Unit 2for Em New

7/27/2019 Unit 2for Em New

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NOTES FOR MEng 2091 Engineering Materials I

UNIT II (MECHANICAL PROPERTIES)

Occurrence of engineering materials/metals

Materials and metals occur in two forms depending upon their electro

positive characteristics.

Free or native state. A few metals particularly noble metals having least

electro positive characteristics occur in free or in native state are called

free/native metals, for example gold, silver and platinum etc.

On the other hand the metals fond in combine form which have high electro

positive characteristics are called combined metals most of these types of

metals occur in nature in compound state for example iron, copper andaluminum (as a mineral).

Mineral. Mineral is defined as it is a compound of ore and gaunge material is

called mineral.

Ore. It is defined as it is a compound/ mixture of metallic and nonmetallic

elements is called ore, for example ferric oxide(Fe2o3), it posses ferrous as a

metallic element and oxygen as a non metallic element.

Gange. It posses un wanted elements like rocky, dusty and sandy particle

Classification of ores. There are two classes of ores native and combine state.

Types of ores. Basically there are so many types of ores but in practical some

most important types of ores are used for engineering purposes in the

different industries which are given below.

Oxide ores. Those ores which contain some %age of oxygen is called oxide

ores.

Carbonate ores. Those ores which contain carbon in combine is called

carbonate ores.

Sulphide ores. Those which contain sulphur are called sulphide ores.

Silicous ores. Those which posses silicon are called silicous ores.

Phosphoric ores. Those which posses phosphorous in combine form are called

phosphoric ores.

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PREPARED BY Mr. B. Ramesh kumar


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Note. Actually these all oxygen, carbon, silicon etc are very harm full

elements for materials/ metals that is why these impurities should be

removed of and purify the engineering materials/ metals for engineering use.

PROPERTIES OF MATERIALS

MECHANICAL PROPERTIES: Mechanical properties are the most important

requirements of materials from the engineering part of view in selecting them

for design purpose.

Mechanical properties include the action of external forces. A designer

(Engineer) must have a considerable knowledge of materials and their

properties.

Elasticity: It is the property of the material, which enables to regain its

original shape, and size after removal of load is known as elasticity.

For each elastic body a certain limit exists beyond which the material will

hold a remaining deformation.

This limit is called elastic limit.

Plasticity: It is the property of the material, which enables the deformation or

permanent

Deformation,under the load. Or in other words that a material cannot regain its

original position after removal of a load is called plasticity.

Ductility: It is the property of the material which enables it to be drawn out

or elongated to an appreciable extent before repute under the load is called

ductility.

This property is most important of the materials under rolling, forging and

extrusion processes.

Hardness: It is property of the material, which enables to resist easy

abrasion indentation, machining and scratching by harder body is called

hardness.

Brittleness. It is the property of material which break without any

deformation under the load is called brittleness.

Malleability. It is the property of material of getting the desire shape under the

compressive load without any breaking or cracking is called Malleability.

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Strength. It is the capacity or property of material to with stand or

sustained the high load under tension is called strength.

Toughness. It is the ability of a material which absorb the energy/ impact

load without any fracture is called toughness.

Creep. It is the ability of a material which resist the slow and continuous

deformation under steady load and some temperature is called creep.

Fatigue. It is the ability of a material which resist the deformation under

repeated load for large number of cycles is called fatigue.

Wear Resistance: It is the property of material which resist to easy

removal of a solid material by rubbing off the surface is called Wear

Resistance.

PHYSICAL PROPERTIES:

Physical properties are employed to describe a material under conditions in

which external forces are not concerned. In case of metals some important

physical properties are given below.

(i) Luster: the ability of the surface of the material to reflect the light is

known as luster.

All metals when polished have luster (accept lead). This property is greatly

classifying a material is metallic or Non metallic.

For Example: Mild, Steel has some smooth finish with bluish black shine,

and cast iron shows sandy fracture.

(ii) Color: This is the property of a material displaying a particular

appearance in a normal daylight is called color.

For Example: Aluminum has white, when the Cu has yellowish, red and

iron has grayish in color and soon.

(iii) Density: The density is defined as the wt: per unit volume of mat: is

known as its density. Different materials posses different density it is thevery help full property of material that we can justify either the metal is

light or heavy. According to periodic table the density of the element

shows that density increase regularly with increasing the automatic

number.

For Example: Al has 2.7, Cu has 8.7 etc.

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(iv). Melting Point: the temperature at which the solid substances

(Metals) changes into the liquid or molten state is called the melting point.

For Example: Al has 660 0C, Cu has 1083 0C and iron has 1535 0C.

(v). Porosity: A material is said to be porous if it absorb lubricants/liquid

easily is called porosity.

(vi).Thermal expansion: It is the property of material when the material

increases in dimensions on application of heat are called thermal

expansion.

Chemical properties.

Corrosion: It is the property of a material by which it deteriorate by

chemical reaction with its environment is known as corrosion, it degradesmaterial properties and reduces economic value of the material.

