mctl_course_material

PESIT-ME Materials characterization & testing lab ME256 SVV

ME256 – Materials characterization & Testing Laboratory (0+0+2)

INDEX

Faculty S.V.Venkatesh

Expt. # Contents Page No. Marks

1. Tension Test 3 – 7

2 & 6. Izod & Charpy Impact Test 8 -12

3. Rockwell Hardness Test 13 – 14

4. Torsion test 15 – 18

5. Compression test 19– 21

7. Shear Test 22– 23

8. Preparation of specimen for Microscopic observation

24

9. Vickers Hardness Test. 25 – 26

10. Bending test 27 - 28

11. Wear Test 29 – 31

12. Brinell Hardness test 32– 33

13. Fatigue Test 34 – 35

14. Non-destructive Test 36 - 40

Reference:-Manual prepared by the college.

Jan 2010


Cycle of Experiments

Faculty S.V.Venkatesh

Experiment #

Description Class #

Introduction 1

Cycle I

1. Tension Test 2

2 & 3. Izod Impact Test & Rockwell Hardness Test

3

4. Torsion test 4

7. Shear Test 5

11. & 9. Wear Test &

Vickers Hardness Test

6

13. Fatigue Test 7

Cycle II

10. Bending test 8

11. Charpy Impact test 9

12. Brinell Hardness test 10

5. Compression test 11

14. Non-destructive test 12

8. Preparation 0f Specimen for Metallographic Examination.

13

Jan 2010


EXPERIMENT No. : 1 - TENSION TEST [IS 1608:1995]

AIM :

A) To determine mechanical properties such as ultimate tensile strength, elastic

modulus, proportionality limit, yield point, fracture stress, percentage elongation &

reduction in area etc. of metals & alloys.

B) To study the behaviour of materials & characterize types of fracture under tensile

load.

APPARATUS USED:

Universal testing machine, Extensometer, Caliper, Scale, test specimen, etc.,

DESCRIPTION OF APPARATUS: Universal testing machine (capacity 40 KN) is

used for evaluating stress - strain properties of materials in tension, compression,

bending and shear. Different load ranges like 40KN, 10KN and 20KN are selected

depending on the nature of materials. Specimens are mounted and gripped using

special grips and load is applied axially and continuously. Extensometers are used for

measuring extension accurately and they are recorded suitably.

THEORY: In static tension test, the operation is accomplished by gripping opposite

ends of the piece of the material and pulling it apart. In a tension test the test specimen

elongates in a direction parallel to applied load.

PROCEDURE: Diameter ‘d’ of the given specimen as shown in fig 1 is measured using

a micrometer and the mean value is noted. Using this average diameter, initial area of

cross section is calculated. The gauge length ‘Lo’ is marked on the specimen accurately

using centre punch. One end of the specimen is firmly fixed on the top plate using grips

such that the gauge length marks face the operator. Extensometer is fixed in the area

containing gauge marks.

Lift the bottom platen of the machine using a hydraulic control and fix the bottom end of

the specimen using special grips available with the machine.

Load range is selected depending on the nature (Ferrous / Non ferrous, composition,

Heat treatment etc.) of the material. Load is applied slowly and continuously. Load and

Extensometer readings are noted simultaneously. After reaching the yield point

(disproportionate elongation) Extensometer is removed and elongation is measured

using a scale mounted on the machine. Load is applied continuously till the specimen

fractures and maximum load is noted. Broken pieces are removed; location and

Jan 2010


characteristics of the fracture are studied. Two fractured pieces are kept together & final

diameter ‘dU’ and final gauge length ‘lU’ of the specimen is measured using a caliper.

Final area of the specimen is calculated. Using load - extension data, stress and strain

are calculated and a graph is plotted.

Specimen details:

1. Thickness of the test piece.

2. Width of parallel length of the flat test piece.3. Diameter of the parallel of a circular test piece.4. Original gauge length.5. Parallel length of extensometer gauge length.6. Total length of test piece.7. Final gauge length after fracture.8. Original cross-sectional area of the parallel length.9. Minimum cross section area after fracture.10. Gripped ends..

Calculation of diameter:-

Sl.No MSR CVD TR AVG

123

Specimen Calculation : Material = Mild SteelOriginal gauge length = LO mm = Final gauge length = LU mm = Initial diameter = d mm = Final diameter = du mm = Original area of cross section, SO (mm2) =d2 /4 = Final area of cross section, SU (mm2) = dU 2 /4 =Ultimate tensile strength = Pmax / SO = Rm = % Elongation, A = ((LU -LO)/LO) x 100 =% Reduction in area, Z = ((SO - SU)/SO) x 100 = Fracture load Pf= Fracture stress = Pf / SO = Elastic modulus E = Slope of the straight line portion of stress - strain graphTABLE:

Sl No. Load P (Newton’s) Extension(mm) Stress (N/mm2) Strain L R

Jan 2010


Jan 2010


Graph: Stress Vs Strain

Question BankExpt. 11. Define: Elastic limit, Proportional limit, Elastic modulus, yield strength Secant modulus, tangent modulus, True stress, true strain Resilience, Toughness, Poisson Ratio2. Write expressions for the following a) Resilience in terms of yield point b) True stress in terms of engg. Stress c) True strain in terms of engg. Stress d) Elastic modulus in terms of Poisson ratio.3. Draw the stress-strain curve for the following materials and compare: a) Mild steel b) Copper c) Aluminium d) Cast Iron e) Glass f) Rubber a) Discuss yield point phenomenon in mild steel. Write a note on Luder’sband and their formation. b) What is gauge length and describe its applications.5. How do you measure strain accurately? Explain the principle of resistance strain gauges.

