Fatigue

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Kingston University London

AEM111 - FURTHER AEROSPACE STRUCTURES AND MATERIALSEXPERIMENTAL NDT AND FATIGUE ASSESSMENT FOR AIRCRAFT ALLOYS

Lecturer: Dr HOSSEIN MIRZAI

Submission: 31/05/2011

Author: Nicolau Iralal Morar

TABLE OF CONTENTS

INTRODUCTION......................................................................................................................2

1.1 FATIGUE TEST.........................................................................................................2

1.1.2 LOW CYCLE FATIGUE...........................................................................................3

1.1.3 HIGH CYCLE FATIGUE..........................................................................................3

1.1.4 METHOD OF CALCULATING FATIGUE STRENGTH............................................4

1.2 NON-DESTRUCTIVE TESTING METHODS (NDT)..................................................5

2. EXPERIMENTAL APPROACH............................................................................................7

2.1 SPECIMENS..................................................................................................................7

2.2 APPARATUS..................................................................................................................7

2.3. EXPERIMENTAL PROCEDURE...................................................................................8

2.4 RESULTS.....................................................................................................................10

2.5 DISCUSSION...............................................................................................................13

3. NON-DESTRUCTIVE TESTING METHODS APPROACH................................................14

3.1 MAGNETIC PARTICLE TEST APPROACH.................................................................14

Advantages.........................................................................................................................14

Disadvantages....................................................................................................................14

3.2 ULTRASONIC TEST APPROACH...............................................................................15

3.3 DISCUSSION...............................................................................................................17

4. CONCLUSION...................................................................................................................18

REFERENCES.......................................................................................................................19

APPENDIX A..........................................................................................................................20

TABLE OF RESULTS............................................................................................................20

TABLE OF RESULTS Al 2011 T3......................................................................................21

TABLE OF RESULTS Al 6082 T6......................................................................................22

APPENDIX B..........................................................................................................................23

SPECIMEN PROPERTIES....................................................................................................23

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INTRODUCTION

Aluminium alloys have been more and more extensively utilised in structural applications

and transportation industry for their light weight and attractive mechanical properties

achieved by thermal treatments. The objective of the present study report is to investigate

the performance of selected aerospace materials, in particular aluminium alloys. The first

objective is to carry out repeated fatigue tests for a range of amplitude stress levels to allow

comparison of results with experimental S-N data. An S-N curve is a suitable method of

establish fatigue endurance limit and life for structural materials. The data obtained is to be

used to establish endurance fatigue limit for such materials and to discuss their significance.

The aluminium alloys used in this study are Al2011 T3 and Al6082 T6. The second task of

the study is to perform the applicable methods of NDT used in the aircraft industry such as

ultrasonic and magnetic particle. Be able to understand the application and describe

methods and principles of operations concerned, as well as any advantages and

disadvantages of the methods used, observations and limitations and accuracy of methods

used.

1.1 FATIGUE TEST

A method for determining the behaviour of materials under fluctuating loads. A specified

mean load (which may be zero) and an alternating load are applied to a specimen and the

number of cycles required to produce failure (fatigue life) is recorded. Generally, the test is

repeated with identical specimens and various fluctuating loads. Loads may be applied

axially, in torsion, or in flexure. Depending on amplitude of the mean and cyclic load, net

stress in the specimen may be in one direction through the loading cycle, or may reverse

direction [1].

Data from fatigue testing often are presented in an S-N diagram which is a plot of the

number of cycles required to cause failure in a specimen against the amplitude of the

cyclical stress developed.

