lab manual- engg mtls

8/3/2019 Lab Manual- Engg Mtls

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MIME 2204 ENGINEERING MATERIALS

LAB MANUAL


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Engineering Materials Lab Manual MIME2204

SALALAH COLLEGE OF TECHNOLOGY

SALALAH

AXIAL TENSION TEST TO OBTAIN STRESS - STRAINCURVE AND THE STRENGTH

AIM

To conduct a tensile test on a mild steel specimen and determine the following:

1. Limit of proportionality

2. Elastic limit

3. Tensile yield strength

4. Ultimate tensile strength

5. Youngs modulus of elasticity

6. Percentage of elongation7. Percentage of reduction in area

EQUIPMENT

Universal testing machine, extensometer, meter scale, vernier, caliper and files.

THEORY

The tensile test is most applied one, of all mechanical tests. In this test ends of testpiece and fixed into grips connected to a straining device and to a load measuring device. Ifthe applied load is small enough, the deformation of any solid body is entirely elastic. Anentirely 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 thetension curve, which is recoverable immediately after unloading ,is termed as elastic and therest of the curve, which represents the manner in solid undergoes plastic deformation istermed as plastic. The stress below which the deformation is essentially entirely elastic isknown as the yield strength of material. In some materials the onset of plastic deformation isdenoted 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

Mechanical Section 2 Engineering Department


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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 ultimatestrengths, which is defined as the ratio of the load on the specimen to the original crosssectional are, reaches the maximum value. Further loading will eventually cause nick

formation and rupture. Usually a tension testis conducted at room temperature and the tensileload is applied slowly. During this test either round of flat specimens may be used. The roundspecimens may have smooth, shouldered or threaded ends. The load on the specimen isapplied mechanically or hydraulically depending on the type of testing machine.PROCEDURE

1. The diameter of the rod is measured using vernier calipers at least at places and the

average is taken.

2. The gauge length is calculated and marked on the specimen

3. The specimen is gripped between the top and middle crosshead of the machine tightlyand the length of the rod between the grips is measured

4. Extensometer is clamped on the specimen.

5. Initial reading of the extensometer is noted.

6. Adjust the machine for a suitable range.

7. Load is gradually increased at convenient multiples and corresponding extensometer

readings are noted. When the elastic limit is reached the extensometer is removed.

8. The yield load, ultimate load and breaking loads are noted down.9. As soon as the rod fails, release the load.

10. Fit the broken places together and measure the distance between the gauge length

11. Measure the average diameter of the rod at broken end

OBSERVATION

1. Material

2. Original dimensions

Length = Diameter =

Area = d2

4

3. Final dimensions

Length = Diameter =

Area = d

2

4



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TABULATION

Diameter of specimen L.C. =

Sl.No M.S.R V.S.C V.S.R = V.S.C X L.C Corrected reading = M.S.R + V.S.R

Unit mm div mm mm

Stress Vs Strain Reading

Sl No Load (P) Deformation () Stress () Strain (e) Youngs modulus (E)

Unit kN mm kN/mm2 No unit N/mm2



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CALCULATION

Load at limit of proportionality(i) Limit of proportionality =

Original area of cross section



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Load at elastic limit(ii) Elastic limit =


Yield load(iii) Yield strength =


Maximum tensile load(iv) Ultimate strength =


Stress below the proportionality limit

(v) Youngs modulus E = Corresponding strain



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Final length (at fracture) - Original length(vi) Percentage of elongation =

Original length

Original area - Area at fracture(vii) Percentage reduction in area =

Original Area

GRAPH

Plot the stress - strain curve with strain on X- axis and strain on Y- axis

RESULT

(i) Limit of proportionality =

(ii) Elastic limit =

(iii)Yield strength =(iv)Ultimate strength =

(v) Youngs modulus =

(vi)Percentage of elongation =

(vii) Percentage reduction in area =



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ROCKWELL HARDNESS TEST

AIM

To determine the Rockwell hardness number for hard and very hard materials.

MATERIAL AND EQUIPMENT

Rockwell hardness testing machine, Specimen

THEORY

This test is used for finding the hardness of hard and very hard materials. For

hard materials like mild steel, Brass and Aluminium the indenter used is hard steel

ball indenter. The diameter of the ball in ball indenter is 1/16. The load applied for

these materials is 100kg and the time of application is 5 to 6 seconds. For very hard

materials like hardened steel and tool steel, diamond cone indenter is used. The apex

angle in cone indenter is 120. The cone is made of industrial diamond. The load to be

applied is 150 kg and the time of application is 6 to 8 seconds.