Jan 2010


6. Draw the stress-strain curve for carbon steel containing 0.3% carbon, 0.6% carbon and 1.5% carbon.7. Draw stress - strain curve for copper at -20C room temperature and 400C.8. Distinguish between a) Resilience and Toughness b) Elastic limit and proportional limit. c) Elastic deformation and plastic deformation d) Ductile fracture and brittle fracture.9. Why necking is observed only in ductile fracture.10. What are the different modes of deformation? Explain them using suitable sketches.11. What are the effects of strain rate on mechanical properties of materials?12. Describe Bauschinger effect and its consequences on metal forming applications.13. Compare Engineering stress-strain curve and true stress-true strain curve for mild steel.14. How does a universal testing machine work?15. What is a ductile fracture? Discuss its features and mechanisms.

Jan 2010


EXPERIMENT No.: 2 & 6 - IMPACT TEST [IS 1598 & 1499 : 1977 ]AIM: To find out the impact strength of the given-notched specimens.APPARATUS:Pendulum type impact testing Machine.THEORY:

Impact test is used to find out the energy required to rupture a material under sudden

application of load. Different types of notched bar impact tests are carried out to

determine the tendency of a material to behave in a brittle manner. Notch creates stress

concentration which will ensure that fracture does occur in notch, energy will spread

evenly along the bar and causes it to plastically deform by breaking rather than bending.

Two standard impact tests presently used in industry are the Izod and Charpy .In the

Charpy test a notched bar is held horizontally as it is hit by the pendulum. In the Izod test

the test bar is held vertically at the bottom end. Both these tests measure energy by

using a swinging pendulum to strike a test sample.

Dimensions of standard Izod and Charpy test specimens are shown in figure 1. The

mounting of the test specimen is shown in figure 2.

The differences between these two tests are in the design of test specimens and the

velocity with which the pendulum hits the test bar. Figure 2(c) illustrates the position of

the pendulum at an angle called the ‘angle of fall’. At this position, the pendulum has

potential energy = Wa, where W is the weight of the pendulum. In falling through an

angle , it picks up momentum & when hits the sample at B, potential energy is zero

whereas it has acquired kinetic energy depending on the velocity. Impact

velocity = 2gr(1-cos) where r is the radius of the pendulum and g is acceleration due

to gravity .In the standard Izod test the pendulum is set to strike the specimen at a

velocity of 11.5 ft/sec while in Charpy the standard velocity is 17.5ft/sec. At O a part of

the energy is absorbed to create fracture and the pendulum swings up to the position C

indicated by an angle known as ‘angle of rise’. The energy absorbed by the specimen

at the time of breaking is given by the equation E = Wr (cos - cos). Where E is the

energy required to break the specimen, W is the weight of the pendulum, r is the radius

or length of the pendulum, is the angle of fall and is the angle of rise. Fracture

surface reveals two distinct zones - one bright and granular area, which represents

Jan 2010


brittle fracture, and the other dull area which represents shear fracture where slight

plastic deformation has taken place.

V - NOTCH

PROCEDURE:Measure the dimensions of the specimens (Izod or Charpy) and note down the weight of

the pendulum W (engraved on the surface) and the length of the pendulum r. Using

positioning gauge place the specimen on the anvil correctly .For Charpy test the

specimen is arranged with the notch on the side away form the striking towards the

edge . Lift the pendulum to its upper position and with no specimen on the anvil, release

it and note down the reading. This reading gives friction offered by bearings and air

resistance of the pendulum. Now place the specimen and allow the pendulum to strike it

and rupture it. Stop the pendulum swing by means of a hand brake. Calculate the angle

of rise B and repeat the experiment with different samples and tabulate the results.

Calculation of Breadth :- (Brass)

S.N MSR CVD TR AVG

1.

2.

3.

Least count = 1MSD / No. of Divisions on VSD = 1/50 = 0.02

Jan 2010


Calculation of Depth:- (Brass)

S.N MSR CVD TR AVG

1.

2.

3.

Calculation of Breadth:- (MS)

S.N MSR CVD TR AVG

1

2

3

Calculation of Depth:- (MS)

S.N MSR CVD TR AVG

1

2

3

Specimen Calculation : = Angle of rise, U=Wr (cos -cos) Weight of the pendulum = W (N) = 21.25KGRadius of the pendulum = r(m) = 0.825mAngle of fall, = 85 degree for Izod test and, = 140 degree for Charpy testImpact velocity, V (m/s) = 2gr (1-cos) =

Material Angle of

rise

ScaleReading

U Kg-m

Frictional Loss – f

Kg-m

Energy consum

edI = u – f

Kg-m

Breadth(b)

mm

Depth Below

theNotch

(d)mm

Cross sectional Area of specimen –

A mm2

A = b x d

Impact Strength = (Ix9.81)/A (N-m)/mm2

MS

Brass

Jan 2010


CHARPY IMPACT TEST

Calculation of Breadth:- (Brass)

S.N MSR CVD TR AVG

1

2

3

Calculation of Depth:- (Brass)

S.N MSR CVD TR AVG

1

2

3

Calculation of Breadth:- (MS)

S.N MSR CVD TR AVG

1

2

3

Calculation of Depth:- (MS)

S.N MSR CVD TR AVG

1

2

3

Wt. Of Pendulum, W (N) = 20.59 KgRadius of pendulum, r (m) = 0.825m = 140*

Jan 2010


Material Angle of

rise

Scale Reading

U

Frictional Loss - f

Energy consume

dI = u - f

Breadth(b)

Depth Below

theNotch

(d)

Cross sectional

Area of the specimen -

A mm2

A = b x d

Impact strength =

I/A (N-M) /mm2

MS

Brass

QUESTION BANKExpt. 2

1. Name the important mechanical test which gives valuable information about materials. Discuss one test in detail.

2. What does impact test signify? Explain with necessary theory, the procedure adopted in the impact test conducted using a pendulum type impact testing machine.

3. What is an impact test? What are the advantages and how does it help in finding out ductile to brittle transformation?

4. What are differences between charpy and izod impact tests? Why an impact specimen has a notch?

5. Draw energy absorbed curves for the following: a) Low, medium and high carbon steels b) Low temperature, room temperature and high temperature c) Fine grain size and coarse grain size in a given metal d) FCC, BCC and HCP metals. e) Different directions in a rolled plate.

