Material Testing Lab Manual AKTU PDF

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MECHANICAL ENGINEERING DEPARTMENT

LAB MANUAL Material Testing Lab (Subject Code: KME 352) List of Experiments: Objectives:  

To understand the principles and performance characteristics different materials. To know about material properties.

1. Strength test of a given mild steel specimen on UTM with full details and stress versus strain plot on the machine. 2. Other tests such as shear, bend tests on UTM. 3. Impact test on impact testing machine like Charpy, Izod or both. 4. Hardness test of given specimen using Rockwell and Vickers/Brinell testing machines. 5. Spring index test on spring testing machine. 6. Fatigue test on fatigue testing machine. 7. Creep test on creep testing machine. 8. Experiment on deflection of beam, comparison of actual measurement of deflection with dial gauge to the calculated one, and or evaluation of young’s modulus of beam. 9. Torsion test of a rod using torsion testing machine. 10.Study of NDT (non-destructive testing) methods like magnetic flaw detector, ultrasonic flaw detector, eddy current testing machine, dye penetrant tests.

Course Outcomes: The students who have undergone the course will be able to measure various properties of materials.

Experiment 1 (Tensile Test) OBJECTIVE: Strength test of a given mild steel specimen on UTM with full details and

stress versus strain plot on the machine. APPARATUS USED: 1. Universal Testing Machine (UTM) Capacity: 400 KN 2. Mild steel specimens 3. Graph paper 4. Scale 5. Vernier Caliper SPECIMEN: Tensile test specimen has been prepared in accordance with Bureau of Indian standards as shown in the figure below THEORY:- Various machine and structural component are subjected to tensile loading in numerous applications. For safe design of these components ,their ultimate tensile strength and ductility are to be determined before actual use. For that the above test is conducted .Tensile test can be conducted on U.T.M. A material when subjected to a tensile load, resists the applied load by developing internal resisting force.This resistance comes due to atomic bonding between atoms of the material .The resisting force per unit normal cross-sectional area is known as stress.The value of stress in material goes on increasing with an increase in applied tensile load, but it has a certain maximum (finite) limit too. The maximum stress at which a material fails,is called ultimate tensile strength Definitions: Limit of proportionality (A): It is the limiting value of the stress up to which stress is proportional to strain. Elastic limi(B)t: This is the limiting value of stress up to which if the material is stressed and then released (unloaded), Strain disappears completely and the original length is regained. Upper Yield Point (C): This is the stress at which, the load starts reducing and the extension increases. This phenomenon is called yielding of material. Lower Yield Point (D): At this stage the stress remains same but strain increases for some time. Ultimate Stress (E): This is the maximum stress the material can resist. At this stage cross sectional area at a particular section starts reducing very fast (fig.1). This is called neck formation. Breaking Point (F): The stress at which finally the specimen fails is called breaking point. Hooks law: Within the elastic limit, the stress is proportional to the strain for an Isentropic material.

Fig. 1 Stress-strain graph of Mild Steel materials.

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Fig. 2 Stress-strain graphs of different

Curve A shows a brittle material. This material is also strong because there is little strain for a high stress. The fracture of a brittle material is sudden and catastrophic, with little or no plastic deformation. Brittle materials 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 stretch very little, and break suddenly. There can be a lot of elastic strain energy in a steel wire under tension and it will “whiplash” if it breaks. The ends are razor sharp and such a failure is very dangerous indeed. Curve C is a ductile material Curve D is a plastic material. Notice a very large strain for a small stress. The material will not go back to its original length.

PROCEDURES: 1. Observe the specimen. Measure the total length and parallel length of the specimen. Also measure the diameter of the specimen. Calculate the gauge length. Mark the gauge length on the central portion of the specimen. 2. Fix the specimen in-between the upper and middle cross heads using the gripping devices. Take precautions to fix the test specimen in such a way as to ensure that the load is applied axially. 3. Fix the extensometer in its position over the gauge points. Adjust the extensometer and the linear scale to read zero initially. 4. Select proper range of loading (i.e. 0 to 40 tonnes). 5. Switch on the machine. Apply the axial tensile load on the specimen gradually. Record the extensometer readings at a constant load increment of 400 kg. 6. The yield point can be observed either: a. by the kickback of the live needle of the load indicating dial. OR b. by the rapid movement of extensometer dial needle at constant load reading. Record the yield load(s), and remove the

extensometer. Continue the axial loading. 7. At one stage, the live needle begins to return, leaving the dummy needle there itself. Note down the load at that point as the ultimate load. Also, observe the neck formation on the specimen. 8. Note down the load at the point of failure of the specimen. 9. Switch off the machine; Remove the failed specimen; Observe the type of fracture. 10. Measure the final gauge length on the tested specimen, if the failure has occurred within the gauge length portion and also, the diameter at the neck. NOTE: a) b) c)

d) e) f)

