FACULTY OF ENGINEERING

Course: ADVANCED MATERIALS PROCESSING

Course work title: Experimental data OF NDT AND FATIGUE ANALYSIS OF AL-ALLOYS OF 6000 AND 2000 SERIES

Module code MNM 413 Module leader Dr Hussein mirzeli

Date of submission 14/12/09

Names Student id numberCharlakola Sateesh Reddy K0951098

Contents:1) SN CURVE

1.1) Introduction1.2) S-N CURVE EXPERIMENT OF ALUMINUM 6000 and 2000 series1.3) Endurance limit.1.4) Ultimate stress.1.5) Ultimate Tensile strength.1.6) Mean Stress.1.7) Air Craft worthiness.1.8) Recorded Data and Graph for 6000 series.1.9) Recorded Data and Graph for 2000 series.

2) Non Destructive Testing

2.1) Introduction.2.2) Magnetic particle Testing.2.3) MPI Utilizing a portable Magnetic York.2.4) Introduction of MPI2.5) Equipment Requirements2.6) Procedure2.7) Advantages of Magnetic particle Testing.2.8) Disadvantages of Magnetic particle Testing.

3) Ultrasonic Testing3.1)Curlin airborne ultrasonic flaw detector.3.2) Features.3.3) Advantages of Ultrasonic flaw detector.3.4) Disadvantages of Ultrasonic flaw detector.

4) Feed Back And Evaluation.

5) Conclusion.

6) REFERENCING

1) S N CURVE:-

1.1)INTRODUCTION:

During the fracture of the materials and in the grown of cracks the concept of fatigue arises. Fatigue is the process in which structural damage accumulates when a material is subjected to repetitive application of loads that may be below the yield point. When a metal sample is subjected for testing of fatigue characteristics, it involves an alternating stress cycle with a mean stress of zero. This results are plotted on a graph i.e. maximum stress(S) against the number of cycles of failure (N) which is known as S-logN curve. Fatigue limit of the material can be determined using the S N curve. These results are obtained until the material is subjected to the failure. The stress at which the failure occurs for a given number of cycles is the fatigue strength and the number of cycles required for a material to fail at a certain stress is fatigue life.

The procedure is to test a first specimen at high peak stress where failure is expected in a short number of cycles. The stress is decreased for each succeeding specimen until one or two specimen does not fail in the specified number of cycles, which is usually 10^7 cycles. The highest stress at which a non failure occurs is taken as a fatigue threshold. Not all materials have a fatigue threshold (most non ferrous materials) for all these materials the test is usually determined after about 10^8 cycles or 5 *10^8 cycles. The s-n relationship is determined for one specific Loading amplitude i.e. amplitude is the express as R ratio value which is minimum peak stress divided by the maxmimum peak stress. R=σmin /σmax. . The following fatigue tests for various amplitude stress are performed by using the specimen aluminium 6000 and 2000 series alloys.

(Link:-

http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/Mechanical/S-NFatigue.htm

1.2) S-N CURVE EXPERIMENT OF ALUMINUM 6000 and 2000 series:

Procedure: A fatigue fracture experiments may run on many hours so each group in a class should do on one or two specimens.

First the test specimens must be prepared in order to experiment it. A minimum of 10 specimens for each part is recommended. They must all be cut from one length of a material. In addition to that one tensile test specimen should be taken in order to obtain the lower yield or 0.2% proof stress, the ultimate strength , the elongation on five diameters across the fracture, and if possible the uniform elongation of the material being investigated. From the tensile test results the maximum bending stress that can be applied must not be greater than the yield or proof stress, and could perhaps be taken as 0.9 of the test value. A set of bending stress from say 0.9 of the yield or proof stress to 0.4 of the ultimate strength be selected to match the number of test specimens for the complete experiment. The surface condition of the standard experiments should be noted. If the equipment is available measure and record the surface roughness in the direction of the stress.

First tighten the drive shaft chuck so that a 1mm shoulder shows between the face of the collect and the start of the specimen.

Push the loading arm to the end of the specimen and adjust the collet to give a sliding fit. Now position the loading 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. Tighten the collet with a spanner .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. Ensure the counter balance and load hangers are in place and switch the electric motor ON and OFF to verify smooth running. Select the bending stress for the test and apply the required weight on the hanger. Set the revolution counter to zero, and fit the safety guard over the apparatus. If the motor starts and note the time and make an estimate of when the fracture might occur.