Jan 2010


EXPERIMENT No. : 3 - ROCKWELL HARDNESS TEST [IS 5652 Part 1: 1993]AIM: To determine Rockwell hardness for given specimens.APPARATUS: Rockwell hardness tester and indentors.THEORY:

The test utilizes the depth of indentation under constant load as a measure of

hardness .The indentor is selected depending on the nature and condition of the

material. Brale indentor, a conical shaped diamond penetrator with 120 degrees apex

angle is used for steel and cast iron. A hardened steel ball (1/16 inch diameter) is used

for non-ferrous metals. A minor load of 10kg is first applied to take care of the roughness

of the surface

Of the specimen and the major load is then applied (60,100,150 kg). The depth of

indentation is recorded on a dial gauge in terms of hardness numbers. Hardened steel is

tested on C scale with diamond indentor and 150kg major load. Softer materials are

tested on the B scale with 1.6 mm diameter steel ball and 90kg major load.

PROCEDURE:

Select suitable load and indentor depending on the nature of the material to be tested.

Specimen is placed on the hardened anvil of the machine which can be raised or

lowered by using a hand operated wheel so that the surface of the specimen just

touches the indentor ,smaller pointer in the dial starts moving and continue to rise the

anvil slowly till the pointer comes to RED dot. This indicates that minor load (10kg) has

been applied. Turn the dial until the mark B-30 (C-0) and the word “SET” is directly

behind the pointer. Release the handle to apply major load. The indentor starts

penetrating, which is read on the dial. Remove the major load by bringing back the

handle to the original position. Read the position of the pointer on the scale, which gives

Rockwell Hardness Number.

Jan 2010


Specimen Calculation

Material Scale used Indentor Total Load Trial - 1

Trial - 2

Trial - 3

Average

Aluminium RB 1/16 - Ball 100 Kg

Cast Iron RC Diamond 150 Kg

Brass RB 1/16 - Ball 100 Kg

M.S. RC Diamond 150kg

QUESTION BANKExpt. 31. Define hardness. What are the units?2. What are the different forms of hardness? Explain them.3. What is MHOS scale hardness . Explain4. Why major and minor load is used in Rockwell hardness test5. What are the indentors used in RB and RC scale. How do you convert hardness values from one scale to another?6. Explain the precautions to be taken in Rockwell hardness test and write expressions relating BHN, RB and RC7. What is rebound hardness and how it is determined.

Mohr’s scale of HardnessDiamond = 10 Sapphire = 9 Topaz = 8 Quartz = 7 Feldspar = 6 Apatile = 5Flourspar = 4 Calcite = 3 Gypsum = 2 Talc = 1

Jan 2010


EXPERIMENT No.: 4 - TORSION TEST [IS: 1717-1984]AIM: To observe the behavior of the given specimen in torsion and find out the material

properties.

OBJECTIVES :

To study the behavior of the given test specimen in torsion.

To determine the modulus of rigidity of the material.

To observe the effect of yielding and mode of fracture.

To determine the modulus of resilience and modulus of rupture.

APPARATUS : TORSION TESTING MACHINE.

THEORY:

Modulus of rigidity: G = T. L .JWhere G= Rigidity modulus

L = Length of the specimen = Angel of twist J = Polar moment of inertia T= Applied torque

Polar moment of inertia: J = x d 4 32Where d = diameter of the specimen

PROCEDURE :

The diameter and length of the specimen provided is measured very carefully using slide

calipers

The specimen is fixed in the chuck using loose pieces provided and tightened them

using Allen key.

The pointer of the protractor is adjusted to the zero position just when the weighing scale

starts showing a deflection. At this point the weighing machine pointer is set to zero of

the scale.

A monotonically (or steadily) increasing torque is applied using the handle of the worm.

At any value of torque applied the corresponding angle o twist indicated by the protractor

is noted simultaneously.

In the initial stage of the handle is turned very slowly and load reading is taken for every

one or half degree twist indicated on the protractor, since during this phase load

deflection is too high.

Jan 2010


In the later stages I.e. when yielding has taken place and there is almost no deflection, in

the weighing scale readings can be taken for every 5-10 degree intervals without much

appreciable errors.

A graph of torque Vs angle of twist is plotted (The scale should be so chosen that the

linear portion and the point of yielding can be easily observed on the plot.) The slope of

linear portion is found out and substituted in equations to get the modulus of rigidity.

The specimen is taken out of the chuck and the failure surface is observed to

understand the type of shear that has taken place (A ductile fracture shows orthogonal

shear surface while a brittle material shows a spiral failure surface.)

Tabular Columns :


Sl.N MSR CVD TR AVG

123

Calculation of length:-

S.N MSR CVD TR AVG

1 2 3

Sl.No. Torque indicated P

(kg-m)

Angle of twist (deg) Torque applied N-m

1

2

3

4

5

6

7

8

9

10

Jan 2010


11

12

13

14

15

Sl. No.

Material C in Metric Units

(kg/mm2)

C in SI Units(N/mm2)

1. Steel 0.84 x 106 0.84 x 105

2. Brass 0.55 x 106 0.55 x 105

3. Aluminium 0.35 x 106 0.35 x 105

4. Cast Iron 0.45 x 106 0.45 x 105

SPECIMEN CALCULATION :Diameter of the specimen = d (mm) =Length of the specimen = L (mm) = Polar moment of inertia, J (mm4) =Modulus of rigidity, G = (L/J) x (T/) = (L/J) x (slope of the curve - T against )

Jan 2010


Question BankExpt. 4

1. Why is torsion formula not applicable to non-circular cross section?2. List the relative advantages & dis advantages of tubular & solid cylindrical torsion

specimens for determinations of shearing strength.3. Explain torsion fracture as in the case of ductile & brittle materials.

