Lab Manual For Mos Lab.docx

LIST OF EXPERIMENTS

1. To study the stress strain tension characteristics of metals by using UTM 2. To carry out Shear test of material supplied 3. To carry out Charpy test, Izod test. 4. To study the stress strain compression characteristics of metals by using UTM 5. To find out the modulus of elasticity of the specimen supplied and to verify the Maxwell’s theorem 6. To determine the hardness using different hardness testing machines: Brinnel’s, Vicker’s and Rockwell’s. 7. Deflection test on beams using U.T.M 8. Deflection test on spring 9. Torsion test.

EXPERIMENT -1

TITLE: To study the stress strain tension characteristics of metals by using UTM Aim: To study the stress strain characteristics of mild steel by Universal Testing Machine Equipment: Universal testing machine, meter rule, dividers and scale, Test specimen. Theory: In tension test of ductile metals, the properties usually determined are yield Strength, ultimate tensile strength, modulus of elasticity, percentage of elongation etc. For brittle materials only compressive strength is determined. The tension test is normally carried out in a Universal Testing Machine (UTM). The specimen can be in the form of a rod or a plate. The dimensions of standard specimen can be known from accepted specifications. The following properties can be determined from the stress strain curve of the material: 1) Proportional limit: is that point on the stress strain curve at which the curve deviates from linearity, i.e. from the relation Stress — Young's modulus x strain. 2) Elastic limit: is the point on the stress strain curve above which plastic deformation (that is permanent deformation) starts. 3) Yield strength: is the stress required to produce a small amount of permanent or plastic deformation. In some materials such as mild steel, where there is occurrence of sharp yield point on the stress-strain curve, the stress value at the lower yield point is taken as the yield strength. In some materials like tor steel which does not have a sharp yield point, the offset yield strength or proof stress is taken as the measure of the yield strength. This is the stress at which a line drawn parallel to the initial portion of the curve, offset by a specified strain, intersects. The offset value is usually a strain of 0.002 (0.2% strain). The value of the yield strength is of great importance in design calculations. 4) Tensile strength or ultimate tensile strength (UTS) is the maximum load divided by the original cross sectional area of the specimen. U.T.S. corresponds to the peak or the highest stress value in the stress-strain curve.

5) Ductility: It is usually measured as percentage elongation in length or percentage reduction in area. These measures of ductility are obtained after fracture, by keeping together the two broken parts of the specimen. and measuring the gauge length at fracture, and area of cross section at fracture. Percentage elongation in length = Percentage Reduction in area =

𝐿𝐹 −𝐿0 𝐿0

𝐴0 −𝐴𝑓 𝐴0

Lo and Ao are initial gauge length and initial area of cross section respectively. Lf and Af are measured gauge length at fracture and area of cross section at fracture respectively. Description: The machine is hydraulically operated, vertical, floor mounted, designed for testing metals and other materials under tension, compression, bending/ transverse loads. The machine comprise of following main parts l. loading frame 2. hydraulic pumping system 3. PC Based control system and application software 4. Accessories l) Loading frame: The loading frame is robust and extremely rigid construction with high stiffness. It consists of a central cross head whose position is adjustable through a geared motor depending on the size of the test specimen. The lower table is carried by the piston of the hydraulic ram of suitable capacity positioned in the cast iron base of the machine. The upper cross head is carried by four steel columns fixed to the lower table. The machine has six pillars in total for stability and rigidly. Compression, transverse, bending, shear and hardness tests are carried out between the central cross head and lower table while the tension test is carried between the central and upper cross heads. Sensing of load is through a strain gauge based transducer (both tension and compression type), while the movement

of

the

lower

table

(ram

stroke)

is

measured

by

displacement

transducer.

