manufacturing of polymer composites ooa prepreg technology · author: mario danzi laboratory of...
TRANSCRIPT
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Author: Mario Danzi
Laboratory of Composite Materials and Adaptive Structures
ETH Zürich
April 2017
12.04.2017 Mario Danzi 1
Manufacturing of Polymer Composites
OOA Prepreg Technology
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Autoclave Processing
Introduction
Boeing 787 Dream Liner fuselage section: autoclave processing
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Why we use the autoclave in composite
processing?
The high compaction pressure provided by the
autoclave permits to manufacture high quality
laminates:
High fiber volume content (55-65%)
Low void content (less than 2%)
Why do we need such a high compaction
pressure? How does the compaction pressure acts
on the laminate?
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Autoclave Processing
Introduction
4-8 bars
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Influence of voids on the apparent shear strength.
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Autoclave Processing
Introduction
Reference: Boyd, J. (2003).
Vacuum Bag only Composite Part
Manufacturing (Tutorial Handout)
(pp. 72). Dayton, OH: SAMPE 2003
Technical Conference/Dayton, OH.
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Compaction of a saturated porous media
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Theory on Laminate Consolidation
Spring / dashpot analogy
Fiber
Tows
Liquid
resin
Mechanical analogy proposed by Taylor.
[D.W. Taylor, Fundamental of Soil Mechanics”, John Wiley and Sons, New York, 1948]
Fiber Preform
Spring model
Force ∝ 𝑆𝑡𝑟𝑎𝑖𝑛
Liquid resin
Uncompressible fluid
Papplied = Pfluid
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Spring analogy
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Theory on Laminate Consolidation
Spring / dashpot analogy
Compaction Pressure
Fluid Pressure
(resin)
Spring Pressure
(fiber)
Mario Danzi
𝜎𝑡𝑜𝑡
𝑝𝑟𝑒𝑠𝑖𝑛 = 𝜎𝑡𝑜𝑡
0
0
𝜎𝑡𝑜𝑡 𝜎𝑡𝑜𝑡
𝜎𝑓𝑖𝑏𝑒𝑟 = 𝜎𝑡𝑜𝑡 𝜎𝑓𝑖𝑏𝑒𝑟
𝑝𝑟𝑒𝑠𝑖𝑛
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Terzaghi’s Law
𝜎𝑡𝑜𝑡 = 𝜎𝑓𝑖𝑏𝑒𝑟 + 𝑝𝑟𝑒𝑠𝑖𝑛
where 𝜎𝑡𝑜𝑡 is the total externally applied stress, 𝜎𝑓𝑖𝑏𝑒𝑟 is the stress carried by the fibers
and 𝑝𝑟𝑒𝑠𝑖𝑛 is the hydrostatic pressure of the resin.
The stress carried by the fiber is determined from the compaction
curve of the textile
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Theory on Laminate Consolidation
Terzaghi’s law
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Theory on Laminate Consolidation
Fiber bed compaction
0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.70
1
2
3
4
5
6x 10
5
Fibre Volume Content [-]
Com
pac
tion
Pre
ssur
e [
Pa
]
Compaction Curve of a Carbon Fibre Woven Fabric
The compaction curve describes the compaction pressure required to compact
a stack of fiber (fiber bed) to a certain fiber volume fraction
Mario Danzi
This curve is characteristic of the textile!!!
vf =N ∗ Aw
𝜌𝑓 ∗ ℎ
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Theory on Laminate Consolidation
Fiber bed compaction
Fiber bed compaction test: 20 layer of fabric are compacted between two plates, using a mechanical testing machine. Force and
displacement (distance between the plates) are measured. The compaction speed is held constant
and very low (0.1 mm/min) to ensure quasi-static conditions. The average FVF is calculated, knowing
the thickness of the sample (cavity height).