1.3) ENDURANCE LIMIT: It is also called as fatigue limit. The specimen will with stand cyclic stress below the stress level without exhibiting a fatigue failure. Rigid, elastic and , low damming materials such as crystalline thermo plastics do not exibit endurance limit. It is also called has fatigue strength or allowed stress. It is very important to the designer to design the part for inspecting the material.

1.4) Ultimate stress: It is defines as the maximum load which can be placed prior to the breaking of the specimen. Stress corresponding to the ultimate load is called ultimate stress.

1.5) Ultimate tensile strength: It is calculated by the formulae σ=20p

Where p=maximum load applied to the material.

1.6) MEAN STRESS:- It is the sum of maximum stress and minimum stress

divided by 2 . i.e. σm=σmax+σmin2

1.7) Air Craft Airworthiness : The airworthiness is used in civil aircraft industries and aviation industry to get a certification. The approach to the civil certification of manned aircraft is to apply defined codes of airworthiness requirements to the design of any aircraft. It is a term used to dictate whether an aircraft is worthy of safe flight. It is maintained by a program of instructions by an authorized aircraft maintenance technician, typically performed annually or after a fixed flight time, such as every 100 hours. The application of airworthiness defines the condition of the aircraft.

Airworthiness is used to determine the deviations caused by the magnetic field components of an aircraft, for this swinging procedure for direct reading and remote reading compasses are used. So this procedure is to be taken where the aircraft field components and the earth’s magnetic field can affect the readings of compasses. The location must be carefully chosen and surveyed to prove it is free from interfering local magnetic fields. The effects of the interfering local magnetic fields are to cause the distortion of the direction and intensity of earth magnetic field.

1.8)RECORDED DATA AND GRAPH FOR 6000 SERIES:An s-n curve recorded during the testing of aluminium 6000 series material.

The recorded values during the testing of the material as follows:

By using these values s-n curve graph is plotted as follows:

STRESS OR LOAD(S)

NUMBER OF CYCLES(N)/1000

15 10.212 30.39 290.68 500.27 990.85 3000

0 500 1000 1500 2000 2500 3000 35000

2

4

6

8

10

12

14

1615

12

98

7

5

Series2

S N CURVE

NO of cycles per 1000

Load( N/M^2)

1.9) RECORDED DATA AND GRAPH FOR 2000 SERIES An another s-n curve recorded during the testing of aluminium 2000 series material.

The recorded values are shown below:

STRESS OR LOAD(S)

NUMBER OF CYCLES(N)/1000

15 12.1

14 12.4

12 13.5

9 299.5

8 1150

By using these values s-n curve graph is plotted as follows:

0 200 400 600 800 1000 1200 14000

2

4

6

8

10

12

14

1615

14

12

9

8

Series2

Load(N/M^2)

S N CURVE

2) NON DESTRUCTIVE TESTING METHOD

2.1) INTRODUCTION:

The Non Destructive Testing method is used to find the damage and irregularities of the structural materials in a product. By conducting the NDT on structural materials we can find the cracks and defects in a product without any damage to the product .NDT is used to look for signs of wear or internal changes on airplanes in aircraft industry. This method is also a function part of quality control which is based on sampling analysis, this method is not just for rejecting the substandard material but gives assurance that the supposedly is good is good.NDT methods are of different types. They are...

1) Radiography-x and Gamma.

2) Magnetic particle Inspection.

3) Dye penetrant Testing.

4) Ultrasonic Flaw Detection.

5) Eddy current and Electro Magnetic Testing.

2.2)MAGNETIC PARTICLE TESTING:

Magnetic particle inspection method has been in existence for over 50 years in the industry. It is one of the Non Destructive Testing method used in aircraft industry. This method is a detection of surface flaws and sub surface defects in ferromagnetic materials such as iron and steel. It is based on a principle that the magnetic flux in a magnetized object is distorted by the presence of discontinuity. At the discontinuity the distortion causes some magnetic field to exit and re-enter the test object. This is called magnetic flux leakage. Fluorescent or black oxide particles in aerosol cans are used in aircraft components or structures inspection while using permanent or electromagnets. Fluorescent particle inspection is evaluated by black light (black light consists of 100 watt mercury vapour projection spot light equipped with a filter which transmits a wave length of 3200 to 3800 angstrom unit). This method is commonly used in inspecting landing gears, gear boxes, pumps, and short struts etc.