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The cyclical stress represented may be stress amplitude, maximum stress or minimum

stress. Each curve in the diagram represents a constant mean stress. Most fatigue tests are

conducted in flexure, rotating beam, or vibratory type machines. The classical fatigue

experiments carried out by Wohler, method of reversing the stress on a part by employing a

cantilever rotated about its longitudinal axis. Hence the stress at any point on the surface of

the cantilever varied sinusoidal. In many applications, materials are subjected to vibrating or

oscillating forces. The behaviour of materials under such load conditions differs from the

behaviour under a static load. Because the material is subjected to repeated load cycles

(fatigue) in actual use, designers are faced with predicting fatigue life, which is defined as

the total number of cycles to failure under specified loading conditions. Fatigue testing gives

much better data to predict the in-service life of materials. Some typical materials that are

subjected to fatigue testing: Metals, Polymers, Composites, Elastomers, Structural

Components, Ceramics. The following ASTM standards apply to fatigue testing are: E1820,

E399, E606, E647 [2].

1.1.2 LOW CYCLE FATIGUE

Low Cycle Fatigue (LCF) describes the service environment of many critical (and primarily

metal) components: low frequency, large loads/strains. The LCF environment is typical of

turbine blades (heat-up/cool down cycling) and other power generation equipment subject to

thermal and/or mechanical cycling (ie. pressure vessels, piping, etc.) LCF typically involves

large deformations, thereby accumulating damage on the specimen. LCF research is

essential for the understanding of failure (in metals), for design and engineering purposes.

1.1.3 HIGH CYCLE FATIGUE

High Cycle Fatigue (HCF) results from vibratory stress cycles at frequencies which can

reach thousands of cycles per second and can be induced from various mechanical sources.

It is typical in aircraft gas turbine engines and has led to the premature failure of major

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engine components (fans, compressors, turbines).While LCF involves bulk plasticity where

stress levels are usually above the yield strength of the material, HCF is predominantly

elastic, and stress levels are below the yield strength of the material [2].

Figure 1: Shows typical S-N diagram curve [2]

1.1.4 METHOD OF CALCULATING FATIGUE STRENGTH

To use graph (Fig. 1) to calculate fatigue strength, the material and the number of cycles is

required. The analytical method for estimating, Sf (N) and Se, as follows:

η=S f (N )

σa'

(Equation 1)

The

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1.2 NON-DESTRUCTIVE TESTING METHODS (NDT)

In the aerospace industry, as with other transportation industries, NDT is well- suited method

of identifying crack and damages in components or structures without eliminating and

destroying them. Aircraft components are inspected before they are assembled into the

aircraft and then they are periodically inspected throughout their useful life. Aircraft parts are

designed to be as light as possible while still performing their intended function.

This generally means that components carry very high loads relative to their material

strength and small flaws can cause a component to fail. Since aircraft are cycled (loaded

and unloaded) as they fly, land, taxi, and pressurize the cabin, many components are prone

to fatigue cracking after some length of time. The parts that are loaded well below the level

that causes them to deform can develop fatigue cracks after being cycled for a long time.

This is what happens in aircraft. After they are used for a while, fatigue cracks start growing

in some of their parts. Cracking can also occur due to other things like a lightning strike [3].

Common NDT methods include ultrasonic, magnetic particle, liquid penetrant, radiographic,

and eddy-current testing. Penetrant is used to check discontinuities i.e cracks, pits etc open

to the surface on parts made of non porous materials. This method depends on the ability of

the penetrant to enter into a surface discontinuity in the material to which it is applied. It is

applicable to all solid non-porous material. The NDT findings are a significant part of damage

tolerance analysis based on the fracture mechanics principles. The techniques for the

present study are magnetic particle and ultrasound techniques. Magnetic particle tests are

used to locate surface and sub-surface discontinuities in ferromagnetic material.

Ultrasonic tests depend on reflected sound effects to locate internal defects and it can be

used to measure the overall thickness of the material and the specific depth of a defect [4].

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2. EXPERIMENTAL APPROACH

The equipment shows the classical fatigue experiments carried out by Wohler. Wohler

selected the method of reversing the stress on a part by employing a cantilever rotating

about its longitudinal axis [2]. This means that the stress at any point on the surface of the

cantilever varies sinusoidal. In the machine used at University laboratory the cantilever is

specially designed to use a relatively simple specimen with a definite minimum cross

section.