The above procedure is valid for steel bar of diameter equal to or greater than 4 mm, or of thickness equal to or greater than 3 mm. For test pieces of rectangular section, a ratio of width to thickness of 8 : 1 should not be exceeded. The gauge length can be calculated from the equation L0 √ A = 5.65D. where A is the initial cross sectional area of the test specimen. It is rounded off to nearest multiple of 5 mm. However, test pieces with other gauge lengths may be used, for technical or economical reasons. Some specimens exhibit both upper and lower yield points, and some specimens exhibit only one yield point. Some materials may not exhibit any yield point at all. For such materials, 0.2% proof stress is to be determined. If the failure occurs outside the gauge length, the value of the percentage of elongation can not be calculated.

OBSERVATION: Following data are recorded for conducting a tensile test. Type of fracture = Material of the specimen = Intial gauge length of the specimen lo = Intial gauge diameter of the specimendo = Extended gauge length at fracture lf = Reduced gauge diameter at the broken end df = Load at Yield point = Ultimate Load= Breaking Load=

TABLE

S. No.

Load P (N)

Extension (δ l) mm

Stress =P/Ao (MPa)

Strain ( l/ lo

1 2 3 4 5 CALCULATION: Initial cross sectional area A0=/4 d02 Final cross sectional area Af=/4 df2 Percentage elongation % (l) = ( lf-lo)/lo Percentage reduction in cross sectional area = (A–a) x 100 / A= Young‟s modulus of elasticity of Mild Steel in tension = Slope of the straight lineportion of the stress vs. strain curve = Et =………………N/mm2 Upper yield stress =σyu = Load at upper yield point / A = ……………..N/mm2 Lower yield stress =σyu = Load at lower yield point / A = ……………..N/mm2 OR Yield stress(σy) = Load at yield point / A ……………….N/mm2 Tensile strength (Ultimate strength) (σult) = Ultimate Load / A Failure or breaking stress(σf) = Breaking load / A =……….N/mm2 RESULTS:  Young‟s Modulus of specimen =  Yield stress =  Ultimate stress =  Breaking stress =  % reduction in Area =  % Elongation= VIVA VICE QUESTIONS 1. Which modulus did you find from the initial portion of the stress-strain curve? If did not use an extensometer but determined strain from the crosshead movement, would the initial slope still allow you to determine an accurate modulus? Explain. 2. Write the definition using symbols for shear modulus, bulk modulus and Poisson's ratio. Write the equations relating these two modulus to Young's modulus. 3. What is the approximate value of Poisson's ratio for metals? What is the physical significance of Poisson's ratio, i.e. what does it represent resistance to?

4. What is the area under the stress-strain curve equivalent to? What does the area under the elastic portion of the stress-strain represent? 5. What % elongation and % reduction in area measures of? 6. Explain the different deformation mechanisms which are active in the different regions of the tensile stress-strain curve. (elastic, yielding, strain hardening, necking etc.)

EXPERIMENT NO: 2 (Shear Test)

OBJECTIVE: To conduct shear test on given specimen under double shear. APPARATUS: i) Universal testing machine. ii) Shear test attachment. iii) Vernier iv) Specimens. DIAGRAM:-

