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Experiment # 3 & 4(UNIVERSAL HARDNESS TESTING MACHINE)Object: - To determine the Hardness of the given specimen through:a) Rockwell’s Hardness Test.b) Brinell’s Hardness Test.c) Vicker’s Hardness Test.Apparatus: - ?1)2)3)4)5)6)7)8)Universal Hardness Testing Machine.Various specimens. (Steel, Aluminium, Brass)Diamond Indenter. (for Rockwell Test)1/16” ball indenter. (for Rockwell Test)1 mm ball indenter. (for Brinell test)2.5 mm ball indenter. (for Brinell test)Diamond pyramid Indenter. (for Vickers Test)L.N key. (for changing of indenters)?Mechanics of Materials Lab (ME-213)Page 1

Theory: Hardness can be defined as a measure of a material’s resistance to localized plasticdeformation. (i.e. small dent or a scratch). Hardness tests are performed more frequently thanany other mechanical test for several reasons.1) They are simple and inexpensive. i.e. no special specimen need to be prepared.2) The test is non-destructive i.e. the specimen is neither fractured nor excessivelydeformed and a small indentation is the only deformation.3) Other mechanical properties often may be estimated from the hardness data.The following are the most common hardness testing techniques. Rockwell Hardness Tests. Brinell Hardness Tests. Vickers Hardness Tests. Knoop Hardness Tests.Rockwell Hardness Tests: It is the easiest among all hardness tests. This test constitute the most common method usedto measure hardness because they are so simple to perform and requires no special skills.Several different scales may be utilized from possible combinations of various indenters anddifferent loads, which permit the testing of virtually all metal alloys and some of thepolymers. The indenters include spherical tungsten carbide balls as well as a conical diamondindenter, which is used for the hardest materials. With this system, a hardness numberdesignated by HR is determined by the difference in depth of penetration resulting from theapplication of an initial minor load followed by a large major load. The utilization of minorload enhances test accuracy. The minor load is 10 kg, whereas major loads are 60, 100 and150 kg respectively. ?Brinell Hardness Test: In this test, a hard spherical indenter is forced into the surface of the metal(specimen) to betested. The material of the indenter is hardened steel whose diameter is 10 mm. The standardload range is between 500 and 3000 kg in 500 kg increments. During a test, the load ismaintained between 10 to 30 sec. However harder materials require greater application ofloads. The hardness obtained through this test is called Brinell Hardness Number (BHN) andis designated by HB. ?Vickers Hardness Test: It is also called ‘diamond pyramid’ test. In this test, a very small diamond indenter havingpyramidal geometry is forced into the surface of the specimen. The applied loads are muchsmaller as compare to Rockwell and Brinell tests. The ranging is in between 1 and 1000 g.Mechanics of Materials Lab (ME-213)Page 2

The resulting impression is observed under a microscope and measured. Then thismeasurement is converted into a hardness number which is designated by HV. This type oftest is well suited for measuring the hardness of small, selected specimen regions. Carefulspecimen surface preparation is necessary in order to ensure a well-defined indentation thatnay be accurately measured.There is another technique of hardness test, known as ‘Knoop Hardness Test’. The testingcriteria and the hardness scale are approximately equivalent to Vickers’s test. However,Knoop’s technique is used for testing brittle materials such as ceramics. ?Load Selection: S NoType of Test1Rockwell2Brinell3VickersLoad & Type of Indenter60, 100 & 150 kgf with ball and diamond coneindenters.5, 10 & 30 kgf with 1 mm diameter ball indenter62.5 & 187.5 kgf with 2.5 mm ball indenter.3, 5, 10, 30 & 100 kgf.IndenterMechanics of Materials Lab (ME-213)Page 3