Technical properties of materials:

(i). Machine ability: It is the property of the material, which enables it to

be machined easily in the desire shape by cutting tools, is called machine

ability. It signifies how much force and power are required to removes

stock from the material. In another sense machine ability has been used to

signify how well a material takes place a good finish.

Simply it is to say that machine ability is the ease by which metal can be

removed in various machining operations.

(ii) Cast ability: it is the ability of a material which can be cast into to the

desire form/component is known as cast ability.

The metals which cannot be easily machined they can cast easily.

For example cast iron cannot easily machined.

(iii) Weld ability: it is the property of a material which can be easily

welded is called weld ability.

Why are alloys so popular?

Because the addition of alloy provides the mechanical properties needed for

strength, corrosion resistance and ductility

How do Plasticity and Ductility differ?

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Plasticity is the ability to be formed by force; ductility is a measure of how much

the shape can change.

5% or less elongation is considered brittle, greater than 5% is considered ductile.

List some products made with Refractory metals. How are the metals made?

Light bulb filaments, electrodes, gas turbines, crucibles. These metals are pure

elements.

Explain how the AISI numbering system is used in classifying steels.

The first two letters of the 4 digit number are the type of steel and the last two

are the percent of carbon.

Tensile Strength Testing

Tensile is a test in which a prepared sample is pulled until the sample

breaks.

Test Measurements are recorded in PSI (Pounds per Square Inch) E7018 =

70,000 PSI Tensile

Test samples called Tensile Bolts can reveal a welds Tensile strength,

Elastic limit, Yield point, and Ductility.

The Elastic Limitof metal is the stress (load) it can withstand and still return

to the original length after the load is released.

Yield Strength occurs when the test sample stretches however will not return

to its original length.

.

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Izod test Brinell TEST MACHINE

UNIVERSAL TESTING MACHINE

Impact Testing

An Impact tester uses a heavy pendulum that is able to measure the amount

of force required to shear or fracture a test sample taken from welds Heat

Affected Zone (HAZ)

Impact testing may be performed using either the Izod or Charpymethod.

(Both methods are similar)

ACharpy or Izod test measures the welds ability to withstand an Impact

force.

Low Charpy test readings indicate brittle weld metal

Higher Charpy readings indicate the samples toughness.

Hardness testing

Hardness may be defined as the resistance to permanent indentation.

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Three common hardness measuring tests are

Rockwell test

Brinell

The Rockwell testing machine operates somewhat like a press, using a

indenterto penetrate the surface of the test sample.

The depth of the indentation determines the materials hardness on a scale of

0-100

Rockwell test Machine

.

The Brinell method presses the indenter into a sample for a given period of

time.

The ability for the sample to resist indentation determines hardness.

After the indenter is used a powerful microscope is used to determine the the

amount of indentation into the components surface.

Chemical analysis is used in metallurgical laboratories to determine the

metals grain and crystalline structures.

Samples are then place under a high power microscope to view the results.

This is referred to as Metalography

Pressure testing or leak testing can be performed with either gasses or

liquids.

When this pressure exceeds the limitations of the structures design it will

rupture under force.

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This rupture will allow engineers to understand the welds weakest areas.

TENSION TEST ON MILD STEEL

AIM:

To conduct tension test on the given mild steel rod for determining the yield stress, ultimate stress,

breaking stress, percentage of reduction in area, percentage of elongation over a gauge length and youngs

modulus.

APPARATUS REQUIRED:

1. Venire caliper.

2. Scale.

THEORY:

The tensile test is most applied one, of all mechanical tests. In this test ends of test piece and fixed into

grips connected to a straining device and to a load measuring device. If the applied load is small enough,

the deformation of any solid body is entirely elastic. An entirely deformed solid will return to its original

form as soon as load is removed. However, if the load is too large, the material can be deformed

permanently. The initial part of the tension curve, which is recoverable immediately after unloading ,is

termed as elastic and the rest of the curve, which represents the manner in solid undergoes plastic

deformation is termed as plastic. The stress below which the deformation is essentially entirely elastic is

known as the yield strength of material. In some materials the onset of plastic deformation is denoted by a

sudden drop in load indication both an upper and a lower yield point. However, some materials do not

exhibit a sharp yield point. During plastic deformation, at larger extensions strain hardening cannot

compensate for the decrease in section and thus the load passes through the maximum and then begins to

decrease. At this stage the ultimate strengths, which is defined as the ratio of the load on the specimen

to the original cross sectional are, reaches the maximum value. Further loading will eventually cause neck

formation and rupture.

Usually a tension testis conducted at room temperature and the tensile load is applied slowly. During this

test either round of flat specimens may be used. The round specimens may have smooth, shouldered or

threaded ends. The load on the specimen is applied mechanically or hydraulically depending on the type

of testing machine

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GRAPH : Draw a graph between Elongations (X-axis) and load (Y-axis).

