Basic Workshop Technology - Engineering Materials

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

(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.