material testing.ppt

8/10/2019 Material testing.ppt

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Material Testing

Group 2:

John Kevin Lagundino

Dexter Jay Pacultad

Heracleo Amoc Jr.


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Material Testing

measurement of the characteristics and

behavior of such substances as metals,

ceramics, or plastics under various

conditions. The data thus obtained can be

used in specifying the suitability of

materials for various applicationse.g.,

building or aircraft construction,machinery, or packing.


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Why are metals tested ?

Ensure quality

Test properties

Prevent failure in use Make informed choices in using materials

Factor of Safetyis the ratio comparing the actual

stress on a material and the safe

useable stress.


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Two forms of testing

Mechanical teststhe material may be

physically tested to destruction. Will

normally specify a value for properties

such as strength, hardness, toughness,etc

Non-destructive tests (NDT)samples or

finished articles are tested before being

used.


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Types of Testing

Mechanical testing:

Tensile

Creep Compression

Bend or flexure

Hardness Impact

Fatigue

Non-destructive

tests:

Magnetic

DyesUltrasound


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Tensile Testing

also known as tension testing,is a

fundamental materials sciencetest in

which a sample is subjected to a

controlled tensionuntil failure. The resultsfrom the test are commonly used to select

a material for an application, for quality

control, and to predict how a material willreact under other types of forces.
http://en.wikipedia.org/wiki/Materials_sciencehttp://en.wikipedia.org/wiki/Tension_%28physics%29http://en.wikipedia.org/wiki/Quality_controlhttp://en.wikipedia.org/wiki/Quality_controlhttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Forcehttp://en.wikipedia.org/wiki/Quality_controlhttp://en.wikipedia.org/wiki/Quality_controlhttp://en.wikipedia.org/wiki/Tension_%28physics%29http://en.wikipedia.org/wiki/Materials_science


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Tensile Testing

Properties that are directly measured viaa tensile test are ultimate tensile strength,

maximum elongationand reduction in

area.From these measurements thefollowing properties can also be

determined: Young's modulus, Poisson's

ratio, yield strength, and strain-hardeningcharacteristics.
http://en.wikipedia.org/wiki/Ultimate_tensile_strengthhttp://en.wikipedia.org/wiki/Elongation_%28materials_science%29http://en.wikipedia.org/wiki/Young%27s_modulushttp://en.wikipedia.org/wiki/Poisson%27s_ratiohttp://en.wikipedia.org/wiki/Poisson%27s_ratiohttp://en.wikipedia.org/wiki/Yield_strengthhttp://en.wikipedia.org/wiki/Strain-hardeninghttp://en.wikipedia.org/wiki/Strain-hardeninghttp://en.wikipedia.org/wiki/Strain-hardeninghttp://en.wikipedia.org/wiki/Strain-hardeninghttp://en.wikipedia.org/wiki/Yield_strengthhttp://en.wikipedia.org/wiki/Poisson%27s_ratiohttp://en.wikipedia.org/wiki/Poisson%27s_ratiohttp://en.wikipedia.org/wiki/Young%27s_modulushttp://en.wikipedia.org/wiki/Elongation_%28materials_science%29http://en.wikipedia.org/wiki/Ultimate_tensile_strength


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Tensile Testing

Tensile Testing Machine


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Tensile specimen

Tensile Testing

Tensile specimens made from analuminum alloy. The left two

specimens have a round cross-

section and threaded shoulders. The

right two are flat specimen designed

to be used with serrated grips.

A tensile specimen is astandardized sample

cross-section. It has two

shoulders and a gauge

(section) in between. The

shoulders are large so they

can be readily gripped,

whereas the gauge sectionhas a smaller cross-section

so that the deformation

and failure can occur in

this area.
http://en.wikipedia.org/wiki/File:Tensile_specimen-round_and_flat.jpg


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Tensile Testing

A standard specimen is prepared in a round or a square section along

the gauge length, depending on the standard used. Both ends of the

specimens should have sufficient length and a surface condition such

that they are firmly gripped during testing.
http://en.wikipedia.org/wiki/File:Tensile_specimen_nomenclature.svg


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The shoulders of the test specimen can be

manufactured in various ways to mate to various

grips in the testing machine (see the imagebelow). Each system has advantages and

disadvantages; for example, shoulders designed

for serrated grips are easy and cheap to

manufacture, but the alignment of the specimenis dependent on the skill of the technician. On

the other hand, a pinned grip assures good

alignment. Threaded shoulders and grips also

assure good alignment, but the technician must

know to thread each shoulder into the grip at

least one diameter's length, otherwise the

threads can strip before the specimen fractures.

