Classification of Engineering Material

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Material is nothing but a matter of substance used to create a certain thing. Engineering materials are the materials used to for the application of engineering works. Based on the mechanical, physical, chemical and manufacturing properties materials are selected according to the application.

Mechanical properties of the materials are strength (compressive or tensile), toughness, stiffness, elasticity, plasticity, ductility, brittleness and hardness. Physical properties of materials are density, conductivity (thermal or electrical), acoustical (sound transmission or absorption), optical, combustibility. Chemical properties of materials are composition (oxide or compound), acidity or alkalinity, weathering corrosion.

Manufacturing properties of materials are castability, machinability rating, machining speeds and feeds and for dimensioning purpose shape and size.

The selection of material for the required functioning application is based on some of the following factors:

  1. Stresses to which the work piece or component will be subjected.
  2. Corrosion resistance.
  3. Temperature, wear and tear resistance.
  4. Flexibility and rigidity.
  5. Easiness of the manufacturing process.
  6. Cost effectiveness for the product development.
  7. Availability of the material.

Classification of Engineering Material :

Depending upon the nature of substance materials are classified as

  1. Metals and alloys
  2. Ferrous metals
  3. Non ferrous metals
  4. Non metals
  5. Ceramics
  6. Polymers
  7. Composites
  8. Semi conductors
  9. Bio materials

1.METALS AND ALLOYS:

Metallic materials are combination of metallic elements.

The most prominent property of metals is electrons are non localized i.e. in atomic arrangement outer valency electrons do not belong to individual atom rather it belong to whole bulk of material.Non localized electron is free to carry charge to conduct electricity. Hence they are good conductors for electrical and thermal charge.

Metals have lustrous appearance. At normal temperature majority of the materials are in solid state, but some metals like mercury lies in liquid state.

Based upon the presence of iron content metals are named as

  1. Ferrous metals
  2. Non ferrous metals

Ferrous metals:

The primary content of ferrous metals is iron and carbon. Ferrous metals are magnetic and are vulnerable to rust when exposed to moisture. Wrought iron won’t rust due to purity and stainless steel due to presence of chromium.

Eg : iron, steel, etc.

Due to their magnetic property ferrous metals are used in motor and electrical applications.

Non Ferrous Metals:

Iron is not primary content. Due to the non presence of iron these metals have high resistance to rust and corrosion and they are non magnetic.

Eg: copper, brass, aluminium, tungsten, lead, zinc, gold, etc.

Alloy:

Alloy is a combination of two or more metals. It is named based on metallic bonding character. It is of two types’ ferrous metal alloy and non ferrous metal alloy. Cast iron is an alloy made from iron, carbon and silicon. Brass is an alloy of copper and zinc.

Applications:

  1. Due to their toughness and ability to sterilize at high temperatures metals are used as needles, surgical blades.
  2. Due to their strength and ability to withstand heavy weights metals like iron and steel are used in construction.
  3. Metals like gold, silver, platinum, etc are used in jewellery.
  4. Metals are used in machines and automobiles as they can withstand high temperature, pressure and workloads.
  5. Aluminium and titanium play important role in light weight category for aircraft alloys.
  6. Tungsten is used in high temperature applications.

2. CERAMICS:

A particle or fibrous which are used in terms of making ceramic products. Ceramics have regular atomic structure and crystal structure. Ceramics are mainly oxides, nitrides and carbides. They are non conducting materials, due to its insulating property they are used as insulators. They are very hard and brittle in nature.

Eg: alumina, silica, silicon carbide, diamond, bricks, etc.

Applications:

  1. Due to the compressive strength bricks are used in construction
  2. Because of their good thermal insulation ceramic tiles are used in ovens.
  3. Some ceramics are transparent to radar and other electromagnetic waves are used in radomes and transmitters.
  4. Glass ceramics have high temperature capabilities so they are used in optical equipment and fiber insulation.
  5. Alumina, silica, silicon carbide are used in making tools.
  6. Diamond is used in ornaments and cutting tool applications.

3. POLYMERS:

Polymers have chain molecule structure of carbon as back bone atoms. They are mainly made up of tough organic materials. They are low density materials and also flexible. In some cases polymers are not flexible.

Polymers are not only used as structural materials, they can be used as fiber and resins in the matrix of composite materials.

Eg : polyester as fibers, phenolics and epoxides as resins.

Elastomers are also polymers but they are considered separately due to their specific design for certain purposes like shock and vibration absorption.

Natural polymers :

Eg : wool, silk, DNA, cellulose, proteins, etc.

Synthetic polymers:

  1. Thermo plastics
  2. Thermosetting plastics

Eg: nylon, polyethylene, polyester, Teflon, epoxy, Bakelite, etc.

Applications:

  1. Polyethylene is used for making carry bags.
  2. Polypropylene is used for making high temperature resistance products like feeding bottle.
  3. Polyether ether ketone and polyethylene ketone are used in mineral water bottle concept.
  4. Poly carbonate is used to make high performance polymers like transparent polymers
  5. Polyaniline is a conducting polymer.
  6. Bakelite used for making insulating materials. 

4. COMPOSITE:

Composite material is the composition of two or more constituent materials with different physical and chemical properties to produce a different characteristic material.

Composite material may be both metals or metal and ceramic or metal and polymer, depending upon the application requirement the combination is made.

Eg : wood, concrete, fiber glass, CFRP (carbon fiber reinforced plastic), GFRP (glass fiber reinforced plastic), etc.

Applications:

  1. CFRP and GFRP are used for automotive body parts.
  2. CRPF and honeycomb composites are used for chassis.
  3. Some fuel tanks are made up of Kevlar reinforced fiber.
  4. Reinforced thermosets are used in springs and bumper system.
  5. Fibreglass reinforced plastic has been used for boat hulls, fishing rods, tennis rackets, helmets, bows and arrows.

5. SEMICONDUCTORS:

Semiconductor is an intermediate conducting material. Their conductivity is not high as like metals and low as like insulating ceramic materials. In these materials resistance decreases as their temperature increases.

The unique atomic structure allows to control the conductivity.

Eg : silicon, germanium, gallium arsenide, selenium, etc.

Applications:

  1. Gallium arsenide is widely used in low noise, high gain and weak signal amplifying devices.
  2. A semi conductor device can perform the function of a vacuum tube having hundreds of times its volume.

6. BIO MATERIALS:

Bio materials are non-viable materials .Eg : alumina, zirconia, titanium, tantalum, niobium, carbon, etc.

Applications:

  1. Metals are used in medicine to cure any micronutrient metal deficiency diseases in humans and animals, like iron is a part of haemoglobin a bio molecule which can be used as ferrous sulphate to cure some forms of anemia.
  2. Implants in the body to repair or replace the damaged tissue.

NOTE:

In composite materials the name itself indicates as composite => composition, it is the composition of two or more materials.

In semiconductors the name itself indicates as semi (half) and conductor (conducting)

The difference between an alloy and composite is that the composite is a reinforcement of other material. Whereas alloy is a combination (mixture) of both or required number of materials in the required quantity as per the necessary product.

Both semiconductors and bio materials are substitutes in metals, ceramics and polymers in the required places.

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