LABORATORY MODULE

PDT 154

MATERIAL TESTING

Semester 2 (2015/2016)

Faculty of Engineering Technology Universiti Malaysia Perlis

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CONTENT

EXPERIMENT 1: LIQUID PENETRANT TESTING

EXPERIMENT 2: MAGNETIC PARTICLE TESTING

EXPERIMENT 3: ULTRASONIC FLAW DETECTION TESTING

EXPERIMENT 4: HARNESS TESTING

EXPERIMENT 5: IMPACT TESTING

EXPERIMENT 6: TENSILE TESTING

SAFETY IN THE LABORATORY All students must read and understand the information in this document with regard to laboratory safety and emergency procedures prior to the first laboratory session. Your personal laboratory safety depends mostly on YOU. Effort has been made to address situations that may pose a hazard in the lab but the information and instructions provided cannot be considered all-inclusive. Students must adhere to written and verbal safety instructions throughout the academic term. Since additional instructions may be given at the beginning of laboratory sessions, it is important that all students arrive at each session on time. With good judgment, the chance of an accident in this course is very small. Nevertheless, research and teaching workplaces (labs, shops, etc.) are full of potential hazards that can cause serious injury and or damage to the equipment. Working alone and unsupervised in laboratories is forbidden if you are working with hazardous substances or equipment. With prior approval, at least two people should be present so that one can shut down equipment and call for help in the event of an emergency. Safety training and/or information should be provided by a faculty member, teaching assistant, lab safety contact, or staff member at the beginning of a new assignment or when a new hazard is introduced into the workplace. Emergency Response 1. It is your responsibility to read safety and fire alarm posters and follow the

instructions during an emergency. 2. Know the location of the fire extinguisher, eye wash, and safety shower in your lab

and know how to use them. 3. Notify your instructor immediately after any injury, fire or explosion, or spill. 4. Know the building evacuation procedures. Common Sense Good common sense is needed for safety in a laboratory. It is expected that each student will work in a responsible manner and exercise good judgment and common sense. If at any time you are not sure how to handle a particular situation, ask your Teaching Assistant or Instructor for advice. DO NOT TOUCH ANYTHING WITH WHICH YOU ARE NOT COMPLETELY FAMILIAR. It is always better to ask questions than to risk harm to yourself or damage to the equipment.

Personal and General laboratory safety 1. Never eat, drink, or smoke while working in the laboratory. 2. Read labels carefully. 3. Do not use any equipment unless you are trained and approved as a user by

your supervisor. 4. Wear safety glasses or face shields when working with hazardous materials

and/or equipment. 5. Wear gloves when using any hazardous or toxic agent. 6. Clothing: When handling dangerous substances, wear gloves, laboratory coats,

and safety shield or glasses. Shorts and sandals should not be worn in the lab at any time. Shoes are required when working in the machine shops.

7. If you have long hair or loose clothes, make sure it is tied back or confined. 8. Keep the work area clear of all materials except those needed for your work.

Coats should be hung in the hall or placed in a locker. Extra books, purses, etc. should be kept away from equipment that requires air flow or ventilation to prevent overheating.

9. Disposal - Students are responsible for the proper disposal of used material if any in appropriate containers.

10. Equipment Failure - If a piece of equipment fails while being used, report it immediately to your lab assistant or tutor. Never try to fix the problem yourself because you could harm yourself and others.

11. If leaving a lab unattended, turn off all ignition sources and lock the doors. 12. Never pipette anything by mouth. 13. Clean up your work area before leaving. 14. Wash hands before leaving the lab and before eating. Mechanical safety

1. When using compressed air, use only approved nozzles and never directs the air

towards any person. 2. Guards on machinery must be in place during operation. 3. Exercise care when working with or near hydraulically- or pneumatically driven

equipment. Sudden or unexpected motion can inflict serious injury. Chemical safety 1. Treat every chemical as if it were hazardous. 2. Make sure all chemicals are clearly and currently labelled with the substance

name, concentration, date, and name of the individual responsible. 3. Never return chemicals to reagent bottles. (Try for the correct amount and share

any excess.) 4. Comply with fire regulations concerning storage quantities, types of approved

containers and cabinets, proper labelling, etc. If uncertain about regulations, contact the building coordinator.

