenance.

TYPICAL PROPERTIES OF REINFORCING FIBER

1. The advantages of carbon fibre products over different woods and metals come to      prominence when a rigid, strong but also lightweight material is needed

2. Further useful properties of carbon fibres are their durability, resistance to fatigue   and that they are chemically inert and still exhibit high strength at high temperatures.

3. It is often preferred to other fibre composites due to the tensile strength and modulus of the high quality fibres which perform better than fibreglass or Kevlar.

TYPE	TENSILE  STRENGTH        (MPa)	ELASTIC MODULUS    (GPa)	DENSITY      ( kg /  m3 )		RELATIVE COST
Boron	3500	380	2600		Highest
Carbon
High strength	3000	275		1900		Low
High modulus	2000	415	1900		Low
Glass
E  type	3500	73	2480		Lowest
S  type	4600	85	2540		Lowest
Kevlar
29	2800	62	1440		High
49	2800	117	1440		High

POLYMER MATRIX COMPOSITES

        It consists of a polymer resin as the matrix, with the fiber as the reinforcement medium. Polymer makes ideal matrix materials as they can be processed easily possess lightweight, inlight of their room temperature properties, & cost. The various types of PMCs are classified according to reinforcement type (i.e. glass, carbon, aramid & boron)

The two main kinds of polymers are Thermosets & Thermoplastics.

Thermosets:-

Thermosets have qualities such as a well bonded three dimensional molecular structure. The most common resins of these types are epoxies, phenolics, polyimides & cyanate esters. The epoxies are more expensive & in addition to commercial application are also utilized extensively in PMCs for aerospace application. For high temperature applications polyimide resins are employed.

Thermoplastics:-

Thermoplastics have one or two dimensional molecular structure & they tend to soften at an elevated temperature & show exaggerated melting point. High temperature thermoplastic resins offer the potential to be used in future aerospace application; such material include Polyetheretherketone (PEEK), Polyphenylene sulfide (PPS) & Polyethereimide (PEI).

APPLICATIONS

1. . Most sports now use carbon fibres in their equipment whether it is to reinforce the traditional materials or create new ones. Golf clubs, tennis rackets and bicycles all use the strength and durability of modern composites to enhance the quality of the sport. Formula One and other motor sports use carbon fibre composites in order to protect the driver in the event of a crash.

2. Reinforced plastic are used for automobile parts. The fatigue properties of the materials & low weight, ability to sustain strains from the engine heat & low frequency road vibrations are features that favors composites in truck & other vehicles.
3. Carbon/graphite is also used as a moderator in both reactor & non-reactor system & exhibit good moderating characteristics. They are also used in space application due to thermal conductivity & strength.
4. Fiber epoxy composites have been used in aircraft engine to enhance the performance of the system
5. The aerospace and automotive industry also use the excellent properties to their advantage and are always researching and developing further improvements in the quality of the fibres.

 

Fig: The Boeing 7E7

CONCLUSION

            There are many fibers which embedded in PMCs & to increase the strength & desired properties of material. Out of which carbon & boron fibers are mostly used but economical point of view carbon has low cost as compared to boron. Polymer matrix are used in large quantities, in light of there room temperature properties, ease of fabrication & cost. Carbon fibers are produced by many processes by using Reyon, Pitch or PAN as a precursor. Pyrolysis of PAN produces fibers of high strength & stiffness. As CFRP is light in weight they are used in aerospace & space application