COMPOSITES
(in aircrafts)
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CUSTOMERS PROFILE :
DOMESTIC CUSTOMERS..
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Indian Air Force
Indian Navy
Indian Coast Guard
Border Security Force
Oil and Natural Gas
Commission
Indian Air Lines
Air Port Authority of India
Private Air Lines
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CONT….
INTERNATIONAL
CUSTOMERS...
Government of Mauritius
British aerospace U.K.
Dornier Germany
Dnuk airways Bhutan
Necon air-Nepal
Everest air Nepal
Sita Air Nepal
South Korea
Namco Greece
Holiday Air Srilanka
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DEFINITION:
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The use of two or more
than two materials are
called composites.
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It is an advanced and
latest technique.
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In aircraft , it is used in
only DORNIER-228.
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It is a non metal alloy.
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REASON BEHIND THE NEED:
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Around 20-30 years ago, a survey was performed for the
quality and cost of the aircraft in all over the world.
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In that survey it was found that Indian aircrafts were
poor in strength and cost were very high.
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The reason behind this was, the Indians were very poor
in man-hour rate and salary paid by company for their
job were more.
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CONT….
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The solution of this problem was that the mentality of
Indians can never be changed, i.e. we can not
compromise with Indians man-hour rate.
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So a material was found which was more in strength and
less in weight.
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Its strength is more than metals.
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ADVANTAGE:
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High tensile and shear
strength,
High impact strength,
High modulus of elasticity,
Less weight,
Strength is around 3 times
than metals,
Low moisture absorption,
Easy repair,
No corrosion (very
important property).
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HOW IT IS MADE?
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A sheet of fiber is moved from one place to another
place.
In that way a series of jet machine are fixed.
This jet machine spray the resin (epoxy) over fiber.
So the resin is impregnated in the shells of fiber.
To avoid dust and moisture, a protective film is rolled
over it at both side.
Then this is stored in cold storage having temperature
-18˚C.
At this temperature the storage life of Prepreg is one
year.
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WHAT IS PREPREG ?
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It is a ready-made material to use on the moulding
tool, supplied in sheet forms, impregnated with the
epoxy resin in partial cured condition.
It is a composite material which is used in aircraft.
It is a very important material.
In all over world only “HEXCEL” composite
company manufacture this Prepreg.
This company belongs to FRANCE.
In Dornier we use four type of Prepreg.
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CONT….
A.
B.
C.
D.
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Carbon
V/913/46/G-814
Kevlar
V/913/50/K-285
Glass
V/913/37/7781
Glass
V/913/37/120
The composite parts is fabricated by only Prepreg
material, called MONOLYTHIC parts.
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But if prepreg is mixed with HONEY COMB, called
SANDWICH parts.
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During riveting and drilling, to avoid fabric expose, we
use Glass V/913/37/120 (.09 mm thick) at the outer
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edges of aircraft components.
WHAT IS HONEY COMB CORE?
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Nomex honey comb core is a polyamide paper dipped in
phenol resin.
It is used with Prepreg material to achieve excess thickness.
This is a very costly material.
These are available in 5mm to 25 mm thickness range.
There are two types of honey comb corea. Hexagon core
b. Ox core
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(where flat surface is required)
(where curve surface is required)
After using of it, we take a x-ray of component to check
the alignment of honey comb with Prepreg.
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WHY IT HAS MORE STRENGTH?
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This is due to 3 factors:
A. Temperature
B. Pressure
C. Vacuum
This Prepreg is only one material which has two livesA. Storage life or self life (SEL T)
B. Room temperature life (RT)
At storage temperature (-18˚C), its life is one year.
At room temperature of working area or layout area
(22˚C), its life is 30 days.
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TRANSPORTATION:
During
transportation, it is
totally packed in a
box.
To achieve -18˚C,
dry ice are used and
a thermometer is
used to measure
temp. in definite
intervals.
FRANCE
DELHI
KANPUR
LUCKNOW
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CONT….
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We avoid the flight in
sunlight but anyhow it
doesn’t possible to
carry in night, at Delhi
airport there is an
arrangement of cold
storage in which those
boxes of Prepreg are
put.
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This procedure are
used due to AVOID
LOSS OF RT.
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IMPORTANCE OF RT:
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There are two stages in which we can't compromise with
procedure.
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RT is one of those stages.
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We can’t carry Prepreg from cold storage (-18˚C) to room
temperature (22˚C) because of defrosting.
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So we first carry the Prepreg from cold storage to cool
storage (0-5˚C) and put it there for 12 hours.
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And then we carry from cool storage to working area or
layup area and put there for another 12 hours.
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CONT….
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Then it is further moved in cool storage for another 12
hours.
This is called one delivery.
In one delivery we loss 36 hours or one & half day.
we have to avoid this RT loss because at room temp. RT
of Prepreg is 30 days and now I have only 28 & half day
left in which we have to cured all the Prepreg.
Hence if there will be more than one delivery, RT will be
loss according to that i.e. working days will be reduced
proportionally.
So we avoid the more delivery.
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ONE DELIVERY
Cold storage
(-18˚C)
Layup area
(22˚C)
12
hours
Cool storage
(0-5˚C)
Loss of RT = 12+12+12=36 hours
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EXAMPLE 1:
Total available Prepreg = 50m
2m
Used Prepreg = 2×20 = 40m
In 20 delivery loss of RT =
20×1.5 day = 30 days
Rest of the material in the cold
storage = 10m
2m
50 m
• Total 20
delivery
2m
2m
Hence 10 m Prepreg which is in the cold storage has no value
because its RT is over.