5. Use volatile and flammable compounds only in a fume hood. Procedures that produce aerosols should be performed in a hood to prevent inhalation of hazardous material.

6. Never allow a solvent to come in contact with your skin. Always use gloves. 7. Never "smell" a solvent!! Read the label on the solvent bottle to identify its

contents. 8. Dispose of waste and broken glassware in proper containers. 9. Clean up spills immediately. 10. Do not store food in laboratories. Additional Safety Guidelines

Never do unauthorized experiments.

Never work alone in laboratory.

Keep your lab space clean and organized.

Do not leave an on-going experiment unattended.

Always inform your instructor if you break a thermometer. Do not clean mercury yourself.

Never taste anything. Never pipette by mouth; use a bulb.

Never use open flames in laboratory unless instructed by TA.

Check your glassware for cracks and chips each time you uses it. Cracks could cause the glassware to fail during use and cause serious injury to you or lab mates.

Maintain unobstructed access to all exits, fire extinguishers, electrical panels, emergency showers, and eye washes.

Do not use corridors for storage or work areas.

Do not store heavy items above table height. Any overhead storage of supplies on top of cabinets should be limited to lightweight items only. Also, remember that a 36" diameter area around all fire sprinkler heads must be kept clear at all times.

Areas containing lasers, biohazards, radioisotopes, and carcinogens should be posted accordingly. However, do not post areas unnecessarily and be sure that the labels are removed when the hazards are no longer present.

Be careful when lifting heavy objects. Only shop staff may operate forklifts or cranes.

Clean your lab bench and equipment, and lock the door before you leave the laboratory.

EXPERIMENT 1: LIQUID PENETRANT TESTING 1.0 Introduction: Examination with penetrant is a non-destructive examination method used to reveal defects which reach the surface of non-porous materials. Defect such as cracks, porosities, cleavages and leaks in steel, cast iron, plastics, ceramics, etc. Penetrant inspection utilizes the natural accumulation of a fluid around a discontinuity to create a recognizable indication of cracks or other surface opening. Capillary action attracts the fluid to the discontinuity as compared to its surroundings. In order to locate the area of excess fluid (defect region), the background area must be of sufficient contrast thus leading to distinct detection of the defect on the surface. The penetrant method is quite slow when one must examine large surfaces, while it can be very quick and easy to use for checking the assembly line production of small parts. Penetrant inspection depends mainly on the ability of liquid to wet the surface of a solid work piece or specimen and flow over that surface to form a continuous and reasonably uniform coating, thus penetrating into cavities that are open to the surface. The ability of a given liquid to flow over a surface and enter surface cavities mainly depends on the surface tension and capillary action. 2.0 Objective:

In this experiment, student will be guided and exposed on how to detect and indicate the surface defects using the liquid penetrant testing technique.

3.0 Materials and Instruments:

Penetrant (dye or fluorescent)

Developer (dry powder, water-based, non-water based wet)

Penetrant cleaner/remover

Reference Standard samples

Lab samples

4.0 Testing procedures:

1. Firstly, clean the surface area which is to be inspected by a cleaner. 2. Then apply the penetrant fluid to the cleaned surface. Application of penetrant

may be achieved by dipping the component in a bath of penetrant liquid, or by spraying or brushing. Let the sample about 20 to 30 minutes after penetrant application (dwell time).

3. Completely remove the excess penetrant from the surface. Avoid neither insufficient cleaning nor over cleaning in clearing the penetrant.

4. After removing the excess penetrant, apply a thin coating of developer over the surface to draw the penetrant out of the crack and increase its visibility.

5. Observe the result. Inspect and recognize the defects with your eyes or under light microscope. Each indication that appears should be evaluated.

5.0 Results and discussion:

Take all the results obtained from the testing and discuss with details in your lab report.

6.0 Questions:

1. What are the advantages and disadvantages of penetrant testing? 2. Describe the basic theory behind penetrant testing. 3. What force causes a liquid to enter a narrow opening? Why is this force

independent of the orientation of the opening? 4. What is dwell time? 5. Why is cleaning a sample important in dye penetrant testing? 6. What are four common methods to remove excess penetrant, and what are

their advantages and disadvantages? 7. Give three purposes of a developer in the dye penetrant process.