One of the Magnetic Particle Inspection methods that are used in aircraft industry is

2.3) MPI utilizing a portable magnetic yoke

2.4) Introduction: ASTM E-1444 establishes a requirement to use a dedicated procedure for the inspection of parts. In the absence of an approved procedure, this procedure has CAR 2A (4) approval and is an acceptable means of compliance for the completion of magnetic particle inspections utilizing a portable magnetic yoke as detailed in CAAP 42 v-3

2.5) EQUIMENT REQUIREMENTS:1) Portable magnetic yoke.2) Light exclusion hood/sheet.

Warning: Black lights should not be used with cracked or missing filters .Harmful ultraviolet ration emitted can damage eyes

3) Black light with a min intensity of 10004) Fluorescent MPI fluid in a spray.5) Castrol fluid indicator strips.6) Permanent marking pen and field indicator.7) Lint free cloth and approved cleaning solvent.

2.6) PROCEDURE: Before inspecting the parts should be clean and free from loose or flaking paint. After a minute carry out the inspection. First yoke legs should be placed on the inspection area, the yoke legs should be spaced approximately 100mm apart.

Inspection area is to be tested for adequate flux density utilizing a type II Castrol strip in accordance with the manufacture’s instructions. The magnetizing current is applied whilst simultaneously spraying the MPI fluid on to the flux indicator strip. A minimum of three second magnetizing is recommended. Three distinct lines should be evident of the flux indicator strip.

Note: If we experience a difficulty in gaining adequate flux density reduce the yoke leg spacing. Maximize the yoke contact area.

Once we obtained an adequate flux density carry out the wet continuous method utilizing the yoke with either AC or DC current. We have to inspect the part for defect inspections. Defect indications will appear as sharp , well defined lines. Conversely non relevant indications will generally appear broad and fuzzy and generally follow part geometry.

We should mark any suspect defect indications for further optical evaluations

If the defect orientation is unknown rotate the yoke through 90 degrees and repeat above 2 paragraphs.

NOTE: In bolts and shear pins only magnetizing through the longitudinal axis of the bolt .If u repeatedly magnetize a bolt in rapid succession the part may become excessively heated.

When the inspection is completed ensure the residual magnetism in the part does not exceed three divisions either side of zero on a field indicator.

Portable yoke with battery pack Portable magnetic particle kit

2.7) ADVANTAGES OF MAGNETIC PARTICLE TESTING:1) It can detect surface and subsurface flaws.2) Equipment cost is lower than the other NDT techniques.3) Surface preparation is less critical than it is in penetrant inspection.

4) Magnetic particle indications are produced directly on to the surface of the part and form an image of the discontinuity.

5) Rapid inspection can be done on large surface areas.

2.8) DISADVANTAGES OF MAGNETIC PARTICLE INSPECTION:

1) It inspects only ferromagnetic materials.2) Large currents are needed for very large parts.3) Proper alignment of magnetic field and defects is critical.4) Post cleaning and demagnetizing is usually necessary.5) Smooth surface is required for application of this method.6) Non-magnetic materials like paints, coatings etc.affect the sensitivity of this

technique.

3) ULTRASONIC TESTING: Ultrasonic denotes high frequency of sound waves beyond the audible range of above 20,000 cycles per second. Generally ultrasonic testing is done by magnetostriction, or piezoelectric Effect. Waves are passed through the material under checking through the coupling media. The waves propagate in to the material in the form of a bean resembling a solid cone diverging steadily. If the material is homogenous, energy travels up back to the surface of the specimen and it is reflected and returns to the transducer. This transducer changes mechanical energy to electrical energy which after amplification is routed through different electronic circuits. Then it reaches the vertical plate of cathode ray tube in the form of unidirectional voltage. This is indirected by a pipe on the time base which is incorporated in between the horizontal plates of CPT to reckon the time of travel of the ultrasonic energy in to the material. Electrical pulse is fed in to

the CRT simultaneously with the same being added to the transducer. This gives the transmission echo on the time base which is the starting point for measuring time of interval on the calibrated scale. If a discontinuity exits now on the path of ultrasonic energy part of it will be reflected and part of it will be transmitted depending upon the acoustic impendence’s of the material and the flaw. The energy reflected from the back surface and that from the flaw, having travelled different path lengths shall be indicated on the CRT screen by the two different echoes on the time base, the space between the echoes giving the difference of the path transverse. The graduations on the time base scale when calibrated with reference to the material under checking will therefore give us the depth of the flaw as well as the thickness of the material.