Safety feature like over travel limit for central cross head, over travel limit for ram and Over Loading Of the system are provided as standard with the machines. 2) Hydraulic pumping system:

Hydraulic power supplies are compact in design and are suitable for the supply of required now and pressure for the movement of the actuator, It has an oil tank Of adequate capacity, vane type pump powered by a thiee phase motor. All the electrical controls including the temperature controller are fixed on one side of the tank. It includes all the accessories like pressure line filter, return line filter, oil level, relief valve, pressure gauge and air cooled heat exchanger. Anti vibration mountings are provided as standard along with the HPS. A suitable water cooled heat exchanger for keeping oil within working temperature range is provided as standard. The system is kept at a distance from the loading unit and connected through flexible pipes. Broad specifications of the system are: 

Flow of the pump 10 LPM



Motor capacity 5 H.P.



Capacity of the tank 100 liters



Operating pressure 200 Bars



Heat exchanger 4500 Kcal/hr



System will be supplied with necessary cable and fittings for the operation of the machine.



Total machine operates on 440V AC, 3 Phase, 50Hz.

3) PC Based control system and application software: Control system provides the digital servo control, Ramp generation for the machine actuator, data acquisition etc. for the continuous operation of the system. (a) Signal Conditioning and Controlling Unit Servo controller basically consists of signal conditioning unit and controlling unit. Signal conditioning unit receives the output signal from the various transducers (Load cell/Pressure Transducers and LVDT) and amplifies and process that signal as per the requirement and transfer it to computer through connecting cables where it is accepted by the data acquisition system. The output from the signal conditioning unit for each transducers range from O - 5V Control is on either load/stress or displacement or strain basis. It consists of dedicated servo controller card that gives the desired processed signal through the P.I.D controller to the Servo valve to operate in load or displacement mode. It also sends the signal to computer and accepts the command from the software to operate in desire manner. The parameters like rate of loading, safety limits for load can initially be programmed through the software.

The facility is given to program the rate of loading from 0.5 kN/sec — 20kN/sec in load control and 0.01 mm/sec — I .5 mm/sec in displacement control. Specification of controller: 

Auto P.I.D operation with automatic pace rate control as programmed in the software



Closed loop update rate is 10 kHz



Control channels — Load/Displacement/Strain (Selectable)



Provision for two auxiliary channels for load cell



Fully computer controlled operation to start, Stop and hold the machine



High speed data acquisition card with 100 kHz sampling rate



Load ranges -O to 200kN and 200kN to 1000kN



Displacement range — 010250 mm



Load resolution - 0.1kN for O to 200 kN and 1kN for 200kN to 1000kN



Displacement resolution — 0.01 mm



Strain resolution — 0.01%



System accuracy:



Load accuracy: of the measured load from 1% to 100% of capacity of machine



Displacement accuracy: 0.5% of measured valve from 1-250 mm



Strain accuracy: g 0.10/0 of measured value of strain



Type of loading — Static (Ramp) in both load and displacement/strain control



Static ramp rate :



Load control mode — 0.5kN/sec to 20kN/sec



Displacement control mode — 0.01 mm/sec to 1.5mm/sec



Strain control mode — 0.0025/sec to 0.025/sec



Environmental temperature — 100 C to 500C



Relative Humidity — to 70%



supply 220 to 240 V (AC), Hz

(b) Dedicated computer for controlling and data acquisition System is provided with dedicated computer with built in data acquisition card. Broad specifications of the computer and data acquisition card are given below. Computer: Intel i5 processor, 320 GB HDD, 2GB RAM, DVD R,'W drive, 17" TFT Screen, LaserJet Colored printer UPS 500V A Data acquisition card: The PCI Bus advanced data acquisition card provides the following advanced features 

32 bit PCI — bus



16 — bit analog input resolution



Auto scanning channel selection up to 16 channels



Up to 100 KHz A/D sampling rates



16 single ended analog input channels



Bipolar input signals



Programmable gain ofxl, x2, x4, x8, x 16



Input range: El w, +51', +2.5V, El .25V, *0.625V.



One 12-bit monolithic multiplying analog output channel



16 digital output and 16 digital input channels



4 extended digital input and output channels on the 37 — pin connector



3 independent programmable 16-bit down counters.



Three A/D trigger modes: Software trigger, programmable pacer trigger and external pulse trigger.



Pre-trigger control



Internal DC to DC converter for stable analog power source.

