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Composites Design and Manufacture (BEng) - MATS 324 Environmental resistance of composites. |
A key text for this area is G Pritchard, Reinforced Plastics Durability, Woodhead Publishing, Cambridge, 1999. ISBN 1-85573-320-x. UOP Library
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Composites in aerospace environments
Composites in the marine environment
Composites in aerospace environments
In the design of composites for aerospace environments, it is necessary to consider that a typical aircraft will be exposed to very low temperatures at cruising height and very high temperatures on the ground in the desert (typically in the range -60 to +60 ºC) and also an extreme range of humidities. In consequence, a key design constraint is the hot-wet glass transition temperature, Tg.
Composites in the marine environment
For general background on Materials in a Marine Environment see, for example:
Additional sources specific to composites include:
APPLICATIONS
Naval vessels
Vosper Thornycroft lead the way to glass fibre reinforced naval vessels with the 450 tonne displacement HMS Wilton launched in January 1972 and commissioned in July 1972. They subsequently developed the Hunt class MCMVs (Mine Counter Measures Vessels) at 725 tonne displacement with the first HMS Brecon launched in June 1978 and commissioned in march 1980. The first 450 tonne Sandown Class SRMH (Single Role Mine Hunter) HMS Sandown was launched in April 1988 and commissioned in June 1989.
The Visby Class of stealth corvettes is being built for the Swedish Navy by the Swedish company Karlskronavarvet. Construction began in 1996. The 600 tonne displacement Visby (K31) was launched in June 2000 and began sea trials in February 2001. She is due to enter operational service in January 2005. The hull material is a sandwich construction comprising a PVC core with a carbon fibre and vinyl laminate. The material provides high strength and rigidity, low weight, good shock resistance, low radar and magnetic signature.
Mirabella V, the largest single masted yacht in the world, was launched in November 2003 and her mast was stepped during December. The 765 tonne (half load displacement) vessel, built by Vosper Thornycroft, has an overall length of 75.22m (247 ft), beam of 14.80m (48.5 ft), draught (keel up) of 4.0m (13 ft), draught (keel fully down) of 10.0m (33 ft) and the mast height is 88.5m (290ft).
Tanks and Pipelines for the Oil and Gas Industry
The Corrosion Resistant Structures Committee of the Reinforced Plastics / Composites Institute within the Society of the Plastics Industry, Inc. [355 Lexington Avenue, New York, New York 10017. (212) 573 9400] has published a guide to assist prospective buyers of glass fibre Reinforced Plastic (RP) tanks.
Other applications of composites in the marine environment include:
- hovercraft flexible skirts
- Adhesives, Sealants and Gaskets, Greases
- Ropes/Cables
- Sailcloth and wet-suits
MATERIALS DEGRADATION
The recommended text for the durability of composites in the marine environment is:
Osmosis and blistering (and how to avoid it !)
See Searle and Summerscales (referenced above), the PassionForPaint website or the West System page entitled Worrying About Osmosis?
The Ken Hankinson book How to Fiberglass Boats (2nd edition) claims to present the most up-to-date and complete information available from a single source for anyone interested in covering new or used boats with a protective layer of fibreglass using either polyester or epoxy resins. This easy-to-read book takes the fear and mystery out of fibreglass work and helps the amateur avoid costly and tedious pitfalls. The clearly described methods are both simple and proven, making a first-class job possible by anyone willing to follow the easy non-technical instructions. Topics include fibreglass sheathing materials and which to use, resins, hardeners, catalysts, pigments, "wet" and "dry" application methods, "tips" the pros use, safety aspects, estimating materials, surface prep for both old and new boats, finishing methods, and much more! In addition to fibreglass, alternative materials such as polypropylene, "Dynel", "Arabol", "Kevlar" and carbon fibre are covered as they apply to sheathings.
Under certain conditions liquids can change to the vapour phase. This phenomenon, known as cavitation, imposes serious limitations on pumps, pipelines and propulsion systems if damage is to be avoided. Karimi and Martin have reviewed the cavitation erosion of materials. A book by Tillner et al has the specific aim of damage limitation and damage avoidance in pumps and their installations. Micrographs of cavitation damage in metals are presented in The Atlas of Metal Damage.
The University of Newcastle Marine Technology cavitation tunnel publications are listed on-line.
Hiroharu Kato has an online bibliography for cavitation in hydrofoils and propellers (201 papers at 08 October 2004).
The Copper Development Association has published data on cavitation erosion resistance.