Jan 2010


EXPERIMENT No. : 5 - COMPRESSION TEST [IS 13780: 1993]

AIM: To conduct compression test on the given material and to determine properties such as

compressive strength, modulus of elasticity, % of contraction & % increase in area.

APPARATUS USED:

Universal Testing Machine, Extensometer, dial gauge, micrometer, caliper, scale,

cylindrical test specimens etc.

THEORY:

Accurate determination of stress and strain in compression is difficult compared to

tension due to the lateral deflection and bending stresses introduced while testing .If the

specimen is long, lateral buckling takes place resulting in failure of the specimen .Ductile

materials bulge after reaching the maximum compression load where as there is no

change in cross section or height of the specimen for brittle materials and they suddenly

fracture.

PROCEDURE: 1. Fix the lower & upper compression platens above the bottom cross head and below

the top Cross head.

2. Measure the initial dia. do and height of the specimen Lo using a slide caliper

3. Place the specimen at the center of the bottom platen and bring the top of the

specimen in contact with the top plate by moving the cross head downwards.

4. Mount the compression dial gauge in the lower head and bring the indicator to zero.

Move the indicator of the load scale to zero.

5. Record the compression dial gauge readings for every 250kg load increase for

Aluminum, Brass, Copper and every 500 kg load for steel and cast iron.

6. The experiment is continued till the specimen fractures and the maximum load is

noted. Stress Strain curve is drawn.

Calculation of initial diameter:-

S.N MSR CVD TR AVG

1

2

3

Jan 2010


Calculation of final diameter:-

S.N MSR CVD TR AVG

1 2 3

SPECIMEN CALCULATIONInitial gauge length = LO mm =Initial Diameter = dO mm = Original Area SO,(mm2)= dO

2 / 4 = Final gauge length = L1 mm = Final diameter = d mm = Final area of cross section, S1 (mm2) = d1

2 /4 = Ultimate load = Fcu (N) = Compressive strength = Rcm = Fcu / SO (N/mm2) = Proof Stress, Rc from graph =Slope of the straight line portion of the graph, E-(N/mm2)Max compression stress = (max force) / (original area) =% increase in area = ((So-S1)/S1) x 100 = % contraction at fracture ((Lo-L1)/L1) x100 =

GRAPH OF LOAD VS COMPRESSION OF DUCTILE MATERAILS

Jan 2010


TABULAR COLUMN

Sl No. Load P (Newton)

Deformation L ( mm)

Stress (N/mm2)

Strain

12345

6789

101112131415161718192021222324252627

Jan 2010


Graph : Stress – Strain

Question Bank

Expt.5:

1. Why compression strength is an important mechanical property? Describe its role in design.2. Is elastic modulus same for compression and tension for a given material.3. Define lateral strain, Poisson’s ratio. What are the values of poisson’s ratio for the following materials?4. How do you decide the specimen dimensions in compression testing?

Jan 2010


EXPERIMENT No. : 7 - SHEAR TEST [IS 5242: 1979]

AIM :

To determine ultimate shear stress of the given specimens in single and double shear.

APPARATUS:

Universal Testing Machine

THEORY: A type of force which causes or tends to cause two continuous parts of the

body to slide relative to each other in a direction parallel to their plane of contact is

known as shear force. The stress required to produce fracture in the plane of cross

section acted on by the shear force is called shear strength. Shear can be applied either

in tension or compression. Rivets , bolts , screw threads and cotter pins are a few

examples of parts that are subjected to shear forces .Forces must be applied

perpendicular to the test specimen otherwise it will experience tensile force.

If the force is resisted by failure through one plane and single area then the

material is said to be in single shear. If two areas resist the fracture then the material is

said to be in double shear. Figure 1 shows single and double shear applied on the given

specimen.

Ultimate shear strength = P/A for single shear where P is fracture load and A is the

area of cross section of the given specimen. In double shear, Ultimate shear strength =

P/2A.

PROCEDURE: Average diameter of the given specimens is measured using a slide

caliper and the area of cross section is calculated .For conducting single shear test,

specimen is loaded using a special fixture till fracture. Fracture load and type of fracture

is noted. Repeat the experiment for double shear as described above.

Jan 2010


Calculation of diameter :- ( Al – single shear)

S.N MSR CVD TR AVG

1

2

3

Calculation of diameter :- ( Al – double shear)

S.N MSR CVD TR AVG

1

2

3

Calculation of diameter :- (Ms – single shear)

S.N MSR CVD TR AVG

1

2

3

Calculation of diameter :- (Ms – double shear)

S.N MSR CVD TR AVG

1

2

3

Jan 2010


SPECIMEN CALCULATION :

Material Type of shear

Diameter d (mm)

Area of CS , A= d2/4,

(mm2)

Fracture load P kg

Ultimate shear strength (N/mm2)

=Px9.81/AAluminium Single P/A

Double P/2AMild steel Single P/A

Double P/2A

Question BankExpt. 71. Discuss the significance of shear test. Explain the necessary theory, the procedure to be adopted in single and double shear strength test.2. What is the shear modulus for the following materials (a) Brass (b) Bronze (c) Aluminium (d) Copper?3. Write the relationship between rigidity modulus and young’s modulus and explain.

Jan 2010


EXPERIMENT NO.: 8 – PREPARATION OF SPECIMEN FOR METALLOGRAPHIC EXAMINATION.

Aim: To prepare specimen for microscopic observations.

Apparatus: Double Disc polishing machine.

Theory: Metallography is a study of the structural characteristics of a metal or an alloy in

relation to its physical and mechanical properties. One important phase of this study is

known as microscopic examination and involves the study of the microstructure at

different magnifications. For microscopic observation, samples are required to be

prepared according to precise procedures. The procedure of specimen preparation

consists of obtaining a flat, semi polished surface by means of grinding the specimen on

a series of emery papers of decreasing grit size followed by grinding on suitable cloths

containing abrasives. These operations ultimately produce a flat, scratch free and mirror

like surface on the specimens for microscopic observations.