PROCEDURE

1. To be tested with 0.0. Emery paper

2. Place the Specimen on the anvil of Polish the specimen the machine

3. Depending on the material of the specimen, select the indent and the corresponding

load

4. Rotate the avail and raise the worktable till the specimen is brought to contact and

mark the set position

5. Apply the load for the specified time after the pointer



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6. Release the load, in the dial comes to rest and the Rockwell hardness number can

be directly read from the dial

7. Repeat the procedure to obtain two more sets of readings for each specimen

8. Take the average of three readings which gives the Rockwell hardness number

OBSERVATION

(i) Thin steel - load 60 kgf , Diamond indenter

(ii) Deep case hardened steel - load 150 kgf , Diamond indenter(iii) Malleable iron - load 150 kgf , 1 / 16 inch ball indenter

TABULATION

Sl

No

Material Load applied Type of

indent

ScaleRockwellHardness

Number

Average

RHN

Unit (Kg)

RESULT

Rockwell Hardness number



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(i) Steel

(ii) Brass

(iii) Aluminium

BRINELL HARDNESS TEST

AIM

To find the surface hardness of the given specimen using Brinell hardness tester

EQUIPMENT

Brinell hardness testing machine, ball indenter, Brinell- Microscope

THEORY

The thickness of the test specimen shall not be less then a times the depth of the

indentation h Depth of indentation h=P / D x H B. Where P is applied in kg D =

diameter of ball in mm. Edge distance = 2.3 times diameter of indentation. Distance

between the centers of two adjacent indentations = 4-6 times diameter of indentation

Test Load = 30 D2 - 15 D2

PROCEDURE

1. Polish the specimen with 0.0 emery paper

2. Place the Specimen on the anvil of the machine

3. Depending on the specimen material and the diameter of the ball indenter, select

the proper load; Select a load of 3000kgf and a steel ball indenter of 10mm

diameter for hard material like steel .Select a load 1500kgf and a steel ball

indenter of 10mm diameter for soft material (Aluminium & brass). Duration of

loading is 10 seconds for hard material and 30 seconds for oft materials

4. Insert the ball indenter in the holder



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5. Rotate the anvil and bring the specimen in contact with the indenter

6. Apply the load for the specified time

7. Release the load and remove the specimen form the anvil

8. Measure the diameter of the impression made by the indenter using Brinell

microscope

9. Repeat the same procedure and take two more readings for each specimen

FORMULA

BHN = ____________P_______________

D/2 (D- (D2-d2)

Applied load (in kg)

___________________________Surface area of indentation (inmm2)

Surface area of indentation = D/2 (D- (D2-d2)

Where D = Diameter of ball used in mmd = diameter of indentation in mmP = load in kg

TABULATION

Material of

the

specimen

Diameter of the

indentation (d)

Average

diameter (d)

Applied

Load (P)

Mean hardness

mm mm kg

Aluminium

123

Brass123

Steel123



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RESULT

Brinells Hardness number

1. Steel =2. Brass =3. Aluminium =

VICKERS HARDNESS TEST

AIM

To determine the Vickerss hardness number for the given specimen

EQUIPMENT

Vickers hardness testing machine, Diamond paint penetration

THEORY

The hardness-testing machine has a c shaped body. The lower part carries a

hand wheel, which is held in a thrust bearing. A spindle is screwed in the centre hole of

the hand wheel. The spindle is adjustable. The turret to which of the thrust piece and the

vertical illuminant of the projection as fastened is arranged above the table. The thrust

piece holds the penetration and the objective, is held in the vertical illuminant the

objective is exchangeable.

The eyepiece and the prison of the projection are screwed in the top of the

plunger. The hangers are fastened to the lever, with a fork. They consist of a rod with

the plate and the weights.

PROCEDURE

1. Polish the surface of the specimen.

2. Place the specimen on the supporting table.



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3. Inset the penetration and Vickers diamond pyramid applicable to the test and the

derived load stage in the thrust piece.

4. Adjust the required load stage by actuating the corresponding push button.

5. The lamp for the projecting device lights up.

6. Insert the standard hardness test specimen. Turn the hand wheel clockwise until the

surface of the specimen is sharply displayed on the focusing screen of the measuring

equipment.

7. Actuate the push button and do not release until the hand lower most upward. Then

releases the push button waits the hand lever stops loading time in 30 sec.

8. When the period of force action is over, push the hand lever until the stop device

engages.

