som experiments

7/30/2019 Som Experiments

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2/17M.E.Ss P.I.I.T., NEW PANVEL MECHANICAL & AUTOMOBILE ENGINEERING DEPARTMENTS STRENGTH OF MATERIALS LAB ORATORY EXPERIMENTS

Experimental Set-up: UNIVERSAL TESTING MACHINE

Observations:1. Diameter of the bar (d) = _____ mm

Area (A) = ______ mm2

2. Gauge length of the bar (l) = _____ mm.3. Initial Scale Reading (S0) = _____ mm.4. Reduced diameter of the bar (d) = _____ mm.

Area (A) = _______ mm2

5. Final Gauge length of the bar (l) = ______mm.6. Diameter of bar (till u not exceeded) = du = _______mm.

Observation Table:

Sr. No.Load

P (kN)

Scale Reading

Si (mm)

Elongation

l

= Si S0 (mm)

Stress

= P/A (MPa)

Strain

= l

/l

Calculations:

1. Poissons Ratio () = Lateral Strain / Linear Strain (till u not exceeded) = (d/d)/ (l/l) =________2. Ductility:

a. % Reduction in c/s area = [(AA)/A] x 100 = _______ %b. % Elongation = [(ll)/l] x 100 = _______%

3. Modulus of Resilience (UR) = Amount ofelastic energy which a material can absorb= (E

2/2E) = ____ J

4. Modulus of Toughness (UT) = Amount of energy which a material can absorb prior to fracture (f x ) = ____ J



EXPERIMENT NO. 2

COMPRESSION TEST ON BRITTLE MATERIAL USING UTM

Aim: a. To conduct compression test on brick and/or concrete materials using Universal Testing Machine.

b. To plot stress-strain curve for compression.c. To determine the Modulus of Elasticity, Ultimate Strength or Rupture Strength.

d. To observe the failure zone of the brittle materials.

e. To measure ductility in terms of % compression and % increase in cross-sectional area.

Apparatus: Universal Testing Machine, Brick and Concrete specimens, Scale, Vernier Callipers, Marker.

Theory: The specimen for compression test is most commonly a simple cylinder having a ratio of length to

diameter, L/d, in the range 1 to 3. However, values of L/d up to 10 are sometimes used where the primary

objective is to accurately determine the modulus of elasticity in compression. Specimens with square or

rectangular cross sections may also be tested.

Buckling may occur if L/d ratio is relatively large. If this happens, the test result is meaningless asa measure of the fundamental compressive behavior of the material. Conversely, if L/d is small, the test

result is affected by the details of the conditions at the end. In particular, as the specimen is compressed,

the diameter increases due to the Poisson effect, but friction retards this motion at the ends, resulting in

deformation into a barrel shape. Although this effect can be minimized by proper lubrication of the ends, it

is difficult to avoid entirely. As a result, in materials that are capable of large amounts of deformation incompression, the choice of too small of an L/d ratio may result in a situation where the behavior of the

specimen is dominated by the end effects. Again the test does not measure the fundamental compressive

behavior of the material. Hence, L/d = 3 is taken for ductile materials, and L/d = 1.5 or 2 are taken for

brittle materials, where the small amount of deformation that occurs causes less difficulty with end effects.

Procedure:

1. Take the brittle material of suitable dimensions.2. Place the specimen properly between the middle and lower crossheads of the UTM, and adjust the

positions of the crossheads so that they just touch the specimen without inducing any compressive

load.

3. Note down the initial scale reading.4. Select suitable loading range of the UTM.5. Making sure the release valve is closed, open the control valve so that the load is applied slowly and

gradually at a constant rate.

6. Record the loads at suitable intervals and the corresponding scale readings till fracture occurs.7. Close the control valve and open the release valve to drain out the oil back in the oil tank.8. Remove the fractured specimen and put off the machine.9. Note down the dimensions of the fractured specimen.10. Observe the fractured zone.