Cavity
Height
h
F
F
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Setup for
compaction
experiments at
CMASLab
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Resin pressure in processing conditions
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Theory on Laminate Consolidation
Laminate compaction
0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.70
1
2
3
4
5
6x 10
5
Fibre Volume Content [-]
Com
pact
ion
Pre
ssur
e [P
a]
Compaction Curve of a Carbon Fibre Woven Fabric
In prepreg processing
with no bleeding, the
nominal FVC is
defined by the
amount of resin.
𝑟𝑒𝑠𝑖𝑛 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 ≈ 3.5 𝑏𝑎𝑟
𝑟𝑒𝑠𝑖𝑛 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 ≈ 2.5 𝑏𝑎𝑟
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At a certain level of the hydrostatic pressure,
entrapped gases will collapse and dissolve into the
resin
This pressure level is approximately 3.5 bar (resin
pressure). However, it depends on temperature,
surface tension, moisture, resin composition and
other factors.
The high autoclave pressure help also to achieve a
better consolidation in corners.
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Autoclave Processing
Void mitigation
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Disadvantages of autoclave processing
High costs of autoclaves
Size constrains
Low availability
Long processing cycles
Operation danger (inert atmosphere - nitrogen)
Expensive tooling systems
High energy consumption
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OOA Prepreg Systems
Motivation
Mario Danzi
Autoclave used for production of the Boeing 787 at
Triumph Aerostructures – Vought Aircraft Industries.
North Charleston, South Carolina, USA.
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OOA Prepreg Systems
Introduction
Oven cured under vacuum bag conditions.
(1 bar compaction pressure)
Entrapped gas can’t be dissolved!!!
Requirements for aerospace primary structures
Less than 2 % void content
High fiber volume content (>50%)
How is it possible to achieve with OOA prepreg
laminates similar quality to autoclave processed
laminates?
Mario Danzi
1 bar
Gas extraction is the key for OOA processing
Porosity in a CF laminate observed at
the microscope (cross-section)
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OOA Prepreg Systems
Characteristics
OOA Prepreg systems are specifically designed for processing without the autoclave.
The major differences to autoclave systems are:
Air permeability of the prepreg
Resin rheology
Low void content is achieved by “breathing” out of entrapped gases and volatiles Air pathways are created by partially impregnated prepreg
Initial dry regions (prior to cure) are wetted out during resin cure cycle (consolidation)
Edges breathing system are used to improve the air extraction from the laminate.
Vacuum level is a key process parameters (reduce residual air)
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Before cure
Fiber Tow Resin
After cure and consolidation
Fiber Tow Resin
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OOA Prepreg Systems
Characteristics
During debulking the uncured prepreg laminate is maintained at room temperature under vacuum
condition.
In OOA processes, debulking steps are extended to enhance the extraction of air and volatilizes
from the laminate.
Optimal debulking time depends on the size of the part and on the air permeability of the prepreg
material.
OOA prepreg manufacturers recommend a minimum of 16 hours debulking at room temperature
under final vacuum bag arrangement (prior to cure). 15
Debulking Cure Lay-up
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OOA Prepreg Systems
Characteristics
Moisture can’t be extracted with room temperature debulking. Only when the
temperature is increased (curing process), the water become volatile (reach the
boiling point) and can be extracted.
The resin viscosity should be tuned in order to retain breathability for a sufficient
amount of time.
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Source:
SAMPE Seattle
tutorial. Chris
Ridgard, 2010
Mario Danzi 12.04.2017
Full vacuum
range
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OOA Prepreg Systems
Limitations
Due to the low compaction
pressure (1bar), the
maximal achievable FVC
is in the range of 50-55%,
depending on the textile
used.
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0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.70
1
2
3
4
5
6x 10
5
Fibre Volume Content [-]
Com
pac
tion
Pre
ssur
e [
Pa
]
Compaction Curve of a Carbon Fibre Woven Fabric
Mario Danzi 12.04.2017
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OOA Prepreg Systems
Limitations
Hand layup of OOA prepreg may not work in cases where:
The part is a full barrel construction cured in a female mold
The part has features with local tight female radii
Uncured ply thickness is greater than the cured ply
thickness. The thickness variation during cure can cause
bridging problems in female radii.