One of the ultrasonic testing used in aircraft industry is

3.1) CURLIN AIRBORNE ULTRASONIC FLAW DETECTOR:

It weighs 6.3lbs (2.9 kg) including batteries. It is easy to read ultra-fast LCD display A trace. User friendly menu structure with context sensitive helps screens for every new item. Direct access to delay, range and gain controls, audio visual flaw alarms, as well as various menus through a new direct access keypad. It features 115db gain. It uses 5 ‘D’- size alkaline or rechargeable NiCad batteries for about 24 to 8 hours, respectively, of typical use (with LCD backlight off). It is shipped completely with curlin Air gage (p/n 150-00000), AC charger or eliminator, and rugged carrying pouch with shoulder strap; hard shelled pelican travel case and operating Manual.

-

Unique, Portable Airborne Ultrasonic Flaw Detector

This curlin air, Airborne Ultrasonic Flaw Detector was initially developed to inspect an ever growing class of materials/products that are too attenuative to inspect with conventional ultrasonic flaw detectors. Because of its non contact airborne feature, the curlin Air, Air borne Ultrasonic Flaw detector offers applications advantages for certain materials/products that are routinely inspected with conventional equipment. The performance of curlin air , Air borne Ultrasonic Flaw detector may seem amazing , especially to those who have experienced with conventional flaw detectors, as well as to those who could not find practical means non destructively inspect their particular product

3.2) Features:NO liquid couplant needed.NO surface contact.Portable.Analog output for use with Data acquisition systems.

In order to work curlin air, Air borne Ultrasonic flaw detector the following major technical issues needed to be addressed.

A frequency of 50KHZ was chosen because it was:

Low enough so ultrasonic attenuation is greatly reduced to levels which permit ultrasound to propagate both through air and the categories of materials targeted for inspection. Yet

High enough so satisfactorily has small diameter, ultrasonic beams can be generated by acceptably small sized transducers.

Tone Bursts: Generate pulsed ultrasonic energy in the form of rapidly reoccurring tone bursts this posses the necessary duration and amplitude to deliver the desired “penetration power”, yet it eliminates standing wave interference.

Sensitivity: To compensate for the large amounts of ultrasonic energy lost by reflection at both material surfaces high levels of low –noise amplification is needed.

An easy way to initially visualize what is happening in ultrasonically and why flaws are detectable is to take a “TREK” along with the ultrasonic tone burst as its travels from the transmitter probe through air to the material being inspected, through the material and eventually through air and to the receiver probe.

The Ultrasonic Trek:

Transmission in to air: Initially a portion of ultrasonic energy is lost as the tone burst is launched in to the air.

Airpath to Material: Once launched the tone bursts travels through the air and loses it further energy due attenuation and beam spread.

Entry in to the Material: Due to reflection at the material surface large amount of incident tone burst energy is lost, only a small amount of ultrasound entering in to the material. This reflection loss is caused by large acoustic impedance mismatch at the air-material interface. The acoustic impedance mismatch can be thought of “valve or shutters” which determine how much ultrasound is permitted to cross the interface.

Travel through Material: As this weekened tone burst travels through the flawless solid material there is again energy loss attenuation and beamspreading.

Exit from the Material: The remaining burst now experiences another huge energy reflection loss due to the excessive material – air acoustic impedance mismatch as was experienced at the above entry surface. At this point ,tone burst has lost more than 99.9% of its energy due to the only two surface reflections.

Airpath to Receiver probe: After exiting the material , the extremely low energy tone burst experiences further attenuation and beamspread loss as it travels along the airpath to the receiver.

Reception From Air: Finally this low-level tone burst impinges on the receiver probe and an additional energy loss is experienced during its ultrasonic transfer to the probe.