Procedure: After cutting the sample, grind it by moving it back and forth across the

entire length on 150 emery paper till parallel scratches are formed. Excessive pressures

should not be applied during emerying. To avoid overheating the samples, they may be

immersed in water for a short time till the temperature reduces to room temperature.

Clean the sample with water and dry it. Rotate the sample by 90 and emery it on 220-

emery paper. Rotation introduces new finer scratches approximately at right angles to

the old coarse scratches. Continue emerging till old scratches are removed. Repeat the

above procedure for 300, 400 and 600 emery papers till you get flat, ground surface.

Finish polishing of a specimen is for the purpose of removing from the surface of

the specimen, the fine scratches introduced during the last grinding operation and of

ultimately producing a highly polished scratch free surface. For fine polishing, hold the

sample on disc polisher rotating at a constant speed for 5-10 minutes depending on the

condition of the sample. Move the sample from centre to periphery of the polishing cloth.

Also rotate the sample to avoid comet tails. Use diamond paste for ferrous alloys and

Alumina or magnesia for non-ferrous alloys. Structure features are revealed with

preciseness and clarity in the specimens if they are etched with suitable etching reagent.

Preferential attack takes place during etching and different phases are revealed.

For etching, samples are immersed in suitable etching agents for a short period

followed by cleaning in water and drying. Following etching reagents are used.

26


a) Etching reagents for microscopic examination of steels and cast irons 2% Nital

(mixture of 98cc of ethyl alcohol and 2cc of nitric acid).

b) Etching reagent for copper and its alloys

i) Chromic acid ii) Acidified ferric chloride (5gms Fecl2 + 50cc of Hcl + 45cc water)

c) Etching reagents for Aluminium base alloys i) HF+Hcl+Hno3+H2O mixture in the ratio

of 1.0:1.5:2.5:95cc ii) HF+H2O (0.5cc HF + 99.5ccH2O)

27


EXPERIMENT No. : 9 - Vickers Hardness Test.

Aim: To find the Vickers hardness Number for mild steel specimen.

Theory: Very hard materials (e.g. mild steel, case hardened steel etc.) can be tested by the Vickers method. If the moderately hard materials like brass, copper and Aluminium are tested in this machine, the indentor makes a deep impression. Hence, a proper indentation cannot be made on the specimen and a correct value of the hardness cannot be obtained for these materials by V.H. test.

VHN =

Note: The impression is a pyramidal base impression where ‘d’ is the diagonal distance and ‘a’ side of the square base. The type of indentor is diamond to cone indentor with apex angle of 136o = (square base)VHN = (P/d^2)/(2sin(alpha/2))

i.e.,

Equipments required:- Vickers –cum-Brinell’s hardness testing machine Cone indentor with pyramidal square base of 136o apex angle. Standard test specimens same as in the previous experiments.

Procedure:- The experimental procedure is exactly same as in experiment No. 3 except for the following differences:The type of indentor is a diamond tip cone indentor with 136o apex angle The standard load to be applied is between 5-30 kg Vickers load.The type of impression is a square base pyramidal impression. The diagonal of the impression is measured as follows: First bring through ‘0’ of main scale to ‘0’ of vernier by operating the micrometer screw. Bring one edge of the square base impression to coincide with main scale division by operating the focusing screen screw. Count the number of M.S.D. from the coincided edge to the division near the uncoincided edge. This gives main scale reading. Now turn

28


the micrometer till the right edge coincides with next forward main scale division. Now count the vernier scale divisions from ‘0’ of main scale to ‘0’ of vernier scale. Record the Number of divisions of the micrometer scale which is just ahead and above ‘0’ index mark. Hence, diagonal width = d1=MSR + VSR + Micrometer reading. Similarly the other diagonal ‘d2’ is calcuated.

Tabulation of Observation: Sl. No.

Material Breadth (b)mm

Depth below the notch (d) mm

C.S. area A = (b.d) mm2

Impact Energy (I)

Specific Impact factor If

Joules Kg-m Joules/mm2 Kg-m/mm2

1 M.S2 BRASS3 COPPER4 ALUMINIUM

Calculation: From test, Impact Energy ‘I’ can be obtained directly

Izod Specific factor If =

= I/A Joules/mm2 or kg-m/mm2

VHN = (P/sin (α/2) x2) / d2

VHS= (P/2xsin (136/2)) / d2 =1.854xP/d2 (kg/mm2)a=d/sin450=d/√2a/2 = d/(2√2)sin (α/2) = a/2

Sloping side = d / [2x√2xsin (α/2)] Area of the shaded triangle=0.5x bxh

29


A1=0.5x a x slaping side =0.5 x d/√2x [d/2x√2xsin (α/2)] =d2 / [4x2 x sin (α/2)]Area of Pyramidal impressionA = A1 x 4 =d2 / [2 x sin (α/2)] VHN = Load/Area= [P x 2x sin (α/2] / d2

30


EXPERIMENT No.: 10 - BENDING TEST [IS: 1599 - 1985]

AIM: To study the behavior of the given specimen in bending and to determine modulus of elasticity.

APPARATUS USED: Universal Testing Machine, bending fixture, deflect meter etc.

THEORY: A specimen is said to be in bending when it is loaded in such a way that

compressive stresses are acting over one part and tensile stresses on the other part.

Bending equation is M/I = f/y = E/R where M is bending moment, I is moment of inertia

of cross section , f is bending stress , R is radius of curvature , E is modulus of elasticity

and y is the distance from the neutral axis to the outer most fiber. To avoid the specimen

from shear, the span L must not be too small with respect to depth H .The value of L =

6H to L=12H is common.

PROCEDURE: Measure the dimensions of the given specimen and mark the span

length L with respect to the length of the specimen. Place the specimen firmly over the

supports. Attach a deflect meter near the centre of the span and adjust it to read zero.

Apply load at the centre of the span and increase it slowly and continuously. Note down

the load P and deflection Y. Record the fracture load and observe the type of fracture.