18 Mario Danzi 12.04.2017
before cure after cure and consolidation
𝐵𝑢𝑙𝑘 𝑓𝑎𝑐𝑡𝑜𝑟 =𝑢𝑛𝑐𝑢𝑟𝑒𝑑 𝑝𝑙𝑦 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 − 𝑐𝑢𝑟𝑒𝑑 𝑝𝑙𝑦 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠
𝑐𝑢𝑟𝑒𝑑 𝑝𝑙𝑦 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠≈ 0.2
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OOA Prepreg Systems
Process steps
OoA prepreg process:
1. Lamination (intermediate debulking)
2. Vacuum bag layup
3. Debulking
4. Heating to curing temperature (consolidation)
5. Curing process
6. Heating to post-cure temperature
7. Post-cure process
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OOA Prepreg Systems
Process steps – Step 1: Lamination
OoA prepreg process:
1. Lamination (intermediate debulking)
2. Vacuum bag layup
3. Debulking
4. Heating to curing temperature
5. Curing process
6. Heating to post-cure temperature
7. Post-cure process
-> Adaptation to mould shape and first ply consolidation
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OOA Prepreg Systems
Process steps – Step 1: Lamination
Most carbon fiber reinforced prepregs for hand layup have
some degree of dry fiber paths to permit air and volatile
extraction during an OOA cure.
Improved laminate surface quality is achieved when the
prepreg is laminated with the drier side towards the mould.
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OOA Prepreg Systems
Process steps – Step 1: Lamination
Intermediate debulking The laminate stack must be debulked at regular intervals during the lay-up process. This ensures that the
prepreg conforms to the tool shape and that an homogeneous consolidation is achieved. Particularly critical are
concave corners.
During debulking, the laminate is covered with a perforated release film, a suitable breather and a reusable
membrane. The prepreg laminate is kept under vacuum for approximately 5 to 10 minutes. It is recommended that
the lay-up is debulked every 3 or 4 plies.
Recommended bagging arrangement for
intermediate debulking.
Source: Cytec, Application guidance
notes for vacuum bag processing
MTM44-1 dual core epoxy prepreg.
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OOA Prepreg Systems
Process steps – Step 2: Vacuum bag layup
OoA prepreg process:
1. Lamination (intermediate debulking)
2. Vacuum bag layup
3. Debulking
4. Heating to curing temperature (consolidation)
5. Curing process
6. Heating to post-cure temperature
7. Post-cure process
-> Good vacuum bag integrity is essential!
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OOA Prepreg Systems
Process steps – Step 2: Vacuum bag layup
Layup, bagging techniques and ancillary
material are essentially the same as those
used for autoclave prepreg curing.
However:
Edges breathing system are used to
enhance the extraction of air and volatiles
from the laminate.
The quality of vacuum become a key
process parameters in oven/vacuum cured
parts.
A vacuum leak check should be performed
prior to cure and heat-up. The test should
not show more than 0.068 bar vacuum
loss in 10 minutes.
Full Vacuum
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OOA Prepreg Systems
Process steps – Step 2: Vacuum bag layup
1. Non perforated release film and edge breathing via glass
(most common)
Recommended bagging arrangement for
processing MTM®44-1. Source: ACG, Users’ manual for LTM prepregs.
Example of layup on a OoA prepreg plate.
Note: The glass fiber strings must extend beyond the
non-perforated release film and be in contact with the
breather.
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OOA Prepreg Systems
Process steps – Step 2: Vacuum bag layup
2. Sealant tape and fiberglass cloth to connect the edges of the laminate with the breather
Vacuum bag arrangement recommended from Cytec for oven cure.
Note: the edge dams need to be higher than the laminate thickness. Source: Cytec, Cycom 5320-1 epoxy resin system.
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OOA Prepreg Systems
Process steps – Step 2: Vacuum bag layup
Reference: Gas transport in out-of-autoclave prepreg laminates, B.Louis, 2007.