PROCEDURE:

1. Measure the diameter of the rod using Vernier caliper.

2. Measure the original length of the rod.

3. Select the proper jaw inserts and complete the upper and lower chuck assemblies.

4. Apply some graphite grease to the tapered surface of the grip surface for the smooth motion.

5. Operate the upper cross head grip operation handle and grip fully the upper end of the test piece.

6. The left valve in UTM is kept in fully closed position and the right valve in normal open position.

7. Open the right valve and close it after the lower table is slightly lifted.

8. Adjust the load to zero by using large push button (This is necessary to remove the dead

weight of the lower table, upper cross head and other connecting parts of the load).

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9. Operate the lower grip operation handle and lift the lower cross head up and grip fully the

lower part of the specimen. Then lock the jaws in this position by operating the jaw locking

handle.

10. Turn the right control valve slowly to open position (anticlockwise) until we get a desired

loadings rate.

11. After that we will find that the specimen is under load and then unclamp the locking handle.

12. Now the jaws will not slide down due to their own weight. Then go on increasing the load.

13. At a particular stage there will be a pause in the increase of load. The load at this point is

noted as yield point load.

14. Apply the load continuously, when the load reaches the maximum value. This is noted as

ultimate load.

15. Note down the load when the test piece breaks, the load is said to be a breaking load.

16. When the test piece is broken close the right control valve, take out the broken

Pieces of the test piece. Then taper the left control valve to take the piston down.

ROCK WELL HARDNESS TEST

AIM:

To determine the Rockwell hardness number of the given specimen.

APPARATUS REQUIRED:

1. Emery paper

2. Penetrator

THOERY:

In Rock well hardness test consists in touching an indenter of standard cone or ball into the

surface of a test piece in two operations and measuring the permanent increase of depth of

indentation of this indenter under specified condition. From it Rockwell hardness is deduced.

The ball (B) is used for soft materials (e.g. mild steel, cast iron, Aluminum, brass. Etc.) And the

cone (C) for hard ones (High carbon steel. etc.)

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HRB means Rockwell hardness measured on B scale

HRC means Rock well hardness measured on C scale

PROCEDURE:

1. Clean the surface of the specimen with an emery sheet.

2. Place the specimen on the testing platform.

3. Raise the platform until the longer needle comes to rest

4. Release the load.

5. Apply the load and maintain until the longer needle comes to rest

6. After releasing the load, note down the dial reading.

7. The dial reading gives the Rockwell hardness number of the specimen.

8. Repeat the same procedure three times with specimen.

9. Find the average. This gives the Rockwell hardness number of the given specime

ROCK WELL HARDNESS TEST Machine

BRINELL HARDNESS TEST

AIM:

To find the Brinell Hardness number for the given metal specimen.

EQUIPMENTS REQUIRED:

1. Brinell Hardness Testing Machine

2. Metal Specimens

3. Brinell Microscope.

FORMULAE:

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Brinell Hardness Number (BHN) = 2P / {D [D - (D 2 d 2)]}

Where,

P = Load applied in Kgf.

D = Diameter of the indenter in mm.

d = Diameter of the indentation in mm.

DESCRIPTION:

It consists of pressing a hardened steel ball into a test specimen. In this usually a steel ball of

Diameter D under a load P is forced in to the test piece and the mean diameter d of the

indentation left in the surface after removal of load is measured. According to ASTM

specifications a 10 mm diameter ball is used for the purpose. Lower loads are used for measuring

hardness of soft materials and vice versa. The Brinell hardness is obtained by dividing the test

load P by curved surface area of indentation. This curved surface is assumed to be portion of

the sphere of diameter D.

TEST REQUIREMENTS:

1. Usual ball size is 10 mm + 0.0045 mm. Some times 5 mm steel ball is also used. It shall be

hardened and tempered with a hardness of at least 850 VPN. (Vickers Pyramid Number). It shall

be polished and free from surface defects.

2. Specimen should be smooth and free from oxide film. Thickness of the piece to be tested shall

not be less than 8 times from the depth of indentation.

3. Diameter of the indentation will be measured n two directions normal to each other with an

accuracy of + 0.25% of diameter of ball under microscope provided with cross tables and

calibrated measuring screws.

PRECAUTIONS:

1. Brinell test should be performed on smooth, flat specimens from which dirt and scale havebeen cleaned.

2. The test should not be made on specimens so thin that the impression shows through the

metal, nor should impressions be made too close to the edge of the specimen.

PROCEDURE:

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1. Specimen is placed on the anvil. The hand wheel is rotated so that the specimen along with the

anvil moves up and contact with the ball.

2. The desired load is applied mechanically (by gear driven screw) and the ball presses into thespecimen.

3. The diameter of the indentation made in the specimen by the pressed ball is measured by the

use of a micrometer microscope, having transparent engraved scale in the field of view.

4. The indentation diameter is measured at two places at right angles to each other, and the

average of two readings is taken.

5. The Brinell Hardness Number(BHN) which is the pressure per unit surface area of the

indentation is noted down.

RESULT:

Thus the Brinell hardness of the Given Specimen is

1. Mild Steel = ---------- BHN

2. EN 8 = ---------- BHN

3. EN 20 = ---------- BHN

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