2.1 SPECIMENS

The specimens used for the experimental approach are Al 2011 T3 and Al 6082 T6. The

below figure 5 illustrates the specimen geometry and dimension references. The appendix B

provides the material composition and mechanical properties of the two specimens.

Figure 2: Specimen geometry

2.2 APPARATUS

Fatigue tester HSM .19 mk. 3 shown in Fig.6 is driven by an induction squirrel cage motor at

5700 rpm (95 Hz) with a counter ratio of 1:100. Power supply provided is 220V single

phase. The motor is connected on one side to a counter mechanism, which can record 5

digit revolution counter. Attached to the shaft at the other end is a fixture. The loading

device consists of a spherical ball bearing and a micro switch, which automatically switches

off the motor when the fracture occurs.

Figure 3: Fatigue tester apparatus (HSM .19 mk. 3)

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The apparatus is supplied with a recommended standard specimen. The bending stress for a load P (N) is:

σ=L×P×32

π×d3 ( Nmm2 )σ=125.7 P×32

π ×43=20 P(N /mm2)

Where: L = Distance from neck to specimen’s contact point with bearing

d = Diameter of the neck

P = Load applied (measured by revolution counter read out)

Figure 4: Counterbalance and load hanger

EXPERIMENTAL PROCEDURE

As fatigue fracture experiments may run on for half an hour or more so the usual procedure

is for each group in a class to set up and start two aluminium specimens and for all the

results to be shared at the end. The load sets was provided in the lab session, and

procedure as follows:

1. Measure the diameter at the neck of the specimen and inspect the surface

roughness.

2. Slide one end of the specimen into the adapter at the shaft end and slide the other

end into the adapter at the load end.

3. Measure the distance from the neck to the specimen’s contact surface with the

bearing. Now position the loading arm so that the dimension of 109.5 mm is attained

from the rear face of the bearing housing to the adjacent end of the neck of the

specimen (Fig. 7). Tighten the collect with the spanner.

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4. Rotate the specimen to check that the end of the cantilever runs axially. If it does not

the specimen must have got bent and should be discarded.

5. Apply the given load. Check with the lab instructor about loading the specimen in

order to have a precise bending loading condition.

6. Set the revolution counter to zero and start the motor.

Results from other load cases will be collected and made available to each group

after all groups have completed the experiment.

7. Normally the test terminates itself through the fracture of the specimen opening the

micro switch and hence stopping the motor. As the onset of fracture approaches the

specimen will bend more and this may open the micro switch before complete

fracture occurs. In this case move the micro switch down slightly and restart the

motor.

8. Collate the results and plot them as they occur on a graph of stress range, , against

logl0 number of reversals N. Note that in the case of a rotating cantilever the stress

range is twice the applied bending stress.

2.4 RESULTS

The repetitive fatigue tests for various amplitude stress levels were conducted in the

laboratory at room temperature. The tests were performed for two aluminium alloy

specimens. The first test was run on an aluminium Al 2011 T3 alloy whilst the second test

was on an Al 6082 T6 alloy. The ultimate yield stress was taken into account to decided

what the maximum stress level applied be.

For the Al 2011 T3 the ultimate yield strength (UTS) is approximately referenced as 379

MPa which equates to 18.95 N. It was decided to use a maximum load of 18 N.

For the Al 6082 T6 the UTD is referenced to be 290 MPa, which equates to 14.5 N, hence

14 N was said to be the maximum load. The results are tabulated and displayed on the

appendix A for both specimens respectively.

