Chap No.:-1Introduction to Engineering Materials

By H . F. AdmarLecturer –Mechanical Engineering

Material

Material Everything than can be seen, touched or used.

Engineering Material Solid material or stuff out of which product can be made which is

useful in engineering profession.

Material Science It is the branch of applied science which deals with engineering

material and investigate the relation ship between structure of material and their properties for practical usefulness.

Classification Of Engineering Material Metals

A) FerrousB) Non-Ferrous

Ceramics

Organics

Need Of Material Science knowledge

Constant challenge of ever increasing demand of material with good characteristics.

Requirement due to new application.

Challenge of decreasing production cost to stay ahead in market.

Properties of Engineering Material

Material PropertyQualitative or Quantative measure or response of material

to externally imposed condition like force and temperature.

Types of Properties Physical---------- Chemical----------- Mechanical--------- Electrical------------ Thermal------------- Magnetic------------ Optical--------------- Technological-------

Properties of Engineering MaterialMaterial Property

Qualitative or Quantative measure or response of material to externally imposed condition like force and temperature.

Types of Properties Physical---------- - Dimension, density, porosity Chemical----------- Composition, corrosion resistance etc. Mechanical---------Elasticity, tensile strength, hardness, toughness

etc. Electrical------------Resistivity, superconductivity etc. Thermal------------- Heat capacity, thermal conductivity etc. Magnetic------------ Permeability, hysteresis Optical---------------Refractive index, Reflectivity, Absoptivity Technological------- Cast ability, Weldbility, solder ability etc

Definition of Metal PropertyPorosity It is the ratio of total pore volume divided by Bulk Volume.

Porosity = Total Pore Volume/ Bulk Volume

CompositionPercentage of various elements which make up metals and

alloys.

StructureIt refers to the microstructure of a material.

Contd.Corrosion ResistanceIt is the deterioration of material by chemical reaction with

its environment.

Stress It is internal resistance set up in a material to deformation

due to externally applied force.

Stress = Load/AreaUnit = ?

ElasticityIt is the ability of material to regain its original shape and

size after removal of load.

PlasticityIt is the ability of material to be permanently deformed

without fracture even after removal of external load.

StrengthIt is the ability of material to withstand stress without

fracture called as strength.

Material has to withstand different types of load i.e. tensile, compressive, shear etc.

StiffnessThe property of material which enables it to resist the elastic

deformation

Material which undergo less deformation has high degree of stiffness.

Ex. Steel beam and aluminum beam.

DuctilityIt is the property of material to undergo deformation under

application of tensile load without fracture.

It is measured in terms of Percentage Elongation/ Percentage reduction of area.

% Elongation = Lf-Lo/Lo * 100 Where Lf = Final Length

Lo= Initial Length

Defination.Malleability It is the capability of material to withstand deformation under

compression without rupture.

Gold is most malleable material.

Brittleness The property of material by virtue of which it will fracture

without appreciable deformation.

It is exactly opposite to ductile.

Material with 5 % elongation are considered to brittle.

Ex. Cast Iron, Concrete, Glass

Hardness It is the ability of material to withstand scratching, wear,

abrasion or indention by harder bodies is known as hardness.

Measured by Penetration Method.

Brinell, Rockwell and Vickers hardness test.

Toughness It is the amount of energy material can absorb before it

fractures.

This property indicate material strength when sudden load is applied.

ResilienceIt is the capacity of material to absorb/store energy and to

resist shock and impact. When stress is applied to body, how much energy it can

store will indicate its resilience capability.

Important for making spring.

Fatigue The failure of material under application of repeated load

or stress is known as fatigue.

Ex. Leaf spring used in automobile, Piston road in IC Engine, Pump and compressor.

CreepSlow and Progressive deformation of a material with time due

to constant stress is known as Creep.

Material subjected to high temperature and constant tensile stress will undergo such deformation.

Ex. Parts of IC Engine.

Electrical PropertyResistivityIt is the property which enable material to impedes or resist

flow of electricity through it.ρ = R.A/l

Where ρ = Resistivity ( in Ohm-cm)R = Resistance in Ω

A = C/s of the conductor in cm2

l = Length of the conductor in cm

Ex. Important property as Long distance transmission line require low resistive material.

ConductivityIt is the reciprocal of resistivity.

α = 1/ρ This property gives idea how easily material allow

electrical current to flow through it.

Ex. Rubber & Steel. Compare ?

Di-electric strength (Breakdown voltage)

It is the property which indicate capability of material to store electrical energy.

OR

Dielectric strength will also indicate minimum voltage which will result in destruction of insulating property

Every electrical apparatus is designed to operate between certain range of voltage beyond which it fails and storage property disappear.

Semi ConductivityConductivity between that of conductor and insulators is

called as semi conductivity.

Material which is semi conductor is neither a conductor nor a insulator.

Ex. Silicon, Germanium, Galena

Super ConductivityMaterial which exhibit zero resistivity and undetectable

magnetic permeability when cooled below absolute zero temperature ( -273* C) is known as super conductive material.

Best material for long distance power transmission line.

Thermal PropertyHeat CapacityIt is the property that indicate material’s ability to absorb

heat from external surroundings.

orIt is amount of energy required to produce a nit temperature

rise.

Mathematically,Heat Capacity C = dQ/ dT

Specific HeatIt is the amount of energy require to raise the temperature of

unit mass by unit degree.

Q= m *Cp *dT or m* Cv*dT

Where Cp = Specific Heat at Const. Pressure

Cv = Specific Heat at Const. Volume

Thermal ConductivityIt is the amount of heat conducted per unit time per unit c/s

area in the direction conduction when temperature gradient across the heat conducting element is one unit.

Unit of conductivity is ?

Thermal ExpansionExpansion of material under application of

thermal energy.

Co-efficient of thermal Expansion Amount of expansion in unit length of a solid material as a

result of a temperature rise of one degree.

Magnetic PropertiesPermeabilityIt is the ratio of magnetic flux and magnetic field strength.

µ = B/H Where B= Magnetic Flux

H= Magnetic field strength

HysteresisLag in the changes of magnetization behind variation of the

magnetic field.

For the same value of input during increasing and decreasing trend, there will be difference in the output value known as Hysteresis loop.

Optical PropertyReflective IndexIt is the ratio of velocity of light in vaccum to the velocity of

light within material Vm.

n = Vv/Vm

orIt is the ratio of sine of the angle of incidence I and sine of

the angle of refraction r.

n = sin t/sin r

Absoptivity Total energy fall on material , partially transmitted,

reflected and absorbed.T+R+A = 1

where T = Energy Transmitted R= Energy Reflected A= Energy Absorbed.

Technological PropertiesCast abilityIt is the ease with which the material can be given various

solid shapes from liquid state.

Factor which effect the cast ability are solidification rate, shrinkage, segregation, gas porosity, hot strength etc.

Machine abilityIt is defined as the ease with which a given material can be

cut or removed by cutting tools in machining operation with satisfactory finish at lowest cost.