MECHANICS OF MATERIALS

(AE-106)

LECTURE: 01

Engr. Abdullah Khan

Visiting Lecturer,

Department of Agricultural Engineering.

CLASS INFORMATION

• COURSE NAME AND CODE: MECHANICS OF MATERIALS (AE-106)

• CREDIT HOURS: 2

• INSTRUCTOR: ENGR. ABDULLAH KHAN,

DEPARTMENT OF AGRICULTURAL ENGINEERING.

• CONTACT NO.: 0315-9608632

• EMAIL: abdullahkhansaddiqui48@gmail.com

• ADDRESS: STATION KOROONA POST OFFICE SARDHERI TEHSIL AND DISTRICT CHARSADDA.

• GRADING CRITERIA: MID TERM = 30%

FINAL TERM = 40%

ASSIGNMENTS = 05%

QUIZZES = 10%

ATTENDANCE = 15%

COURSE CONTENT

1. Introduction, types of stresses and strains, elastic limit, modulus of elasticity, yield point.

2. Factor of safety, mechanical properties of materials, stresses due to change of temperature.

3. Poisson’s ratio, elastic constant: young’s modulus, shear modulus, bulk modulus, and relation between elastic

constants.

4. Methods for the determination of stresses on oblique sections.

5. Use of Mohr’s circle to stress problems.

6. Bending moments and shear forces in beams for cantilever beam.

7. Bending moments and shear forces in beams for simply supported beam and over hanging beam.

8. Bending stresses in beams, theory of simple bending, derivation of flexure formula.

Mid Term

COURSE CONTENT

9. Center of gravity, moment of inertia, and radius of gyration.

10. Section modulus

11. Deflection of beams; area moment method and mohr’s theorem.

12. Castigliano’s theorem.

13. Failure theories

14. Stresses in thin cylinders and spherical shells.

15. Stresses in composite bars and riveted joints.

16. Torsion theory for shafts of circular section, power transmitted by shaft, torsion combined with bending.

17. Open and closely coiled helical springs subjected to axial loading .

Final term

RECOMMENDED STUDY SOURCES

1. Dr. R.K. Bansal (2009). A text book of Strength of Materials. Fourth edition.

Laxmi Publication Private Ltd, New Delhi.

2. Strength of Material by Professional Staff of Benette College.

3. Shigley, J.E. and C. R. Mischhe, (2000). Mechanical engineering Design. Tenth edition. McGraw Hill

publications Inc. USA.

4. Muvdi, B.B. And W. McNabb. (1984). Engineering Mechanics of Materials. McMillan Publishing CO., New

York.

5. Provided lecture notes.

LEARNING OBJECTIVES

To equip the students with

1. The basic understanding of

• Force vectors and their operations, force equilibrium,

• Stresses and strains of a body when the body is subjected to external loads.

2. Provide essential technical basis for the

• Analysis and

• Design of agricultural machinery and civil structures.

LEARNING OUTCOMES

Upon the completion of the course, the student should be able

1. To use vectors to represent the force acting on a system and correctly plot free body diagram and check the

equilibrium of a rigid body

2. Know the types of internal loadings, the relationships between stress and strain and the basic mechanical

properties of materials

3. Compute the stress of a beam section due to tension, compression, torsion, bending, shear and combined loading

4. Transform stress (strain) components from one orientation to another learn the concepts for the design of beams

WHAT IS MECHANICS OF MATERIALS?

• Three fundamentals areas of engineering mechanics are

1. Statistics

2. Dynamics

3. Strength of Materials.

Study of the external effects of forces on rigid bodies,

that is, bodies for which the change in shape

(deformation) can be neglected.

In contrast, Strength of Materials deals with the relation

between externally applied loads and their internal

effects on bodies.

The bodies are no longer assumed to the rigid: the

deformations, however small, are of major interest.

PROPERTIES OF MATERIALS

Different materials possess different properties

in varying degree and therefore behave in

different ways under given conditions.

Th

ese

pro

per

ties

incl

ud

e

Mechanical

Electrical

Thermal

Chemical

Magnetic

Physical

A design engineer is interested in

the behavior of materials under load

which is mechanical in nature, for

the design of machines & structures.

Any material subjected to a load either deforms, yield,

or break, depending upon the magnitude of the load.

We are basically interested in knowing as to how

a particular material will behave under applied

load i.e. In knowing the mechanical properties.

WHY TO STUDY TO MECHANICAL PROPERTIES OF MATERIALS?