(C) Application Software:

Application software is the integral part of the system for precise controlling, operation and data acquisition, storage, processing, analysis and reporting. It provides flexibility to user to do statistical analysis of test results and report generation as per relevant standards such as ISO, ASTM, DIN etc. Salient features: 

Programmable rare of loading (Pace Rate) and other sample parameters



Inching (Rapid approach)/ Release operation



Independent taring of presetting of load facility for auto zeroing of deflection at preset load.



Facility to test parameter setting and creation of test methods/profiles up to 30.



Save and recall of test methods for accurate and repeatable testing



Auto release of system facility after sample failure



To see the post failure behavior of the specimen



Operator selectable measurement unit — English, Metric, SI etc.



Programmable limits for load, displacement and strain



Facility to hold machine load up to 24 hours with continuous pump running up to full machine capacity and restart the loading during the test.



Online display of numerical value of load, displacement and extensometer



Automatic scaling of graphs in real time plotting o Load v/s Time o Displacement v/s Time o Load v/s Displacement o Stress v/s Strain o Load v/s Extensometer o Extensometer v/s Time



Automatic display of breaking load at the end of the test



Password protected transducer calibration facility with 10 calibration points per transducer with piece wise linear fit between point for maximum accuracy



Real time clock for tracking date, time and runs



Facility to save and retrieve test data along with order information about the specimen such as age, specimen no. , size, dimensions etc. in user defined file/ directory.



Calculation of various parameters such as load and elongation at yield, peak load and displacement at break, yield stress, modulus of elasticity, ultimate tensile strength, proof stress, compressive strength etc.



Multi graph and zooming option for comparison



Facility to print the data and all the graphs



Advanced statistical analysis (such as mean, SD, Variance etc.) for processing of test results Batch summary report with multi graph facility for comparison up to 30 specimen



Facility to export data to excel or PDF, detailed summary report.

Accessories: a) Tensile test on round and TMT bar 6-40mm Dia and Flat Section also. b) Compressive test on Specimen Dia up to 300mm c) Flexure/Bending with Table Length 1000mm d) Shear — Single and Double complete with Bushes for testing 6mm -32 mm Dia Rods. e) Brinell hardness test complete with Ball Indenter 2.5mm, 5.0mm and I Omm and Microscope. f) Wire Rope attachment for use with 20mm dia wire ropes. g)

Bolt

h)

Roller

Test

attachment

Support

System

for

conducting

length

up

to

test

on

2000

mm

Suitable for mechanical testing of following material 

Stainless steel



Modified stainless steel



Polymers such as FRP, Polyamides, Epoxy



Different metal such as copper, aluminum alloys etc



Different material beams, cubes, column etc

bolt

sizes

Length

for

from

M-6

testing

to

Leaf

M-30. Springs.

Procedure:

1. Mark the gauge length on the test piece (according to IS 1608 10 5.65N170 ) 2. Measure the diameter of the test piece at several sections by Vernier calipers and note down the mean diameter. 3. Fix the specimen firmly to the jaws of the testing machine 4. Start the machine and gradually increase the tensile load. Collect the readings from the software assisted computer in control panel until the fracture Of specimen occurs. Note down the reading where the load reaches to maximum. 5. Remove

the

fractured

specimen

from

the

machine

its

diameter

and

the

final gauge length. 6. Observe the stress Strain curve for the tested specimen in software assisted computer in Control panel and manually plot the graph between stress vs strain and mark the corresponding points listed below. a proportionality limit b elastic limit c Yield point d Ultimate stress e Breaking stress 7. Calculate the required objective. Observations and calculations: Calculation of the diameter Least count of Vernier calipers = S. No.

Average

M.S.D

V.S.D

M.S.D + (V.S.D X L.C)

Average diameter of the specimen (d): Area of the specimen: Gauge length Lo: S. No.

Load (KN)

mm

mm2 mm Elongation ( ∆ L)

Stress ( Load / Area)

Results: values according to IS: 432 Part-I for different type of steel.

Strain ( ∆ L / L)

Discussion: Compare the experimental results with the theoretical values for test specimen, comment on any reason for discrepancy, comment on any instrumental/experimental errors, and area of application.