Tensile Testing


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Tensile Testing

A. A Threaded shoulder for use with a threaded gripB. A round shoulder for use with serrated grips

C. A butt end shoulder for use with a split collar

D. A flat shoulder for used with serrated grips

E. A flat shoulder with a through hole for a pinned grip
http://en.wikipedia.org/wiki/File:Tensile_specimen_shoulders.svg


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CreepTesting

Creep Testing

A creep-testing machinemeasures the Creep(the

tendency of a material after being subjected to high

levels of stress, e.g. high temperatures, to change

its form in relation to time) of an object. It is a devicethat measures the alteration of a material after it has

been put through different forms of stress. Creep

machines are important to see how much strain

(load) an object can handle under pressure, soengineers and researchers are able to determine

what materials to use.

C T i
http://en.wikipedia.org/wiki/Creep_%28deformation%29http://en.wikipedia.org/wiki/Creep_%28deformation%29


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The device generates a creep time-

dependent curve by calculating the steady

rate of creep in reference to the time it

takes for the material to change. Creepmachines are primarily used by engineers

to determine the stability of a material and

its behaviour when it is put throughordinary stresses.

CreepTesting

C T ti


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Design

Researchers look to test objects with a

creep machine to understand the process

of metallurgy and the physical mechanical

properties of a metal, test the developmentof alloys, receive data from the loads that

are derived and to find out whether a

sample or material is within the boundaryof what they are testing.The basic design

of a creep machine is the furnace, loading

device and support structure.

CreepTesting

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Load platformor sometimes called load hanger is

where the object will endure pressure at a constant

rate. Gripsare used to hold the material you are testing

in a certain position. Position is important because if

the alignment is off, the machine will deliver

inaccurate readings of the creep of the material. Dial Gaugeis used to measure the strain. It is the

object that captures the movement of the object in

the machine. The load beam transfers the

movement from the grip to the dial gauge. Heating Chamberis what surrounds the object and

maintain the temperature that the object is subjected

to.

CreepTesting

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Applications

Creep machines are most commonly used

in experiments to determine how efficient

and stable a material is. The machine is

used by students and companies to createa creep curve on how much pressure and

stress a material can handle. The machine

is able to calculate the stress rate, timeand pressure.

CreepTesting

C T ti


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Applications

Displacement-Limited applications: the size must

be precise and there must be little errors ortendency to change.This is most commonly found in

turbine rotors in jet engines.

Rupture Limited applications: in this application

the break cannot occur to the material but there can

be various dimensions as the material goes through

creep. High pressure tubes are examples of them.

Stress relaxation limited application: the tension

at the beginning becomes more relaxed and the

tension will continue to relax as the time goes by,

such as cable wires and bolts.

CreepTesting


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Compressive Testing

determine a materials response to crushing, orsupport-type loading (such as in the beams of a

house). Testing machines and extensometers

for compression testsresemble those used for

tension tests. Specimens are generally simpler,

however, because gripping is not usually a

problem. Furthermore, specimens may have a

constant cross-sectional area throughout theirfull length. The gauge lengthof a sample in a

compression test is its full length.
http://www.britannica.com/EBchecked/topic/144838/crushing-strengthhttp://www.britannica.com/EBchecked/topic/130327/compressive-strength-testhttp://www.britannica.com/EBchecked/topic/227017/gauge-lengthhttp://www.britannica.com/EBchecked/topic/227017/gauge-lengthhttp://www.britannica.com/EBchecked/topic/130327/compressive-strength-testhttp://www.britannica.com/EBchecked/topic/144838/crushing-strength


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Bend Test

Bend test - Application of a force to the center

of a bar that is supported on each end to

determine the resistance of the material to astatic or slowly applied load.

