manufacturing of polymer composites ooa prepreg technology · author: mario danzi laboratory of...

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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?

12.04.2017 3


Introduction

4-8 bars

Mario Danzi

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Influence of voids on the apparent shear strength.



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

12.04.2017 5

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

Mario Danzi

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Spring analogy

12.04.2017 6


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

12.04.2017 7


Terzaghi’s law

Mario Danzi

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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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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


Setup for

compaction

experiments at

CMASLab

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Resin pressure in processing conditions

12.04.2017 10


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


Com

pact

ion

Pre

ssur

e [P

a]


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

Mario Danzi

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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.

12.04.2017 11


Void mitigation

Mario Danzi

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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

12.04.2017 12

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)

14

Before cure

Fiber Tow Resin

After cure and consolidation

Fiber Tow Resin

Mario Danzi 12.04.2017

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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.

16

Source:

SAMPE Seattle

tutorial. Chris

Ridgard, 2010


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.

17

0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.70

1

2

3

4

5

6x 10

5


Com

pac

tion

Pre

ssur

e [

Pa

]



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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



2. Vacuum bag layup

3. Debulking

4. Heating to curing temperature

5. Curing process



-> Adaptation to mould shape and first ply consolidation


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OOA Prepreg Systems


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


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



2. Vacuum bag layup

3. Debulking


5. Curing process



-> Good vacuum bag integrity is essential!


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OOA Prepreg Systems


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


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


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


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


Initial thickness: 2mm

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OOA Prepreg Systems


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



2. Vacuum bag layup

3. Debulking


5. Curing 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


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


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


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



2. Vacuum bag layup

3. Debulking


5. Curing process



-> Final consolidation of the laminate. Moisture is extracted. Resin rheology plays an important role.


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OOA Prepreg Systems


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


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


Prepreg air permeability during heating up phase (relevant for moisture evacuation)

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OOA Prepreg Systems

Process steps – Step 5: Curing process



2. Vacuum bag layup

3. Debulking


5. Curing process



-> Consolidation and air extraction until gelation


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OOA Prepreg Systems

Process steps – Step 6: Heating up



2. Vacuum bag layup

3. Debulking


5. Curing process




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OOA Prepreg Systems

Process steps – Step 7: Post-cure process



2. Vacuum bag layup

3. Debulking


5. Curing 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

12.04.2017 39

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

12.04.2017 40

OOA Prepreg Systems

Applications

Source: SAMPE Seattle tutorial. Chris Ridgard, 2010

Mario Danzi

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Tooling


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

http://www.virgingalactic.com/multimedia/album/graphics-and-illustrations/







http://www.learjet85.com/en/multimedia.html#a64-74






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Marine

High performance yachts

Interior trim and structure

Low temperature curing resins

(VTM260 @ 65°C)


OOA Prepreg Systems

Applications


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Aviation: Boeing demonstrator launch fairing

Constructed of Cytec 5320 prepreg

12.04.2017 44

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)


OOA Prepreg Systems

Applications

Source: SAMPE Seattle

tutorial. Chris Ridgard, 2010

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Infrastructures


OOA Prepreg Systems

Applications


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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

mailto:[email protected]



http://www.structures.ethz.ch/







manufacturing of polymer composites ooa prepreg technology · author: mario danzi laboratory of...

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