EXPERIMENT – 2 TITLE: To carry out Shear test of material supplied Aim: Determination Of ultimate shear strength Of test specimen by single and double shear test Equipment: Shear box assembly, specimen to be tested, Vernier calipers and universal testing machine. Need and scope of the experiment: For rivets in trusses, plate girders etc., mild steel and high tensile steels are used. Rivets are subjected to bearing and shearing stresses. The behavior of the steel rod under shear is investigated experimentally. Procedure: 1. Find the diameter of the given rod with the help of Vernier calipers. Measure the diameter of the specimen at three sections. 2. Depending on the diameter of the rod, select circular discs. 3. Place circular discs in the shear box and place the specimen passing through all the circular discs. 4. Now keep the shear box assembly on the lower cross head Of the universal testing machine. 5. Operate the movable cross head until it touches the shear box. 6. Start the machine and note the maximum reading from the software assisted computer in the control panel. Let it be 'P' Observations and calculations: Calculation of the diameter Least count of Vernier calipers = S. No.

M.S.D

V.S.D

M.S.D + (V.S.D X L.C)

Average Average diameter of the specimen (d): Area of the specimen:

mm2

mm

Shear strength can be calculated as below: 𝐿𝑜𝑎𝑑 (𝑃)

Shear strength = 𝑁 𝑋𝐴𝑟𝑒𝑎 𝑜𝑓 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝑠𝑝𝑒𝑐𝑖𝑚𝑒𝑛 N = 1 for single shear N = 1 for double shear Shear Strength: Specimen Particulars

S. No.

Ultimate Load (P) KN

Ultimate shear Strength (N/mm2)

Test specimen

Average:

Result: Average ultimate shear strength of the given mild Steel specimen

N/mm2

Discussion: Observe the number of pieces into which the specimen is cut and examine the nature of the failure of the specimen. The shear surface will be smooth. QUESTIONS 1. What is meant by single and double shear? 2. In what manner material fails in double shear? 3. What is the capacity of a Universal testing machine you have used? 4. What is ultimate shear stress? 5. Define Hooke's law using shear stress? 6. What are you determining in Single and Double shear test?

EXPERIMENT -3

Title: To carry out Charpy test, Izod test. Object: Determination

Of

the

energy

absorbed

and

impact

strength

to

failure

of

given

specimen

using Charpy and Izod impact testing machine. Need and scope of the experiment: The

necessity

high

speed

for

impact

machinery

tests

under

has

arisen

repeated

due

forces

of

the

impulsive

of

materials

character,

even

used

when

in such

material has shown satisfactory strength and deformation in a static tensile test. Various forms of impact test has been devised, of which Izod impact test and Charpy impact test are the two general methods used to determine the imperfections in material likely to fracture by shock The

Izod

impact

test

has

long

been

used

as

the

standard

form

of

test

for

checking the brittleness of metals, the need has arisen for test at elevated and subzero temperatures. Apparatus:

(i)

Impact testing machine

(ii)

Izod specimen of 10mm x square cross section and 75mm length, with a V-notch 450 angle, 2mm deep and 0.25 mm root radius along the 28mm away from the c/s surface according to ASTM E23. The specimen is kept as a cantilever beam in vertical position. The angle of drop of pendulum is 900 (exact 85021 ') and the impact velocity is approximately 3.856m/sec. The specimen bends and fractures at high strain rate.

(iii) Charpy specimen of x 1 Omm. square cross section and 55mm length, with a V-notch 450 angle, 2mm deep and 0.25 mm root radius along the middle of the length according to ASTM E23. For a U-notch specimen, the dimensions are 5mm deep, 2mm width and Imm root radius according to ASTM E23. The specimen is kept as a simply supported beam in horizontal position and loaded behind the notch by the impact of a heavy swinging pendulum. The angle of drop of pendulum is 1400. The impact velocity is approximately 5.3465m/sec. The specimen bends and fractures at high strain rate. Procedure: Izod test 1. Without the specimen in the machine, swing the pendulum to ensure free movement. 2. Lift the pendulum and lock it at 900 3. Place the Izod test specimen as shown in

