MAHATMA GANDHI MISSION’SJawaharlal Nehru Engineering College

N-6, CIDCO, Aurangabad

Laboratory ManualSTRENGTH OF MATERIALS

DEPARTMENTOF

CIVIL ENGINEERING

STRENGTH OF MATERIALS

List of Practical

1) To Study The Universal Testing Machine (U.T.M.)

2) Tensile Test on a Metal.

3) To Determine Hardness of Materials.

4) Torsion Test on Mild Steel Rod.

5) To Determine Impact Strength of Materials. (Charpy test, Izod test )

6) To Determine Modulus of Elasticity of Beam Simply Supported atends.

7) Shear Test on Metal.

8) To Determine the Stiffness of Spring and Modulus of Rigidity ofSpring Wire

9) To Determine Compressive Strength of Brick.

10) To Determine Moisture Content in a Brick.

EXPERIMENT NO. – 01

AIM: - Study of Universal Testing Machine (U.T.M.)OBJECTIVE:- To Study the various component parts of the UniversalTestingMachine (U.T.M.) & test procedures of various practical have to be performed.APPARATUS:- Universal Testing Machine with all attachment i.e. shear testattachment, bending attachment, tension grips, compression test attachment etc.THEORY: - The Universal Testing Machine consists of two units.

1) Loading unit, 2) Control panelLOADING UNIT: -It consists of main hydraulic cylinder with robust base inside. The pistonwhich moves up and down. The chain driven by electric motor which is fitted onleft hand side. The screw column maintained in the base can be rotated usingabove arrangement of chain. Each column passes through the main nut which isfitted in the lower cross head.

The lower table connected to main piston through a ball & the ball seat isjoined to ensure axial loading. There is a connection between lower table andupper head assembly that moves up and down with main piston. Themeasurement of this assembly is carried out by number of bearings which slidesover the columns. The test specimen is fixed in the job is known as ‘Jack Job’.To fix up the specimen tightly, the movement of jack job is achieved helically byhandle.CONTROL PANEL:-It consists of oil tank having a hydraulic oil level sight glass for checking the oillevel. The pump is displacement type piston pump having free plungers thoseensure for continuation of high pressure. The pump is fixed to the tank frombottom. The suction & delivery valve are fitted to the pump near tank Electricmotor driven the pump is mounted on four studs which is fitted on the right sideof the tank. There is an arrangement for loosing or tightening of the valve. Thefour valves on control panel control the oil stroke in the hydraulic system. Theloading system works as described below.

The return valve is close, oil delivered by the pump through the flow controlvalves to the cylinder & the piston goes up. Pressure starts developing & either

the specimen breaks or the load having maximum value is controlled with thebase dynameters consisting in a cylinder in which the piston reciprocates.The switches have upper and lower push at the control panel for the downward& upward movement of the movable head. The on & off switch provided on thecontrol panel & the pilot lamp shows the transmission of main supply.METHOD OF TESTING:-Initial Adjustment: - Before testing adjust the pendulum with respect tocapacity of the test i.e. 8 Tones; 10 Tones; 20 Tones; 40 Tones etc. For ex: - Aspecimen of 6 tones capacity gives more accurate result of 10 Tones capacityrange instead of 20 Tones capacity range. These ranges of capacity areadjusted on the dial with the help of range selector knob. The control weightsof the pendulum are adjusted correctly. The ink should be inserted in penholder of recording paper around the drum & the testing process is starteddepending upon the types of test as mentioned below.TENSION TEST:-Select the proper job and complete upper and lower check adjustment. Apply