Relevance of edge breathing
Configuration 1
Configuration 2
Configuration 3
Configurations 1 & 2
Configurations 3
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Initial thickness: 2mm
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OOA Prepreg Systems
Process steps – Step 2: Vacuum bag layup
3. Z direction breathing using perforated release film (resin bleeding)
Recommended bagging arrangement for processing of
prepreg systems foreseeing bleeding of resin in excess.
Source: ACG, Users’ manual for LTM prepregs.
Example of bleeding of the prepreg resin in a
VB process. The air bobbles follow in
direction of the pressure gradient.
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OOA Prepreg Systems
Process steps – Step 3: Debulking
OoA prepreg process:
1. Lamination (intermediate debulking)
2. Vacuum bag layup
3. Debulking
4. Heating to curing temperature (consolidation)
5. Curing process
6. Heating to post-cure temperature
7. Post-cure process
-> Air extraction and ply consolidation. Extract as much air and volatiles as possible before starting the curing process.
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OOA Prepreg Systems
Process steps – Step 3: Debulking
Prepreg air permeability during debulking (@ 25°C)
The air permeability of the prepreg is
reduced during debulking.
Most change in permeability occurs
initially. A plateau around 60% of the
initial value.
12.04.2017 Mario Danzi 30 Reference: Gas transport in out-of-autoclave prepreg laminates, B.Louis, 2007.
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OOA Prepreg Systems
Process steps – Step 3: Debulking
Gas evacuation model developed by Arafath et al.* for MTM45-1 / 5HS for 1-D in-plane
gas evacuation
54.0
1
2
ln92.0
1
oo m
m
k
L
P
utime
% gas removed (m/mo) Time Required
10% 0.9 ~ 1.7 min
50% 0.5 ~ 55 min
80% 0.2 ~ 4.4 hours
90% 0.1 ~ 8.6 hours
Reference: Arafath, A. R. A., Fernlund, G., Poursartip, A.
(2009, July 27-31). Gas Transport in Prepregs: Model and
Permeability Experiments. Paper presented at the ICCM-17,
Edinburgh Scotland.
For 1 meter long laminate breathing on one side
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µ dynamic viscosity of air (1.82E-5 Pa*s)
Po atmospheric pressure (101 325 Pa)
L in-plane evacuation length
m/mo mass fraction of gas remaining in laminate
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OOA Prepreg Systems
Process steps – Step 4: Heating up and consolidation
OoA prepreg process:
1. Lamination (intermediate debulking)
2. Vacuum bag layup
3. Debulking
4. Heating to curing temperature (consolidation)
5. Curing process
6. Heating to post-cure temperature
7. Post-cure process
-> Final consolidation of the laminate. Moisture is extracted. Resin rheology plays an important role.
12.04.2017 Mario Danzi 32
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OOA Prepreg Systems
Process steps – Step 4: Heating up and consolidation
During heating up and curing phase, resin viscosity drops and fills vacuum channels
Consolidation and fully impregnation of the textile layers take place.
Prepreg resin viscosity (data for the MTM44-1 resin system, DoC close to zero)
@ 25°C: 500 Pa*s @ 80°C: 200 Pa*s
@ 130°C: 10 Pa*s (curing temperature) @ 160°C: 1.5 Pa*s
Laminate cross-sections prior (left) and after (right) cure: 8-plies MTM45-1/5HS.
