Durability of compositesin the marine environment

John SummerscalesPlymouth University

Plymouth• Advanced Composites Manufacturing

Centre• only UK undergrad. composites

degrees:BEng (honours)Mechanical Engineering with Composites

BSc (honours)Marine and Composites Technology

Marine Centre at Coxsideunder re-development fordiving and diver trainingplus technical support tomarine-based projects andresearch activities.

Plymouth Sound• Third largest natural harbour in the

world• Hosted America’s Cup in September

2011

External presentations

• Ifremer/ONR International Workshop onDurability of Marine CompositesNantes - France, 23 August 2012.

• Wuhan University of TechnologyWuhan – China, 06 September 2013.

• ICACME 2013: First International Conference Advanced Composites for Marine Engineering Beijing – China, 10 September 2013

Key references

• J Summerscales and TJ Searle (1999)Review of the durability of marine laminatesin G Pritchard (ed.)Reinforced Plastics DurabilityWoodhead Publishing, Cambridge, pp 219–266.

• J Summerscales (2014)Durability of composites in the marine environment in P Davies and YDS Rajapakse (eds.)Durability of composites in a marine environmentSpringer, Dordrecht (NL), pp 1-13.

Applications• marine renewable energy• offshore oil and gas• defence vessels• submarines• lifeboats• powerboats• sterngear• yachts• canoes• surfboards• … and all the others

Durability

• defined as good for the full intended working life of the system

• the downside is end-of-life considerationso only a limited number of museums

want to keep artefacts for ever o if sufficiently desirable

objects may be trading in the antiques market

o if too durablethen difficulties arise in “recycling”

Outline of lectureglass transition temperature

diffusion of moisture

osmosis and blistering

cavitation erosion

galvanic corrosion

marine coatings

antifouling paints flame, smoke and toxicity (FST)

Temperature

Glass transition temperature

Tg is a function of:

molecular structure

Crystallinity or extent-of-

cure

chain endsto backbone ratio loading rate moisture

content

Tg = glass

transition

below Tg: elastic/brittl

e

above Tg:viscoelastic/toug

h

key design parameter

in aerospace

“hot wet Tg”

Wright (Composites, July 1981) found "as a rough rule-of-thumb“that there was a drop in Tg of epoxy resins of 20°C for each 1% of water pick-up (up to 7% moisture content).

Peak surface temperature vs ambient air temperature

blackbrownred greenorange tanpurple bluelight blue Alyellowwhite

surface °C

120

100

80

60

40

20

0 10 20 30 40 50 ambient °C

redrawn from SP Systems design allowable booklet

Moisture diffusion

Moisture (Fickian diffusion)

… or Flory-Huggins or Langmuir/Henry/clustering models ?

Moistu

re

con

ten

t

√(time)

equilibrium/saturation

Saturation moisture content (M%)*

• M% dependent on (resin) chemistryo M%max <0.5% (only apolar groups)

polyolefins, PTFE, polystyrene, polydimethylsiloxane

o M%max <3.0% (non-hydrogen donors) polyethers, polyesters

o M%max <10% (H-donors in hydrogen bonding)

polyvinylalcohol, polyacrylic acid, polyacrylamide

* Xavier Colin and Jacques Verduat Ifremer-ONR workshop on Durability of composites, 2012.

Osmosis… and blistering

Osmosis ...

• Osmosis can be defined (Clegg, 1996) as “the equalisation of solution strengthby passage of a liquid (usually water) through a semi-permeable membrane

mem

bra

ne

Weak solution Strong solution

Osmosis ...

• normally the fluid will pass through the material without affecting it

• but, there may be soluble materials ….

Osmosis and blistering

• a little solvent and a lot of solute-> a strong solution

• strong driving force for osmotic cell• high pressures generated cause/expand

void containing strong solution• swelling leads to blisters with

associated surface undulation• Image from:

http://www.wessex-resins.com/westsystem/wsosmosis.html

http://www.insightmarinesurveyors.co.uk/osmois%20ringed.jpg

Osmosis and blistering: causes

raw materials

• residual glycol• high acid value resin• too little or too much styrene• too much catalyst (carrier)

chemical/physical factors

• soluble binder/release systems• gel-coat thickness and quality • permeability of gel-coat < laminate• dark pigments

process factors

• inadequate mixing• incomplete wet-out or consolidation• elapsed time between layers • degree of cure

Osmosis and blistering

• For marine applications, considero changing from orthophthalic

to isophthalic polyester resino and to improve “iso” resin further,

use NPG (neo pentyl glygol): HO-CH2-C(CH3)2-CH2-OH 2,2-dimethyl-1, 3-propanediol

• Durability:o ortho < iso < NPG

Chemical structure from: http://chemicalland21.com/specialtychem/perchem/NEOPENTYL%20GLYCOL.htm

Natural fibre composites

• fibre composed primarily ofcellulose, hemicellulose, lignin and pectin

• limited solubility in water• successful applications include

o Araldite: 6.5 metre racing yacht o Flaxcat: light-weight catamaran/Delft

• … but time will tell ?• LCA important if product life

< “traditional” equivalent

Cavitation erosion

Cavitation= spherical bubble collapse

• The following slides use images extracted fromnumerical simulation in Kawitachnik video

(http://www.youtube.com/watch?feature=player_detailpage&v=Ibd-v1YbD8c )

• vapour bubble collapse caused by cavitationcreates impinging jet of liquid onto solid surface$

• pressure pulse* o impact stress may exceed 1000 MPao duration of pulse ~2-3 μs

$ W Lauterborn and H Bolle, … cavitation bubble collapse …, J Fluid Mechanics, 1975, 72(2), 391-399.