9. Now the impression can be measure using the measuring device.

10. Turn the measuring equipment so that the diagonal of the Vickers impression

is parallel with the continues cross line of the scale of the measuring equipment.

11. As the magnification is 140 fold, the mean diagonal in mm will be, measure

diagonal in mm divided by 2.

12. The Vickers hardness number can be found out using the table.

RESULT

The Vickers hardness of the given specimen is = ------------------



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MECHANICAL PROPERTIES FOR

UNHARDENED OR HARDENED SPECIMEN

AIMTo find hardness number and impact strength for unhardened, hardened

specimen or Quenched and tempered specimen and compare mechanical properties.

MATERIAL AND EQUIPMENT

Unhardened specimen, Hardened or Quenched and tempered specimen, muffle

furnace, Rockwell testing machine, impact testing machine.

PROCEDURE

Case (i) - Unhardened specimen

Choose the indenter and load for given material.

Hold the indenter in indenter holder rigidly

Place the specimen on the anvil and raise the elevating screw by rotating the

hand wheel upto the initial load of 10 kgf (i.e. short hand and long hand showed

read 3

Apply the major load gradually by pushing the lever and then release it as

before.

Note down the readings in the dial for corresponding scale.

Take min 5 readings for each material.

Case (ii) - For unhardened specimen

Keep the specimen in muffle furnace at temperature of 700 to 850 for 2 hours

The specimen is taken from muffle furnace and quenched in water or oil

Then above procedure is followed to test hardness



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Case (iii) - For Tempered specimen

Keep the specimen in muffle furnace at temperature of 650 for 2 hours

Allow the specimen for air cooling after taking from muffle furnace

Then same procedure is followed foe the specimen

OBSERVATION

Cases for hardness =

Cross sectional area =


SI.No Material SelectedTemperature

(C)

SelectedLoad

(N)

Indenterdetail

Scale RHN

Trial1

Trail2

Trail3

Mean

1 Deep case

Hardened steel

2. Deep case

Hardened steel

3. Mild steel

4. Mild steel


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CHARPY TEST

SI.No Material and Condition Energyabsorbed

Cross-sectional areabelow the notch

Impact strength

Unit Jouls mm2 J/ mm2

1. Mild steel-unhardened

2. Quenched

RESULT

1. Hardness in

(i) Deep case hardened steel(a) Unhardened

(b) Quenched

(ii) Mild steel

(a) Unhardened(b) Quenched

2. Impact strength in(i) Deep case hardened steel(a) Unhardened(b) Quenched



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Specimen Preparation and Microscopic Examination

Objectives:

1. Familiarization with the procedure for preparation of a material specimen for microscopic

examination.2. Familiarization with compound optical microscopes and metallography.3. Examination of surface characteristics of engineering materials.4. Grain size determination of metals.

Background:

The preparation of a metallurgical specimen generally can be divided into a series of stages:Sectioning, Mounting, Grinding and Polishing, and Etching.

Sectioning

Sectioning is the removal of a small representative volume of material from the parent piece.The microstructure of the material must not be altered in the process. Cold work and heat arethe two most likely conditions that can quickly bring about structure changes. Quiteobviously operations such as sawing that generates heat or shearing that introduces cold workare not preferable for sectioning. Cutting using a bonded abrasive wheel with coolant offersthe best solution to minimize or eliminate heat and deformation.

Mounting

Metallurgical specimens are mounted primarily for (1) convenience in handling and (2) protection and preservation during subsequent grinding and polishing. Two methods arefrequently used: compression mounting and cold mounting. Compression mounting is done

by mounting the specimen in a cylinder of hard polymer under pressure and elevatedtemperature in a molding machine (Figure 1). The method is often preferred when speed anda relatively hard mounting is required. For metallurgical examination, specimens are usuallymolded in cylinders 1, 11/4, or 11/2 inches in diameter. Compression molding materials are

(1) thermosetting or (2) thermoplastic polymers. Bakelite and diallyl phthalate fall into thefirst category while transoptic material into the second. By definition, thermosetting materialsrequire heat and pressure during the molding cycle, and therefore may be ejected at highmolding temperature. Transoptic materials remain molten at high temperature and becometransparent with increasing pressure and decreasing temperature. Molding pressure,temperature, and time duration are the major variables involved in compression mounting. Byequipment design, temperature may be held constant leaving pressure and time duration asvariables. Cold mounting is done by placing the specimen at the center of a metal or Pyrexring on a glass plate and pouring liquid mounting material into the ring to cover thespecimen. Allow the mounting material to cure at room temperature for 60 to 90 minutes

before removing the ring. The method offers particular advantages when a specimen is too



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delicate to withstand the pressure and heat involved in compression molding. With coldmounting, large groups of specimens may be easily prepared in a short time.Common types of cold mounting material include (1) epoxides (2) polyesters and (3) acrylics.These materials are two-component types consisting of a resin and a hardener. Since the

curing process (polymerization) is an exothermic reaction the mixing by volume or weightratios of each type is critical.

