Automotive Materials UNIT-2 (2 Marks)
Unit -2
2 marks Questions.
1. Differentiate Thermoplasts and Thermosets polymer?
A.
2. What are the synthetic polymers?
A. Synthetic polymers are human-made polymers. From the utility point of view they can be classified into four main categories: thermoplastics, thermosets, elastomers and synthetic fibers. They are found commonly in a variety of consumer products such as money, super glue, etc.
A wide variety of synthetic polymers are available with variations in main chain as well as side chains. The back bones of common synthetic polymers such as polythene, polystyrene and poly acrylates are made up of carbon-carbon bonds, whereas hetero chain polymers such as polyamides, polyesters, polyurethanes, polysulfides and polycarbonates have other elements (e.g. oxygen, sulfur, nitrogen) inserted along the backbone. Also silicon forms similar materials without the need of carbon atoms, such as silicones through siloxane linkages; these compounds are thus said to be inorganic polymers. Coordination polymers may contain a range of metals in the backbone, with non-covalent bonding present.
3. What are advantages of FRP?
A. There are following :
· Infinite potential
· Low weight
· Mechanical strength
· High impact strength
· Resiliance
· Formability
· Chemical resistance
· Corrosion resistance
· Weather proof
· Electrically insulating
· Thermally insulating
· Fire resistance
· Low thermal expansion
· Anti magnetic, no spark
· Durable custom colours
· Long life
4. What is the difference between Addition and condensation polymerization?
A.
Addition polymerization
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Condensation polymerization
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The process of synthesizing addition polymers is known as addition polymerization. There should be multiple bonded monomers to initiate such reaction. This is a chain reaction; therefore, any number of monomers can join into a polymer. There are three steps to a chain reaction, they are initiation, propagation and termination. For an example, we will take the synthesis of polyethylene, which is an additional polymer used to make products like garbage bags, food wrap, jugs, etc. The monomer for polyethylene is ethene (CH2=CH2). Its repeating unit is –CH2-. In the initiation step, peroxide radical is generated. This radical attacks the monomer to activate it and produce a monomer radical. During the propagation phase, the chain grows. Activated monomer attacks another double bonded monomer and attaches together. Ultimately the reaction stops when two radicals join together and form a stable bond. Chemists can control the length of the polymer chain, reaction times and other factors to obtain the required polymer.
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Any condensation process, which results in the formation of polymers, is known as condensation polymerization. A small molecule like water or HCl is released as a by-product during the condensation polymerization. The monomer should have functional groups in ends, which can react together to continue the polymerization. For example, if the joining ends of two molecules have a –OH group and a –COOH group, a water molecule will be released and an ester bond formed. Polyester is an example for a condensation polymer like that. In the synthesis of polypeptides, nucleic acids or polysaccharides, condensation polymerization takes place within biological systems.
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5. Write an example for composite material? What are the different types of composites?
A.
• Examples:
Cemented carbides (WC with Co binder)
Plastic molding compounds containing fillers
Rubber mixed with carbon black
Wood (a natural composite as distinguished from a synthesized composite)
Types of Composite Matrix Materials
There are three main types of composite matrix materials:
• Metal Matrix Composites
• Ceramic Matrix Composites
• Polymer Matrix Composites
6. What is matrix and reinforcement?
A. Matrix
The matrix is the monolithic material into which the reinforcement is embedded, and is completely continuous. This means that there is a path through the matrix to any point in the material, unlike two materials sandwiched together. In structural applications, the matrix is usually a lighter metal such as aluminium, magnesium, or titanium, and provides a compliant support for the reinforcement. In high-temperature applications, cobalt and cobalt–nickel alloy matrices are common.
Reinforcement
The reinforcement material is embedded into a matrix. The reinforcement does not always serve a purely structural task (reinforcing the compound), but is also used to change physical properties such as wear resistance, friction coefficient, or thermal conductivity. The reinforcement can be either continuous, or discontinuous. Discontinuous MMCs can be isotropic, and can be worked with standard metalworking techniques, such as extrusion, forging, or rolling. In addition, they may be machined using conventional techniques, but commonly would need the use of polycrystalline diamond tooling (PCD).