The stresses were calculated using equation as follows:

σ=20×P (Eq.3)

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Al 2011 T3

Load Stress Reading

No. Of cycles (nc)

By:5 100 No fail 4688300 Alex Wine

6 120 Fail 7753000 MS

7 140 Fail 236000 MS

8 160 Fail 338600 Alex Wine

9 180 Fail 85800 MS

10 200 Fail 84900 MS

11 220 Fail 32000 Alex Wine

12 240 Fail 30200 Group

13 260 Fail 27400 Group

15 300 Fail 9800 Group

16 320 Fail 3500 Group

18 360 Fail 2100 Group

18 360 Fail 1875 Group

Al 6082 T6

Load

Stress (MPa)

No. Of cycles(nc)

Reading By:6 120 57889400 No fail MS

6.7 134 2411100 Fail Alex Wine7 140 1526100 Fail MS8 160 1028600 Fail MS

8.65 173 728400 Fail Alex Wine9 180 263000 Fail MS

10 200 209700 Fail MS10.6 212 114800 Fail Alex Wine11 220 85500 Fail Group11 220 72300 Fail Group12 240 65300 Fail Group12 240 49500 Fail Group14 280 20100 Fail Group14 280 16300 Fail Group

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1E+03. 1E+04. 1E+05. 1E+06. 1E+07. 1E+08.0

255075

100125150175200225250275300325350375400

Al 2011 (T3)

Al 2011 T3 Experiment

Number of Cycles ( N )

Stre

ss, S

( M

Pa )

Figure 5: Al 2011 T3 S-N diagram curve

1E+04. 1E+05. 1E+06. 1E+07. 1E+08.50

75

100

125

150

175

200

225

250

275

300Al 6082 (T6)

Al 6082 T6 Exper-iment(2011)

Number of Cycles ( N )

Stre

ss, S

( M

Pa )

Figure 6: Al 6082 T6 S-N diagram curve

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Figure 7: Al 2011 T3 S-N diagram curve comparison between 2010/11

Figure 8: Al 6082 T6 S-N diagram curve comparison between 2010/11

2.5 DISCUSSION

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Fatigue testing was done to determine the effect of repeated stress variation on aluminium

alloy specimens for the present subject study. Since each specimen must be tested to failure

to obtain one piece of data, a number of specimens were used to complete one experiment

set. However, the number of tests was limited due to the malfunction of the test machine.

Only the high load and low cyclic frequencies were performed with maximum of number of

two tests being performed from the beginning. For the present study, data was gathered for

low cycles (14N to 8N load) from the experimental testing performed on the laboratory and

high cycles (7N to 6N load) were gathered from the current year student as he used for his

final year dissertation.

From the experiment, S-N diagrams were created from the data could be gathered with

regards to the stress variation of the aluminium alloys under the conditions of constant

amplitude stress.

The results and S-N diagram shows that at high stress intensities, the number of cycles to

failure were low, while the life expectancy of the sample increases with reduction of stress.

As mentioned previously, some of the fatigue data was collected from the fellow colleague

who had performed fatigue test for his dissertation prior to fatigue test machine break-down

as mentioned and referenced previously.

From the chart plotted, the endurance limit could be determined. For the case of non-ferrous

metals and alloys, such as aluminium, they do not reveal precise endurance limits. It can be

see that from the S-N diagram charts illustrated. The endurance limit represents a stress

level under which the material does not fail, hence can be cycled infinitely. If the applied

stress is below the endurance limit of the material then the material is assumed to have an

infinite life. The figure 5 and 6 illustrates that AL 2011 T3 and Al 6082 T6 specimens does

not have an endurance limit and has a continually decreasing S-N response. For such

cases, fatigue strength Sf for a given number of cycles is specified.

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The specified fatigue strength for the AL 2011 specimen is assumed to be at 120 MPa for

both years. From the selected specimens failure did not occur at a 6N load and number of

cycles at which this point is in the region of 1.11 x 107 cycles. This is known as the effective

endurance limit.

The AL 6082 T6 specimen has also been analysed for performance comparison purposes.

From figure 6, the effective endurance limit found to be 1.8 x 107 MPa for AL 6082 T6. Both

non failures occurred at a load of 6N. The load below at which there is an infinite life is 110

MPa in 2010 experiment and 105 MPa in 2011. With comparison with the AL 2011, the load

below which there would be an infinite life was taken as 120 MPa. The results show that the

Al 6082 composition performs better than the AL 2011. Although the loads at which this

specimen operates at is lower by 12.5%, of the two materials, it is better to use the AL 6082

as it has a better fatigue life, the AL 6082 performs better by 38%.