Impact of the material Flaw: Ironically, while impedance mismatches at the two material surfaces considered energy stealing materials, the large air material

mismatch caused by a flaw becomes a great ally. Basically the tone burst experiences another 99% energy loss when it impinges on a flaw. Even “pressed together" delaminations at this test frequency will still reflect 99% plus of the signal energy. Thus the flaw “blocks” huge percentage of the normal tone burst energy-making the flaw readily detectable.

3.3) ADVANTAGES OF ULTRASONIC DETECTOR:1) Minimum part preparation is required.2) Only single side access is required.3) Method can be used for much more than just flaw detection.4) Depth of penetration of flaw detection is superior to other methods.5) It is sensitive to surface and sub surface discontinuities.6) Less preparation time is required.7) Thickness and lengths up to 30ft can be tested.

3.4) DISADVANTAGES OF ULTRASONIC DETECTOR:

1) Surface must be accessible to probe and couplant.2) Skill and training required is more extensive than other technique.3) Surface finish and roughness can interfere with inspection.4) Thin parts may be difficult to inspect. 5) Linear defects oriented parallel to the sound beam can go undetected.6) Reference standards are often needed7) Cannot detect linear defects parallel to the sound beam

4) FEEDBACK AND EVALUATION: In the experiment weight added is taken in newtons and the no of revolutions can be seen on the display. Corresponding to the each weight one value is obtained for the number of revolutions. In S N graphs the values are plotted. Joining all these values gives the SN curve. When weight

is 15N for 6000 series the number of revolutions are 102 and when the weight is 12 N the number of revolutions are 303, when the weight is 5n the number of revolutions are 30000. From this we can say that as the weight goes on decreasing the number of revolutions are increasing. But only at very low weights the properties of the fatigue failure can be clearly analysed.

From this we can evaluate that as the weight goes on decreasing the number of revolutions goes on increasing. This means that as we apply less weight more time is required for the fatigue failure.

5) CONCLUSION:-

As we can conclude that SN curve is the best and convenient method to find the failure analysis and Non destructive testing is a convienent method to find the flaws and defects in the materials. The magnetic particle testing and ultrasonic testing is used to find the defects and flaws in the aircraft materials.

6) REFERENCING 1)http://www.sv.vt.edu/classes/MSE2094_NoteBook/97ClassProj/anal/kelly/fatigue.html

2)http://www.ndted.org/EducationResources/CommunityCollege/Materials/Mechanical/S-NFatigue.htm

3) http://images.google.co.uk/imgres?imgurl=http://www.maintenanceworld.com/Articles/material-engineering/Fatigue-Failures/mean20stress.jpg&imgrefurl=http://www.maintenanceworld.com/Articles/material-engineering/Fatigue-Failures.html&usg=__ku3YR10GAOxLXHuoWzourKYZl5M=&h=324&w=415&sz=10&hl=en&start=1&um=1&tbnid=XlXtnoDqV4xlrM:&tbnh=98&tbnw=125&prev=/images%3Fq%3Dmean%2Bstress%26hl%3Den%26sa%3DN%26um%3D1

4) http://en.wikipedia.org/wiki/Airworthiness

5) http://www.insight-ndt.com/papers/technical/t001.pdf

6)http://www.asnt.org/publications/Materialseval/basics/jan97basics/jan97basics.htm

7) http://www.ndt.net/article/ecndt98/aero/031/031.htm#2

8)http://209.85.229.132/search?q=cache%3AjqgSPcLwtwsJ%3Awww.casa.gov.au%2Fnewrules%2Fairworthiness%2Fdownload%2Fcaap042v-03.pdf+MPI+utilizing+a+portable+magnetic+yoke&hl=en&gl=uk

9http://www.ndted.org/EducationResources/CommunityCollege/MagParticle/Equipment/EquipmentPortable.htm

10) http://www.kqsndt.com/pages1/ndrmain.htm

11) http://www.ndt-ed.org/AboutNDT/aboutndt.htm

12)http://www.advancedndt.co.uk/Curlin_Air_Non_Contact_Ultrason.html ttp://www.advanced-ndt.co.uk/ Curlin_Air_Non_Contact_Ultrason.html

13) http://www.advanced-ndt.co.uk/Curlin_Air_Non_Contact_Ultrason.html.