Recent cavitation research projects include:
- Investigation of the Dynamics of Attached Cavitation on Hydrofoils, by S. Ceccio and D. George at the University of Michigan
- A Euler Solver and Its Application on the Analysis and Design of Cavitating Propellers, by J.K. Choi and S. Kinnas at the University of Texas
- A Technical Note on Cavitation Erosion Tests Using Soft Films, by J.M. Doucet and N. Bose at the Memorial University of Newfoundland)
- Hydrofoil Cavitation Improvement with Elastically Coupled Composite Materials, by S. Gowing, P. Coffin, and C. Dai at David Taylor Model Basin
- Experimental Results From the NUWC’s Supercavitation High Speed Bodies Test Range, by P.J. Corriveau, I.N. Kirschner, J.D. Hrubes, C.M. Curtis at Naval Undersea Warfare Center)
- Minimizing of Cavitation-Erosion Damage for Various Mechanical Structures using Composites under the various Condition of Fluid Flow System, by Yong-Zik Kim, Jung-Ju Lee, Soon-Chul Kwon, Yun-Hae KIM at Korea Maritime University. This work was presented at ICCE-7 in Denver during 2-8 July 2000.
The published work on cavitation erosion of polymeric materials and their composites is very limited:
- V Schroeder, Cavitation erosion tests with polyamid specimens and stainless steel specimens, Zeitschrift fur Werkstofftechnik – Materials Technology and Testing, 1986, 17(10), 378-384 (in German)
- PV Rao, Evaluation of epoxy-resins in flow cavitation erosion, Wear, 1988, 122(1), 77-95.
- RB Bhagat, Cavitation erosion of composites – a materials perspective, Journal of Materials Science Letters, 1987, 6(12), 1473-1475.
- H Bohm, S Betz and A Ball, The wear-resistance of polymers, Tribology International, 1990, 23(6), 399-406.
- DA Hammond, MF Amateau and RA Queeney, Cavitation erosion performance of fiber-reinforced composites, Journal of Composite Materials, 1993, 27(16), 1522-1544.
- New composites reduce cavitations in giant marine propeller tests, Materials World, July 2003, 11(7), 8.
The corrosion of metals and semiconductors involves the flow of an electric current within the material. Most of the constituent materials in fibre-reinforced laminates are insulators and, in consequence, electrochemical corrosion is not an issue. However, carbon (graphite) acts as a noble metal, lying between platinum and titanium in the galvanic series. Carbon fibres should not be used where they can come into contact with structural metals (especially aluminium or magnesium) 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.
The National Paint and Coatings Association glossary contains terms used commonly in the paint and coatings industry to describe the characteristics, usage and components of paints and coatings.
PaintSquare is the on-line home of The Journal of Protective Coatings & Linings (JPCL) and Protective Coatings Europe (PCE) and a portal to the protective and marine coatings industry.
Since its inception in 1926, the Paint Research Association (PRA) has been the premier research association in the coatings field. Today, it is the largest independent coatings centre of its kind, basing itself on a worldwide membership, trans-national activities and a global network of contacts.
The Oil & Colour Chemists Association was founded in 1918. More commonly known as OCCA, it is a learned society comprising individual, qualified persons employed in, or associated with, the world-wide surface coatings industries. The majority of its Members are working in a technical capacity, however its membership includes senior personnel in many roles throughout the surface coating industries. The word 'Oil' in its title refers to the vegetable oils, which once formed a major part of surface coatings' formulations.
VIDEO: Tony Ryan, Watching Paint Dry, 2011
Toxic compositions (tri-butyl tin, cuprous oxide)
The prevention of the attachment of barnacles, mussels and algae to the underwater surfaces of ships has been an age old problem of the maritime world. In the fourth century BC, Aristotle credited small fish (barnacles) with the ability to slow down ships [Saroyan et al]. Saroyan [1969] suggested that fouling growths caused loss of ship speed, increased friction and over-consumption of fuel, promotion of corrosion by mechanical damage, increased weight, prevented operation of moving parts of equipment, reduction of the size of conduit openings and increased noise in sonar signals. The US Navy [New Scientist] has reported that barnacles and other marine encrustations on hulls increase drag, slow the vessel down and estimate that this consumes 25% of the fuel used.
In 1824, Sir Humphrey Davy stated that the anti-fouling action of copper sheathing on wooden ships was related to its rate of solution in seawater [Saroyan et al]. Copper compounds are still generally regarded as one of the best antifouling agents. They are normally applied as cuprous oxide (Cu2O) or cuprous thiocyanate in a paint film.