some Greece to the tapered surface of specimen or groove. Then operate the uppercross head grip operation handle & grip the upper end of test specimen fullyin to the groove. Keep the lower left valve in fully close position. Open theright valve & close it after lower table is slightly lifted. Adjust the lowerpoints to zero with the help of adjusting knob. This is necessary to removethe dead weight of the lower table. Then lock the jobs in this position byoperating job working handle. Then open the left control valve. The printer ondial gauge at which the specimen breaks slightly return back & correspondingload is known as breaking load & maximum load is known as the ultimate load.COMPRESSION TEST:-Fix upper and lower pressure plates to the upper stationary head & lower tablerespectively. Place the specimen on the lower plate in order to grip. Then adjustzero by lifting the lower table. Then perform the test in the same manner asdescribed in tension test.FLEXURAL OR BENDING TEST:-Keep the bending table on the lower table in such a way that the centralposition of the bending table is fixed in the central location value of the lowertable. The bending supports are adjusted to required distance. Stuffers at the backof the bending table at different positions. Then place the specimen on bending

table & apply the load by bending attachment at the upper stationary head.Then perform the test in the same manner as described in tension test.

BRINELL HARDNESS TEST:-Place the specimen on the lower table & lift it up slightly. Adjust the zero fixedvalue at the bottom side of the lower cross head. Increase the load slowlyultimate load value is obtained. Then release the load slowly with left controlvalve. Get the impression of a suitable value of five to ten millimeter onthe specimen & measure the diameter of the impression correctly by microscope &calculate Brinell hardness.SHEAR TEST:-Place the shear test attachment on the lower table, this attachment consists ofcutter. The specimen is inserted in roles of shear test attachment & lift the lowertable so that the zero is adjusted, then apply the load such that thespecimen breaks in two or three pieces. If the specimen breaks in two piecesthen it will be in angle shear, & if it breaks in three pieces then it will be indouble shear.STUDY OF EXTENSOMETER:-This instrument is an attachment to Universal / Tensile Testing Machines. Thismeasures the elongation of a test place on load for the set gauge length. The leastcount of measurement being 0.01 mm and maximum elongation measurement upto 3 mm. This elongation measurement helps in finding out the proof stress at therequired percentage elongation.WORKING OF THE INSTRUMENT:-The required gauge length(between 30 to 120 ) is set by adjusting the upper knifeedges ( 3 ) A scale ( 2 ) is provided for this purpose . Hold the specimen in theupper and lower jaws of Tensile / Universal Testing Machine. Position theextensometer on the specimen. Position upper clamp (4) To press upper knifeedges on the specimen. The extensometer will be now fixed to the specimen byspring pressure. Set zero on both the dial gauges by zero adjust screws (7). Startloading the specimen and take the reading of load on the machine at requiredelongation or the elongation at required load. Force setter accuracies mean ofboth the dial gauge (8) readings should be taken as elongation. It is veryimportant to note & follow the practice of removing the extensometer from thespecimen before the specimen breaks otherwise the instrument will be totally

damaged. As a safety, while testing the instrument may be kept hanging from afixed support by a slightly loose thread.

TECHNICAL DATA:-Measuring Range: 0 – 3 mmLeast Count: 0. 01 mmGauge Length adjustable from: 30 - 120 mmSpecimen Size: 1 to 20 mm Round or Flats up to 20 x 20 mm

A) Stress-strain graph for Mild Steel

B) Stress-strain graph for Different materials

Curve A shows a brittle material. This material is also strong becausethere is little strain for a high stress. The fracture of a brittle material issudden and catastrophic, with little or no plastic deformation. Brittlematerials crack under tension and the stress increases around the cracks.Cracks propagate less under compression.

Curve B is a strong material which is not ductile. Steel wires stretchvery little, and break suddenly. There can be a lot of elastic strain energy ina steel wire under tension and it will “whiplash” if it breaks. The ends arerazor sharp and such a failure is very dangerous indeed.

Curve C is a ductile materialCurve D is a plastic material. Notice a very large strain for a small stress.The material will not go back to its original length.

EXPERIMENT NO. – 02AIM: -To determine tensile strength of a metal.OBJECTIVE: -To conduct a tensile test on a mild steel specimen anddetermine the following:

(i) Limit of proportionality(ii) Elastic limit(iii) Yield strength(iv) Ultimate strength(v) Young’s modulus of elasticity(vi) Percentage elongation(vii) Percentage reduction in area.