There were a maximum of two tests conducted for each load, and at each load both failures

and non-failures occurred. This may be due to the following reason: the surface roughness

causes microscopic stress concentrations which can lower fatigue strength.

Grain size. The grain size has an impact on the fatigue life. Generally smaller

grain sizes yield longer life. The presence of surface defects or scratches will

also have a influence than in a coarse grained alloy

Temperature. The temperature also a diverse effect on fatigue life as higher

temperatures generally decrease fatigue strength.

Compressive residual stresses from machining, cold working, heat treating will oppose a

tensile load and thus lower the amplitude of cyclic loading.

Because the system is hydraulically operated, it is possible to achieve both high loads and

high cyclic frequencies. The test system should be fitted with a control system that is

capable of controlling the test and measuring data at high frequencies. It is also important

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that the load measurement system can accurately measure specimen load, and compensate

for load errors induced by the dynamic movement of the test system.

Accuracy depends upon three different factors: (1) the design of the machine :( 2) the use of

the machine and resulting wear in the bearings, seals and ; (3) the proper - manipulation of

the machine according to established instructions.

In the above-mentioned investigations which were carried out by means of electrical strain

gauges, deviations of the actual load from the nominal load of more than 30 to 40 per cent

were observed in some cases. When caused by uncorrected inertia forces, the accuracy

could lie substantially improved by applying correction factors as mentioned above, but in

some machines the errors resulted from the design of the machine or neglected

maintenance of its proper function. The latter objection applied particularly to hydraulic

machines.

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3. NON-DESTRUCTIVE TESTING METHODS APPROACH

3.1 Magnetic Particle Inspection (MPI)

Method

When an object is magnetized, iron powder applied to the surface will accumulate over

regions where the magnetic field is disturbed as a result of surface flaws.

Application/advantages

MPI is a simple and fast method to detect surface defects in ferromagnetic materials.

Limitation

The MT is applicable only to ferromagnetic materials. It is for example not applicable to stainless weld deposit on ferromagnetic base material. Trained operators are necessary to avoid misinterpretations.

Principle

Figure 9: An Illustration of the Principle of Magnetic Particle Inspection [4]

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Figure 10: An Illustration of Magnetic Particle Inspection [4]

Comments

Magnetic particle testing is used for locating surface or near surface discontinuities in

ferromagnetic materials. This method involves the establishment of a magnetic field within

the material to be tested. Discontinuities at or near the surface set up a disturbance in the

magnetic field. The pattern of discontinuities is revealed by applying magnetic particles to

the surface, either by dry powder or suspended in a liquid (wet method). The leakage field

attracts the magnetic particles, and thus the discontinuities may be located and evaluated by

observing the areas of particle build-up. These magnetically held particles form an indication

of the location, size and shape of the discontinuity. Some of the factors which determine the

detectability of discontinuities are the magnetizing current, the direction and density of the

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magnetic flux, the method of magnetization and the material properties of the object to be

tested.

The electric current used to generate the magnetic field may be alternating (AC) or direct

(DC). The primary difference is that magnetic fields produced by DC are far more

penetrating than those produced by AC. Compared to liquid penetrant inspection, the MPI

has the following advantages: it will also reveal those discontinuities that are not surface open

cracks (cracks filled with carbon, slag or other contaminants) and therefore not detectable by

liquid penetrant.

Different nature of defects is detectable by the magnetic particle method such as cracks

caused by quenching, fatigue and embrittlement. Subsurface defects can also be detected

by this method of NDT however subsurface defects can only be located when they are

relatively close to the surface.

Prior to the application of magnetic particle method, the materials requires to be examined

that are capable of being magnetised at certain degree. There are several ways to

magnetise materials.

The most common methods are as follows:

Residual methods, the magnetism of the component is relied on when the magnetic

powder is applied.

Continuous methods in which the current inducing the magnetic flux in the part to be

inspected is allowed to flow while the power is applied.

