- 1A. Advantages and limitations of ferrous materials in engineering application
- 1B. Advantages and Limitations of Non-Ferrous Alloys in Engineering Application
- 1C. Advantages and limitations of polymers in engineering application
- 1D. Advantages and limitations of using ceramics in engineering application
- 2A. Selection of ferrous metals in engineering application
- 2B. Non-ferous alloys in engineering application
- 2C. Polymers used in engineering application
- 2D. Ceramics in engineering application
- 3A. Surface hardening treatments
- 3B. Hardening of steel surfaces
- 3C. Erosion corrosion
- 3D. Classes of stainless steel
- 3E. Wear processes
- 3F. Mechanisms of abrasive process
- 4A. Stages of fatigue failure process
- 4B. Variables affecting fracture toughness and appearance of materials
- 4C. Selection of creep resistant alloys
- 5A. Conditions for underbead cracking
- 5B. Reasons for Pre-Heating and Post Heating Welded Steel Component
- 5C. Changes in HAZ of cold worked
The main component of ferrous metals is iron but it also contains other metals and elements though in small amounts. These metals are magnetic since they have a large iron content that attracts a magnetic field. There are several advantages of using ferrous materials in engineering applications these include; the raw materials for their production are found abundantly on the earth’s crust (Callister,2000). Secondly they can be produced easily through an economical extraction process, alloying, refining as well as fabrication techniques. Finally they are versatile when it comes to physical and mechanical properties. There are also some limitations when using these ferrous materials in engineering application and these are; the fact that they have a relative high density, they have a low corrosion resistance and hence they require coating and finally they have low thermal and electrical conduction properties.
1B. Advantages and Limitations of Non-Ferrous Alloys in Engineering Application
Non-ferrous metals are alloys with no iron in them. Their properties differ from those of ferrous metals. Their properties are a result of the metals that are not present in ferrous metals but are present in them. Some of their advantages when used in engineering applications are that they are easily fabricated, their ductile nature, they have a light weight, they are corrosion resistant and they are very strong at temperatures which are elevated (DeGarmo, Black & Kohser,1997). There are also some limitations to their use and they include a low modulus of elasticity, they are expensive when compared to iron and steel, they have a high density, they can be susceptible to corrosion in certain environments and their electrical and thermal conductivity is medium (Crook &Farmer, 2002).
1C. Advantages and Limitations of Polymers in Engineering Application
These are substances that are made up of a mixture of many compounds. Their properties are therefore dependent on the rate of loading as well as temperatures. Polymers have many properties due to the mechanical behavior that they posses. Therefore there exist different polymers each with different characteristics. Polymers are advantageous when it comes to engineering applications because they are light in weight, resistant to corrosion, formability, have a low energy content, versatility in design, range from soft to hard and they have optical properties. The limitation of using polymers is its low thermal conductivity.
1D. Advantages and Limitations of Using Ceramics in Engineering Application
Ceramic are materials whose nature and properties is determined by they bonding that is found within the atoms. These are traditional materials made from substances that occur naturally as well as those which are highly refined or chemical, magnetic and electrical applications. Ceramics are advantageous in engineering application since some of them have high thermal conductivity while other have a low thermal conductivity. They are chemically stable in a wide range of temperatures. They resist high temperatures, high melting point and chemicals (Lahiri & Majumder, 2012). There exist ratios that are high between weight and strength. They also have a low rate of corrosion. When it comes to their limitations they posses low toughness as a small crack leads to their eventual fracture. It is quite difficult to make predictions of their strength of interfacial bond .they have a limited repair ability when damaged.
2A. Selection of Ferrous Metals in Engineering Application
Ferrous metals posses different properties that are put into use in various industries. They have different specifications when it comes to mechanical and physical properties. For instance iron mild steel is malleable and ductile and hence used for production of bolts, nuts and screws. Iron can also be used as tool steel since it is hard and very ductile hence used in producing shears, drills and hammer heads.
Alloy steels have high hardenabilty compared to plain carbon steels. This is because alloy steels are made up of many elements and hence they have improved properties. The alloy steels are stronger, resistant to erosion and have improved harden ability (DeGarmo, Black & Kohser,1997). One the other hand carbon content in the plain carbon steel determines its strength since carbon content is inversely proportional to ductility. Therefore a low hardenability results from a decrease in plain carbon. This means that the quality of the steel go down through impairing in low and high temperatures resulting to a loss in embrittlement and strength. Therefore if other elements are added to steel then their hardenability will be improved (DeGarmo, Black & Kohser, 1997.
