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An Introductory Guide
in Industrial PlantsComposites
Preface
The Queensland Government’s Fibre Composites Action Plan – New Technology Taking Shape launched in April 2006 sets out over 50 initiatives under six theme areas, ranging from innovation to skills and training.
The Fibre Composites Action Plan identified the potential for significant benefits from increased use of composites in target sectors such as mining, minerals processing and associated infrastructure.
Deborah Wilson Consulting Services (DWCS) and GHD were engaged to undertake a study to assess this opportunity and develop approaches that make the choice of composites in mining applications easier, and more relevant to delivering cost savings and other benefits to industry.
The Queensland Government, through the Department of Employment, Economic Development and Innovation (DEEDI), funded this study as part of a larger initiative to help one of the State’s most promising new industries grow and compete on a global level.
The aim of the study was to deliver:
case studies on successful use of composites in the mining industry and the •benefits composites deliver
business case information on the use of composites in different applications in •mining, minerals processing and associated infrastructure
information covering availability, technical guides and benefits of using •composites in common applications in the mining industry
improved links between composites suppliers, manufacturers and the mining •industry to better respond to mining industry needs
information kits, presentations and technical seminars on the findings and •applications where composites deliver value to the mining industry
a model for the composites industry to use in profiling valuable applications for •composites in other industries.
This introductory guide addresses a number of these aims. It has been prepared following a review of relevant technical literature and discussions with the composites industry.
DisclaimerThis publication was funded by the
Queensland Government (through the
Department of Employment, Economic
Development and Innovation). It is
distributed by the Queensland Government
as an information source only. The State
of Queensland makes no statements,
representations, or warranties about
the accuracy or completeness of, and
you should not rely on, any information
contained in this publication.
Readers should not act or rely upon any
information contained in this publication
without taking appropriate professional
advice relating to their particular
circumstances.
The Queensland Government disclaims all
responsibility and all liability (including
without limitation, liability in negligence)
for all expenses, losses, damages and
costs you might incur as a result of the
information being inaccurate or incomplete
in any way, and for any reason.
in Industrial PlantsComposites
An Introductory Guide
Table of contents
1. Introduction ___________________________________ 3
2. Overview of materials and products _______________ 4
2.1 Qualitative comparison of materials ___________ 4 2.2 Benefits of composites ______________________ 5 2.3 Product applications ________________________ 6 2.3.1 Current applications _____________________ 6 2.3.2 Future applications ______________________ 7 2.3.3 Pipes and ducts _________________________ 7 2.3.4 Tanks and process vessels ________________ 8 2.3.5 Launders _______________________________ 9 2.3.6 Joints and fittings ________________________ 9 2.3.7 Coatings and linings ____________________ 10
3. Composite product manufacturing _______________ 11
3.1 Components ______________________________ 11 3.2 Fibre reinforcement ________________________ 11 3.3 Resins ___________________________________ 13 3.4 Additives ________________________________ 14 3.5 Cores ____________________________________ 14 3.6 Example of a composite laminate ____________ 15 3.7 Manufacturing processes ___________________ 15 3.8 Manufacturers ____________________________ 15
4. Australian case stories _________________________ 16
5. Technical performance _________________________ 18
5.1 Design ___________________________________ 18 5.2 Standards ________________________________ 18 5.3 Guides __________________________________ 19 5.4 Relative performance of materials ___________ 19 5.5 Service life _______________________________ 20 5.6 Mechanical properties _____________________ 20 5.6.1 General _______________________________ 20 5.6.2 Strength ______________________________ 20 5.6.3 Fatigue ________________________________ 21 5.6.4 Creep _________________________________ 22 5.6.5 Abrasion resistance _____________________ 22 5.7 Thermal properties ________________________ 22 5.8 Chemical properties _______________________ 23 5.9 Electrical properties _______________________ 26 5.10 Performance of composites in fire ____________ 26 5.11 UV resistance _____________________________ 27 5.12 Working with composites on site _____________ 28 5.13 Inspection and testing _____________________ 28
6. Economic comparison __________________________ 30
7. Environmental comparison _____________________ 31
8. References ___________________________________ 32
9. Australian manufacturers of composite industrial products ____________________________ 34
10. Australian composites design and engineering service providers ___________________ 41
11. Acknowledgements ____________________________ 43
List of abbreviations
ACI American Concrete Institute
AS Australian Standard
BS British Standard
CFRP Carbon Fibre Reinforced Plastic
CTE Coefficient of Thermal Expansion
FRP Fibre Reinforced Plastic
GRP Glass Reinforced Plastic
HDT Heat Distortion Temperature
ISO International Standards Organisation
PTFE Polytetrafluorethylene
PVC Polyvinyl Chloride
PVDF Polyvinylidene Fluoride
UV Ultraviolet (sunlight)
3
1 Introduction
A composite is a material made up of two or more components so the beneficial properties of each component are utilised. In this guide, composite refers to a material composed of a thermosetting resin and fibre reinforcement. Composites are also referred to as fibreglass, glass reinforced plastic (GRP), fibre reinforced plastic (FRP) and carbon fibre reinforced plastic (CFRP). As there are many different resins, reinforcements and methods of putting the two together, there are a multitude of materials which can be described as composites.