The procedure used in university laboratory for the magnetic particle method us as follows

[3]:

1. Connect footswitch via socket on the left hand side of the unit.

2. Connect pump via the socket on the right hand side of the unit.

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3. Connect the UV light to the “UV light” socket in the left hand side.

4. Turn Mains supply on at the wall isolator.

5. Switch on via RCD switch “Unit on” illuminates.

6. Turn on the UV light and allow 10 minutes to warm up.

7. Slide out the ink hopper to within 75 mm of the top flange with Fluorescent

Magnetic ink.

8. Slide in the Hopper gently

9. Turn on the agitation and dispensing pump using the twist switch on the right

hand of the machine.

10. With the inking out hose pointing to the drain tray, depress the ink applicator

button on the end of the hose to initially bleed the system.

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3.2 ULTRASONIC TEST APPROACH

Method

Ultrasonic pulses are directed into a test object. Echoes and reflections indicate presence,

absence, and location of flaws, interfaces, and/or defects.

Application

Ultrasonic testing is a sensitive NDT-method, which can be used on metals or non-metals.

Best results are obtained when the sound beam is perpendicular to the defect. Defects may

be detected at depths ranging from 5 mm to 10 m in steel.

Limitations

Operation of ultrasonic equipment requires experienced personnel. False indications may

arise from multiple reflections and geometric complexity. Small and thin objects and coarse-

grained materials may be difficult to test. For example, welds involving nickel base alloys

and austenitic stainless steels tend to scatter and disperse the sound beam: penetration of

the sound beam into these materials is limited and interpretation of the results may be

difficult.

Principle

Figure 11: An Illustration of Ultrasonic Flaw Detection [4]

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Comments

Ultrasonic methods of NDT use beams of sound waves (vibrations) of short wavelength and

high frequency, transmitted from a probe and detected by the same or other probes. Usually,

pulsed beams of ultrasound are used and in the simplest instruments a single probe, hand

held, is placed on the specimen surface. Ultrasonic energy is transmitted between the

search unit and the test part through a coupling medium such as oil, grease. An oscilloscope

display with a time base shows the time it takes for an ultrasonic pulse to travel to a reflector

(a flaw, the back surface or other free surface) in terms of distance travelled across the

oscilloscope screen. The height of the reflected pulse is related to the flaw size as seen from

the transmitter probe. The relationship of flaw size, distance and reflectivity are complex, and

a considerable skill is required to interpret the display [5].

Ultrasonic examinations are performed for the detection and sizing of internal defects, flaws

or discontinuities in piping, castings, forgings, weldments or other components. Exact sizing

techniques have been developed to detect and monitor progressive cracking in a variety of

equipment. Ultrasonic testing is often performed on steel and other metals and alloys,

though it can also be used on concrete, wood and composites, albeit with less resolution. It

is a form of non-destructive testing used in many industries including aerospace, automotive

and other transportation sectors [5].

Figure 12: Ultrasonic Sound Equipment [6]

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When testing materials with ultrasound, two types of probes may be used; the normal probes

(0°) (longitudinal waves) and the angle probes (transverse waves). The normal probe (0°)

generates longitudinal waves and transmits them (via a couplant such as oil, grease or

water) into a test object in a direction normal to the surface to which the probe is applied.

The pulse propagates in a straight direction, but due to beam spread, the sound field will

become cone-shaped. The angle of beam spread is related to probe diameter and

frequency. In fig. 7.3 the principle of application of a normal probe is shown. The commonly

frequencies used are 2 MHz and 4MHz [6].

The angle probe is constructed to transmit transverse waves at a defined angle into a test

object. Typical angles are 35°, 45°, 60°, 70° and 80°. The most commonly used angels are

45°, 60°, and 70°. On materials with sound-velocities different from steel, the angle will

change according to Snell’s Law. For instance, a probe of 60° in steel will give 56° in

aluminium, 37° in copper and 35° in cast iron [6].