2B. Non-ferous Alloys in Engineering Application
The non-ferrous metals have many properties but there are some of the non-ferrous metals whose applications are more suitable than others. Aluminum is suitable in Aircraft industry, road signs, cooking utensils because it is light. Aluminum use is increased in motor vehicles, engine blocks where the low weight increase fuel economy. Copper is a good electrical conductor hence used in electrical wiring. Zinc is used in decorative articles since it is ductile and malleable in hot and cold temperatures. Lead is highly resistant to corrosion hence used in mild steel as a protective coating.tin can be used to coat mild steel hence put into use in canning industry (DeGarmo, Black & Kohser, 1997).
Non-ferrous alloys exist in both cast and raw forms. The principal behind the existence of these two forms is cast non-ferrous alloys need high temperatures to be melted and then the liquid is poured into a mould and cooled before other parts are added. These alloys are thus brittle and hence they can not be easily formed through deformation. Wrought non ferrous alloys are shaped through pressing and shaping and hence this makes them more tensile and stronger. They can thus go through mechanical deformation.
2C. Polymers Used in Engineering Application
Polymers have specific properties from their families like thermosets, thermoplastics and elastomers alongside general properties. Due to their characteristics they can be applied in materials which require moderate strength, low thermal and electrical conductivity, variety of colors are light in weight, and are easily fabricated. Their common use is household appliances such as containers. Those polymers that are pliable and soft can be used as materials for cushioning. Other can also be used for the insulation of electrical appliances.
There are two types of composite materials namely dispersion strengthening and fiber strengthening. The dispersion strengthening materials have a uniform dispersion of some substances that give motion of dislocations plastic in nature and hence reducing the plastic deformation in a solid. On the other hand fibers strengthening entail the inclusion of fibers with plastics and hence this combination has an influence on the strength and thermal conductivity dependent on their ration (Vernon, 1992).
2D. Ceramics in Engineering Application
Ceramics have many properties that can not be found in metals or plastics. They are used as non-reactive materials in chemicals erosive and corrosive fluids of low temperatures and corrosive gases and melts that have high temperatures. They can be used for thermal, optical, electrical and magnetic applications. They are used in mining and chemical engineering since they are non-reactive to erosive or corrosive fluids. They can also be used in heat engines and exchangers as they can resist thermal shock, corrosion and oxidation that involve high temperature (Richerson, 1988).
Ceramics are of two types industrial or engineering and domestic. Engineering ceramics is whereby ceramics are used for making materials in industries like automotive industry. On the other hand domestic ceramics are used for constructing as tiles for floors and walls in interior design.
3A. Surface Hardening Treatments
Carburizing is a treatment method for making metal surfaces hard using heat. Heating metals in presence of materials that contain carbon, leads to its absorption with the metals. Carburizing can lead to increase in the surface hardness, carbon content on the surface, wear resistance, tensile strengths and change its volume as well as making it gain growth (Vernon, 1992).
Nitriding on the other hand makes surfaces harder through spreading of nitrogen on surfaces of metals using heat. Nitriding results to increased surface hardness, wear resistance, yield limit and reducing density of surface and elongation, carburizing is more suitable as a method of hardening surfaces as compared to nitriding (Vernon, 1992). Carburizing also results to greater depth and hardness as compared to nitriding. Carburizing is applied in gears, and bearings while nitriding is applied in valve guides and seating’s.
3B. Hardening of Steel Surfaces
Steel surfaces need to be carburized since it is a suitable method for some steels particularly a steel alloys that contain 0.5% carbon while quenching and re-heating is used for steel that 0.4-0.5% carbon and 0.4-0.8% cast iron.
3C. Erosion Corrosion
Metals undergo erosion corrosion when they are subjected to mechanical action like suspension of particles which are insoluble and hence they deteriorate as a result of the mechanical force. In instances where erosion factors hasten corrosion the attack is referred to as erosion corrosion (Schweitzer,2010). Erosion corrosion can be prevented by lowering flow rates of fluid path materials that contain high temperature fluids in them. Reduction in velocity, turbulence elimination and designing piping systems properly also reduce erosion corrosion (Schweitzer, 2010).
3D. Classes of Stainless Steel
Ferritic stainless steel can be either ductile or brittle nature when their temperatures are reduced. They are hence used in thin walls due to their brittle characteristic. Martensitic stainless steel is strong and resistance to corrosion. It can therefore it can be put into use in light weight structures. Austenitic stainless steel is used in all temperatures from low to high. At low temperatures they are very tough while at high temperatures they are resistant to oxidation. They can therefore be used as non-magnetic metals (DeGarmo, .Black & Kohser, 1997).
3E. Wear Processes
Adhesive process involves the deformation of plastics in very small fragments on the surface after a frictional contact. It frequently occurs sue to the shearing at a particular point of contact. Abrasive process involves removing materials from a surface by the use of hard particles which are forced and moving against the surface of solids. Erosive process occurs as a result of an impact of solid or liquid particles on the surface of an object. (DeGarmo, Black & Kohser, 1997).