APPARATUS:(i) Universal Testing Machine (UTM)(ii) Mild steel specimens(iii) Graph paper(iv) Scale(v) Vernier Caliper

THEORY:-The tensile test is most applied one, of all mechanical tests. In thistest ends of test piece are fixed into grips connected to a straining device and to aload measuring device. If the applied load is small enough, the deformation ofany solid body is entirely elastic. An elastically deformed solid will return to itsoriginal form as soon as load is removed. However, if the load is too large, thematerial can be deformed permanently. The initial part of the tension curve whichis recoverable immediately after unloading is termed. As elastic and the rest ofthe curve which represents the manner in which solid undergoes plasticdeformation is termed plastic. The stress below which the deformationsessentially entirely elastic is known as the yield strength of material. In somematerial the plastic deformation is denoted by a sudden drop in load indicatingboth an upper and a lower yield point. However, some materials do not exhibita sharp yield point. During plastic deformation, at larger extensions strainhardening cannot compensate for the decrease in section and thus the load passesthrough a maximum and then begins to decrease. This stage the “ultimatestrength”’ which is defined as the ratio of the load on the specimen to original

cross-sectional area, reaches a maximum value. Further loading will eventuallycause ‘neck’ formation and rupture.

PROCEDURE:-1. Measure the original length and diameter of the specimen. The length

may either be length of gauge section which is marked on the specimenwith a preset punch or the total length of the specimen.

2. Insert the specimen into grips of the test machine and attach strain -measuring device to it.

3. Begin the load application and record load versus elongation data.4. Take readings more frequently as yield point is approached.5. Measure elongation values with the help of dividers and a ruler.6. Continue the test till Fracture occurs.7. By joining the two broken halves of the specimen together, measure the

final length and diameter of specimen.

OBESERVATION:- A) Material:i) Original dimensions

Length = ------------

Diameter = ---------

Area = ------

ii) Final Dimensions:

Length = ------------

Diameter = ---------

Area = -------

OBESERVATION TABLE:-

To plot the stress - strain curve determine the following

Sr.No

Load(N)

OriginalGauge length

Extension(mm)

Stress =Load/Area

(N/mm2)

Strain =Increase in length /Original length

12345

i) Elastic limit = N/mm2

ii) Yield strength = Yield LoadOriginal Cross Sectional area N/mm2

iii) Ultimate strength = N/mm2

iv) Young’s modulus, E = N/mm2

v) Percentage elongation =

%

vi) Percentage reduction in area = %

RESULT:-i) Average Breaking Stress =ii) Ultimate Stress =iii) Average % Elongation =

PRECAUTIONS:-1. If the strain measuring device is an extensometer, it should be removed

before necking begins.2. Measure deflection on scale accurately & carefully

EXPERIMENT NO-03

AIM: -To determined Shear strength of Steel.OBJECTIVE: - To conduct shear test on specimens under single shear and doubleshearAPPARATUS: - Universal testing machine, Shear test attachment, SpecimensTHEORY: - Place the shear test attachment on the lower table, thisattachment consists of cutter. The specimen is inserted in shear test attachment &lift the lower table so that the zero is adjusted, then apply the load such that thespecimen breaks in two or three pieces. If the specimen breaks in two pieces thenit will be in single shear & if it breaks in three pieces then it will be in doubleshear.PROCEDURE:

1. Insert the specimen in position and grip one end of the attachment inthe upper portion and one end in the lower portion.

2. Switch on the main switch of universal testing machine.3. The drag indicator in contact with the main indicator.4. Select the suitable range of loads and space the corresponding weight

in the pendulum and balance it if necessary with the help of smallbalancing weights.

5. Operate (push) buttons for driving the motor to drive the pump.6. Gradually move the head control level in left-hand direction till the

specimen shears.7. Down the load at which the specimen shears.8. Stop the machine and remove the specimen

OBESERVATIONS:-

Diameter of the Rod, D = ….. mm

Cross-section area of the Rod (in single shear) =π/4x d2 =…..mm2

Cross-section area of the Rod (in double shear) = 2x π/4x d2 =….. mm2

Load taken by the Specimen at the time of failure, W = …. N

Shear Strength of rod in single Shear =

Shear Strength of rod in double Shear =

RESULT: The Shear strength of mild steel specimen is foundi) In single shear = ….. N /mm2

ii) In double shear = ….. N /mm2

PRECAUTIONS:-1. The measuring range should not be changed at any stage during the test.2. The inner diameter of the hole in the shear stress attachment should be

slightly greater than that of the specimen.3. Measure the diameter of the specimen accurately.

