1 Flashcards
Why would I add nickel to anything?
Limits grain growth ?
Resistance to heating and corrosion
What steel has 36% nickel in it?
Invar steel, used for measuring instruments
What does chromium do?
Chromium enlarges grain growth.
Nickel and chrome are used to control grain growth
What is chromium used to make?
Ball and roller bearings
Low levels of nickel chrome would be used to make? (3% nickel / 1% chromium)
Piston engine components
High level nickel chromium steels would be used to make? (18% chromium/ 8% nickel)
STAINLESS STEELS, AUSTENTIC AT ROOM TEMPRETURE AND NON FERROUS
What does 0.3% molybdenum do?
Largely eliminates TEMPER BRITTLENESS producing NICKEL CHROME MOLY STEEL
What is vanadium used for?
The tools and springs
Cobalts used for?
High speed cutting tools and permanent magnets
Molybdenum gives?
A fine grain structure, makes it stronger without affecting ductility.
CHROME MOLYBDENUM STEEL is very suitable for what?
For welding and is used principally for welded structural parts
How much carbon in Maraging steel
0.03%
Why do we produce maraging steel? And what’s its advantages?
Marraging steel contains little to no carbon.
Simpler to weld
Simpler heat treatments are possible
Better resistance to stress corrosion and hydrogen embrittlement
What is carburising?
Add carbon to the outer surface of low carbon steel or low alloy steel.
When carburised steel is heat treated what happens?
The case is hardened while the core remains tough
Carburising using the box process what is needed?
Charred leather or charcoal, sodium
Carbonate and heated to 900 degrees
Cyanide hardening what is needed?
Molten salts, sodium carbonate and sodium cyanide. Heated to 900 degrees
What is gas carburising?
900 degrees for 3 hrs using methane and propane gases
Flame hardening
Flamed with oxy-acetylene and cooled by a water jet. Only steels with 0.4% carbon can be flame hardened
Induction hardening?
Eddy currents in the surface of the component, cooled by jets of water
American identification of steel has how many numbers?
4
The first digit identifies?
The principal alloying element
The second digit?
The percentage of this alloying element
The last 2 digits?
The percentage in hundredths of a percentage of the carbon in the steel
(Amount of carbon)
How is bauxite used to make aluminium?
Mixed with caustic soda to make an oxide. It’s an electrolytic process
Main advantage of pure aluminium?
Key disadvantage?
High corrosion resistance
Low strength
How can I protect aluminium alloys from corrosion?
Alclad or electrolytic process known as anodising
Soloution heat treatment is also known as?
Age hardening
If I solution heat treat something? How long have I got to work it?
2 HOURS
AFTER 2 HOURS DO IT AGAIN
How many times can a material be soloution heat treated?
3 time
After finishing working it, how long do I have to wait before riveting it?
24 hours
How long after that till aircraft can go flying
5 days
Pure aluminium is annealed by heating to a temperature of?
360 degrees followed by cooling in air
How can I delay the period of time for soloution heat treatment?
Refrigeration @ -20 degrees, soloution treated rivets may also be stored this way
Precipitation heat treatment is known as?
ARTIFICAL AGE HARDENING
How many times can ALCLAD be heat treated?
3 times as it decreases corrosion resistance
Age hardening of rivets can be delayed by?
Storing the rivets at a low temp immediately after quenching
If the rivets have not been used within 2 hours?
They may have to be heat treated again up
To a maximum of 3 times, further heat treatments would increase the grain size and result in low strength
Maximum time for quenching from furnace to quenching?
20 seconds, if not the grains grow to big causing hydrogen embrittlement
Salt bath fire extinguisher?
Dry sand
When should our identification of heat treatments be made?
Immediately after the heat treatment
ALUMINIUM ALLLOY IDENTIFICATION!
COPPER
MAGNESIUM
ZINC
COPPER 2000
MAGNESIUM 5000
ZINC 7000
ALUMINUM AND ITS ALLOYS ARE INTERNATIONALLY CLASSIFIED INTO ….. GROUPS, identified by a ……. Figure series number
8
4
In aluminium alloy identification such as 7075. The first digit indicates what?
The principal alloying element. So in this case ZINC
The second digit identifies?
THE ALLOY MODIFICATION STATE. 0 indicates that the alloy is original. 1 indicates that the alloy has been modified once.
THE THIRD AND FOURTH DIGITS IDENTIFY?