Various Indenter TypesLoad SelectorsMechanics of Materials Lab (ME-213)Page 4

Procedure: Rockwell Hardness Tests: 1)2)3)4)5)6)7)8)9)Fix the indenter into the moveable sleeve with the help of L.N key.Place the specimen onto the sample holder.Select the load at which the test will perform.The preload is applied by bringing the specimen into contact with the indenter byturning the hand wheel clockwise.The movement of the indenter is displayed by a bar graph and the correct pre-loadposition is indicated when the horizontal bar touches the end of the fixed bar.When the point is reached, an audible beep will be heard and the vertical movementof the indenter should be stopped.The rest of the loading cycle is automatic. The application and removal of theadditional load again displayed by the bar graph.At the end of the load cycle, record the hardness number which will be displayed.Now change the indenter and repeat the procedure for different specimen. Reference Text Book Fundamentals of Materials Science and Engineering by William D Callister.Brinell Hardness Test: 1) For performing Brinell hardness test, two type of indenters are available for thehardness tester i.e. 1” ball and 2.5” ball indenters.2) Fix the indenter into the moveable sleeve with the help of L.N key.3) Place the specimen onto the sample holder.4) Set the Brinell test from the display panel and select the load at which the test willperform.5) Now having focused the test surface and selected the test area advance the indenter toits forward position and initiate the load cycle by pressing the „S‟ key.Mechanics of Materials Lab (ME-213)Page 5

6) A bar graph will now appear on the screen which indicates the downward movementof the indenter carrier and the audible signals will signal the following critical testevents.7) The first signal will indicate the application of the test load and a countdown inseconds of the full load dwell period will appear.8) There will be a further signal that will indicate the end of the test load dwell time.9) At the end of the loading cycle, d1 will appear on the display to prompt measurementof the impression.10) A circular impression has been formed that we can see from the eye piece ofmicroscope.11) Since there are two knurled knobs on the measuring eye piece, the right-hand knobmoves both lines simultaneously, and this should be adjusted first until the left handline just touches the left hand corner of the diagonal. The left-hand knob adjust theright hand line independently and this again should be adjusted until the line touchesthe right hand corner of the impression.12) There are two types of lines which can be seen on the specimen through the eye piece.Now adjust the right hand line and then adjust left hand line.13) With both lines touching the impression corner, load the data by pressing the pushbutton and live reading of d1 will be appeared on the screen.14) Now rotate the microscope and repeat for the vertical diagonal if necessary, otherwiseload the first reading a second time, to complete the measurement.15) The hardness number and scale will be appeared on the screen. Note the reading.Vickers Hardness Test: 1) For performing Vickers hardness test, diamond indenters are used.2) The procedure is similar to the Brinell hardness test except that a pyramid typeimpression has been formed that we can see from the eye piece of microscope.3) The procedure for measuring d1 and d2 is also similar to the Brinell hardness test.Mechanics of Materials Lab (ME-213)Page 6

Reference Text Book Fundamentals of Materials Science And Engineering by William D Callister.Mechanics of Materials Lab (ME-213)Page 7

Results: 1) Rockwell Test: S#Type of IndenterMaterialLoad Graph: - (Between Load and Hardness)Mechanics of Materials Lab (ME-213)Page 8

2) Brinell Test: S#Type rdness.1.2.3.4.5.6.Graph: - (Between Load and Hardness)Calculations: - *(Perform the sample calculations)Mechanics of Materials Lab (ME-213)Page 9

3) Vickers Test: Type eticalHardness.1.2.3.4.5.6.Graph: - (Between Load and Hardness)Calculations: - *(Perform the sample calculations)Discussion: - ?Conclusion: - (Compare the results obtained in the lab with the results obtained by relevant formulae). Rockwell Test. ?Brinell Test. ?Vickers Test. ?Abstract: - ?References / Bibliography: - ?Mechanics of Materials Lab (ME-213)Page 10