EXPERIMENT NO:- 04

AIM: -To determined young’s modulus of elasticity of material of beam simplysupported at ends.OBJECTIVE:-To find the values of bending stresses and young’smodulus of elasticity of the material of a beam simply supported at the endsand carrying a concentrated load at the centre.APPARATUS: - Universal testing machine, Beam of wooden materialTHEORY:- If a beam is simply supported at the ends and carries a concentratedload at its centre, the beam bends concave upwards. The distance between theoriginal position of the beams and its position after bending at different pointsalong the length of the beam be maximum at the centre in this case. Thisdifference is known as ‘deflection’ In this particular type of loading the maximumamount of deflection (δ) is given by the relation,

δ = ….. i)

E =δ

…… ii)

BENDING STRESS:- From simple bending theory,= σ

Where, M = Bending moment in N-mmI = Moment of inertia in mm4

σ=

=Bendingstress

Bending stress in N/ mm2

y = Distance of the top fiber of the beam from the neutral axisW = Load acting at the center in NL = Length of the beam between the supports in mmE = Young’s modulus of material of the beam in N/mm2

I = Second moment of area (moment of Inertia) of the cross-section of the beam, about the neutral axis in mm4

PROCEDURE:-

1. Adjust cast- iron block along the bed so that they are symmetrical withrespect to the length of the bed.

2. Place the beam on the knife edges on the block so as to project equallybeyond each knife edge. See that the load is applied at the centre of thebeam

3. Note the initial reading of vernier scale4. Add a weight of 20N (say) and again note the reading of the vrenier

scale.5. Go on taking readings adding 20N (say)each time till you have

minimum six readings.6. Find the deflection (δ) in each case by subtracting the initial reading of

vernier scale7. Draw a graph between load (W) and deflection (δ). On the graph choose

any two convenient points and between these points find the correspondingvalues of W and δ. Putting these values in the relation

δ = Calculate the value of E

8. Calculate the bending stresses for different loads using relation

σ =OBESERVATION TABLE:-

Sr.No.

Load‘W’(N)

BendingMomentM = WL/4(Nmm)

BendingStress

σ = MyI(N / mm2)

Deflection‘δ’ (mm)

Young‘s ModulusE =δ

(N / mm2)12345

RESULT:1. The Young’s modulus for wooden beam is found to be ----- N/mm2

PRECAUTIONS:1. Make sure that beam and load are placed in a proper position2. The cross- section of the beam should be large3. Note down the readings of the vernier scale carefully

EXPERIMENT No:- 05

AIM: - To determine impact strength of materialsOBJECTIVE: -To Determine the impact strength of materials by Izod and Charpyimpact testAPPARATUS: - Impact testing machine, specimens of size 75 mm X 10mm X10mm and 10 mm x 10 mm X 55mmDIAGRAM:-For Izode test

THEORY:-

An impact test signifies toughness of material that is ability of material to absorbenergy during plastic deformation. Static tension tests of unnotched specimens donot always reveal the susceptibility of a metal to brittle fracture. This importantfactor is determined by impact test. Toughness takes into account both thestrength and ductility of the material. Several engineering materials have towithstand impact or suddenly applied loads while in service. Impact strengthsare generally lower as compared to strengths achieved under slowly appliedloads. Of all types of impact tests, the notch bar tests are mostextensively used. Therefore, the impact test measures the energy necessary tofracture a standard notch bar by applying an impulse load. The test measures thenotch toughness of material under shock loading. Values obtained from thesetests are not of much utility to design problems directly and are highly arbitrary.Still it is important to note that it provides a good way of comparing toughness

of various materials or toughness of the same material under different condition.This test can also be used to assess the ductile brittle transition temperature ofthe material occurring due to lowering of temperature.