Results: The following important stress values have been found out:

1. Ultimate Tensile Strength (u) = Fracture (Breaking) Strength (B) = ______ MPa2. Youngs Modulus of Elasticity in compression (EC) = Slope of- curve = ______ MPa3. Poissons Ratio () = ______ (till u not exceeded).4. Ductility:

a. % increase in c/s area = _______ %b. % compression = _______%

5. Modulus of Toughness (UT) = ____ JConclusions: The initial portions of compressive stress-strain curves have the same general nature as those in

tension. Many materials that are brittle in tension have this behavior because they contain cracks or voids

that grow and combine to cause failures along planes of maximum tension, i.e., perpendicular to the

specimen axis. Examples are gray cast iron, concrete etc. Such voids or cracks have much less effect in

compression, so that materials that behave in a brittle manner in tension usually have considerably higher

compressive strengths. Quite ductile behavior can even occur for materials that are brittle in tension, e.g.,polymers.



Where compressive failure does occur, it is generally associated with a shear stress, so that thefracture is inclined about 45 to the specimen axis. This type of fracture is evident for gray cast iron, an

aluminium alloy and concrete.

The ultimate strength behavior in compression differs in a qualitative way from that in tension.

Note that the decrease in load prior to final fracture in tension is associated with the phenomenon ofnecking. This of course does not occur in compression. In fact, an opposite effect occurs, in that the

increasing cross-sectional area causes the stress-strain curve to rise rapidly rather than showing a

maximum.

As a result, there is no load maximum in compression prior to fracture, and the engineering

ultimate strength is same as the engineering fracture (breaking) strength. Brittle and moderately ductilematerials will fracture in compression. But many ductile metals and polymers simply never fracture.

Instead, the specimen deforms into an increasingly larger and thinner pancake shape until the load required

for further deformation becomes so large that the test must be suspended.

Brittle materials are found to be less tough than ductile materials, because even though stress

values are high, but the corresponding strains are very small.

Specimen Dimensions:

Observations:

1. (Width x Thickness x Length) of the specimen (for rectangular c/s): W = _____ mm, T = ______ mm,L = ______ mm.

Diameter of the Specimen (for circular c/s) = D = ______mm, Length (L) = _______ mm.

2. Initial Scale Reading S0 = ______ mm.3. Final dimensions of the specimen:

W = _____ mm, T = ______ mm, L = ______ mm. (rectangular c/s)D = ____ mm, L = _____ mm (circular c/s)

Observation Table:

Sr. No.Load

P (kN)Scale Reading

Si (mm)Compression

l= Si S0 (mm)Stress

= P/A (MPa)Strain

= l /l

Calculations:1. Poissons Ratio () = Lateral Strain / Linear Strain = ________2. Ductility:

c. % increase in c/s area = [(AA)/A] x 100 = _______ %d. % compression = [(LL)/L] x 100 = _______%

3. Modulus of Toughness (UT) = Amount of energy which a material can absorb prior to fracture (1/2) x ( x ) = ____ J



EXPERIMENT NO. 3

ROCKWELL HARDNESS TEST

Aim: a. To understand the principle of the Rockwell Hardness Test.

b. To obtain the Rockwell Hardness Numbers (HRB & HRC) for the given test specimen.

Apparatus: Rockwell Hardness Testing Machine, Standard Cone and Ball type indentors and their attachments,

Test specimens.

Principle of Test: A penetrator of standard type is forced into the surface of the test piece in two stages. A

preliminary initial load of 10 kgf is applied and an additional load (140 kgf for cone and 90 kgf for ballindentors) is later applied as shown in the figure, for 20 seconds, and removed. The permanent increase in

depth of indentation is a measure, under specific conditions, from which a value is deduced known as

Rockwell Hardness Number (HRB-Hardness Rockwell Ball & HRC-Hardness Rockwell Cone).

Procedure:

1. Select a test piece of which the hardness is to be measured. Ensure that the surface is free from dirt,oxides, scales or other harmful matter, if any.

2. Select a suitable type of indentor and fix it into the attachment of the machine.3. Place the selected test (work) piece over the table such that it is properly supported making sure that it

doesnt step when the major (additional) load is applied.

4. Raise the main screw by rotating the hand-wheel so that the indentor just touches the surface of the testpiece at a suitable location.5. Apply the preliminary load F0 (10 kgf) to establish reference position for depth measurement, thereby

penetrating through any surface scales or foreign particles. This is done by rotating the hand-wheel

further and ensures that proper pressure is applied, making sure the small pointer on the dial gauge

doesnt overstep the red-point mark.

