Introduction
1.
Material science provides the necessary information and knowledge regarding the
nature and behaviour of all types of engineering materials. The engineering
usefulness of materials is decided based on this information.
2.
Material is something that consists of matter. Materials comprise a wide range
of metals and non-metals which must be operated upon to form the end product.
Whether this end product is a bridge, a computer, a space vehicle or an
automobile, a technician must have an intimate knowledge of the properties and
behavioral characteristics of the materials he intends to use.
3.
The word ‘materials’ however, does not refer to all matters that are found in
universe but refer to that part of inanimate matters or materials which are
required to fulfill the growing needs of mankind and are used by technologists,
engineers and metallurgists. Therefore, these are commonly referred to as
‘Engineering Materials’. There is an ever increasing demand of materials of
greater strength, lightness, safety, reliability, electrical conductivity,
electromagnetism, hardness, hardenability, cutting power, softness, cheapness,
resistance to corrosion, radiation and heat, etc.
Classification
4.
Most of the engineering materials are broadly classified into Metals and Non-
Metals. Further classification of these two groups is given below:
(a) Metals
(i) Ferrous
(ii) Non-Ferrous
(b) Non-Metals
(i) Ceramics
(ii) Organics
(iii) Composites
Metals
5.
Metals play a major role in the industrial and everyday life of human beings.
Metals are composed of elements, which readily give up electrons to provide a
metallic bond and electrical conductivity. Examples are Iron, Aluminium,
Magnesium, Titanium, Brass, Copper, Nickel, Chromium, Cadmium, Duralumin,
Silver, Gold, Zinc, etc.(Refer Fig 1)
6.
Metals generally possess the following characteristics:
·
(a) Lustre
(b) Hardness
·
(c) Low
specific heat
(d) Plastic deformability
·
(e)
Strength
(f) Relatively high melting
point
·
(g)
Ductility
(h) Malleability
·
(j)
Opacity
(k) Rigidity
·
(l)
Weldability
(m)
Castability
·
(n)
Stiffness
(o) Dimensional stability
·
(p)
Machinability
(q) Formability
·
(r)
Good thermal & electrical conductivity
Fig 1 Metals
7. Metals are further classified as ferrous
and non-ferrous.
(a) Ferrous.
Metals which contain iron and its alloys are called ferrous metals, e.g.
Cast Iron, Pig Iron, Wrought Iron, Mild Steel, High Carbon Steel, Stainless
Steel, Tungsten Steel, etc.
(b) Non-Ferrous. Metals which do not contain iron are called non-ferrous metals, e.g. Aluminium, Magnesium, Titanium, Brass, Copper, Nickel, Chromium, etc. Non-ferrous metals in their pure state are employed to a very limited extent but in alloyed forms are used extensively for manufacturing aircraft structures.
Non- Metals
8. Ceramic
Materials.
Ceramics are
chemical compounds of metallic and non-metallic elements. Ceramic materials
usually consists of oxides, carbides, borides, nitrides, silicates of various
metals, rock or clay mineral materials. (Refer Fig 2, 3 & 4)
9. The
important characteristics of ceramics are:
(a) Brittleness
(b)
Rock like appearance
(c) Hardness (d) Resistance to high temperature
(c) Hardness (d) Resistance to high temperature
(e) Abrasiveness
(f)
Corrosion resistance
(g) Insulation (to
flow of electric current) (h)
Opaque to light
(i)
High temperature strength
Fig 2 Ceramic Material (Brick / Cement / Sand) Fig 3 Porcelain Ceramic Material
10. Examples of Ceramic Materials are: Sand, Brick, Cement / Concrete, Plaster, Glass, Tungsten Carbide, Silicon
Carbide, Abrasives, Refractories etc.
Fig 4 Space Shuttle Heat Shield made of Ceramic Material
11. Organic Materials.
These are polymers, composed of carbon compounds. Polymers are solids composed
of long molecular chains. There are two types of organic materials, natural
(e.g. rubber, wood) and synthetic (e.g. synthetic rubber, plastic, PVC, nylon).
(Refer Fig 5 & 6) The important characteristics of organic materials are:
(a) Light in
weight
(b) Combustible
(c) Soft
(d)
Ductile
(e) Poor
conductors of heat & electricity
(f) Poor
resistance to
temperature
12.
Examples of Organic Materials are: Rubber,
Wood, Textile, Fuels, Plastics, Paper, Lubricants, Paint
and Varnishes, Adhesives, Explosives etc.
Fig 6 Oraganic Materials
13.
Composite Materials.
Composite materials are the most advanced substance for fabrication of aircraft
parts (Refer Fig 7, 8 & 9). The term composite is used to describe two or
more materials that are combined to form a much stronger structure than
individual material by itself. Some examples are as follows:
(a) Glass Fibre
Reinforced Plastics (GFRP)
(b)
Carbon Fibre Reinforced Plastics (CFRP)
Fig 7 Composite Materials
14. Some application of
Composite Materials are:
(a) Internal ribs
of aircraft
(b) Landing gear door
(c)
Spars and fairing block of aircraft
(d) Artificial limbs
(e)
Car / truck body
(f)
Helmet
Fig 8 Aircraft Fin (Composite Material)
Fig 9 Aircraft Composite Structure
Engineering
Requirements of a Material
15.
The main engineering requirements of the materials fall under three categories:
(a) Fabrication
requirements
(b) Service
requirements
(c) Economic
requirements
16.
Fabrication Requirements.
Fabrication requirements mean that material should be able to get shaped (e.g.
cast, forged, formed, machined , etc.) and joined (e.g. welded, brazed) easily.
Fabrication requirements relate themselves with material’s machinability,
ductility, castability, heat treatability, weldability, malleability, etc.
17.
Service Requirements. Service
requirements imply that the materials selected for the purpose must stand up to
service demands, e.g. proper strength, wear resistance, corrosion resistance,
etc.
18.
Economic Requirements.
Economic requirements demand that the engineering part should be made with
minimum overall cost. This may be achieved by proper selection of both
technical and marketing variables.