The specific aluminum alloy
What are the 2 divisions of aluminum alloys?
NON HEAT TREATABLE
AND HEAT TREATABLE
How are non heat treatable alloys strengthened
BY CONTROLLED WORKING OR COLD ROLLING
The 2000, 4000, 6000, 7000 and 8000 series alloys are strengthened by?
Soloution heat treatment followed by age hardening
The 1000, 3000, 5000 series alloys are what to increase there strength?
COLD WORKED
Non heat treatable aluminum alloys can be hardened by?
STRAIN HARDENING ALSO KNOWN AS COLD ROLLING
The cold worked temper of wrought alloys is indicated by the letter …….. followed by a number.
H
A second digit, 2,4,6 or 8 indicates what?
The final degree of hardness
The heat treated temper of aluminum alloys is indicated by the letter?
T. T showed the type of heat treatment
T3 means?
SOLUTION HEAT TREATED AND STRAIN HARDENED (COLD ROLLED)
T4 means?
SOLUTION HEAT TREATED THEN NATURALLY AGED
T42?
SOLUTION HEAT TREATED BY THE USER REGARDLESS OF THE PREVIOUS TEMPER
How to protect magnesium from corrosion?
CHROMATE IT
WHAT DOES TITANUIM LOOK LIKE AND WHATS IT GOT
GREYISH WHITE AND GOT A HIGH STRENGTH TO WEIGHT RATIO. HIGH RESISTENCE TO CREEP AND CORROSION
WHAT HAPPENS IF CADMIUM COMES INTO CONTACT WITH TITANIUM?
It will cause it to become embrittled
FINE TITANIUM SWARF OR POWDER IS FIRE RISK. IT SHOULD BE EXTINGUISHED USING?
DRY POWDER
What is inconel good for?
It’s quite tough at high temps and does not oxidise very much because of the protective film of chrome oxide which forms on the surface
A nimonic alloy?
High temps, gas turbine engines and resistance to creep
Monel metal is used for what?
Good resistance to corrosion and is used for rivets
What do we use copper for?
Electrical cables and equipment. Reddish brown in colour.
Brass is used for?
Pitot heads
Low tin bronzes are used for what?
Springs and instrument parts
High tin bronzes are used for what?
Bearings and bushes which are subjected to heavy loads
Tungum is good for what?
Good heat resistance and resistance to corrosion. Used to make hydraulic pipelines
Lead is used for what?
Lead is a major constituent of soft solder, mass balance weights and protection from x rays
CHAPTER 3:
What are the 2 forms of casting?
Sand casting
Die casting
What am I doing when casting?
pouring molten metals it into a mould.
What is sand casting?
Foundry sand is moulded around a suitable pattern in such a way that the pattern can be withdrawn to leave a cavity of the correct shape in the sand
What is DIE CASTING
In Die casting a permanent metal mould is used and the charge of the molten metal is usually forced in under pressure
What is forging?
The process of forming a product by hammering or pressing
What sort of process is drawing and What sort of components is made from drawing?
Drawing is exclusively a cold working process.
Rod wire and hollow tubes are produced by drawing them through a die
What is pressing?
A disc of metal is placed over a die then forced the metal disc through the die forming a cup shaped item.
Extrusion is the process of what?
The process of forcing metal in its plastic state through a die. This can produce complex cross sectional shapes required for aircraft construction
Aluminum alloy is heated between 350 degrees and 500 degrees
What is sintering?
Powder metallurgy where you have heat and pressure.
A pourus material made up by fusing powdered metal under heat and pressure.
What is spinning?
Flat disc in a lathe and bend it using shapes
CHAPTER 4 - what is a malleable metal?
One that can be deformed by a great deal of compression before it shows signs of cracking
What is a ductile metal?
A ductile metal is one that can be deformed by a great deal of tension before it fractures
What is a tough metal?
A tough metal can be bent many times before it breaks
What is a tensile test?
Stretching until it breaks
What is a compression test?
Measures the force required to compress or shorten a piece of metal until it breaks
What is a toughness test?
The ability to resist mechanical shock
How is the ductility of a material found?
A bend test
What do we find out from a tensile test?
THE YIELD POINT
If you go beyond the yield point what happens?
Permanent extension?
How do I calculate the tensile strength of the material
MAXIMUM FORCE USED
/
Original cross sectional area
What is proof stress?