An elementary knowledge of the properties of the various

materials enables the designer to decide which particular

material is the best to use for any particular purpose.

An elementary knowledge of the principal processes

by which iron and steel are produced is also essential

to every engineer,

As in specifications of engineering designs and

structures it is frequently stated by which particular

process the material to be employed is to be made.

Certain terms relating to the properties of

materials are constantly being used by

engineers.

The exact meaning of these terms must

therefore be explained at this stage.

1. Tenacity / Strength

It is the resistance offered by a material

when subjected to external loading.

So, stronger the material the greater

the load it can withstand.

Depending upon the type of load applied the

strength can be

Tensile Compressive Shear Torsion

2. Hardness

It is the ability of a material to resist

scratching, abrasion, indentation.

Thus machine cutting tools are

made hard

To prevent them from being

blunted

By contact with the materials

they are intended to cut.

Softness is the converse of Hardness.

3. Brittleness

The property of material to break readily without

much permanent distortion, subjected to shocks.

Usually the tensile strength of brittle materials is

only a fraction of their compressive strength.

Therefore, a non-ductile material is said to be

a brittle material.

Brittle

Material

Should not be considered as lacking strength.

It only shows the lack of plasticity.

Do not have Yield Point on Stress-Strain Diagram + Low Value of E

Glass Cast IronExamples

4. Ductility

The property possessed by certain bodies that they

may be drawn out in the direction of their length.

The elongations are permanent.

It enables the material to draw out into

thin wire on application of the load.

Possess the properties both of

tenacity and softness.

The ductility decreases with

increase of temperature.

Mild steel, gold, silver,

copper, aluminum, etc.

Examples

5. Malleability

Malleability of a material is its ability to be flattened

into thin sheets without cracking by hot or cold

working.

A body is said to be malleable when it can be beaten out

and extended in all directions.

Ductility is a tensile property, whereas malleability is a

compressive property

Malleability

increases with

increase of

temperature.

Aluminum, copper, tin, lead,

steel, etc. are malleable

metals.

6. Welding Power

Separate pieces of certain metals, when heated to a

high temperature, may be joined together by

hammering so as to form one piece. Such metals are

said to be weld able.

7. Elasticity

Elasticity of a material is its power of coming back to its

original position after deformation when the stress or

load is removed.

Elasticity is a

tensile

property.

The greatest stress that a material

can endure without taking up

some permanent set is called

elastic limit.

8. Stiffness (Rigidity)

The resistance of a material to deflection is called stiffness

or rigidity.

Stiffness is measured by young’s modulus E.

The higher the value of the young’s

modulus, the stiffer the material.

9. Plasticity

The plasticity of a material is its ability to undergo some

degree of permanent deformation without failure.

Due to this properties various metal can be transformed

into different products of required shape and size.

Plasticity is an important property and widely used in

several mechanical processes like forming, shaping,

extruding and many other hot and cold working processes.

In general,

plasticity increases

with increasing

temperature

This conversion into

desired shape and size

is effected either by the

application of pressure,

heat or both.

10. Toughness 11. Hardenability

The toughness of a material is its ability to withstand

both plastic and elastic deformations.

Toughness is a measure of the amount of energy a material

can absorb before actual fracture or failure takes place.

“The work or energy a material

absorbs is called modulus of

toughness”.

For e.g., If a load is suddenly

applied to a piece of mild steel

and then to a piece of glass the

mild steel will absorb much more

energy before failure occurs.

Thus, mild steel is said to be

much tougher than a glass.

wrought iron, mild

steels

It is a highly desirable

quality for structural

and machine parts to

withstand shock and

vibration.

Hardenability is the degree of hardness that can be

imparted to metal by process of hardening.

The material is heated above a certain temperature and then

suddenly quenched in a cold oil or water bath.

Hardness

does not directly relate to

the hardenability.

Hardenability is indicative of the degree of hardness that

the metal can acquire through the hardening process. i.e.,

Heating or quenching.

12. Impact Strength 13. Resilience

It can be defined as the resistance of the material to

fracture under impact loading.

i.e., Under quickly applied dynamic loads.

Two standard

tests are normally

used to determine

this property.

The IZOD

impact test.

The

CHARPY

test.

Resilience is the capacity of material to absorb

energy elastically.

On removal of the load, the energy stored is released as in

a spring.

The quantity gives capacity

of the material to bear

shocks and vibrations.

The maximum energy

which can be stored in a

body up to elastic limit

is called the proof

resilience.