EXPERIMENT 2: MAGNETIC PARTICLE TESTING 1.0 Introduction:

The magnetic particle testing (MPT) technique is a non-destructive examination which is well suited to the detection of surface defects such as cracks, lack of fusion and laminations, used for the testing of ferromagnetic materials, which can be easily magnetized. Ferromagnetic materials include most of iron, nickel and cobalt alloys and many of the precipitation-hardening steels. The MPT equipment is cheap, robust and can be handled by semi-skilled personnel without requiring elaborate protection such as that needed for radiography (B. Raj, T. Jayakumar & M. Thavasimuthu, 2002) The use of this method exploits the fact that a surface defect in a magnetized ferromagnetic item will disturb the magnetic field in the object of the test. The defect will cause some of the lines of magnetic force to depart from the surface and thus to form a magnetic leak field. This leak field can be found by placing fine iron particles on the surface. The leakage field will hold the magnetic particles in a ridge on top of the crack. By taking advantage of this effect the magnetic particles will form a ridge which is many times wider than the crack itself, thus making an otherwise invisible crack become visible (G. B. Knud, 1989) 2.0 Objective:

In this experiment, student will be guided and exposed on how to detect and measures the sample surface defects using the magnetic particle testing technique.

3.0 Materials and Instruments:

Electromagnet handle (Yoke)

Contrast paint

Magnetic Powder (iron oxide)

Reference Standard samples

Lab samples

4.0 Testing procedures:

1. Clean the surface of the sample being analyzed. Cleaning can be carried out with solvent, rotating steel brushes, sand blasting or grinding.

2. Spray with a thin layer of paint (max. 50 – 75 µm) on the sample surface. 3. Magnetize the sample using an electromagnet. 4. Magnetic particles (dry and wet powder) should be applied while the sample is

under the influence of the magnetic field. Use either pulverized iron oxide powder (Fe3O4) or carbonyl iron powder.

5. Observe the distribution of the magnetic particles on the surface analyzed. Inspect and recognize the defects with your eye. Each indication that appears should be evaluated.

5.0 Results and discussion: Take all the results obtained from the testing and discuss in details in your lab report. 6.0 Questions:

1. Describe the basic theory of Magnetic Particle Testing. 2. What are the limitations and the biggest advantages of MPT? 3. Describe the four major types of current used in MPT and what types of

defects they are best suited to find. 4. What are the distinguishing characteristics of paramagnetic, diamagnetic, and

ferromagnetic materials? 5. Why do samples have to be magnetized in two directions to find all the

defects in the sample?

EXPERIMENT 3: ULTRASONIC FLAW DETECTION TESTING 1.0 Introduction:

Ultrasonic testing is a versatile NDT method which is applicable to most materials, metallic and non-metallic. By this method, surface and internal discontinuities such as laps, seams, voids, cracks, blow holes, inclusions, and many others can be accurately evaluated from one side. Ultrasonic testing utilizes high frequency acoustic waves generated by piezoelectric transducer. Frequencies from 1 to 10 Mega Hertz (MHz) are typically used, although lower or higher ranges are sometimes required for certain applications. The resultant acoustic wavelengths in the test material (depend on the ultrasonic wave velocity) are of the order of one to ten millimeters. A highly directional sound beam is transmitted to the test piece through a suitable couplant, usually grease or oil like material. The pulse-echo technique is the most versatile ultrasonic method for nondestructive testing and is the most widely used. Weld testing is the largest application of ultrasonic testing. Additionally, many of the semi-finished products in the steel and non-ferrous metal industries, i.e. bars, rods, sheets, pipes, rails etc. are ultrasonically tested. Apart from these very simple shaped items, objects which are large like forgings are tested using automatic or semi-automatic test stations. Smaller objects and those which are more complicated are tested manually. Another important application of ultrasonic testing is the finding of dangerous incipient defects in components in service, e.g. fatigue cracks and effects of corrosion. In power plant, boiler components must be tested regularly for fatigue cracks in welds and for corrosion in certain areas (B. Raj, T. Jayakumar & M. Thavasimuthu, 2002) 2.0 Objective: In this experiment, student will be guided and exposed on how to determine the thickness and flaw detection of a sample using the ultrasonic testing equipment. 3.0 Materials and Instruments:

Ultrasonic Quantum TE

Transducers

Couplant/oil

Reference Standard samples

Defect welding sample

4.0 Testing procedure:

1. Clean the surface of the sample being analyzed. Cleaning can be carried out with solvent, rotating steel brushes, sand blasting or grinding.