QuestionsQ1 Why hardness test are performed more often than any other mechanical tests?Q2 Why the hardness testing machine is called ‘Universal Hardness Testing Machine’?Q3 Should brittle materials possesses larger hardness number? Give reasons to your answer?Q4 If the specimen material is softer, what will be the effect of its hardness?Q5 What does the Rockwell Hardness scale shows. Explain its importance and significance?Q6 What is the relation between hardness and stiffness? Show with graphs?Q7 Which type of hardness test is performed on polymers?Q8 What is Indenter? Briefly describe various type of indenters?Q9 What do we understand by the term „dwell time‟?Q10 How many types of load selector present in Hardness Tester. Name and explain thepurpose of each type of load selector?Q11 Illustrate the purpose of pressing “S” key during the hardness tests?Q12 What is the effect on hardness of material when the applied load is increased? (Discussall three hardness test results)Q13 How can a Brinell hardness number for steel alloys can be converted into its tensilestrength?Q14 Which type of impression is formed in Vickers hardness test?Q15 Enlist the factors if there are difference in results obtained in the experiment and byrelevant nics of Materials Lab (ME-213)Page 11

Experiment # 8FATIGUE TESTING MACHINEObject: a) To draw the S-N diagram by with the help of fatigue test.b) To study the effect of various curvature radii and surface qualities on fatigue.Theory: When a metal is subjected to repeat cycles of stress or strain, it causes its structure tobreakdown ultimately leading to fracture. This behaviour is called fatigue. Fatigue failure iscatastrophic which means that it happens suddenly. It is generally responsible for a largepercentage of failures in various mechanical and automotive components. Fatigue is a form offailure that occurs in structures subjected to dynamic and fluctuating loads. Under thesecircumstances, it is possible for failure to occur at a stress level considerably lower than theyield strength for a static load. It generally occurs after a lengthy period of repeated stress orstrain cycling.The process of fatigue failure is characterized by three specifics steps.a) Crack initiation.b) Crack propagation.c) Final failure.Wohler Machine1.2.3.4.5.6.7.8.Proximity sensor.Spindle with specimen receptacle.Floating Bearing.Scale.Spring Balance.Hand Wheel.Proximity Switch.Protective Hood.Mechanics of Materials Lab (ME-213)Page 1

9. Drive Motor.10. Emergency off switch.11. Counter.12. Connection socket. (optional)13. Motor Protection switch.Wohler in 1871 was the first to introduce the concept of the so-called S-N diagram. That whythis machine is called Wohler machine. In the moving fatigue testing machine, a rotatingspecimen is clamped on one side is loaded with a concentrated force. As a result analternating bending stress is created in the cylindrical specimen. Following a certain numberof load cycles, the specimen will rupture as a result of material fatigue. With this machine, itis possible to demonstrate the basic principles of fatigue strength testing, including theproduction Stress-No. of cycles diagram (S-N diagram). The specimen is subjected to a purereversed bending stress in the machine. With different specimen shapes, it is possible to showthe influence of the notch effect and the influence of surface quality on fatigue strength. ?Specimen Material C35E (Alloy of Cr Mo Ni)Procedure: - Part (a)1) First of all fold up the protective hood.2) Relieve the load device using the hand wheel by moving the floating bearing down tothe bottom. Remove any specimens which may be in position.3) Lightly tighten the union nut on the collets chuck.4) Fold down the protective hood and loosen the emergency off switch.5) Reset the counter using the RST button. The counter must display zero.6) After checking all these parameters, the experiment can begin.7) Make sure that the floating bearing must be at the height of the spindle.8) Insert the test bar in the floating bearing of the load device.9) Afterwards insert the test bar in the collate chuck and push in as far as the end stopand carefully tighten the collets chuck using a wrench.10) Now check the concentricity of the specimen by rotating the spindle by hand and folddown the protective hood. (Remember the unit can only be placed in operation if the protectivehood is correctly closed)11) Loosen the emergency off switch and quickly apply the load by rotating the handwheel.12) Read off the load from the scale on the spring balance.13) Reset the counter using the RST button in order to begin counting.14) The motor stops automatically when the specimen ruptures. Read off the number ofload cycles from the counter and record it in the observation table.15) Repeat the experiment for the next specimen.16) The stresses are entered over the endurance in the semi-logarithmic diagram i.e. theattached worksheet and draw the graph between stress and no. of cycles. This graph iscalled S-N diagram.Mechanics of Materials Lab (ME-213)Page 2