Procedure

Ultrasonic examination must be performed in accordance with a written procedure. In

general each procedure must include at least the following information, as applicable: Type

of instrument; Type of transducers; Frequencies; Calibration details; Surface requirements;

Type of couplants; Scanning techniques; Recording details; Reference to applicable welding

procedures

The following steps show describe how the ultrasonic scan should be conducted [3]:

1. Turn on the oscilloscope. Ensure the probe is connected correctly.

2. Lay the specimen to be examined on a flat surface.

3. Apply a film of oil on the components to be examined.

4. Gently run the crystal sensor over the top surface of the specimen. The readings

should be taken in parallel of the specimen.

5. Adjust the gain of the oscilloscope to provide a clear reading.

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Figure 13: Figure 14: Application of use for the crystal sensor

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3.3 DISCUSSION

3.3.1 Magnetic particle Inspection

A number of factors can influence the production and quality of indications defect size depth

of defect below surface magnetising current level of magnetisation relative orientation of

defect and direction of magnetisation magnetic properties of test piece size and magnetic

properties of detecting the subject part.

The magnetised part that a uses dry method are pleasant to work compared to immersed by

the oil paste suspension, as are highly advantageous for large areas are to be inspected and

recovery of the oil-paste suspension would be hard. Also dry method (using powder) is

better for locating near-surface plate electrodes which make contact with the opposite

surfaces of a bench.

Also magnetic particle indications are formed directly on the surface of the part, shaping an

image of the discontinuity. This method is cost effective since the equipment costs are

relatively low. The main drawback is that only ferromagnetic materials can be inspected.

Also, requires alignment of magnetic field and defect is significant as they produce some

discrepancies.

Large currents are needed for very large parts and the surface has to be relatively smooth.

Non-magnetised coverings adversely affect the sensitivity plus, demagnetisation and post

cleaning is usually necessary.

Overall the orientation of the flaw with respect to the direction of the flow of magnetic flux

greatly influences the likelihood of creating a leakage field. Ideally the flaw should be at 90°

to the flux flow, but detection may still be possible at 45°. Components should be tested in at

least two directions to ensure maximum detection of flaws.

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3.3.2 Ultrasound Test

Ultrasonic Inspection is a very useful and versatile NDT method. Some of the advantages of

ultrasonic inspection that are often cited include: It is sensitive to both surface and

subsurface discontinuities; the depth of penetration for flaw detection or measurement is

superior to other NDT methods; only single-sided access is needed when the pulse-echo

technique is used; It is highly accurate in determining reflector position and estimating size

and shape; minimal part preparation is required, electronic equipment provides

instantaneous results; detailed images can be produced with automated systems. It has

other uses, such as thickness measurement, in addition to flaw detection.

As with all NDT methods, ultrasonic inspection also has its limitations, which includes

surface must be accessible to transmit ultrasound, skill and training is more extensive than

with some other methods, It normally requires a coupling medium to promote the transfer of

sound energy into the test specimen, materials that are rough, irregular in shape, very small,

exceptionally thin or not homogeneous are difficult to inspect, cast iron and other coarse

grained materials are difficult to inspect due to low sound transmission and high signal noise,

linear defects oriented parallel to the sound beam may go undetected.

Possible errors may occur if thickness measurements are to be carried out on an object with

a coated surface; the coating may give rise to measurement errors. To avoid such errors

must use single crystal probes, and then measure the material thickness between first and

second echo. Also if using double crystal probes, the coating must be removed before

measurement is carried out.

Overall, for the effective results the calibration of the apparatus and probes are of decisive

importance. For the calibration of the equipment range scale and the angular determination

of angle probes, a calibration blocks are used.