6. Apply additional load F1 (140 kgf for diamond-cone and 90 kgf for ball indentors) by operating thehand lever, and wait for a period of 20 seconds. Thereby, the total load (F = F0 + F1) is obtained andthe movement of the indicator of the dial gauge stops.

7. The lever is operated again in backward direction to remove the additional load. At this stage, theindicator of the dial gauge moves in the reverse direction and becomes stationary.

8. Read the position of the indicator on the dial gauge, and this will give the Rockwell Hardness Number.Use B scale for Ball indentor and C scale for Cone indentor.

9. Follow the same procedure for different readings. Omit the first two readings as these tend to givefaulty results. Take the average of the rest of the readings.

Conclusions: The Rockwell Hardness Number of the given test specimen (Carbon Steel) is found to be _____HRB

and _______HRC. These are found to be in good agreement with the established values for the material.

Hence, suitable tests may be further carried out to estimate hardness for different materials, with the use ofcorresponding standard indentor types. Also, hardness tests may be carried out for cylindrical work-pieces

(on cylindrical surfaces) by taking suitable correction factors.

Note: Each Rockwell hardness scale has a maximum useful value around 100. An increase of one unit of

regular Rockwell hardness represents a decrease in penetration of 0.002 mm. Hence, the hardness numberis:

002.0

hMHRX

where, h = (h2 h1) is in millimeters and M is the upper limit of the scale. For regular Rockwell hardness,M=100 for scales using the diamond point (C scale), and M=130 for all scales using ball indentors

(B scale). The hardness numbers are designated HRX, where X indicates the scale involved.

In practice, the hardness numbers are read directly from the dial on the hardness tester, rather than

being calculated.



Diamond Cone Brale Indentor

Experimental Set-up: ROCKWELL HARDNESS TESTER

Observation Table:

Sr. No. Indentor Type Total Load F (kgf)Rockwell Hardness

Number (HRX)

Average Reading

(HRX)

1Ball Type Indentor

Diameter of Ball = 1.588 mm100

HRB

HRB2 HRB

3 HRB

4 Diamond Cone Type Indentor

(Brale Indentor)

Included angle at tip = 120

150

HRC

HRC5 HRC

6 HRC



EXPERIMENT NO. 4

BRINELL HARDNESS TEST

Aim: a. To understand the principle of the Brinell Hardness Test.

b. To obtain the Brinell Hardness Number (BHN or HB) for the given test specimen.

Apparatus: Brinell Hardness Testing Machine, Standard Ball type indentor and its attachment, Test specimen,

Hand Microscope and Micrometer Unit for measuring indentation diameter.

Principle of Test: A ball indentor of diameter D is forced by applying a load into the surface of the test piece.

The diameter of indentation d marked on the surface of work-piece is measured, and BHN is calculatedby dividing the test load by the curved surface area of the indentation.

Procedure:1. Select a test piece of which the hardness is to be measured. Ensure that the surface is free from dirt,

oxides, scales or other harmful matter, if any.

2. Choose a ball indentor of standard diameter D and fix it into the attachment of the machine.3. Place the test piece over the table such that it must be properly supported making sure it doesnt slip

when the major load is applied.

4. Raise the main screw by turning the hand wheel so that the indentor just touches the surface at asuitable location.

5. Apply the preliminary load F0 (10 kgf) to establish reference position for depth measurement, therebypenetrating through any surface scales or foreign particles. This is done by rotating the hand-wheelfurther and ensures that proper pressure is applied, making sure the small pointer on the dial gauge

doesnt overstep the red-point mark.

6. Apply additional load F1 by operating the hand lever, and wait for a period of 20 seconds. Thereby,the total load (F = F0 + F1=187.5 kgf) is obtained and the movement of the indicator of the dial gauge

stops.

7. The lever is operated again in backward direction to remove the additional load. At this stage, theindicator of the dial gauge moves in the reverse direction and becomes stationary.

8. Remove the test piece and use hand-microscope & micrometer unit to measure the diameter ofindentation d on the test specimen. Use the formula to calculate BHN.

9. Follow the same procedure for different readings. Omit the first two readings as these tend to givefaulty results. Take the average of the rest of the readings.