THEORY:-Place the shear test attachment on the lower table, this attachment 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 the specimen breaks in two or three pieces. If the specimen breaks in two pieces then it will be in single shear & if it breaks in three pieces then it will be in double shear. PROCEDURE: 1. Insert the specimen in position and grip one end of the attachment in the upper portion and one end in the lower portion. 2. Switch on the main switch of universal testing machine machine 3. The drag(red) indicator in contact with the main(black) 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 small balancing weights. 5. Operate (push) buttons for driving the motor to drive the pump. 6. Gradually apply the pressure through pressure valve till the specimen shears. 7. Note down the load at which the specimen shears. 8. Stop the machine and remove the specimen Repeat the experiment with other specimens. OBESERVATIONS:Diameter of the Rod, D = ….. mm 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 Newton Strength of rod against Shearing = τ x 2x πd2/4 Shear Stress (τ) = W / 2.πd2/4 N/mm2 RESULT: The Shear strength of mild steel specimen is found to be = ……………… 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 3 IZOD and CHARPY TEST OBJECTIVE:-To conduct the impact test (Izod / Charpy) on the impact testing machine.

APPARATUS USED -Impact testing machine, Izod and charpy test specimen of mild steel and/or aluminum, vernier caliper. THEORY- An impact test signifies toughness of material that is ability of material to absorb energy during plastic deformation In manufacturing locomotive wheel, coin, connecting rods etc., the component are subjected to impact (shock) load. These load are applied suddenly. The stress induced in these component are many times more than the stress produced by gradual loading. Therefore impact tests are performed to assess shock absorbing capacity of materials subjected to suddenly applied loads. These capabilities are expressed as (i) rupture energy (ii) modulus of rupture, and (iii) notch impact strength. Two types of notch impact test are commonly conducted these are 1-Charpy test 2-Izod test In both tests, standard specimen is in the form of a notched beam. In charpy test, the specimen is placed as ‘simply supported beam’ while in izod test it is kept as a ‘cantilever beam’. The specimens have V shape notch of 45Degree in izod test and U shaped notch in charpy test. The notch is located on tension side of specimen during Impact loading. Depth of notch is generally taken as t/5 to t/3 where t is the thickness of the specimen. TEST SET UP AND SPECIFICATIONS: Capacity Energy Range Charpy 0-300 J Izod 0-164 J Model ITM 300 Mfd. By :: 1. 2.

Pendulum type impact testing machine. The machine consists of: A pendulum of mass 18.748 kg, length = 825 mm with an angle of swing of 160o.

3. 4. 5. 6. 7.

Specimen holder (different for Izod and Charpy tests) Striking edge (different for Izod and Charpy tests) Lock lever and pendulum releaser. Pendulum brake. A calibrated dial to measure the Impact energy, with red and black indicators. Slide Calipers and Scale

8.

Standard Specimen for CHARPY test:

Standard specimen for IZOD test

PROCEDURE:  

Check the specimen for the its standard dimensions. Depending upon the type of test, fix the corresponding striking edge to the hammer.

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To find the frictional loss: a) Raise the pendulum to its highest position where it gets locked. At this position, the potential energy stored in the pendulum is 30 Nm. b) Set the dial to read 30 Nm with the indicator showing black colour. c) Press the lock lever first and then the pendulum releaser to release the pendulum. d) Stop the oscillations of the pendulum using the damper plate / brake. e) Record the reading on the dial which indicates the frictional loss directly.

Note: Read the black or red scale according as the indicator is black or red respectively. Fix the specimen in its holder. For Izod Test: The specimen should be placed vertically as a a) cantilever with the shorter end of the specimen projecting above the holder and V-Notch on the tension side. b) For Charpy Test: The specimen should be placed horizontally as a simple beam and the U-notch on the tension side. Note: Use the appropriate centraliser to keep the specimen in its proper position. ii) iii) iv) v) vi)

Raise the pendulum to its highest position where it gets locked. Set the dial to read 30 Nm with the indicator showing black colour. Release the pendulum by pressing down the lock lever first and then the pendulum releaser to strike the specimen. Use the damper plate / brake to stop the oscillations of the pendulum. Record the dial reading on the red or black scale depending upon whether the indicator is red or black respectively. Observe whether the specimen has broken completely or not.