PROCEDURE:- (a) lzod test

1. With the striking hammer (pendulum) in safe test position, firmly hold thesteel specimen in impact testing machine’s vice in such a way that thenotch face the hammer and is half inside and half above the top surface ofthe vice.

2. Bring the striking hammer to its top most striking position unless it isalready there, and lock it at that position.

3. Bring indicator of the machine to zero, or follow the instructions of theoperating manual supplied with the machine.

4. Release the hammer. It will fall due to gravity and break the specimenthrough its momentum, the total energy is not absorbed by the specimen.Then it continues to swing. At its topmost height after breaking thespecimen, the indicator stops moving, while the pendulum falls back.Note the indicator at that topmost final position.

5. Again bring back the hammer to its ideal position and back

( b) Charpy TestProcedure points 1 to 4 are same as above in procedure of Izode test

5. The specimen is placed on supports or anvil so that the blow of hammeris opposite to the notch.

OBESERVATION:- (a) Izode Test / Charpy Test

1. Impact value of - Mild Steel ------------N-m2. Impact value of - Brass------------N-m3. Impact value of - Aluminum ------------N-m

RESULT:-i. The energy absorbed for Mild Steel is found out to be….. . Joules.ii. The energy absorbed for Brass is found out to be ….. Joules.iii. . The energy absorbed for Aluminum is found out to

be…… Joules

PRECAUTION:-1. Measure the dimensions of the specimen carefully.2. Hold the specimen firmly.3. Note down readings carefully.

EXPERIMENT NO-06

AIM: - Hardness Test of MaterialsOBJECTIVE: - To conduct hardness test on mild steel, carbon steel, brass andaluminum specimensAPPARATUS:-Hardness tester, soft and hard mild steel specimens, brass,aluminum etc.DIAGRAM:-

THEORY: - The hardness of a material is resistance to penetration under alocalized pressure or resistance to abrasion. Hardness tests provide an accurate,rapid and economical way of determining the resistance of materials todeformation. There are three general types of hardness measurements dependingupon the manner in which the test is conducted:

a. Scratch hardness measurement,b. Rebound hardness measurementc. Indention hardness measurement

In scratch hardness method the material are rated on their ability to scratch oneanother and it is usually used by mineralogists only. In rebound hardnessmeasurement, a standard body is usually dropped on to the material surface andthe hardness is measured in terms of the height of its rebound .The general means

of judging the hardness is measuring the resistance of a material to indentationThe indenters usually a ball cone or pyramid of a material much harder thanthat being used. Hardened steel, sintered tungsten carbide or diamond indentersare generally used in indentation tests; a load is applied by Pressing the indenter atright angles to the surface being tested. The hardness of the material depends onthe resistance which it exerts during a small amount of yielding or plastic. Theresistance depends on friction, elasticity, viscosity and the intensity anddistribution of plastic strain produced by a given tool during indentationPROCEDURE:-

1. Place the specimen securely upon the anvil2. Elevate the specimen so that it come into contact with the penetrate and

put the specimen under a preliminary or minor load of 100+2N withoutshock

3. Apply the major load 900N by loading lever4. Watch the pointer until it comes to rest5. Remove the major load6. Read the Rockwell hardness number or hardness scale

OBESERVATION TABLE:-

S.NO Specimens

Reading (HRC/ HRB)

Mean1 2 3

1 Mild Steel HRB =

2 High Carbon steel HRC =

3 Brass HRB =

4 Aluminum HRB =

RESULT:- The hardness of the metal is found to be…….PRECAUTION:-

1. Brinell test should be performed on smooth, flat specimens from which dirtand scale have been cleaned

2. The test should not be made on specimens so thin that the impressionshows through the metal, nor should impression be made too close to theedge of a specimen