Results and Conclusions:1. The Brinell Hardness Number for the given test-specimen (Carbon Steel) = _______HB.2. As per empirical correlation, Ultimate tensile strength of the material: u = ________MPa.3. These are found to be in good agreement with the established values for the material. Hence, suitable

tests may be further carried out to estimate hardness for different materials, with the use of

corresponding standard indentor types.


8/17

M.E.Ss P.I.I.T., NEW PANVEL MECHANICAL & AUTOMOBILE ENGINEERING DEPARTMENTS STRENGTH OF MATERIALS LAB ORATORY EXPERIMENTS

Observations:

1. Specification of Standard Test Specimen (made of Carbon Steel): RE / 2.5 / 187.5 kgf / 202 HB.2. Least Count of Microscope Micrometer = 0.01 mm.3. Indentor Diameter D = 2.5 mm.4. Test Load P =187.5 kgf .

Observation Table:

Sr. No. Diameter of Indentation d (mm) Average d (mm) BHN (or HB)

Calculations:

Brinell Hardness Number (BHN) =tationreaOfIndenSphericalA

kgfinTestLoad=

5.022

2 dDD

D

P

= ___________

Ultimate Tensile Strength u 3.45 BHN = __________ MPa.


9/17


EXPERIMENT NO. 5

IZOD IMPACT TEST

Aim: a. To observe the behaviour of specimen under Izod Impact Load.

b. To measure the amount of energy absorbed by the specimen using Impact Testing Machine.

Apparatus: Impact Testing Machine (Pendulum type), Specimen of mild steel material.

Theory:Toughness is a measure of the amount of energy a material can absorb before fracturing. It becomes of

engineering importance when the ability of a material to withstand an impact load without fracturing is considered.

Impact test conditions were chosen to represent those most severe relative to the potential for fracture, viz.,

(1) deformation at a relatively low temperature, (2) a high strain rate (i.e., rate of deformation), and (3) a triaxial

stress state (which may be introduced by the presence of a notch). The impact test is a common method whichmeasures the impact energy (notch toughness).

A material possessing a large amount of impact resistance is said to be a tough material. Toughness is the

ability of the material to resist both fracture and deformation. Toughness is different from either strength or

ductility. To be tough, a material must be both fairly strong and fairly ductile to resist both cracking and bending

under impact loading.

Impact testing machines usually take the form of a pendulum which is carried to strike a sudden blow

against the test specimen in a certain standard manner. The energy absorbed from the swinging pendulum by the

specimen is taken as the impact energy value of the material used. The load is applied as an impact blow from a

weighted pendulum hammer that is released from a cocked position at a fixed height "h". The specimen is positionedat the base as shown. Upon release, a knife edge mounted on the pendulum strikes and fractures the specimen at the

notch, which acts as a point of stress concentration for the high velocity impact blow. The pendulum continues its

swing, rising to a maximum height "h", which is lower than "h". Based on the difference between h and h, the

energy absorption of the specimen is computed.

Notches are provided in the impact specimen to increase the stress concentration and the tendency to

fracture.

Procedure:1. Set the pointer to the maximum energy level on the scale when the pendulum is freely suspended.2. Raise the pendulum hammer to the required height. Release it allowing a free swing and observe the

initial energy.3. Raise the pendulum again to the same height as before and clamp it and set the point to the maximum

energy on the scale.

4. Place the specimen as a vertical cantilever beam at the bottom in the anvil so that the notch faces thehammer and is half inside and half above the top surface of the anvil.

5. Release the hammer by operating the mechanism. The hammer strikes the specimen and breaks orbends the specimen.

6. Note the final reading on the scale.7. Calculate the shock absorbing capacity.

Conclusions:1. The specimen bends and breaks, or partially bends and breaks indicating different degrees of

toughness.2. Notch is placed facing the hammer resembling a cantilever beam, so that failure occurs in the tensile

zone corresponding to the maximum stress concentration zone.