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OOA Prepreg Systems
Process steps – Step 4: Heating up and consolidation
0
1E-14
2E-14
3E-14
4E-14
5E-14
6E-14
30 40 50 60 70 80 90 100 110 120
Temperature (°C)
Pe
rme
ab
ilit
y (
m2)
2-Ply
4-Ply
8-Ply
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Prepreg air permeability during heating up phase (relevant for moisture evacuation)
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OOA Prepreg Systems
Process steps – Step 5: Curing process
OoA prepreg process:
1. Lamination (intermediate debulking)
2. Vacuum bag layup
3. Debulking
4. Heating to curing temperature (consolidation)
5. Curing process
6. Heating to post-cure temperature
7. Post-cure process
-> Consolidation and air extraction until gelation
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OOA Prepreg Systems
Process steps – Step 6: Heating up
OoA prepreg process:
1. Lamination (intermediate debulking)
2. Vacuum bag layup
3. Debulking
4. Heating to curing temperature (consolidation)
5. Curing process
6. Heating to post-cure temperature
7. Post-cure process
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OOA Prepreg Systems
Process steps – Step 7: Post-cure process
OoA prepreg process:
1. Lamination (intermediate debulking)
2. Vacuum bag layup
3. Debulking
4. Heating to curing temperature (consolidation)
5. Curing process
6. Heating to post-cure temperature
7. Post-cure process
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OOA Prepreg Systems
Process steps
0
1
2
3
4
5
6
7
8
9
20
40
60
80
100
120
140
160
180
200
0 50 100 150 200 250 300 350 400 450
Co
mp
acti
on
pre
ssu
re [
ba
r]
Tem
pera
ture
[°C
]
Time [min]
Typical process parameters for VB processing
Temperature
Compaction Pressure
3 4 5 6 7
2 h @ 130°C
2 h @ 180°C
Cure Post-cure
Generally, OoA prepregs are cured at lower temperature than autoclave prepregs.
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Major application sectors:
Tooling
Prototyping in aerospace
Infrastructure
Marine
Wind energy
Tidal energy
Aerospace structures
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OOA Prepreg Systems
Applications
Mario Danzi
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Tooling
One of the main requirements for a
composite tool is vacuum integrity
(Leak Prevention Frame technique)
Special techniques for the incorporation of
inserts, temperature control systems and
monitoring systems are required
Tool of a Volvo 70 sailboat, two days of
lamination
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OOA Prepreg Systems
Applications
Source: SAMPE Seattle tutorial. Chris Ridgard, 2010
Mario Danzi
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Tooling
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OOA Prepreg Systems
Applications
Source: SAMPE Seattle tutorial. Chris
Ridgard, 2010 and Cirrus aircraft.
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OOA Prepreg Systems
Applications
Source:
http://www.virgingalactic.com/multimedia/album
/graphics-and-illustrations/
Spaceship 2 and White Knight 2 (
Scaled Composites (California, USA)
OOA Material: Advanced Composites Group
MTM45-1 (Umeco)
Source:
http://www.learjet85.com/en/multime
dia.html#a64-74
Bombardier Learjet 85
Fuselage and wings Cytec 5320
Source: SAMPE Seattle tutorial.
Chris Ridgard, 2010
McDonnell Douglas Bird of Prey
OOA Material: LTM10 first generation
OOA prepreg
Mario Danzi
Prototyping in aviation
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Marine
High performance yachts
Interior trim and structure
Low temperature curing resins
(VTM260 @ 65°C)
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OOA Prepreg Systems
Applications
Source: SAMPE Seattle tutorial. Chris Ridgard, 2010
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Aviation: Boeing demonstrator launch fairing
Constructed of Cytec 5320 prepreg
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OOA Prepreg Systems
Applications
Sectioned Boeing fairing Cross-section cut of laminate
Source: Composites World. www.compositesworld.com Mario Danzi
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Space
Delta Launcher Fairrings
(LTM45EL Doublers)
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OOA Prepreg Systems
Applications
Source: SAMPE Seattle
tutorial. Chris Ridgard, 2010
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Infrastructures
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OOA Prepreg Systems
Applications
Source: SAMPE Seattle tutorial. Chris Ridgard, 2010
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Contact:
Mario Danzi
ETH Zürich
Institute of Design, Materials
and Fabrication
LEE O 225
Leonhardstrasse 21
8092 Zürich
Phone: +41 44 632 26 24
E-Mail: [email protected]
www.structures.ethz.ch
47
Thank you for your attention
Questions?
Mario Danzi
Production of OOA components for the Clean Sky A4 Demonstrator,
Clean Sky Eco Design ITD.
12.04.2017