OBSERVATION: Material of the specimen = Mass of the pendulum = 187.5 kg Length of the pendulum = 825 mm Angle of swing = 90o (IZOD Test) & 160o (CHARPY Test) Frictional Loss = Uf

Izod Impact Test Specimen Specimen No. Dimension

Enrgy Observed Uo N m

Impact Enrgy Ui= Uo-Uf

Impact Strength = KU = UI/A Nm/mm2

Remarks

Charpy Test Specimen Specimen No. Dimension

Enrgy Observed Uo N m

Impact Enrgy Ui= Uo-Uf

Impact Strength = KU = UI/A Nm/mm2

Remarks

RESULTS: The energy absorbed for given material ………… in Izod test is found out to be (K) --------------- Joules. The energy absorbed for given material ………… in Charpy test is found out to be (K) --------------- Joules. Impact strength of the specimen (Izod Test) (K/A) = ------------------J/mm2 Impact strength of the specimen (Charpy Test) (K/A) = ------------------- J/mm2 PREACAURIONS: 1. Hold the specimen (lzod test) firmly. 2. Utmost care must be taken to see that no person is present in the line of oscillation of the pendulum. 3. Use the damper plate / brake to stop the oscillations of the pendulum. 4. During the test, if the test piece is not completely broken, the impact value obtained is indefinite. Then the test report should state that the test piece was unbroken by

EXPERIMENT NO. 4 (Hardness Test) OBJECT-To determine the hardness of a given specimen using Brinell / Rockwell / Vicker testing machine APPARATUS USED – Brinell / Rockwell / Vicker testing machine, specimen of mild steel/cast iron/ non –ferrous metal, optical microscope

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THEORY- Hardness is a surface property. It is defined as the resistance of material against permanent deformation of the surface in the form of scratch, cutting, indentation, or mechanical wear. The need of hardness test arises from the fact that in numerous engineering applications, two components in contact are made to slide or roll over each other. In due course, their surfaces are scratched and they may fail due to mechanical wear. This result in not only a quick replacement of both parts but also incurs a big loss in terms of money. For example, piston ring of an I.C ingine remains in sliding contact with the cylinder body when the piston reciprocates within the cylinder. If proper care is not taken in selection of materials for then, The piston rings and cylinder will wear soon. In this case the replacement or repairing of cylinder block will involve much time, trouble and money. Therefore, the material of piston rings and cylinder block should be taken such that the wear is least on the cylinder. Thus in case of repairing, comparatively cheaper piston rings can be easily replaced. This envisages that material of cylinder block should be harder than the material of piston rings so that the cylinder wears. The least. This can be ascertained by conduct of a hardness test. That is why it is essential to known as to how this test can be conducted. There are three general types of hardness measurements depending upon the manner in which the test is conducted: A. Scratch hardness measurement, B. Rebound hardness measurement C. Indention hardness measurement. In scratch hardness method the material are rated on their ability to scratch one another and it is usually used by mineralogists only. In rebound hardness measurement, a standard body is usually dropped on to the material surface and the hardness is measured in terms of the height of its rebound. The general means of judging the hardness is measuring the resistance of a material to indentation. The indenters usually a ball cone or pyramid of a material much harder than that being used. Hardened steel, sintered tungsten carbide or diamond indenters are generally used in indentation tests; a load is applied by pressing the indenter at right angles to the surface being tested. The hardness of the material depends on the resistance which it exerts during a small amount of yielding or plastic. The resistance depends on friction, elasticity, viscosity and the intensity and distribution of plastic strain produced by a given tool during indentation

BRINELL HARDNESS TEST: In Brinell‟s hardness test, a hard steel ball, under specified conditions of load and time, is forced into the surface of the material under test and

the diameter of the impression is measured. Hardness number is defined as the load in kilograms per square millimeters of the surface area of indentation. This number depends on the magnitude of the load applied, material and geometry of the indentor. Material

Ball Indenter diameter (mm) 5 2.5

Mild steel

750 kgf

Cast Iron

750 kgf

187-5 kgf 187.5 kgf

Brass Gun Metal Aluminum

250 kgf 250 kgf 125 kgf

62.5 kgf 62.5 kgf 31.25 kgf

LOAD RANGE FOR BRINELL HARDNESS TEST: The load to be applied can be obtained by the formula P = KD2 kgf. where K = Constant for a given metal (listed in Table-1) D = Diameter of the ball indenter in mm. Table 1: Values of „K‟ and range of hardness for different metals (for Brinell Hardness Test) Sl. No.

Metal

Value of K

1.

Mild steel

30

2.

Cast Iron

30

3.