4. Select the test and its parameter given in the digital indicator. 5. Remove the lock nut and engage the lever. 6. Pendulum

will

strike

the

specimen

and

Energy

result

will

display

in

digital

absorbed

Izod value or impact strength =

N-m

𝐸𝑛𝑒𝑟𝑔𝑦 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 (𝑁−𝑚) 𝐶𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑎𝑟𝑒𝑎

Charpy test 1. Without the specimen in the machine, swing the pendulum to ensure free movement. 2. Lift the pendulum and lock it at 1400 3. Place the Charpy test specimen as shown in fig: 4. Select the test and its parameter given in the digital indicator. 5. Remove the lock nut and engage the lever. 6. Pendulum will strike the specimen and result will display in digital indicator.

Izod value or impact strength =

𝐸𝑛𝑒𝑟𝑔𝑦 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 (𝑁−𝑚) 𝐶𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛 𝑎𝑟𝑒𝑎

Charpy Test specimen

Results: Energy required to fracture the specimen, U =___________________J Izod value = _________________________Nm/mm2

indicator.

Izod Test specimen

Energy required to fracture the specimen, U =___________________J Charpy value = _________________________Nm/mm2

QUESTIONS 1. What is strain energy? 2. The machine on which you have performed test for measuring energy required to fracture the specimen is 3. How do you measure the toughness of a material? 4. Why notch is prepared in the specimen? 5. Draw a neat sketch of specimen for Char-py impact test. 6. How will you determine Charpy impact value for a given material? 7. Will the energy require for fracture the specimen remains Same by increasing or decreasing the height of hammer? 8. What is instantaneous stress? 9. What is the difference between impact

produced by gradually applied load and

by suddenly applied load on a body or a specimen? 10. Why impact test is required for a material? 11. What property Of metal does the impact test measure? 12. What is the difference between Izod's and Charpy's tests?

EXPERIMENT - 4

Title: To find out the modulus of elasticity of the specimen supplied and to verify the Maxwell’s theorem Objective: Determination of the Young’s modulus of a given material by conducting test on simply supported beam and verification of Maxwell's reciprocal theorem. Equipment: Bending attachment, scale, dial gauge, universal testing machine. Formulae: Concentrated load at center and deflection measured at quarter span.

Deflection is measured at D is given by 𝑌𝑑 =

11 768

𝑋

𝑊𝐿3 𝐸𝐼

Procedure:

1.

Measure the width and depth of given beam (steel or wood) by Vernier calipers.

2.

Measure the distance between the two supports (span) with a scale.

3.

Set the dial gauge at 'D' and adjust its value on the outer ring to zero by turning it.

4.

Apply the load at the center Of the beam using bending attachment.

5.

Find the deflection in dial gauge.

6.

Gradually increase the load within elastic limit only and note down the corresponding deflection reading in dial gauge.

7.

Find the deflection while unloading also. Get the mean of deflections found in step 6 and 7.

8.

Draw a graph between load on y-axis and deflection on x-axis.

9.

For verification of Maxwell's reciprocal theorem, interchange the loading and dial gauge positions and repeat the above procedure.

Observations and calculations: Breadth of the beam (b) Least count of Vernier calipers = S. No.

M.S.D

V.S.D

M.S.D + (V.S.D X L.C)

Average Average breadth of the beam (b):

mm

Depth of the beam (d) Least count of Vernier calipers = S. No.

M.S.D

V.S.D

M.S.D + (V.S.D X L.C)

Average Average depth of the beam (d):

mm

Moment of Inertia, I = bd3/12 = _______________mm4 Dial Gauge reading @D S. No.

Load (W)

Deflection @D Mean

Loading

unloading

1 2 3 4 5 6 7 8 Graph:

Draw a graph between load and deflection. From Graph find the Young's modulus of the given material.