2. Set up and select the appropriate and suitable transducer use for analysis. 3. Apply some couplant/oil on the surface area to be analyzed before put the

transducer. 4. Put and hold the transducer on the sample surface for a minute. 5. Observe the peak signal in oscilloscope. Determine and recognize all the

defects existed. Each indication that appears should be evaluated. 5.0 Results and discussion: Takes all the results obtained from the testing and discuss in details in your lab report. 6.0 Questions:

1. Describe the basic theory of Ultrasonic testing. 2. What are the limitations and the advantages of ultrasonic testing? 3. What is the difference between longitudinal and transverse waves? Which has

a higher velocity? 4. Describe the four basic methods of ultrasonic attenuation. 5. What is the difference between wave scattering and wave absorption? 6. How is an oscilloscope used to interpret the ultrasonic signal?

EXPERIMENT 4: HARDNESS TESTING

1.0 Objective To introduce the principles of indentation hardness testing, emphasizing the limitations and significance of the results.

2.0 Introduction Hardness is generally considered as resistance to penetration. Harder materials have greater resistance to penetration. Hardness is directly related to the mechanical properties of the material. Factors influencing hardness include microstructure, grain size, strain hardening, etc. Generally as hardness increases so does yield strength and ultimate tensile strength (UTS), thus specifications often require the results of hardness tests rather than tensile tests. The most popular methods are Brinell, Vickers and Rockwell hardness tests for metals and alloys.

Brinell Test In a standard Brinell test 10 mm diameter hardened steel ball is forced to penetrate the material by 3000 kgf for steels and cast irons. The load and ball diameter selection is important depending on the hardness of materials and 500 kgf is used for softer materials with the same ball diameter. Keeping the ratio of load P to the square of diameter D2 constant (30 for steels and cast irons and 5 for soft metals and alloys), different load and ball diameter combinations can be selected and used in Brinell hardness testing. The Brinell Hardness Number (BHN) is obtained by dividing the applied force P, in kgf; by the curved surface area of the indentation, which is actually a segment of sphere. The geometry of indentation is given in Figure-1, and the hardness is determined according to the relationship,

BHN =2P

𝜋𝐷 [𝐷 − (𝐷2 − 𝑑2)1

2⁄ ]

Where, D is the diameter of the indenter ball and d is the average diameter of the indentation, both in mm.

Figure 1: Geometry of deformation under a Brinell hardness indente

Vickers Test

The Vickers hardness test is based on the same principle as the Brinell test, except the indenter is a diamond pyramid with square base. The angle between the faces of pyramid is 136° as shown in Figure 2. The Vickers Hardness Number (VHN) of materials is obtained by dividing the applied force P, in kgf, by the surface of the pyramidal depression yielding the relationship

VHN =1.8544𝑃

𝑑2

Where, d is the average length of diagonals in mm. Due to the shape and hardness of indenter the method is applicable to metals and alloys with wide variety of hardness. Test load is selected between 1 and 120 kgf depending on the hardness of materials. It is also possible to apply micro hardness testing by keeping the force between 5 grf and 2 kgf in Vickers scale.

Figure 2: Vickers hardness indentation

3.0 Equipment

Brinell hardness tester

Microhardness (Vickers) tester

Different test specimens

4.0 Procedure

1. Determine the proper Rockwell hardness scale, calibrate the Rockwell hardness tester, take five readings per specimen,

2. Perform Brinell hardness measurements on designated specimens (3 readings)

3. Using microhardness tester, determine the VHN at 0.20 mm distances from the surface to the centre of case carburized specimen, until the hardness remains unchanged.

4. Determine the core hardness of the carburized steel.

5.0 Result Calculate the range and mean in hardness values for each test specimen which will be considered in lab report. 6.0 Discussion Take all the results obtained from the testing and discuss with details in your lab report. 7.0 Questions

1. How do the Rockwell and Brinell tests actually measure hardness? Give any appropriate sketches and formulae. Are there any units involved?