Proof stress of an alloy is that stress which will produce a permanent extension off 0.1% in gauge length of the test piece
When a metal is subjected to both tensile stress and high temperature of a long period continuous and permanent elongation takes place, this is known as creep. What is the final fracture called?
RUPTURE
DEFINE HARDNESS?
RESISTANCE TO INDENTATION
How does a brinell hardness tester work?
A steel ball bearing is pressed for 15 seconds. Then the diameter of the dent is measured.
How does the vickers hardness tester work?
A diamond pressed for 15 seconds then the diameter is measured. Most accurate out of all.
How does the Rockwell hardness tester work?
Uses 2 types of indenter a steel ball for for use with unhardened steel and soft metals .
And A SPHERICAL TIPPER DIAMOND CONE KNOWN AS THE BRALE INDENTER FOR USE WITH HARDER MATERIALS.
LARGE SCALE POINTER INDICATES HARDNESS
What is the advantage of the shore scleroscope hardness test
ITS PORTABLE
Impact tests measure what?
Resistance to shock - TOUGHNESS
2 machines for measuring resistance to shock or toughness?
IZOD AND CHARPY TEST
Which one is preferred for the extremes of temperatures?
CHARPY
What is the striking energy of a izod test
160j through 60 degrees
What is the striking energy of a CHARPY test
300j thought 160 degrees
What is fatigue?
Fatigue is defined as the progressive deterioration of the strength of a material
What is cyclic fatigue?
Caused by repeated fluctuating loads
What is corrosion fatigue?
This is fatigue accelerated by surface corrosion.
What is fretting fatigue?
This is caused by small scale rubbing movements is heavily loaded joints
What is thermal fatigue?
Thermal cycles
What is sonic fatigue caused by?
RESULT OF HIGH FREQ STRESS FLUCTUATIONS DUE TO VIBRATIONS CAUSE BY JETS KF PROPELLER NOISES
What do I find out from a fatigue test?
FATIGUE OR ENDURANCE LIMIT /FINDING THE SAFE LIFE
Does a polished test piece have a better endurance or fatigue limit?
YES
What are the 2 groups of plastics?
THEROMOPLASTIC
AND
THERMOSETTING
Thermoplastic materials can be what?
Become soft when heated and can be moulded again and again
Thermosetting materials?
Become permanently hard during the moulding process and cannot be softened again
How can we bend or shape plastics?
120 degrees in either glycerin or water
Perspex or plexiglas should be stored how?
Vertically or 12 sheets can be stored flat with soft packing between each sheet
Polyvinyl chloride PVC is often used to make?
Protective gloves and aprons or seat covers in light aircraft
TUFNOL AND MICARTA ARE USED TO MAKE WHAT?
FAIRLEADS AND PULLEYS
Perspex should be stored where?
In a cool, well ventilated place where it can not be affected by sunlight, direct heat or vapours dopes paints and solvents.
If the aircraft is to be left out in strong sunlight it is advisable to?
Fit white cotton covers over the Perspex windscreens
When cleaning and polishing Perspex application cloths are used …….. but polishing cloths may be …….
Once
Re used as long as they stay clean and soft
what are the 2 components to a composite?
Matrix and the fibres or (reinforcing material)
Define strength?
The ability to support a load without breaking
Define stiffness?
Ability to support a load without bending
Define impact resistance
The ability to withstand impact without shattering
Freshly drawn fibres are very strong but not?
BRITTLE
The fibres are drawn into bundles called rovings which can be further processed into?
Woven fabrics or chopped strands
E GLASS?
An electrical grade with high resistivity
S GLASS
High tensile glass fibre
Glass fibre cloth is formed by?
Twisting together glass fibre strands or threads .
How can a fibreglass or a glass fibre be recognised?
As a white gleaming cloth
Kevlar is what? And has what properties
An aramid fibre. And has high strength and impact resistance
Kevlar 49 is the grade used in aircraft composites? How much lighter is it than glass fibres?
40%
What colour is Kevlar?
Yellow with black traces
Carbon fibres are made from what?
Pure carbon and black in colour
Kevlar threads are woven into cloth every 2 inches ……… and every 6 inches across ……
Along the weft
The warp
Why is boron not commonly used in aviation??
Hazardous and very expensive
What are the most used re-enforcing fibres?
Glass fibre, aramid and carbon/graphite
Warp direction is designated at?
0 degrees
The weft or fill is designated at
90 degrees
Why is the Selvage edge removed?
Because the weave is different from the body of the fabric and would not give the same strength
What is the bias?