Result: Young's modulus of the given material Esteel = ____________________N/mm2

= mean X L.C (mm)

QUESTIONS 1. What is meant by beam 2. Draw a neat sketch Of experimental Set-up and show position of load applied on the beam. 3. How deflection is measured? 4. How will you determine modulus of Elasticity Of a beam material from load- deflection curve? 5. What is meant by simple supported beam? 6. Define the terms concentrated load and distributed load. 7. Name the type Of internal stresses for which a transversely loaded beam is subjected. 8. What is meant by pure bending? 9. State Maxwell 's reciprocal theorem.

EXPERIMENT - 5 Title: To determine the hardness using different hardness testing machines: Brinnel’s, Vicker’s and Rockwell’s. Aim: To determine the Rockwell hardness for the given test specimen Equipment: Rockwell Hardness Testing Machine, test specimen. Description: Hardness may be defined as resistance of metal to plastic deformation usually by indentation. However the term may also refer to stiffness or temper or resistance to scratch, abrasion or cutting. There are three general types of hardness measurements depending upon the manner in which the test is conducted. 1. Scratch hardness measurement. 2. Rebound hardness measurement. 3. Indentation Hardness measurement. In scratch hardness method the materials are rated on their ability to scratch one another and mineralogists use it. In rebound hardness measurement, a standard body is usually dropped on to the material surface and the hardness is measured in terms of the height of its rebound. The general means of judging the hardness is the resistance of a material to indentation. Indentation hardness may be measured by various hardness tests such as Brinell, Rockwell, etc. Rockwell hardness testing differs from Brinell testing. In Rockwell testing, the indenters and loads are smaller and therefore the resulting indentation on the specimen is smaller and shallower.

ROCKWELL METHOD Rockwell testing is suitable for materials having hardness beyond the scope of Brinell testing. Rockwell testing is faster as compared to Brinell testing, because the diameter of the indentation need not be measured. The Rockwell machine gives arbitrary direct reading, Unlike Brinell testing, Rockwell testing needs no surface preparation (Polishing) of the specimen whose hardness is to be measured. There are two scales on Rockwell testing specimen. i.e B scale and C scale. B scale uses a steel ball indenter where as a diamond cone penetrate is employed for measuring Hardness on C scale. B scale is for testing materials of medium hardness such as low and medium carbon steels in the annealed condition. The working range of this scale is from 0 to 100. C scale is used for testing materials harder than B-100. C scale is commonly used for testing the hardness of alloy cast irons. In Rockwell hardness testing, the minor load for all cases is 10 Kg. whereas major loads for scales C and B are 150 Kgf and 100kgf respectively, including minor load.

Some time we are using the scale F at 60kgf for annealed copper alloys and thin soft sheet metals according to ASTM E18 or IS 1586. For more details, table is given below:

Brinell hardness test: In this test, as per standard Brinall hardness test is conducted as per the ASTM EIO or IS 1500 specifications. For testing of iron and steel, a load of 3000 kg is applied on a 10 mm diameter ball indenter for at least 10 sec. and for non ferrous metals and alloys, a load of 500 kg is applied on the same indenter for at least 30 sec. The loads are gradually applied by means Of hydraulic mechanism. The ball indenters are made of either high carbon steel or tungsten carbide. After full application of load for the above times, load is slowly removed. The indenter is taken out and the diameter of circular impression is measured by a spherical microscope. This measuring instrument magnifies the image and with the calibrated grid provided in the eye piece, measurement of diameter is done with an accuracy of 0.01mm. The Brinell's hardness number is found J)ut by the equation given below. The Brinell hardness number gives the comparative hardness of a body. A specimen indented by the standard ball is shown.

Test requirements:

1. It is desirable to conduct the test at a temperature of 270+20 as per I.S. Code. 2. The testing machine shall be protected throughout the test from shock and vibrations. 3. The test piece shall be placed on a rigid support. The contact surfaces shall be clean and free from foreign matter. (Such as oil and dust) 4. The thickness of the test piece shall be at least 8 times the permanent indentation of depth. No deformation shall be visible at the back of the test piece after the test. 5. The distance between the centers of the two adjacent indentations shall be at least 4 times the diameters of the indentation and the distance from the center of any indentation to the edge of the test piece shall be at least 2.5 times the diameter of the indentation unless agreed otherwise.