3. Shock absorbing capacity under impact loading of mild steel material is found to be _________ J.


10/17


Loading Arrangement Specimen Dimensions

Experimental Set-up: IZOD IMPACT TESTING MACHINE

Observation Table:

Sr. No. Material Initial Energy IE

(J)

Final Energy FE

(J)

Shock Absorbing

Capacity(Toughness)

FE-IE (J)


11/17


EXPERIMENT NO. 6

CHARPY IMPACT TEST

Aim: a. To observe the behavior of specimen under Charpy Impact Load.

b. To measure the amount of energy absorbed by the specimen using Charpy Testing Machine.

Apparatus: Impact Testing Machine (Pendulum type), Specimen of mild steel material.

Procedure: The procedure for this test is similar to that of Izod Impact Test. The difference here is that the strikingenergy is much more greater, and the specimen is kept as a simply supported beam and placed on the anvil

so that the notch faces opposite direction to the striking edge of the hammer. Here, the same V-notch may

be used for the specimen, or use can be made of a U-notch at half the depth value. Stress concentration is

produced at the notch to a greater extent which induces the failure to take place at that location.

Conclusions:1. The shock absorbing capacity of mild steel material = _______ J.2. The specimen bends and breaks, or partially bends and breaks indicating different degrees of

toughness.

Loading Arrangement

Observation Table:

Sr. No. Material Initial Energy IE(J)

Final Energy FE(J)

Shock AbsorbingCapacity

(Toughness)

FE-IE (J)


12/17


EXPERIMENT NO. 7

FLEXURE TEST ON TIMBER BEAM USING UTM

Aim: a. To observe the bending phenomenon of a rectangular timber beam for given loading, till fracture occurs.

b. To compare flexure of timber beams of same cross section, but with different orientations.

c. To determine the bending strength, elastic modulus of the material.

Apparatus: Timber beams, Universal Testing Machine, Supports, Spanner for tightening, Loading tool, Scale.

Theory: Bending (flexure) tests on smooth (unnotched) bars of material are commonly used, as in various

ASTM (American Standard for Testing & Materials) standard test methods for flat metal spring material,

and for concrete, natural building stone, wood, plastics, and glass. Bending tests are especially needed to

evaluate the tension strength ofbrittle materials; as such materials are difficult to test in simple uniaxial

tension due to cracking in the grips. The specimens usually have rectangular cross sections and may beloaded in either three-point bending or four-point bending. Here, we use 3-point bending for the

experiment.

In bending, note that the stress varies through the depth of the beam in such a way that yielding

first occurs in a thin surface layer. This results in the load versus deflection curve not being sensitive to the

very beginning of yielding. Also, if the stress-strain curve is not linear, as after yielding, the simple elastic

bending analysis is not valid. Hence, bending tests are most meaningful for brittle materialsthat haveapproximately linear stress-strain behavior up to the point of fracture.

For materials that do have approximately linear behavior, the fracture stress may be estimated

from the failure load in the bending test using simple linear elastic beam analysis.

I

yM.

where, M=Bending Moment, y=half depth of beam, I=moment of inertia of c/s area about the neutral axis.

f() is usually identified as the bend strength or the flexural strength or rupture modulus in bending.

Yield strengths in bending are also sometimes evaluated. Here, load corresponding to fracture is

replaced by load corresponding to a strain offset at the beginning of yielding.

The elastic modulus may also be obtained from a bending test. In a 3-point bending test, usinglinear-elastic analysis, the maximum deflection occurs at the mid-span.

EI

PL

48

3

The value of E may then be calculated from the slope (dP/dy) of the initial linear portion of the

load versus deflection curve.

d

dP

I

LE

48

3

Elastic moduli derived from bending are generally reasonably close to those from tension or

compression tests of the same material, but there are possibilities of several discrepancies.

Procedure:1. Take two timber beams of same length and same size.2. Support the first beam on simple supports, and place it symmetrically.3. Fix the loading tool in the jaws of the middle crosshead of UTM.4. Adjust the load pointer such that it is at zero position when the tool just touches the beam centrally.5. Note down the initial scale reading.6. Operate the control valve, and gradually apply the load at a consistent rate.7. Note down the different loads and the corresponding scale readings till the specimen shows first sign

of crack.

8. Stop the loading, operate the release valve.9. Repeat the experiment for other beam having same cross section but with different orientation.10. Compute the results and compare the two orientations.