* A Karimi and JL Martin, Cavitation erosion of materials, International Metals Reviews, 1986,

31(1), 1-26.

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion

• Collapsing bubble:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion• Collapsing bubble creates jet

towards a hard surfaceloosens structure and removes material:

Solid surfacemodel from Lauterborn and Bolle - video from Kawitachnik

Cavitation erosion in NAB propeller

photographs courtesy of Peter Dyson

Cavitation erosion• very limited public domain data

on fibre-reinforced composites • how much good data is locked away in

publicly-funded defence “stealth” research ?o National Technical Information Service

(US NTIS) search for “cavitation erosion”:returned “0 document found”.

o OpenGrey SIGLE (System for Information on Open Grey Literature in Europe) search for “cavitation erosion composite(s): 1(2) non-polymer items returned.

o Karimi and Martin review:2 references (of 231) for rain erosion of composites

Cavitation erosion

• composites may perform better than metals because fibre > grain sizeo student projects* suggested

CFRP proportional loss in weightonly 40% of that for Al under identical conditions

o but difficult experiment CFRP absorbs some water may have low initial - but accelerating - loss

rate

* Handley ..and.. Ladds (1995)

Cavitation erosion/ADCOAbu Dhabi Commercial Oil• oil pipe diffuser section• steel component replaced every month• composite “temporary” replacement

removed from service after nine months

Galvanic corrosion

Galvanic corrosion

• corrosion involves flow of an electric current

• most constituents of fibre-composites are insulators and henceelectrochemical corrosion is not an issue

• However, carbon (graphite) acts as a noble metal, lying between platinum and titanium in the galvanic series. 

Galvanic corrosion

• Carbon fibres should not come into contact with structural metals(especially Al or Mg)in the presence of a conducting fluid(eg sea-water).

• A thin glass fibre surface layer may be sufficient to prevent the formation of such a galvanic corrosion cell.

Marine coatingsincluding antifouling

paints

Marine coatings

• Surface coatings may be foro provide aesthetic finisho improve resistance to corrosiono protect against fouling

especially for marine or process plant applications

• gel-coat is normally applied to the mould before the laminate is laid-up/injected

• a major issue in the marine industry is“print-through”o surface echoes topology of reinforcement

Benefit of antifouling

• Aristotle (fourth century BCE) observed that small fish (barnacles) could slow down ships.

• US Navy [New Scientist, 1975] reported that barnacles and other marine encrustationson hulls increase drag, slow the vessel down and estimate this consumes 25% of the fuel.

• US NSWC Carderock estimatedo biofouling reduces vessel speed by 10%o added drag increases fuel consumption by

40%.

Antifouling paints

Toxic compositions

cuprous oxide –

increasing concern

tri-butyl tin – now

banned worldwide

Exfoliating/ self-polishing

surfaces

microparticles -increasing

concern

Non-toxiclow surface

energy compositions

Adhesion to substrate

issues

Polymer “brush” coatings

Prevention of attachment

Reduced adhesion strength

Degrade or kill

organisms

Biomimetic approach: shark skin analogue

surface microstructur

e, Rz = 76 μm

soft silicone material

(shore A = 28)

low surface energy

(25 mN/m)

Flame, smoke

and toxicity

Flame, Smoke and Toxicity (FST)

important for …

submarines underground railways

sub-surface mines

Flame, Smoke and Toxicity (FST)

F = flame

low spread of flame

S = smoke

minimal emission of

smoke

T = toxicit

y

no Toxic products of combustio

n

phenolic resins burn to just H2O

and CO2

in the presence of a good supply of

air

Balmoral offshore lifeboat

• glass reinforced plastic fire-retardant resins carries 21-66 people • certification required to withstand 30 m high kerosene flames and temperatures of 1150°C • throughout the fire test, the temperature inside never exceeded 27°C.

Image from the front cover of International Reinforced Plastics

IndustryMay/June 1983, 2(5), 1

Summary• temperature

o stay below Tg• moisture diffusion

o this will happen• (osmosis and) blistering

o avoid with correct materials selection• cavitation erosion

o need more research• galvanic corrosion in CFRP systems

o avoid by isolating conductive elements• marine coatings• flame, smoke and toxicity

Acknowledgements

• Plymouth Sound images• http://upload.wikimedia.org/wikipedia/commons/9/94/Plymouth_Sound.jpg• http://www.heart.co.uk/plymouth/events/going-out/americs-cup-action-plymouth/americas-cup-action-2/• http://www.heart.co.uk/plymouth/events/going-out/americs-cup-action-plymouth/americas-cup-action-6/

Thank you for your attention…. any questions ?