Grinding and Polish

Grinding and polish are accomplished by sequential coarse grinding, medium grinding, andrough and final polishing. The specimen should be carefully rinsed before proceeding fromone operation to the next. Coarse grinding is done on a wet-belt grinder with 120 and 240 grit

belts. The purpose of coarse grinding is to obtain a flat surface free from previous cutting toolmarks. Medium grinding is accomplished using successively finer grits of metallographic

grinding paper. The paper is supported on a hard, flat surface such as glass or steel. Thespecimen is moved along the length of grinding paper without rotation or a rocking motion.When grinding is completed on one grit the scratches should all run in the same direction.Before proceeding to the next finer grit the specimen should be washed to avoid brining large

particles to the finer grit. The specimen is rotated 90 degrees between grits so that scratchesfrom each successively finer grit run at right angles to those from the previous one. The

polishing on grit is complete when coarser scratches from previous grit have been totallyremoved.

Rough and final polishing is accomplished on cloth-covered wheels charged with fineabrasive alumina particles suspended in water. Nylon cloth and 1.0-mm alumina particle sizeare used for the rough polish; a velvet cloth and 0.05-mm particle size for the final polish. Afew drops of water are added to the rotating wheel to improve polishing action andcleanliness. Initially the specimen is held at one position on the wheel, without rotation, untilmost of the previous grinding marks are removed. The specimen can then be rotated slowly,counter to the wheel rotation, until only scratches from the alumina are visible. The final

polish should be completed at a slow speed on a different polishing wheel.

Etching

The specimen surface is fairly smooth immediately after the final polish. A smooth surfacedeflects lights from the illuminator in the metallurgical microscope along the same directionshowing no contrast and cannot reveal surface characteristics. Surface characteristics such asdifferent phases, inclusions, porosity, cracks, intergranular corrosion can be revealed byetching. Etching is defined as the process to reveal structural details by preferential attack ofa metal surface with an acid or other chemical solutions.

Experimental Procedure:

1. Obtain a steel specimen from the instructor and remove as much surface scale as possible.



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The steel specimen has been heat treated to form a desired structure for this exercise.

2. Mount the specimen in a phenolic cylinder using a compression mounting press. Watchcarefully the demonstration of the use of compression mounting press. Appropriate molding

pressure and time should be used in the process.

3. Prepare the specimen by coarse grinding on a wet-belt grinder, hand polishing on foursuccessively finer grits of polishing paper, and fine polishing on two polishing wheels with1.0-mm and 0.05-mm alumina powders. Rinse the specimen thoroughly between steps.

4. Etch the steel specimen by immersing it in a nital solution (5% concentrated nitric acid inalcohol). Start with 5 seconds of immersion. Rinse the specimen with water, dry with papertowel, immerse briefly in alcohol, and blow dry the specimen with a blow dryer.

5. Examine the specimen under microscope and identify the surface features. The specimen

surface may be over etched or under etched. An over etched specimen surface shows patchesof dark color with no identifiable features. On the other hand, a shiny, smooth surface withlittle or no surface features revealed indicates an under etch. Repeat the final polishing toremove the damaged surface and etching for less time if the specimen is over etched. In thecase of under etch; repeat the etching step to enhance the contrast.

Microscope Focusing Procedure

1. Initially the lowest power objective lens is used for focusing the specimen. Turn thelowest-power objective lens into place. If necessary, turn the coarse stage height control tolower the sample stage to make room so the objective lens can be turned into place.



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2. Turn the stage height focusing control to position the specimen about half a centimeterunder the objective lens.

3. Look through the eyepieces and use the focusing controls (coarse and fine stage heightcontrols) to bring the specimen into appropriate focus.

4. Scan the specimen surface by moving the stage using the stage position controls and selectthe areas that may warrant more complete study at higher magnification.

5. Turn the higher-power objective into place.

6. Adjust the stage height using the fine control until the specimen comes into sharp focus. Besure that the objective lens does not touch the specimen surface at any time. Otherwise theobjective lens may be scratched and permanently damaged.

7. A drop of oil on specimen surface usually is needed at higher magnification (greater thanX2000) to help with focusing.


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