3F. Mechanisms of Abrasive Process
There are several mechanisms involved in abrasive wear and they are micro-plouging whereby materials are cut by debris in the form of flakes and used of ductile materials. Micro-cutting involves wear debris being cut or removed using sharp grit .micro-fatigue results from cycling loading from friction whereby the surface is deformed by grits. Micro-cracking involves high load of grit moving across a surface resulting to the cracking of the surface (DeGarmo, Black & Kohser, 1997).
4A. Stages of Fatigue Failure Process
Crack initiation is the first stage where a crack forms at a point of high stress .this is followed by crack propagation whereby the crack continues to grow at that area. The third stage is final failure whereby the crack reaches a critical size due to the continuous growth of crack.
4B. Variables Affecting Fracture Toughness and Appearance of Materials
Temperature increase results to dislocation of metals hence the yield strength is lowered. Surfaces of ductile metals thus appear dull and fibrous. Ductile brittle transitions appear cleavage or granular. Notch surety is another variable whereby is notch or cracks are present, a triaxial tension stress occurs adjacent to the notch or crack when a load is put. This results to formation of a brittle fracture incase there is prevention from plastic deformation. Thickness is a variable that is independent as the toughness of the fracture depends on how thick a material is. The materials thickness is inversely proportional to the toughness of the fracture (Callister, 2000).
4C. Selection of Creep Resistant Alloys
Super alloys have good properties like good mechanical strength as well as creep resistance and hence they have slow movements towards deformation when they are stressed. Therefore there are factors that should be considered when selecting super alloys and these are the cost, macinability, high tensile strength an high stress levels at high temperatures for periods that are extended.
5A. Conditions for Underbead Cracking
Underbead cracking occurs in welded steels as a result of various conditions which are existence of a heat affected zone crack forming adjacent to the fusion line. Another condition is presence of hydrogen in weld zone. This type of cracking occurs mostly in alloy steel.
5B. Reasons for Pre-Heating and Post Heating Welded Steel Component
The three reasons are slowing down of cooling rate, reduction of shrinkage stress and distortion of wells and finally the promotion of fusion and moisture removal.
5C. Changes in HAZ of Cold Worked
A high dislocation is given by cold worked. The material is made brittle as a result of low temperatures. They are given a finer grain as well as a decrease in the amount of boundaries that are in existence between the grains found in their surfaces. Cold working is therefore a process whereby metals undergo plastic deformation below recrystallization (Huda, 2009).
Different Engineering Materials
The engineering materials available for use in different applications are wide in range. These materials all have particular properties and characteristics linked to them. There are also various advantages and disadvantages for each of the materials .there is a detailed discussion of the definition of these materials and structures
Metals are of two types ferrous and non-ferrous which can be put into application in different ways. Ferrous metals are widely used due to the large quantity of iron in the earth’s crust as well as their production in an economical extraction (Callister, 2000). The element iron is fourth most plentiful on the crust of the earth and for a very long time it has been used as a basic metal in engineering (DeGarmo, Black & Kohser, 1997). Nonferrous alloys are used for high resistance to particular wear apart from abrasion or resistance to wear in environments where corrosion is too high or beyond ferrous alloys service temperatures (Crook &Farmer.H, 2002).Nonferrous metals have an important role in modern technology due to their large number and their wide variety they provide a range that has no limit of properties to design engineers (DeGarmo, Black & Kohser, 1997).
Apart fro ferrous and non-ferrous metals there are also other engineering materials and these are ceramics and polymers. Ferroelectric liquid crystals that are stabilized by polymers are a representation of functional materials that can be applied in areas like privacy windows, optical shutters, photonics that can be switched on and dynamic holography (DeGarmo,Black &Kohser,1997).they are low in density, their tooling costs are low, resistance to corrosion, and versatile in design. Ceramics include both traditional materials from heating of substances occurring naturally and those materials that have undergone refining and synthesis for material’s that are used for modern mechanical, chemical, magnetic optical and electrical applications (Richerson,1988).It has good resistance to thermal shock as well as oxidation under high temperatures hence used in development of heat engines and exchangers (Richerson,D ,1988). domestic ceramics have been put into use in household products.
Abrasive materials are those materials that are hard and can cut or cause abrasion to other substances DeGarmo, Black & Kohser, 1997). Abrasive systems involve flow of mineral ore through feed chute into upper portions of the zone for crushing which is made up of two plates one that is stationery while the other is in motion. Rock chunks make their way into the top and their sizes reduce every time there is cycling of jaws towards each other.
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