The bias is when the weft threads are at 45degree angle to the warp threads
Chopped glass fibres that are compressed together are known as?
MATS
Plain weaves are the simplest form
Of weaves but?
It can be difficult to drape around complex shapes
Twill weaves provide?
A superior wet out and drape properties.
Satin weaves?
Are very flat and drape well, facilitate wetting out and have good mechanical properties.
A rove or roving is formed by what?
Combining strands of fibre without twisting them to form mats
What is the key to the strength of a composite?
It lies in the ability of the matrix to transfer stress to the re enforcing fibre
Polyester resins are cured by the addition of what?
A catalyst
What are catalysts known as?
Peroxides and are thin liquids
What is added to a polyester resin to speed up the cross linking process?
Accelerator
Epoxy resins are mixed with what to allow them to cure?
Hardner
Epoxies have a very good resistance to what?
Chemicals
Epoxy resins are more difficult to use than polyester resins and?
Are hazardous to health and expensive
Curing a polymer from a thick liquid to a strong solid is a chemical process that may be brought around by?
Cold or hot curing
Cold curing takes place at what temp?
Room temp (21) degrees
In the cold curing process how long does it take for the resin to harden?
30 mins
Hot curing cures at what temp?
200 degrees
If too much resin is used, the composite will be..?
Weak
If 3 layers of cloth are used, the fibre orientation should be?
0 45 and 90 degrees
A better hot cure system uses an autoclave. How does an autoclave work?
Uses a vacuum to suck out the air and controlled heaters to cure the resin
Pre pregs can only be used with what curing system?
Hot curing systems
Pre pregs are stored how?
Stored in a sealed bag at -18 degrees
What must be recorded when taking a pre preg out of the fridge?
Date and time and transfer of the material out of the fridge
Who gives a the maximum out of freezer life?
The manufacturer
2 main hazards when dealing with polyester and epoxies resins.
Skin contact and inhaling fumes
Polymer resins are sticky liquids which is difficult to remove from?
The skin
Dermatitis is an inflammation of the skin leading to
Sores, rashes and cracks in skin
Accelerators are very reactive substances and must always be added to the resin before the?
Catalyst
NEVER MIX A
CATALYST AND ACCELERATOR
When machining composites wear eye protection conforming to
BS166
In a sandwich construction the core is used to make a thick beam because?
The stiffness of the beam depends on its thickness
Balsa wood is often used on?
A/c floors
Three honeycomb materials most commonly used in aircraft is
Aluminium, glass fibre reinforced plastic and aramid fibre reinforced paper
2 methods of honeycomb manufacture
Corrugation
And expansion
The corrugation process is?
Sheets are cut to length and bonded together
The expansion process is?
Known as the HOBE, sheets of the core material are coated with adhesive and stacked to form a hobe
The three cell shapes are?
HEXAGONAL SHELL
OVER EXPANDED CELL - OXCORE
FLEXIBLE CORE OR FLEXI CORE
Hexagonal shells are good for?
Flat panels
OX CORE
Used for single curvature
Flexi core?
Double curves
If there is no lightning protection in the composite the lightning exits through it
Evaporating the resins leaving bare cloth
What may be laminated under the top layer of fabric?
A fine aluminium mesh
For lightining protection aluminium may also be?
Flame sprayed onto the component
When honeycomb sandwich structures are damaged what effect does this have?
Separation of the honeycomb from the FRP skins
Composites are more sensitive to compressive loading than
Tensile loading
WHAT DO YOU DO TO FIND BVD
TAP TEST, X-RAYS CAN ALSO BE USED
When drilling a composite what drill bit do we use?
Carbide drill bits with angles of 135 degrees
Aluminum fasteners must not be used with carbon or graphite, why?
Because of their tendency to corrode the aluminum
How can minor damage such as scratches pits and dents be normally repaired?
Mixing a small amount of resin and hardener and filling the area
Blisters of less than one inch diameter can be repaired by?
Injecting mixed resin using a hypodermic syringe
Small holes may be fixed by
Chopped glass fibres to fill the hole
Vaccum baggin
How is the fibre/resin ratio controlled?
By emoting access resin
What is the release film for?
The release film allows the vaccum bagging materials to be separated from the repair after curing
What does the bleeder fabric do?
The bleeder fabric absorbs the resin bleeding out of the repair
If the resin is heated to rapidly what happens?
It does not have time to flow before it gels