EXPERIMENT NO-07

AIM:- Torsion test on mild steel rodOBJECTIVE:- To conduct torsion test on mild steel or cast iron specimens tofind out modulus of rigidityAPPARATUS:- A torsion testing machine, Vernier Caliper, mild steel specimenTHEORY:-A torsion test is quite instrumental in determining the value of modulus of rigidityof a metallic specimen. The value of modulus of rigidity can be found outthought observations made during the experiment by using the torsion equation= θ =Where,

T= Torque appliedJ = Polar moment of inertiaG = Modulus of rigidityθ = Angle of twist (radians)L = Length of rodq = shear stressR = radius of rod

PROCEDURE:-1. Select the driving dogs to suit the size of the specimen and clamp it in the

machine by adjusting the length of the specimen by means of a slidingspindle

2. Measure the diameter at about three places and take the average value3. Choose the appropriate range by capacity change lever4. Set the maximum load pointer to zero5. Set the protector to zero for convenience and clamp it by means of knurled

screw6. Carry out straining by rotating the handweel in either direction7. Load the machine in suitable increments8. Then load out to failure as to cause equal increments of strain reading9. Plot a torque- twist (T- θ) graph10. Read off co-ordinates of a convenient point from the straight line portion

straight line portion of the torque twist (T- θ) graph and calculate the valueof ‘G’ by using relation=

OBESERVATION:-1. Gauge length of the specimen, L = ………2. Diameter of the specimen, d = ………3. Polar moment of inertia, =

OBESERVATION TABLE:-

Sr. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Torque

(T)

Angle of

Twist (θ) in

‘radians’

Modulus

of rigidity

(G) N/mm2

RESULT:- Modulus of rigidity of mild steel rod is ------------- N/mm2

PRECAUTIONS:- 1) Measure the dimensions of the specimen carefully2) Measure the Angle of twist accurately for the

corresponding value of Torque

EXPERIMENT NO-08

AIM: - Compressive Strength of BrickOBJECTIVE: -To determine Compressive Strength of brickAPPARATUS: A Compressive testing machine , Bricks, Vernier Caliper, plywood cover etc.

FORMULA: - Compressive Strength =

THEORY: - Bricks are used in construction of either load bearing walls or inportion walls in case of frame structure. In load bearing walls total weight fromslab and upper floor comes directly through brick and then it is transferred to thefoundation. In case the bricks are loaded with compressive nature of force onother hand in case of frame structure bricks are used only for construction ofpartition walls, layers comes directly on the lower layers or wall. In this casebricks are loaded with compressive nature of force. Hence for safety measuresbefore using the bricks in actual practice they have to be tested in laboratory fortheir compressive strength.

The usual crushing strength of common hand molded well burnt bricks is @ 5to 10 N/mm2 varying according to the nature of preparation of the clay. Pressedand machine molded bricks made of thoroughly plugged clay are much strongerthan common hand molded bricks made from carelessly prepared clay.

PROCEDURE: -1. Take 5 Bricks and remove unevenness observed in the bed faces to provide

two smooth and parallel faces by grinding.2. Measure it’s all dimensions. (L X B X H)3. Fill the frog ( where provided ) and all voids in the bed face flush with

cement mortar ( 1 cement, 1 clean course sand of grade 3mm )4. Store under the bricks for 24 hours.5. place the specimen with flat faces horizontal and mortar filled face facing

upwards between the two plywood sheet each 3 mm thickness and carefullycentered between plates of the testing machine.

6. Apply load axially of a uniform rate.

7. Note down the load at failure. That load shall be the maximum load atwhich the specimen fails to produce any further increase in the indicatorreading on the testing machine.

Note: In place of plywood sheets plaster of Paris may be used to ensure a uniformsurface for application of load.

OBSERVATION TABLE:-

Sr.No.

L X B XH

mm3Area

L X B

mm2

Load(N)

(P)

Compressive

StrengthP/A(N/mm2)

Average

Compressive

Strength

12345

CALCULATION:-Compressive Strength =

RESULT: - The average compressive strength of new brick sample is found to be………. N/mm2

PRECAUTION: - 1) Measure the dimensions of Brick accurately2) Specimen should be placed on the of lower plate3) The range of the gauge fitted on the machine should not be more

than double the breaking load of specimen for reliable resultsCONCLUSION: The given sample can be used / cannot be used as buildingmaterial

EXPERIMENT NO-09

OBJECTIVE: To determine the water absorption of burnt clay building Bricks.