Procedure: - (Part b)The procedure is similar to the previous test except that you need to switch off themotor after completion of the required number of cycles.Results: a) Number of load cycles for test bar under different loadsNo.12345Load (N)200170150130120Stress σ (N/mm2)400340300260240Endurance (n)14130489001680004560001281800Duration (min)51760162457b) The Influence of Various Curvature Radii and Surface Qualities:Test bar # 1 Small radius and smooth.Test bar # 2 Large radius and smooth.Test bar # 3 Large radius and rough.The following numbers of load cycles are achieved until the specimen ruptures.No.123Load ( F)Stress (σa)200 N400 N/mm2Specimen 111.40017.18014.060Specimen 211.40017.36012.920Specimen 311.80023.90016.600Average11.53319.48014.526Number of load cycles N ( 200) to rupture.Drawing: -? (Using AutoCAD or any CAD software)Discussion:- ?Conclusion: - ?With an identical curvature radius, the specimen with the smoother surface (i.e. test bar # 2)has a higher endurance than the one with the rougher surface (i.e. test bar # 3).(More elaboration is required)?Abstract: - ?References / Bibliography: - ?Mechanics of Materials Lab (ME-213)Page 3

Specimen DrawingsS-N DiagramQuestionsQ1 What do you understand by the term “Fatigue strength”?Q2 How many types of fatigue exists? Name them?Q3 Fatigue failure is „catastrophic‟. What does it mean?Q4 What is ‘Endurance’? Is there any difference between endurance and # of cycles?Q5 Explain the process of crack initiation in fatigue?Q6 How does the cracks propagate in the specimen that leads to its final failure?Q7 Enlist the factors that affect the fatigue life of specimen?Q8 How can the fatigue life and surface hardness of steel alloys can be upgraded?Q9 What is „thermal fatigue‟? Does this experiment belong to it?Q10 What is the effect on the fatigue life of specimen having good surface finish hanics of Materials Lab (ME-213)Page 4

Experiment # 7TORSION TESTING APPARATUSObject: To investigate the relationship between torque and twist for various circular cross sectionsspecimen.Apparatus: - ? (Take help from figures)Theory: The elastic deflection and eventual failure of beams in bending is related to the behaviour ofthe beam material in direct tension and compression. However there is another way ofdistorting material that occurs when it is twisted. As a simple case, a length of round rod canbe twisted about its longitudinal axis in such a way that no bending or direct stress isinvolved. This is called pure torsion.ORTorsion is one of the common modes of deformation in which a solid or tubular member issubjected to torque about its longitudinal axis resulting in twisting deformation. Torsion ofshaft is very common in mechanical engineering where power transmission takes place. ?Angle of Twist, θ TL/GJWhere T Torque. (N-mm)L Length of rod. (mm)G Modulus of Rigidity of material. (N/mm2)J π / 32 d4 Polar Moment of Inertia. (mm4)d diameter of rod. (mm)Mechanics of Materials Lab (ME-213)Page 1

Procedure: 1) Measure and record the diameter of aluminium rod.2) Fit the round aluminium specimen into the chuck on the torsion head and in the chuckfitted to the vertical pier whose function is to hold the end of the torsion specimen.3) The chuck in the vertical pier has a through hole right through it and the pie, thus allowingthe test specimen length to be fully adjustable.4) Then the torsion specimens are secured within the chucks by using the chuck key.5) Rotate the chuck keys within the chucks bring the chuck jaws around the specimens andlock them into position.6) After clamping specimen in position, put the load hanger on the cord.7) Now set the pointer to be 400 mm from the vertical pier with integral chuck and bring theprotractor block close to the pointer and zero the pointer.8) Afterwards add a load from 5N to 15N in 5N increments and record the twist of thespecimen for each increment in table # 7(a).9) Remove the load, move the rotation angle and pointer to 200 mm from the clamp andrepeat the above procedure.10)

Mechanics of Materials Lab (ME-213) Page 1 Experiment # 4 (UNIVERSAL TESTING MACHINE- TENSILE TEST) Object: - To compare various mechanical properties of a ductile material with a brittle material using tensile test on Universal Testing Machine. Apparatus: - 1) Universal Testing Machine (Instron 30kN) 2) Flat Steel Specimen