2. Describe the procedure for the Rockwell test, explaining the reason for the pre-load.

3. What is the limitation on the thickness of specimens for a hardness test? Explain. Calculate the minimum thickness for one specimen for the Rockwell test and one for the Brinell test.

4. What are the limitations for distance from specimen edge to indentation and distance between indentations? Explain why these limitations exist in both cases.

5. What surface condition is necessary for Brinell, Rockwell and Vickers? 6. Why is the mean pressure (stress) under the indenter much greater than the

yield stress? How much greater is it? What are the advantages of Vickers test against Brinell test?

EXPERIMENT 5: IMPACT TESTING

1.0 Objective To conduct Charpy V-notch impact test and determine the ductile-brittle transition temperature of steels. 2.0 Introduction Notched-bar impact test of metals provides information on failure mode under high velocity loading conditions leading sudden fracture where a sharp stress raiser (notch) is present. The energy absorbed at fracture is generally related to the area under the stress-strain curve which is termed as toughness in some references. Brittle materials have a small area under the stress-strain curve (due to its limited toughness) and as a result, little energy is absorbed during impact failure. As plastic deformation capability of the materials (ductility) increases, the area under the curve also increases and absorbed energy and respectively toughness increase. Similar characteristics can be seen on the fracture surfaces of broken specimens. The fracture surfaces for low energy impact failures, indicating brittle behaviour, are relatively smooth and have crystalline appearance in the metals. On the contrary, those for high energy fractures have regions of shear where the fracture surface is inclined about 45° to the tensile stress, and have rougher and more highly deformed appearance, called fibrous fracture. Although two standardized tests, the Charpy and Izod, were designed and used extensively to measure the impact energy, Charpy V-notched impact tests are more common in practice. The apparatus for performing impact tests is illustrated schematically in Figure 3. The load is applied as an impact blow from a weighted pendulum hammer that is released from a position at a fixed height h. The specimen is positioned at the base and with the release of pendulum, which has a knife edge, strikes and fractures the specimen at the notch. The pendulum continues its swing, rising a maximum height h ' which should be lower than h naturally. The energy absorbed at fracture E can be obtained by simply calculating the difference in potential energy of the pendulum before and after the test such as,

E = m. g(h − h′) Where, m is the mass of pendulum and g is the gravitational acceleration. The geometry of standard Charpy test specimen is given in Figure 4. If the dimensions of specimens are maintained as indicated in standards, notched-bar impact test results are affected by the lattice type of materials, testing temperature, thermo-mechanical history, chemical composition of materials, degree of strain hardening, etc.

Figure 3: Apparatus for impact testing of materials.

Figure 4: Specimen and loading configuration or Charpy V-notched impact

test.

Body centred cubic (BCC) metals, particularly steels, often exhibit a decrease in impact energy as the temperature is lowered. The temperature at which a sharp decrease in impact energy occurs is called the ductile-brittle transition temperature (DBTT). This transition temperature is generally chosen as a lower limit for the application of such metals. Some steels may show transition characteristics in their failure mode from ductile to brittle gradually as temperature is decreased. In this case different approaches may be used in determining transition temperature but the average energy concept is the most popular one. Determination of transition temperature can also be done by examining the fracture surfaces of specimens tested at different temperatures. For example the temperature, at which the fracture surface consists 50% cleavage (crystalline) and 50 % ductile (fibrous) types of fracture, is called fracture appearance transition temperature (FATT). Another common criterion is to determine the transition temperature on the basis of an arbitrary energy absorbed. For example 20 J transition temperatures is an accepted criterion for low-strength ship steels. 3.0 Procedure

Note: Test one material with two specimens for each temperature,

1. Check the zero calibration of the impact tester. 2. First, test a specimen at room temperature. 3. Based on the room temperature result, decide whether to concentrate on

higher or lower temperature. 4. Test specimens over a selected range of temperatures, attempting to

establish a fully ductile test, a fully (or nearly) brittle test, and as many temperatures in between as possible.

5. Note fracture energy and estimate the % brittleness from the appearances of fracture surfaces of the specimens.

4.0 Results

1. Display the test data in a table. 2. Find DBTT of the steel that you tested.

5.0 Discussion

Take all the results obtained from the testing and discuss with details in your lab report.