13/17


Results and Conclusions:

1. ORIENTATION 1:

1. Elastic Modulus (E) = _______ MPa.

2. Flexural Strength () = ______ MPa.

2. ORIENTATION 2:1. Elastic Modulus (E) = _______ MPa.

2. Flexural Strength () = ______ MPa.

3. The values of E and for both orientations are found to be more or less same. Hence,E=_______MPa and =______MPa may be taken as the average values for timber material.

4. Orientation 2 is found to withstand a greater amount of load even though the cross section dimensionsare same, which is due to a greater value of the area moment of inertia, signifying more resistance to

bending. Conversely, for the same amount of load, orientation 2 is found to consist of less amount of

induced bending stress compared to the other orientation. Hence, the orientation 2 is preferred for

safe design.

Loading of specimen: Orientation 1 Orientation 2

Observations:1. Length of the specimen (L) = _____ mm.2. Width of the specimen (W) = _____ mm.3. Thickness of the specimen (T) = _____ mm.4. Distance of the extreme-most fiber from neutral axis (y1) = ______ mm, (y2) = ______mm.5. Maximum load to fracture (P) = ______ kN.6. Initial Scale Reading (S0) = ______ mm.7. Slope of P- curve = ________ N/mm.

Observation Table: (for both orientations, draw separate tables).

Sr. No. Load P (kN) Scale Reading Si (mm) Deflection at mid-span

= Si S0 (mm)

Calculations:

1. Maximum Bending Moment (at mid-span) = M = P.L/4 = __________ N-mm. (calculate for bothorientations i.e., M1 and M2).

2. Area Moment of Inertia = I = AB3/12 = _________ mm4.(Note: Here, A = Length of parallel edge of c/s, to the Neutral Axis; and B = Length of

perpendicular edge. Calculate I for both the orientations i.e. I1 and I2).

3. Flexure StrengthI

yM. = _________ MPa. (calculate for both orientations).

4. Modulus of Elasticity =

d

dP

I

LE

48

3

= ________ MPa. (calculate for both orientations).

P

P/2 L P/2

y1 y2


14/17


EXPERIMENT NO. 8

TENSILE TEST ON THIN ALUMINIUM ROD USING TENSILE TESTING MACHINE

Aim: To conduct tensile test on thin aluminium rod using tensile testing machine so as to achieve the following

objectives:

1. To plot stress-strain curve.2. To observe elastic and plastic zones.3. To determine the stresses corresponding to Proportional Limit, Elastic Limit, Yield points, Ultimate

Strength and Fracture (Breaking) Strength.

4. To determine Modulus of Elasticity, Poissons Ratio, and measure of Ductility.5. To determine the Modulus of Resilience and Fracture Toughness.

Apparatus: Tensile Testing Machine, thin aluminium rod, vernier calipers, allen key, scale.

Procedure:1. Measure the diameter of the aluminium rod.2. Take a suitable gauge length so that it may be fixed between jaws of the tensile testing machine.3. Adjust the scale and load setting of the machine.4. Mark initial scale reading corresponding to zero load.5. Gradually increase the load by putting the machine on. The movement of bottom jaw of the machine

is electrically operated instead of the hydraulic action as seen in UTM.

6. Note down the intermediate loads and the corresponding scale readings till fracture occurs.7. Unload the specimen after fracture.8. Rejoin the pieces, and measure the final length and the diameter of the specimen.


1. The following important stress values have been found out:a. Yield Stress (y) = ______ MPa

b. Ultimate Tensile Strength (u) = ______ MPac. Fracture (Breaking) Stress (f) = ______ MPa

2. Youngs Modulus of Elasticity (E) = Slope of linear- curve = ______ MPa3. Poissons Ratio () = ______ (till u not exceeded).4. Ductility:

a. % Reduction in c/s area = _______ %

b. % Elongation = _______%5. Modulus of Resilience (UR) = ____ J6. Modulus of Toughness (UT) = ____ J7. Ductility measured as % reduction in area, is based on the minimum diameter at fracture and so is a

measure of highest strain along gauge length. But, ductility measured as % elongation at fracture, is an

average over an arbitrary chosen length (gauge length). % reduction in area is not affected byarbitrariness of L/d ratio, and hence is a more fundamental measure of ductility than is the elongation.