Flexural strength or modulus of rupture -

The stress required to fracture a specimen in a

bend test. Flexural modulus - The modulus of elasticity

calculated from the results of a bend test, giving

the slope of the stress-deflection curve.


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(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learningis a trademark used herein under

license.

(a) The bend test often used for measuring the strength ,and (b) the deflection obtained by bending


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Schematic for a 3-

point bending test. Able to measure the

stress-strain behavior

and flexural strength

of brittle ceramics.

Flexural strength(modulus of rupture or

bend strength) is the

stress at fracture.

Flexural Strength

See Table 7.2 for more values.


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Hardness of Materials

Is the measure of the resistance of a metal to

permanent plastic deformation. The hardness of a

metal is measured by forcing an indenter into its

surface. The indenter material which is usually aball, pyramid, or cone is made of a material much

harder than the material being tested.


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Hardness Testers


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Hardness testing machine

The indenter is

pressed into the metal

Softer materials leave

a deeper indentation


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Brinell hardness test

Uses ball indentor.

Cannot be used for

thin materials.Ball may deform on

very hard materials

Surface area of

indentation ismeasured.


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Vickers hardness test

Uses square

pyramid indentor.

Accurate results.

Measures length of

diagonal on

indentation.


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Rockwell hardness tests

Gives direct reading.

Rockwell B (ball) used

for soft materials.

Rockwell C (cone) usesdiamond cone for hard

materials.

Flexible, quick and

easy to use.


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Impact Tests

Toughness of metals is the ability to

withstand shock load and impact. It will not

fracture when twisted.


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I d


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Izod test

Strikes at 167 Joules.

Test specimen is held

vertically.

Notch faces striker.


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Ch i t t t


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Charpy impact test

Strikes form higher

position with 300

Joules.

Test specimen is heldhorizontally.

Notch faces away form

striker.


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F ti


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Fatigue

Fatigue is due to the repeated loading and unloading.

When a material is subjected to a force acting in differentdirections at different times it can cause cracking. In time thiscauses the material to fail at a load that is much less than itstensile strength, this is fatigue failure. Vibration for example is a

serious cause of fatigue failure.

Fatigue can be prevented with good design practice.

1. A smooth surface finish reduces the chance of surface cracking.

2. Sharp corners should be avoided.

3. Corrosion should be avoided as this can cause fatigue cracks.


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Non-destructive testing (NDT)


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Why use NDT?

Components are not destroyed

Can test for internal flaws

Useful for valuable components

Can test components that are in use


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Penetrant testing

Used for surface flaws.

The oil and chalktest is a traditional

version of this type of testing. Coloureddyes are now used.


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Magnetic particle testing

Used for ferrous metals. Detects flaws close to the surface of the material. The component to be tested must first be

magnetized.

Magnetic particles which can be dry or in solutionare sprinkled onto the test piece.

The particles stick to the magnetic field and flawscan be inspected visually by examining the pattern

to see if it has been distorted. The component must be demagnetized after testing.


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Eddy current testing

Used for non-ferrous metals A.C. current is passed through the coil.

The test piece is passed under the coil

causing secondary currents called eddycurrents to flow through the test piece.

This causes a magnetic field to flow in

the test piece. The flaws are detected on an

oscilloscope by measuring a change in

the magnetic field.


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Ultrasonic testing


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Ultrasonic testing

Ultrasonic Sound waves are bounced off the component

and back to a receiver. If there is a change in the timetaken for the wave to return this will show a flaw. This issimilar to the operation of a sonar on a ship.

Operation.

1. The ultrasonic probe sends the sound wave through the

piece.2. The sound wave bounces of the piece and returns.

3. The results are then placed on the display screen in theform of peaks.

4. Where the peaks fluctuate this will show a fault in thepiece.

Uses.

This is generally used to find internal flaws in largeforgings, castings and in weld inspections.


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material testing.ppt

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