Procedure: Rockwell method

1. Test piece is placed upon the machine. The dial may be showing any reading. 2. Hand wheel is turned, thereby raising the test piece up against the steel ball indenter till the needle of the small dial is against the red mark. This applies minor load. 3. Major load is applied by pressing the crank provided on the right hand side of the machine. Time is given as 30 sec so as to make the load reach specimen fully. 4. When the penetration is completed, the crank is turned in the reverse direction thereby with drawing the minor load but the leaving the major load applied. 5. The pointer moves further and becomes stand still. This reading is taken as Rockwell Hardness Number - B/C/F scale.( HRX, X may be B/C/F i.e. HRB or HRC or HRF) 6. Hand wheel is rotated and the test piece is lowered. 7. The calibration is according to the following equation

a) For Brale indenter / Diamond indenter 𝐻𝑎𝑟𝑑𝑛𝑒𝑠𝑠 𝑁𝑢𝑚𝑏𝑒𝑟 = 100 −

𝐷𝑒𝑝𝑡ℎ 𝑜𝑓 𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑚𝑚 0.002

𝐻𝑎𝑟𝑑𝑛𝑒𝑠𝑠 𝑁𝑢𝑚𝑏𝑒𝑟 = 130 −

𝐷𝑒𝑝𝑡ℎ 𝑜𝑓 𝑝𝑒𝑛𝑒𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑖𝑛 𝑚𝑚 0.002

b) For ball indenter

Brinnel Hardness test: 1. The surface to be indented should be flat and it is free from dirt, scales and pits. 2. Fix the Brinell's hardness attachment to the centre crosshead of Universal testing machine 3. Place the test specimen on the lower crosshead of UTM 4. Start the machine and apply the load on the test specimen according to the I.S. standards 5. Once indentation is done remove the work piece from the UTM. Measure the diameter of indentation using Brinell's microscope. 6. Find the Brinell's hardness number by using empirical formula. 7. Carry the same procedure for further specimens

Precautions Rockwell Hardness l. successive impressions should not be superimposed on another nor may be too close together when making hardness determinations.

2. No reading should be made too close to the edge and Specimen should not be so thin that the impression comes through the other side. 3. Small dirt, scale Should be avoided because of the great sensibility of the Rockwell test.

Brinnel Hardness

1. Diameter of each indentation shall be measured in two at right angles to other and the mean value of the two readings be used for the purpose of determining hardness number. 2. Center of shall not less than a half times diameter of the impression from any edge of the test piece. 3. thickness of the test piece should be such that no marking showing the effect of the load shall on the underside. 4. This test should not be used for steel with hardness exceeding BHN 450 as no dent (impression) will left on surface. 5. It is desirable to conduct the test at a temperature of 270 ± 20 as IS. Code.

S. No.

Material

d1 (mm)

d1(mm)

Average

Diameter

Load

of

applied

Indenter 01

Steel 1 2

02

Copper 1 2

03

Aluminum 1 2

Result:

Rockwell Hardness test By Practical Average Rockwell's Hardness Number of steel = Average Rockwell's Hardness Number of Copper = Average Rockwell's Hardness Number of Aluminum =

By Equation Rockwell's Hardness Number of steel = Rockwell's Hardness Number of Copper = Rockwell's Hardness Number of Aluminum =

Brinell Hardness test Average Brinell's Hardness Number of steel = Average Brinell's Hardness Number of Copper = Average Brinell's Hardness Number of Aluminum =

BHN

EXPERIMENT – 6 Title: Deflection test on springs Aim: To determine the Shear Modulus (or) Modulus of Rigidity of the given spring material Equipment: Spring Testing Machine 2000 kN, vernier calipers, helical spring specimen Procedure 1. Note the particulars of the spring such as mean diameter of the spring, mean diameter of the spring wire, number of turns. 2. Place the spring in such a way that the axis of the spring is truly vertical and exactly below the centre of the loading frame. 3. Note the initial reading of the deflection gauge and ensure the load indicates dial gauge should be zero. 4. Apply

the

required

amount

of

load

by

manually

operated

hydraulic

pump

and

note the corresponding deflection gauge reading. 5. Repeat step (5) by increasing the load on the spring. Take at least 15 sets of readings. Precautions: 1. Load should be applied on the spring without any eccentricity. 2. Deflection gauge needle should touch the bottom plate of the providing ring and should be vertical. 3. Gently apply the load by manually operated hydraulic pump, without any vibrations either in the spring or in the loading frame. Observations:

Modulus of rigidity of the given spring = C = Mean radius of the spring, R Number of turns in the spring, n

= =

Mean diameter of the spring wire, d = W — Load applied on the spring (kg) = 𝛿 - Deflection of the spring (cm)

=

64𝑊𝑅 3 𝑛 𝛅𝒅𝟒

Result: Average Shear Modulus of the given spring, C = _______________x 105 kg/cm2

OUESTIONS 1. Give some practical application related to spring test? 2. What is Wahl factor? 3. Derive the equation for shear stress in spring and Why we neglecting the d/4R? 4. Explain different type Of springs?

EXPERIMENT - 7 Title: Torsion test Aim: To find the modulus Of rigidity Of a given specimen Equipment: Torsion testing machine. test specimen, Vernier callipers and rule Specimen for the test: The specimen should be of such size as to permit the desired strain measurement to be made sufficient accuracy. It should Of such properties that the stress due to gripping ends does not affect the portion of the specimen on which measurements are made. The ends of the specimen should be such that they can securely gripped without any local failure at the grips. Theory For

a

shaft

subjected

to

a

torque

'T',

the

relation

between

torque,

shear

stress

and angle of twist is given by 𝑇 𝑓𝑠 𝐺θ = = 𝐼𝑃 𝑅 𝐿 T = torque in N-mm 𝐼𝑃 = polar moment of inertia of specimen in mm4 𝑓𝑠 = shear stress at a radius R of the specimen, N/mm R = radius of the shaft in mm G = modulus of rigidity in N/mm2 θ = angle of twist in radians (l degree 0.01745rad L = length of the shaft in mm Hence

𝐺θ 𝐿

𝑇

𝐿

𝑃

θ

=𝐼 𝑋

For a solid circular shaft of diameter'D' = 𝐼𝑃 =

𝜋 𝐷4 32

For circular shaft of external diameter D and internal diameter d, 𝐼𝑃 =

𝜋 (𝐷 4 −𝑑4 ) 32

Procedure 1. Measure the diameter of test specimen using vernier calipers. 2. Measure the gauge length of the specimen. 3. Hold the specimen in between the plates with a dog holder. 4. Adjust the circular main scale with zero of the vernier scale and also ensure that torque reading show the value in digital indicator. 5. Apply

an

increasing

automatic control.

torque

to

the

specimen

in

suitable

increments

by

using

6. Continue the test and record the corresponding readings of torque and angle Of twist, until fracture occurs. 7. Plot a graph of torque vs angle of twist and determine the Modulus of Rigidity. Observations: Diameter of the specimen : Gauge length : olar moment of inertia : S. No.

Angle of twist in degrees

Angle of twist in degrees

Torque (T) Kg-cm

Precautions: 1) The test piece should, as far as possible, be straight and of sufficient length to provide the desired length between the grips. 2) Any straitening should be done by hand without damaging the test piece. 3)

The

free

length

between

the

grips

should

be

provided

strictly

to

IS-1717.

4) If the failure of the specimen takes place with in twice the diameter of the grips, the test should be considered as invalid and should be repeated. 5) The surface of the test piece after failure should be examined so that it is free from cracks. Results: Modulus of rigidity of given specimen________________N/mm2 Discussion: Compare

the

comment

on

experimental any

reason

results for

with

discrepancy,

the

theoretical

comment

on

values any

for

test

specimen,

instrumental/experimental

errors, and area of application. QUESTIONS 1. Give some practical application related to torsion test? 2. Drive the torsion equation? 3. Explain the term polar moment of inertia? 4. Which type of failure occurs for the ductile and the brittle material torsion test? 5. Draw the torsional stress and strain variation along the c/s of the circular and Tubular?