Plot load deflection curve and determine the properties of the material in

bending.Flexure Stress or Bending Stress: (fb): (from Bending Test):

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Sl. No.

Material fb in (kg/mm2) fb in (N/mm2)

1. Ordinary Wood

180 18

2. Yellow Wood

220-250 22-25

3. Cast Iron 2800 280

SPECIMEN CALCULATION :

Calculation of breadth:-

S.N MSR CVD TR AVG

1

2

3

Calculation of depth:-

S.N MSR CVD TR AVG

1

2

3

Span length, L (mm) = Breadth, B (mm) = Depth, H (mm) = Maximum load, P (N) = Maximum deflection Y (mm) = Moment of inertia, I (mm4) = BH3/ 12 = Maximum bending moment, M = P x l /4 = Modulus of elasticity, E (N/mm2) = L3/48I (Slope of load deflection graph)

P - load in KN

Deflection - Y mm

Question BankExpt. 101. State and explain the assumptions on which the theory of simple bending is based.2. What type of loading will give constant moment & shear over a length of the beam?

Does this type of loading has any advantage.3. Define the following terms (I) Neutral axis (ii) Centroidal axis4. Why it is preferable to measure the deflection of a beam specimen to the top rather

than the bottom of the beam?5. What are the limits of Length to dia (L/d) ratio for flexural test & why?6. How failure in bending occurs in the following materials? (a) Cast Iron (b) Mild steel (c) Wood.

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EXPERIMENT No.: 11 - WEAR TEST

AIM: To determine the wear rate of different materials by using pin & disc apparatus.

APPARATUS USED: Pin & disc apparatus, Brass & Aluminium specimens.

Theory: In a pin–on–disk wear test a standard test specimen is held pressed against a

rotary flat disk, then brought perpendicular to the disk. They may be positioned vertical

or horizontal but the test results may differ. The specimen may have a spherical end or

flat end. Normally the load is applied through a lever arm. The wear results are generally

reported as volume loss or weight loss. Wear results are usually obtained by conducting

a test for a selected sliding distance and for selected values of load and speed. The test

specimen is cylindrical or spherical and the diameter ranges from 2mm to 10mm.

Procedure:1. Clean and dry the surface of the specimen. Remove all dirt and foreign matter from

the surface of specimen using suitable cleaning agent.

2. Measure the appropriate specimen dimension and also weigh the specimen.

3. Insert the pin specimen securely in the holder and set the specimen perpendicular to

the disk.

4. Add suitable weight to the lever.

5. Start the motor and adjust the speed to the desired value while holding the pin

specimen out of contact with the disk and stop the motor.

6. Begin the test with the specimen in contact under the load and start the stop clock.

Note down the frictional force. The test is stopped at the end of the desired time

7. Remove the specimen and clean off any loose debris. Re measure the specimen

dimension and weight.

8. Repeat the test with additional specimen.

Specimen calculation :

Material: BrassLength before the test: Diameter: Weight before the test: Weight after the test: % Loss in weight = (Initial weight – final weight) /Initial weight x 100 =% Loss in volume = (Initial volume – Final volume)/Initial volume x 100 =% Reduction in length = (Initial length – Final length)/Initial length x 100 =

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Material: AluminiumLength before the test: Diameter: Weight before the test: Weight after the test% Loss in weight = (Initial weight – final weight) /Initial weight x 100 =% Reduction in length = (Initial length – Final length)/Initial length x 100=

Material: MSLength before the test: Diameter: Weight before the test: Weight after the test: % loss in weight = (Initial weight – final weight) /Initial weight x 100=% Loss in volume = (Initial volume – Final volume)/Initial volume x 100 =% Reduction in length = (Initial length – Final length)/Initial length x 100=Distance from the loading point of the fulcrum L2: Distance between the specimen and the fulcrum L1: Applied load, P: Frictional force Fr:Normal load on the specimen: F = (PxL2 ) / L1

Coefficient of friction: = Fr / FTime: 5 min

Tabular Column (Initial)


Material Tr. No

MSR CVD TR AVG

Brass

1 2 3

Aluminium

1 2 3

Mild steel

1 2 3

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Material Tr. No

MSR CVD TR AVG

Brass

1 2 3

Aluminium

1 2 3

Mild steel

1 2 3

Tabular Column (Final)


Material Tr. No

MSR CVD TR AVG

Brass

1 2 3

Aluminium

1 2 3

Mild steel

1 2 3

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Sl. No.

Material W1 (g) W2 (g) W=W1-W2 (g)

Frictional force Fr

(N)

Coeff. Of friction

()

Avg. ()

1. Brass

2. M.S

3. Aluminium

Question Bank

1. What is wear?

2. What are different types of wear? Explain.

3. What are the different types of wear testing machines?

4. What is the importance of wear testing?

5. Define wear coefficient.

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EXPERIMENT No.: 12 - Brinell hardness TEST [IS 1500: 1983]

AIM: To determine the Brinell Hardness Number (BHN) of the given specimens.

APPARATUS: Brinell hardness Tester, Microscope with a micrometer eye piece.

THEORY: Hardness is the resistance offered by the body to the penetration of another

body which does not undergo plastic deformation .In this test, a 10mm case hardened

steel ball or tungsten carbide ball penetrates the surface of the test specimen with one of

the three standard loads - 500kg, 1500Kg, 3000kg. Once the indentor is forced into the

metal, load is released and the diameter of the indentation is measured by means of a

microscope. BHN is calculated using the equation = 2P / D [D - D2 - d2 ]

Where P is load in kgs, D diameter of the indenter and d is diameter of indentation.

Load is calculated for different materials as follows:

P= 30D2 for iron and steel

P= 10D2 for bronze & brass.