8. Ductile materials are tougher than Brittle materials.

Aluminium Rod Specimen:

Length L d


15/17


Experimental Set-up: TENSILE TESTING MACHINE

Observations:1. Diameter of the bar (d) = _____ mm

Area (A) = ______ mm2

2. Gauge length of the bar (l) = _____ mm.3. Initial Scale Reading (S0) = _____ mm.4. Reduced diameter of the bar (d) = _____ mm.

Area (A) = _______ mm2

5. Final Gauge length of the bar (l) = ______mm.6. Diameter of bar (till u not exceeded) = du = _______mm.

Observation Table:

Sr. No.Load

P (kN)

Scale Reading

Si (mm)

Elongation

l= Si S0 (mm)

Stress

= P/A (MPa)

Strain

= l /l

Calculations:1. Poissons Ratio () = Lateral Strain / Linear Strain (till u not exceeded) = (d/d)/ (l/l) =________2. Ductility:

a. % Reduction in c/s area = [(AA)/A] x 100 = _______ %b. % Elongation = [(ll)/l] x 100 = _______%

3. Modulus of Resilience (UR) = Amount ofelastic energy which a material can absorb= (E

2/2E) = ____ J

4. Modulus of Toughness (UT) = Amount of energy which a material can absorb prior to fracture (f x ) = ____ J


16/17


EXPERIMENT NO. 9

TORSION TEST ON DUCTILE MATERIAL USING TORSION TESTING MACHINE

Aim: To conduct torsion test on mild steel shaft using torsion testing machine so as to achieve the following

objectives:

1. To plot torque-angular deflection (T-) curve.2. To determine the shear modulus (G).3. To estimate the shear strength ()and fracture strength (max).4. To observe the failure zone.

Apparatus: Torsion testing machine, mild steel rod, vernier callipers, scale.

Theory: Tests of round bars loaded in simple torsion are relatively easy to conduct, and unlike tension tests

they are not complicated by the necking phenomenon. The angle of twist , which is proportional to shearstrain, is generally increased at a constant rate. Torque T, which is of course related to shear stress, is

measured as the test proceeds. Within the initial linear-elastic behavior portion of the test, the shear

modulus G is proportional to the slope (dT/d) and so can be evaluated.

Fracture strength values are subject to a similar situation as in bending tests, namely that non-

linear stress-strain behavior may result in stresses calculated based on linear-elastic behavior not being

accurate. This limitation can be overcome by testing thin-walled tubes in torsion, for which the error isalways small. However, even for solid bars in torsion, the test results may be useful for comparing the

strength and ductility of various materials.

Procedure:

1. Measure the diameter d and length l of the specimen.2. Fix the specimen between the two jaws of the machine tightly, and adjust the pointer to zero of the

twisting moment scale, and to zero of the angle-of-twist disc.

3. Apply the torque and record the torques and the corresponding angle of twists.4. Record the twisting moment at fracture, and observe the failure zone of the specimen.


1. Shear modulus (Modulus of Rigidity, G) = _________ MPa.2. Fracture strength (Shear Strength, max) = ________ MPa.3. In a torsion test, brittle materials fail on planes of maximum tension, which occur at 45 to both the

specimen axis and the specimen surface. This produces a helical spiral fracture. In contrast, ductile

materials generally fail on planes of maximum shear, that is, on planes transverse and longitudinal to

the specimen axis, as for the mild steel material.

Mild Steel Specimen:

Length L d


17/17


Experimental Set-up: TORSION TESTING MACHINE

Observations:

1. Diameter of the shaft (d) = _____ mm2. Gauge length of the bar (l) = _____ mm.

Observation Table:

Sr. No. Torque T

(kgf-cm)

Angle of Twist

(degrees)

Torque T

(N-mm)

Angle of Twist

(radians)

Calculations:1. Polar moment of inertia (Jp) = (/32) x d4 = ________ MPa.2. From Torsion formula:

l

G

Jp

T

Jp

l

x

T

G

i.e., G = (Slope of T- graph within elastic limit) x (l/Jp)3. Shear strength () is found from the relation:

rJp

Te where, Te = Torque at elastic limit, r = radius.

4. Fracture strength (max) is found from the relation:

rJp

T maxmax where, Tmax = Torque at fracture.

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