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4. CONCLUSION

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REFERENCES

[1]

[2]

[3]

[4]http://www.ndt-ed.org/GeneralResources/MethodSummary/.htm

[accessed on 21/05/2011]

[5] http://engg-learning.blogspot.com/2011/03/non-destructive-techniques.html

[accessed on 21/05/2011]

[6] http://www.krautkramer.com/ [accessed on 21/05/2011]

[7] http://www.aalco.co.uk/.../Aalco-Metals-Ltd_Aluminium-Alloy_2011-T3_3.pdf.%20ashx [accessed on 21/05/2011]

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APPENDIX A

TABLE OF RESULTS

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TABLE OF RESULTS Al 2011 T3Table 1: Al 2011 T3 - 2011 Experimental Results

Load 18 18 18 16 16 16 14 14 14 16 16 16

Cycles0000000 0000000

000000

00000000

000000

00000000 0000000

000000

000000

0000000 000000

00000000

Stress

MPa)

Load 14 14 14 12 12 12 10 10 10 8 8 8

Cycles 0000000 0000000 000000

0

0000000 000000

0

0000000 0000000 000000

0

00000 0000000 000000

0

0000000

Stress

MPa)

Source:

Table 2: Al 2011 T3 - 2010 Experimental Results

Load 18 18 18 16 16 16 14 14 14 16 16 16

Cycles0000000 0000000

000000

00000000

000000

00000000 0000000

000000

000000

0000000 000000

00000000

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Stress

MPa)

Load 14 14 14 12 12 12 10 10 10 8 8 8

Cycles 0000000 0000000 000000

0

0000000 000000

0

0000000 0000000 000000

0

00000 0000000 000000

0

0000000

Stress

MPa)

Source:

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TABLE OF RESULTS Al 6082 T6Table 3: Al 6082 T6 - 2011 Experimental Results

Load 18 18 18 16 16 16 14 14 14 16 16 16

Cycles0000000 0000000

000000

00000000

000000

00000000 0000000

000000

000000

0000000 000000

00000000

Stress

MPa)

Load 14 14 14 12 12 12 10 10 10 8 8 8

Cycles 0000000 0000000 000000

0

0000000 000000

0

0000000 0000000 000000

0

00000 0000000 000000

0

0000000

Stress

MPa)

Source:

Table 4: Al 6082 T6 - 2011 Experimental Results

Load 18 18 18 16 16 16 14 14 14 16 16 16

Cycles0000000 0000000

000000

00000000

000000

00000000 0000000

000000

000000

0000000 000000

00000000

31 | P a g e

Stress

MPa)

Load 14 14 14 12 12 12 10 10 10 8 8 8

Cycles 0000000 0000000 000000

0

0000000 000000

0

0000000 0000000 000000

0

00000 0000000 000000

0

0000000

Stress

MPa)

Source:

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APPENDIX B

SPECIMEN PROPERTIES

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Material Characteristics

2011 Aluminium T3

Al 2011 is the most machinable of the commonly available aluminium alloys. Machining

this alloy can produce excellent surface finishes on your product, and small, broken

chips.

Weld ability, strength, and anodizing response are all rated as average at best, and this

alloy does not have a high degree of corrosion resistance.

If the ability to make your part quickly is important to you, and strength is not the primary

desire, 2011 represents a good choice if you're using aluminium.

Temper: T3 - Solution heat treated, cold worked and naturally aged.

CHEMICAL COMPOSITIONElement %PresentSilicon (Si) 0.4 TypicalIron (Fe) 0.7 TypicalCopper (Cu) 5 to 6Lead (Pb) 0.2 to 0.6Bismuth (Bi) 0.2 to 0.6Zinc (Zn) 0.3 TypicalOthers (Total

)0.15 Typical

Aluminium (Al) BalancePHYSICAL PROPERTIESProperty ValueDensity 2.82Kg/m³Melting Point 535°CThermal Expansion 23x10-6/KModulus of Elasticity

71GPa

Thermal Expansion 138W/m.KElectrical Resistivity 0.045x10-6 Ω .mMECHANICAL PROPERTIESProperty ValueProof Stress 290-300 MPaUltimate Tensile Strength 379 MPaElongation 15%Shear Strength 220 MPaHardness Vickers 110 HV

Table 5: Al 2011 T3 Characteristics

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Material Characteristics

6082 Aluminium T6

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