Continuous reinforcement uses monofilament wires or fibres such as carbon fiber or silicon carbide. Because the fibres are embedded into the matrix in a certain direction, the result is an anisotropic structure in which the alignment of the material affects its strength. One of the first MMCs used boron filament as reinforcement. Discontinuous reinforcement uses "whiskers", short fibres, or particles. The most common reinforcing materials in this category are alumina and silicon carbide.
7. Give the example for metal- matrix composites and ceramic-matrix composites?
A.
Metal matrix composites
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Ceramic matrix composites
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For example, carbon fibers are commonly used in aluminum matrix to synthesize composites showing low density and high strength. However, carbon reacts with aluminum to generate a brittle and water-soluble compound Al4C3 on the surface of the fiber. To prevent this reaction, the carbon fibers are coated with nickel or titanium boride.
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The important commercially available CMCs are C/C, C/Sic, Sic/Sic and Al2O3/Al2O3.
silicon carbide (Sic), alumina (Al2O3) and mullite (Al2O3–SiO2) fibers
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8. Enlist the different type of common engineering polymers.
A.
· Acrylonitrile butadiene styrene (ABS)
· Nylon 6
9. What are the different types of plastics?
A.
· Polyethylene terephthalate (PET or PETE)
· High-density polyethylene (HDPE)
· Polyvinyl chloride (PVC)
· Low-density polyethylene (LDPE)
· Polypropylene (PP)
· Polystyrene (PS)
10. What are the special properties of plastics that make them useful engineering material?
A.
· Strength. The plastics are sufficiently strong and can be used for load bearing structural members
· Weather Resistance
· Fire Resistance
· Durability
· Dimensional Stability
· Chemical Resistance
· Thermal Resistance
· Working Conditions
11. Write the applications of PVC.
A.
· Signs
· Flooring
12. Define the term FRC.
A. A fiber-reinforced composite (FRC) is a composite building material that consists of three components:
(i) the fibers as the discontinuous or dispersed phase,
(ii) the matrix as the continuous phase, and
(iii) the fine interphase region, also known as the interface. This is a type of advanced composite group, which makes use of rice husk, rice hull, and plastic as ingredients. This technology involves a method of refining, blending, and compounding natural fibers from cellulosic waste streams to form a high-strength fiber composite material in a polymer matrix. The designated waste or base raw materials used in this instance are those of waste thermoplastics and various categories of cellulosic waste including rice husk and saw dust.
FRC is high-performance fiber composite achieved and made possible by cross-linking cellulosic fiber molecules with resins in the FRC material matrix through a proprietary molecular re-engineering process, yielding a product of exceptional structural properties.
Through this feat of molecular re-engineering selected physical and structural properties of wood are successfully cloned and vested in the FRC product, in addition to other critical attributes to yield performance properties superior to contemporary wood.
This material, unlike other composites, can be recycled up to 20 times, allowing scrap FRC to be reused again and again.
The failure mechanisms in FRC materials include delamination, intralaminar matrix cracking, longitudinal matrix splitting, fiber/matrix deboning, fiber pull-out, and fiber fracture.
13. State the characteristics of ceramics materials.
A. PROPERTIES OF CERAMIC MATERIALS
The following properties of ceramic materials make them useful for engineering applications
1. Mechanical properties
2. Electrical properties (including magnetic properties)
3. Chemical properties
4. Thermal properties
5. Optical properties
6. Nuclear properties.
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14. Classify the ceramics.
A. 
15. State the characteristics of glass.
A. Characteristics of glass:
· It is hard brittle material.
· It is weather resistant.
· It can be given a high polish.
· It can absorb, reflect and refract light.
· It is an excellent insulator against electricity.
· It can be blown, drawn and pressed to any shape.
· It is amorphous and brittle.
· It is possible to change some of its properties like hardness, fusibility and refractive poer etc to suit different purposes.
· It can be frosted by sand blasting.
· It is incombustible.
· It is greater dimensional stability.
· It has a compatibility with or material.
· It is non rotting material.
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