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 ?