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EXAMPLE 2:
Total Prepreg = 6m
Used Prepreg = 6m
Total delivery = 3
Loss of RT = 3×1.5 day =
4.5 day
6m
Available day for curing =
25.5 day
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DATA PROFILE:
Material Type of
Qty per
component aircraft
Kevlar
64
Total
type
qty per
aircraft
92
Glass
32
39
Carbon
49
54
total
145
185
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IMPORTANCE OF VACUUM:
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This is another stage in which we can't compromise
with procedure.
After the bagging procedure, we have to vacuum of all
component.
For this purpose we attach a suction pump and a
vacuum pump.
If there will be a pin point puncher in our bagging
system, suction gauge will not be deflected.
Vacuum is used due to removal of air between layers of
Prepreg.
After the vacuum procedure we carry the case in to
Autoclave (electric furnace).
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CONT….
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In Autoclave furnace we apply the pressure from above
and vacuum from bottom at a definite temperature so
that at that temp. ,resin converts in to liquid form and
take the shape of tool.
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But during this procedure, resin does not move uniform
so we use a breather and release film.
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For easy releasing the cured component from the
moulding tool, we use a releasing oil (# 20).
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We use the VEXPOL as a releasing agent.
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THE FOLLOWING POINTS ARE VERY IMP.
DURING PREPREG LAYUP:
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Layer material
Layer specification
Layer size
Layer sequence
Layer orientation
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THE FOLLOWING MATERIALS ARE USED
FOR THE VACUUM BAGGING:
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Release film
Breather
Bagging film
Vacuum valve
Sealant tape
thermocouple
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FURNACE SPECIFICATION:
MONOLITHIC:
Temperature cycle
Heating rate
1˚C-2˚C per min
Dwell
75˚C- 40 min
Heating rate
1˚C-2˚C per min
Curing
135˚C – 60 min
Cooling rate
1˚C-2˚C per min
135 ˚C
polymerization
Temp. cycle
75˚C
Pressure cycle
a)
2.5 bar
b)
5.0 bar
Vacuum cycle
c)
-0.8 bar
d)
-0.2 bar (till
curing)
temp. in ˚c
22˚C
Pressure cycle
Vacuum cycle
Time in min.
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FURNACE SPECIFICATION:
SANDWICH:
polymerization
Temperature cycle
1˚C-2˚C per min
Dwell
75˚C- 40 min
Heating rate
1˚C-2˚C per min
Curing
135˚C – 60 min
Cooling rate
1˚C-2˚C per min
Pressure cycle
a)
1 bar gauge
b)
2 bar gauge
Vacuum cycle
c)
- 0.8 bar
d)
- 0.2 bar (till
curing)
135 ˚C
Temp. cycle
75˚C
Pressure cycle
22˚C
temp. in ˚c
Heating rate
Vacuum cycle
Time in min.
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TESTING:
DT
(destructive test)
SHEAR
( ILSS )
NDT
(non destructive test)
TENSILE
( FTT )
ILSS – inter laminar shear stress
(monolithic, sandwich)
FTT – flat wise tensile stress (sandwich)
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ILSS
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For ILSS, we use the criteria which is given by Germany.
This criteria is called DON – 128.
For this we take a piece of component having following
specification:
1.
Same material,
2.
Same batch,
3.
Same box,
4.
Same RT life,
5.
Same SELF life.
Now we take 8 layers of Prepreg and stick together.
The thickness of complete part will be 8 × 0.25 = 2 mm.
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CONT….
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Now we take 6 pieces of this material having dimensions
(20×10×2).
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Now we find out the shear stress by formula:
0.25 × LOAD
 Shear stress
AREA
We check the load at that point when our component
breaks.
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Now we find the avg. of these 6 values of shear stress.
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CONT….
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Now we match the values given in DON – 128 criteria
which are given below:
A.
B.
C.
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Kevlar Glass Carbon -
39.25 ± 3.12 N/mm²
56.40 ± 4.16 N/mm²
61 – 76 N/mm²
If our value does not match, component will be reject.
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FTT
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This is done for sandwich component.
For this we take a piece of component having following
specification:
1. Same material,
2. Same batch,
3. Same box,
4. Same RT life,
5. Same SELF life,
6. Same thickness.
Now we take 2 layers of Prepreg and stick together.
We take the two pieces of this.
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CONT….
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Now we fix component according to this shape:
Aluminium bar
Prepreg
A
Honey comb
Adhesive
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We put this block in cooling medium for 12 hours.
We apply adhesive in the ratio of 100:10.
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CONT….
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Now we apply the tensile load by UTM machine.
We never check the load at which component fail.
If during tensile test, Prepreg leave honeycomb, part will
be reject.
This can be happened because of following two reasons:
A.
B.
100:10 ratio b/w Prepreg and adhesive do not
achieve.
Cooling is not done for 12 hours.
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NDT
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This is also called tap test or coin test/
This is done at sound proof place.
This is done with the help of coin.
We perform hammering action manually with uniform
pressure and sense the sound.
If at any place, there will be a crack, sound will be
different.
So we will reject that part.
After that we perform following action:
A. X-ray – Kevlar, Glass
B. Ultra sonic – scan pulse echo - carbon
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THANK YOU FOR GIVING ME YOUR
VALUABLE TIME…..
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