P = 5xD2 for aluminiumP = D2 for lead, tin and tin alloysBHN = P / (Area of indentation) = (2xP) / (3.142xD [D - √ (D2-d2)] (kg/mm2) h = depth of impression or indentation in mmd = diameter of impression or indentation in mmD = diameter of indenter ball in mm

In triangle OAD, OA = √ (OD2 – AD2) =√ [(D/2)2 – (d/2)2]

Depth of impression = h = OB = (D/2) - √ [(D/2)2 – (d/2)2]Area of indentation = A = Arc length ‘CBD’ x Depth = 3.142 x D x h

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= 3.142 x (D/2) x [(D) - √ [D2 – d2]]

PROCEDURE:

Select suitable load and indentor depending on the nature of the material to be tested.

Specimen is placed on the hardened anvil of the machine, which can be raised or

lowered by using a hand-operated wheel. Specimen is made to touch the indentor and

the load is applied. After applying the load for thirty seconds, load is removed and the

diameter of the indentation is measured using microscope .BHN is calculated using the

above formula.

Specimen Calculation

Sample LoadKg

Surface condition

Diameter of indenter, D- mm

Diameter of indentation d -mm

BHN

Aluminium

Machined 5mm - ball

Copper Machined 5mm - ball

Brass Machined 5mm - ball

Steel Machined 5mm - ball

Cast Iron Machined 5mm - ball

Question Bank-Expt. 12

1. Discuss Brinell hardness test as applied to ductile and brittle materials. 2. How do you calculate load for different materials. What are the different loads and Indentors used in BHN3. Write the relation between diameter of the indentor and indentation. How do you measure the diameter of indentation accurately?4. Discuss surface preparation & precautions to be taken in Brinell Hardness testing.5. Discuss the relation between BHN and other mechanical properties

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EXPERIMENT No.: 13 – FATIGUE TEST

Aim: To determine the fatigue strength (or bending strength due to reversal of stresses) of the material.

Equipments: 1. Rotating cantilever type fatigue testing machine 2. Fatigue test specimen Theory: Structural members like crafts and certain machine parts are subjected to fluctuating loads which causes variation of stresses in the member. Even if the fluctuation stresses are smaller than the ultimate strength of the material, under static load, failure may occur if the load is repeated a sufficient number of times. The stress required to cause failure decreases as the number of cycles of stress increases. This phenomenon of decreased resistance of a material to repeated stress is called fatigue and the testing of materials by application of such stresses is called fatigue test or Endurance test. Endurance Limit: It is defined as the maximum value of stress or limiting stress below which the specimen will not fail even after any number of reversals of stresses. It is a usual practice in Endurance tests to plot S max (Max Stress) against log N. the curves approach a symptotic after a certain state. The magnitude of Endurance limit is disclosed by a definite discontinuity in the curve as shown in the Fig.

Endurance Ratio: The ratio of Endurance limit to static strength is known as Endurance ratio. For most of the structural materials, the Endurance limit in complete reversed bending is 0.2 to 0.6 times of the static strength. Range of Stress (R): if Smax and S min (or fmax and fmin) are the maximum and minimum values of varying stress, then the algebraic difference. R= (fmax - fmin) is called the Range of Stress (R).

The mean stress, fmean =

The cycle is completely defined if the range of stress and maximum stress are given.

For repeated loading, fmin = 0, so that fmean = and R = fmax. For reversal of stress, fmin

= -fmax. So that fmean =0 and R =2 fmax.

In the test, when the specimen is subjected to sagging. Bending moment induced due to applied load, the bottom fibre is subjected to tensile stress and the top fibre to compressive stress. But when the specimen undergoes half a revolution, the fibre at bottom will go to top and hence will be subjected to max compression stress. (as at B). After another half revolution, it will again subjected to max. Tensile stress (as at D) and the cycle repeat for each revolution.

Calculations:

For any number of cycles of stress to produce failure of specimen recorded by the counter = N1.The bending stress at failure of specimen is calculated by the failure formula M1 = F1 x z.M1= B.M due to P1 = P1 x L where P1= Total applied load in pan. L=Lever arm (measured). F1 = Bending stress due to M1. Z= Section Modulus = (d3/32) for

39


circular specimen, f1 at number of cycle of stress N1 = (( 32 x M1) / ( x d3)) = (( 32 x P1 x L) / ( x d3)).

CYCLES OF STRESS

Procedure:

(1) Fix the specimen in the machine and set a particular loading P1 in the loading pan. Set the counter to zero. Start the machine and find the number of cycles of stress N1 to cause the failure of the specimen. This is recorded from the revolution counter N1. Calculate the maximum stress (bending stress) f1 (or s1) from failure equation f1 = M1 / 2 where M1 = P1 x L & Z= (d3 / 32)(2) Set another load P2 i.e. increase the load in the pan. For this load, repeat the procedure i.e. record the total cycle of stress N2 to cause failure of the specimen. Find the corresponding stress (max), f2 of s2. (3) The above procedure is continued for at least 6 trials to obtain sufficient number of points for plotting a graph of Max stress (S) and number of cycle of stress (N). This curve is called S-N-curve. (4) Plot a graph of the various values of S (s1, s2, s3…….) on Y-axis and number of cycles of stress N (N1, N2, N3……) on X-axis. The curve becomes very flat for smaller stress levels. The stress levels at which the curve is asymptotic is known as the endurance limit as shown in the graph.

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NON DESTRUCTIVE TESTING OF METALS

A Non Destructive Testing (NDT) is an examination of a component in any manner which will not impair its future use. Although NDT do not provide direct measurement of any properties (mechanical, physical, etc) yet they are extremely useful in revealing the defects in the component that, could impair their performance when put into service.NDT makes components more reliable and safe and economical.

Comparision between destructive and non-destructive testing:

Destructive Testing Non - Destructive Testing

Sample is destroyed when tested. Needs a specimen preparation. Numerical value cannot be assigned. Cannot be done during intermediate stages of processing. Does not need skilled labour.