6.0 Questions

1. Give the estimated values of DBTT for your steel. Suggest 2 ways in which DBTT can be lowered.

2. What are the 3 basic factors which contribute to brittle fracture of steels? Do all 3 have to be present for brittle fracture to occur?

3. Explain how a triaxial stress state can arise at the root of a notch. Would this occur in thick or thin material? Thus, when does a biaxial stress state occur?

4. What are the main uses of the Charpy test? 5. List the ASTM and TS specifications for the two impact tests with titles. 6. Explain the relation between fracture toughness (KIC) of steels and impact

energy. 7. Explain the effect of carbon content on transition behaviour of plain carbon

steels in annealed condition. 8. Explain the effect of manganese on DBTT of steels.

EXPERIMENT 6: TENSILE TESTING OF METALS 1.0 Objective

The tensile test measures the resistance of a material to a static or slowly applied force. This laboratory experiment is designed to demonstrate the procedure used for obtaining mechanical properties as modulus of elasticity, yield strength, ultimate tensile strength (UTS), toughness, uniform elongation, elongation and reduction in area at rupture. Besides the true stress- true strain curve can also be determined with the help of the tensile test. 2.0 Introduction

In this test the load is applied along only one axis, and the rate of loading is constant. This test is done on a universal mechanical testing machine which is typically screw-driven or hydraulically powered. In some cases the machine may be computer controlled. The primary data generated are load vs. elongation which are to be converted into stress vs. strain data.

In modern tensile testers, load is measured using a load cell, in older or simpler testing machines, a purely mechanical or hydraulically device may be employed for measuring the load. Strain can be measured from the displacement of the crosshead or directly from the specimen. Typical devices for measuring strain are mechanical dial indicators, electrically-resistive strain gages attached to the specimen, or extensometers that employ either an optical device, a strain gage or an inductive or capacitive transducer. Strain transducers have the advantage that they measure only the displacement in the gage length of the specimen. This eliminates error due to the deformation in the ends of the specimen, slack in the load train, and the stiffness of the testing machine. There are different types of specimen depending on the type of the grips and on the form of the available material (sheet, rod, etc.). Generally all specimens have two main parts, the gage section and the ends. The dimensions of the specimens are standardized (TS, DIN, ASTM etc.) A good surface finish is required so that surface flaws do not provide stress concentrations to cause premature failure.

Engineering stress, S =𝐿𝑜𝑎𝑑

𝐴𝑜 True stress, σ =

Load

𝐴𝑖

Engineering strain, e = ∆𝑙

𝑙0 True strain, ε = ln (

𝑙

𝑙0)

0.2% yield stress is the stress for 0.2% permanent strain

𝑇𝑆 =Load max

𝐴0 True fracture stress, σ𝑓 =

Load 𝑓

A𝑓

% Elongation =(𝑙𝑓 − 𝑙𝑜) . 100

𝑙𝑜 % Reduction in area =

(𝐴𝑜 − 𝐴𝑖) . 100

𝐴𝑜

3.0 Procedure A servo-hydraulic or servo-mechanical testing machine is used. The specimen of known dimensions are loaded in the machine and strained at a constant rate. The load is measured by a load cell. The crosshead movement and/or strain are recorded; for strain measurement an extensometer is used. The X-Y plots are obtained. However the computer can also plot an engineering stress-strain curve directly, using the appropriate conversion factors and specimen area and gauge length. After the specimen is broken, the final length and diameter are measured. The fracture type and the fracture surface are investigated, in order to determine the fracture mode.

4.0 Results

1. Plot a load - elongation curve for each specimen. 2. Determine the engineering stress-strain curve and the true stress- true strain

curve. 3. Determine the 0.2% yield stress, UTS, % elongation, % reduction in area,

modulus of elasticity. Determine the mathematical expression for the true stress true strain curve for the second material.

4. Identify the fracture mode, i.e. ductile or brittle and explain the reasons. 5. Find the mechanical properties of the tested material from Handbooks and

make comparisons. Or if the material is not known try to guess it with the help of the mechanical properties.

5.0 Discussion Take all the results obtained from the testing and discuss with details in your lab report. 6.0 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.)