In the 1960's, the shipping industry began using paints containing an organo-tin compound called tributyltin (TBT) to prevent the fouling of marine surfaces. This chemical act as a highly toxic material that kills larvae and other sea life that comes into contact with the ships. By the 1980's it became evident that TBT is responsible for a host of environmental problems resulting from persistence of these compounds in the sediments and killing sea life besides those attaching to ships. TBT was soon found to cause deformations in oysters, sex changes in whelks and possible toxic effects in higher organisms as TBT enters the food chain. The International Maritime Organization (IMO), an agency of the United Nations responsible for ship safety and maritime pollution, adopted a Resolution in 1990 to urge governments to eliminate TBT in antifouling paints. In 1998, the IMO approved another Resolution for the global prohibition of the application of TBT as biocide in antifouling paints on ships by January 1, 2003 and a complete ban on the presence of TBT antifouling paints on all ships by 1 January 2008. [http://ens.lycos.com/e-wire/Aug00/22Aug0001.html .. webpage no longer available]. For a chronology of TBT as an antifouling coating see the MST326 page on the Precautionary Principle.
Turner [2010] has reviewed the likely biogeochemical pathways for toxins from anti-fouling paint particles generated during the maintenance of recreational boats, abandoned ships and grounded vessels.
E Paint (Falmouth MA) have introduced a new antifouling coating which relies on a combination of visible light, oxygenated water and a catalyst in the coating to generate a steady source of hydrogen peroxide (H2O2) [Porter]. After release, the H2O2 is rapidly decomposed to oxygen and water molecules. The H2O2 is effective against hard fouling agents (e.g. barnacles, mussels and tubeworms) and is complemented by zinc pyrithione to combat soft fouling agents (e.g. algae).
Non-toxic low surface energy compositions
These coatings have low surface energy and as a consequence fouling organisms find it difficult to adhere to the surface. Such coatings are not normally suitable for drying moorings. A major benefit is low water resistance on the hull, leading to improved fuel economy and more responsive handling. Swain noted that there is no true non-stick marine coating: the current technologies use fouling followed by release. He found that successful surfaces reduced adhesion below the level where the force of water to release the fouling was 34 kPa (5 psi), while the best coatings had adhesion factors below 7-14 kPa (1-2 psi). Silicone polymers are the normal choice as there is no known environmental damage from these coatings. However, they are relatively expensive, weaker and more vulnerable to damage and their effectiveness may be compromised by improper application (the correct environment is the key to success).
Exfoliating/self-polishing surfaces
As the name suggests, the flow of water over the hull continually erodes the surface of the coating exposing a fresh layer of biocide. A thick coating can provide multi-season performance subject to an annual check and revival of the coating by abrasion/water-jetting. Such coatings are not normally suitable for drying moorings. Hoare [1997] and Thompson et al [2004, 2005] have raised the issue of the final destination of plastic particles that enter the marine environment.
Bio-inspired approach (biomimetics)
Liedert and Kesel sought to verify the efficiency of biologically inspired surface microstructures as an alternative to biocide paints using shark skin as the analogue. The highest antifouling performance (about 95% reduction of settlement of barnacles) was achieved by a combination of the following parameters:
The Brennan Research Group at the University of Florida have developed a biomimetic design, Sharklet AFTM microtopographical surfaces, inspired by the structure of shark scales which reduces the settlement of algae spores by over 60% when the characteristic dimension of the surface is 4.2μm or less.
Sullivan and Regan produced synthetic sharkskin samples using a silicone elastomer (Dow Corning Sylgard 184 PDMSe polydimethylsiloxane) and a slow swimming catshark Scyliorhinus caicula as the template. In comparison to a smooth planar surface of identical elastomer, contamination rates were reduced with smaller, densely packed denticles attracting least fouling.
References for Marine Coatings:
FIRE: FLAME, SMOKE AND TOXICITY (FST)
Mouritz and Gibson [2006 book] have published a book which covers all of the key issues on the behaviour of composites in a fire, including thermal degradation mechanisms, thermal softening, fire damage mechanics, and deterioration of mechanical properties. Also covered are fire protection materials for composites, fire properties of nanocomposites, fire safety regulations and standards, fire test methods, and health hazards from burning composites.
The International Maritime Fire and Rescue Information website FireNet (Maritime) includes a Special Interest Network being developed to cover Ship Fire Fighting Techniques, Training, Procedures and any interesting marine related topics within this type of environment.
NoFire Technologies are manufacturers of patented high performance fire retardant paint and products. They specialise in research, design and engineering of fire and heat protection system solutions for industry, government and public safety. After extensive independent and Naval testing, NoFire A-18 NV is been listed on the U S Navy Qualified Products List (QPL) and NoFire A-18 Fire Retardant Marine Paint is approved by US Coast Guard for use on all ships.
References for Fire, Smoke and Toxicity (FST)
Further reading