Sample is tested without destroying. No need of specimen preparation. It reveals the defects in the components that could affect its performance. Can be done during intermediate stages. Needs skilled labour

Advantages of NDT:1. Component is undestructive, so cost is reduced and saving of material.2. No specimen preparation.3. Testing of copenent can be done during its intermediate stages of production/processing thus, saving of money & time.4. Defects size, location and its criticality can be exactly found out. Thus, helps in designing the product and to improve a processing method.5. Remianing life of a component can be assessed by testing a compoenent.6. Reduction of costly re-works.

Disadvantages of NDT:1. Needs skilled labour2. Damage to operator (only in few techniques)3. Results depend on area of testing/inspection.

Liquid / Dye penetration test:

Aim: To detect the flaws that, are open to the surface by penetration test.

Apparatus: Penetrant, developer and UV light source

Theory: A liquid penetrant test is non-destructive type, used to detect the flaws that are open to the surface. Ex: cracks, seams, porosity, cold shuts etc. It can be efectively used not only in the inspection of ferrous metals, but is especially usefull for non-ferrous metal products and on non-porous non-metallic materials such as ceramics, plastics and glass.

Principle of Liquid penetrant test is that the liquid used enters the small openings such as cracks or porosity by capillary action. The ate and extenet of this action are depending upon the properties such as surface tension, adhesion cohesion, viscosity. They are also influenced by factors such as condition of surface of material and interior of the dis-continuity. For liquid to penetrate effectively, the surface of the material must be thoroughly cleaned of all material that would obstruct the entrance of the liquid into

41


the defect. The dye penetrant test based on the liquid penetrant is sensitive extremely versatile and very reliable method of test. It is quite inexpensive doesn’t require any special apparatus and is simple in application, only a modereate skill is required.

In this test, the strongly colored red penetrant fluid/dye has a property of seeping into surface flaws, when applied on an impervoius surface.

Procedure: 1. Clean the surface of the component, free of dust and dirt with a piece of cloth.2. Brush the surface of the component to removal scale, rust, paint etc by soft

brush.3. Spray the cleaner to remove oil, grease etc.4. Apply dye penetrant adequately to cover the surface to be inspected. Allow 3 to 5

minutes for the dye to penetrate into the cracks.5. Wipe off the excess penetrant on the surface.6. Again spray the surface with the cleaner to remove the remanants of the red dye.7. Spray the developer evenly on the surface to give a thin even finish. This layer

absorbs the penetrant from the cracks and the red spots and appears on the surface to give a visible indication of the flaws.

8. Crack if any will be indicated with the red dye absorbed by the white absorbant.

Results: Report the type of defects present in the given component.

Magnetic particle inspection

Aim: To detect the surface / sub surface defects in a given ferro-magnetic matertial.

Apparatus: Magnetic field generator and ferro-magnetic powder.

Theory: This method of inspection is used on magnetic ferrous casting for detecting invisible surface of slightly sub surface defects. Deeper sub surface defects arenot satisfactorily detected because of the influence of distorted lines of magnetic flux on the magnetic field spread over the casting surface becomes weeker with distance. So that sensitivity fall away rapidly by the depth. The defects that are commonly revealed by magnetic particle inspection are quenching cracks, thermal cracks, seams, laps, grinsging cracks, hot tears etc. The principle of this method is when a piece of material is placed in a magnetic field and the lines of magnetic flux get intersected by a dis-continuity such as cracks of slag inclusion in casting, magnetic poles are induced on either side of discontinuity causing an abrupt change in path of magnetic flux flowing through the casting normal to the discontinuioty resulting in local flux leakage and interference with the magnetic lines of force. This local flux disturbance can be detected by its affect upon magnetic particles that collect on the region of discontinuity and pile up and bridge over the discontinuity.

Procedure:1. Clean the surface of the test specimean.2. Demagnetise the component to remove any residual magnetic field in it.3. Apply a thin layer of ferro magnetic particles over the surface to be tested.4. Magnetise the test specimen.

42


5. Observe the shape and size of the magnetioc particles collected, which is the shape and size of the defect.

Result: Report the type and sie of the defcte in the given component. Ultrasonic test

Aim: To find the location of the interior crack or cavity in the specimen using the ultra sonic flaw detector.

Appartus: Ultra sonic flaw dectector.

Theory: Ultrasonic inspection is employed to detect and locate defects such as shrinkage cavities ,internal burst or cracks,porosity and large non-metallic inclusions,wall thickness can be measured in closed vessels or in cases where such measurement can not other wise be made ultrasonic vibrations with frequencies in the range between 20khz-20mhz can be used to locate defects in ferrous and non-ferrous metallic objects as wel as in plastics and ceramics.these waves can be trnamitted through the solids(even liquid and air as well) and get reflected by the sub-surface defects.Ultrasonic waves form a basis for detection ,location and size estimation of defects.LetA=Time elapsed between the pips of front surface echo and bottom surface echo. (Sec)B= Time elapsed between the pips of front surface echo and cavity surface echo. (Sec)H= Thickness of the test specimen (mm) Location of the crack from the front surface x=B/AxH

Procedure:1. Clean the surface of the test piece.2. Place the probe against the surfae of the test piece using thin oil film.3. Switch on the power supply of the ultrasonic wave generator.4. Adjust the cycles of transmitting and receiving signals to the desired value.5. Select the segment of time which contains the echo pips.6. Observe the echo from the cavity, if any on the crt and measure the relative

distance of the pips on the time axis.

Results: Report the type of defect and its location from the front surface.

Questions:1. What is non-destructive testing?2. Give a comparision between destructive and non-destructive testing? Mention

few examples?3. Describe the liquid/dye penetrant test method? Mention its advantages and

disadvantages?4. Describe the magnetic particle method? Mention its advantages and

disadvantages?5. On what principle does ultrasonic inspection equipment operate?6. How is the depth of a flaw measured in ultrasonic testing?7. Hardness testing is a destrutive or non-destructive testing?

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mctl_course_material

Documents

test specimen

static tension test

flat test piece

circular test piece

total length of test

gauge length marks

final gauge length lu

fracture stress