APPARATUS: A sensitive balance capable of weighing within 0.1 percent of themass of the specimen and a ventilated Oven.

THEORY: Bricks for external use must be capable of preventing rain water frompassing through them to the inside the walls of reasonable thickness. A good brickshould absorb water maximum 1 th of the weight of the brick.

PROCEDURE:

1. Take 5 Bricks and dry in a ventilated oven at a temperature of 105 to 1150ctill it attains substantially constant mass.

2. Cool the specimen to room temperature and obtain its weight (w1).Specimen warm to touch shall not be used for the purpose.

3. Immerse completely dry specimen in clean water at a temperature of 270 ±20c for 24 hours.

4. Remove the specimen and wipe out any traces of water with a damp clothand weigh the specimen (W2).

5. Complete the weighing within three minutes after the specimen has beenremoved from water.

6. Water absorption , percent by mass, after 24 hours, % water absorption isgiven by formula

= W2 – W1 / W1 X 100

OBSEVATION TABLE:

SampleNo.

Dry weight of theBrick W1

Weight ofthe wetBrick W2

% water absorption= W2 – W1 / W1 X100

Remark

0102030405

I.S. Requirement:

After immersion in cold water for 24 hours, the average water absorption of thebricks shall not be more than 20% by weight up to class 125 and 15% by weightfor higher classes.

RESULT: The moisture content of the given sample of brick is ……%

CONCLUSION: The given sample can be used / cannot be used as buildingmaterial

EXPERIMENT NO:- 10

AIM: - Spring TestingOBJECTIVE: -To determine the stiffness of the spring and modulus of rigidityof the spring wireAPPARATUS: - 1. Spring testing machine

2. A spring3. Vernier caliper, Scale

DIAGRAM:-

THEORY: - Springs are elastic member which distort under load and regain theiroriginal shape when load is removed. They are used in railway carriages, motorcars, scooters, motorcycles, rickshaws, governors etc. According to their usesthe springs perform the following Functions:

1) To absorb shock or impact loading as in carriage springs.2) To store energy as in clock springs3) To apply forces to and to control motions as in brakes and clutches.4) To measure forces as in spring balances.5) To change the variations characteristic of a member as in flexible

mounting of motorsThe spring is usually made of either high carbon steel (0.7 to 1.0%) or mediumcarbon alloy steels. Phosphor bronze, brass, 18/8 stainless steel and Monel andother metal alloys are used for corrosion resistance spring. Several types of springare available for different application. Springs may classified as helical springs,leaf springs and flat spring depending upon their shape. They are fabricated ofhigh shear strength materials such as high carbon alloy steels spring formelements of not only mechanical system but also structural system. In severalcases it is essential to idealise complex structural systems by suitable springPROCEDURE:

1) Measure the diameter of the wire of the spring by using the micrometer.2) Measure the diameter of spring coils by using the vernier caliper3) Count the number of turns.4) Insert the spring in the spring testing machine and load the spring by a

suitable weight and note the corresponding axial deflection in tension orcompression.

5) Increase the load and take the corresponding axial deflection readings.6) Plot a curve between load and deflection. The shape of the curve

gives the stiffness of the spring.

OBESERVATIONS:Diameter of the spring wire, d =………mm(Mean of three readings)Least count of vernier caliper = ……mmDiameter of the spring coil, D = ……mm(Mean of three readings)Mean coil diameter, Dm = D - d……mmNumber of turns, n =

OBESERVATION TABLE:

Sr.No.

Load,W

(N)

Deflection,(δ)

(mm)

Stiffness K = W / δ

N / mm

12345

Mean k = ……

Modulus of Rigidity =

Spring Index = Dm / D

RESULT: The value of spring constant k of closely coiled helical spring is found to

be --------- N / mm

PRECAUTION:- 1)The dimension of spring shall be measured accurately

2) Deflection obtained in spring shall be measured accurately