Composites offer unique products in many of Queensland’s most important industry sectors, including advanced manufacturing, aerospace, building and construction, defence, infrastructure, marine, mining and transport. As composites are light-weight and corrosion-resistant, the materials have the potential to reduce costs, save time and provide a safer work environment. At a time of fluctuating steel prices and long delivery times, composites offer a real alternative to reduce capital and operational costs, and downtime. Composites’ light-weight nature provides operational savings for trucks and mobile equipment, and their corrosion-resistance prevents the hazards of rusting steel structures.
Composites have been used in many Australian industries since the 1940s. For example, in the minerals processing and chemical industries, the materials are used in a variety of applications including tanks, pipes, process vessels and floor grating. In the mining industry, the materials are used in applications including ducts, truck bodies and rock bolts. It seems the Bronze Age and Iron Age have passed, and the composites age is now upon us.
The Queensland Government is capitalising on Queensland’s strengths as a world leader in the research, development and commercialisation of fibre composites technologies through the implementation of its Fibre Composites Action Plan, and significant investment under the Smart Futures Fund.
For more information on Queensland’s Fibre Composites industry please visit: www.composites.industry.qld.gov.au
Lucy Cranitch, GHD, produced this guide. It aims to provide an introduction to composites in the mining, mineral processing and chemical industries, and to assist in the decision to purchase a composite component. It does not provide design details of composite components.
For more information on GHD please visit www.ghd.com.au
A composite is a material
made up of two or more
components so the beneficial
properties of each
component are utilised.
Carbon fibre-epoxy drill rod prototype with embedded strain gauges and carbon nanotube-epoxy threads
Image courtesy of Teakle Composites
4
2 Overview of materials and products
2.1 Qualitativecomparisonofmaterials
The table below provides a quick comparison of materials.
Table 1 Qualitative comparison of materials
Material Advantages Disadvantages
Mild steel High strength
High stiffness
High ductility
Susceptibility to corrosion
Susceptibility to fatigue
High weight
High energy required for production
Stainless steel Corrosion resistance High cost
Aluminium Low weight
High ductility
Ease of recycling
Susceptibility to corrosion in strong acids and alkalis
High energy required for production
Plastic (polyethylene, polypropylene, polyvinyl chloride (PVC), etc)
Corrosion resistance
Low cost
Low coefficient of friction
Ease of recycling
Susceptibility to creep
Low stiffness
Non-conductive properties can be a disadvantage
Limited temperature resistance above 200°C
Composite Corrosion resistance
Low weight
High strength
Conductivity or non-conductivity
Low coefficient of friction
Limited temperature resistance above 250°C
Sensitivity to impact damage
Wagners Composite Fibre 100 x 100 mm pultruded sections
Image courtesy of Wagners CFT Manufacturing Pty Ltd
5
2.2 Benefitsofcomposites
Corrosion resistantWith the selection of correct materials, composites will not deteriorate in acids, alkalis, solvents and salt water, and can be used from pH 0 to 14. Composites are therefore used widely in tanks, pipes and process vessels in chemical extraction of base and precious metals. Plant operating time can therefore be maximised. Both minerals processing and chemical plants use this durable material for plant infrastructure, such as gratings and hand rails, where rusting of steel structures can place the safety of plant personnel at risk. Since composites do not require painting, there are also reduced maintenance costs.
DurableComposite materials are durable due to their high strength and high resistance to fatigue, abrasion and creep. Agitated tanks made from composites have been found to operate successfully for many years despite the cyclic loads experienced. In pipelines, resistance to abrasion combined with a low coefficient of friction aids process flow and reduces downtime. This overall durability of composites reduces the need for maintenance and repair, which maximises plant running time.
Light in weightComposites are relatively light in weight compared to steel, iron and concrete. For example, typical composite pipes are approximately 25 per cent of the weight of ductile iron and 2 per cent of concrete equivalent pipe mass per metre. The reduced weight of composite pipes, tanks and process vessels has led to lower transportation and installation costs for the mining industry, and reduced plant downtime through enabling installation at sites where access is restricted. Where electrical guarding and hatches need to be lifted by plant operators, the composite option at less than 10 kg per sheet is certainly preferable to the steel option at more than 20 kg. This also applies to hatches and all components that must be lifted to ensure the safety of all personnel.
Electrically insulating or conductiveFor safety reasons, the electrical insulation of process equipment is critical where high electric currents or voltages are used. Composites that are electrically insulating are used in high electric currents or voltage environments, such as pot rooms in aluminium processing and in electrowinning. The radio and magnetic transparency of composites is useful in a number of applications. In applications where static charge can build-up, static dissipation and grounding of equipment is critical to keep plants operating and to prevent fires where flammable solvents are used. Conductive properties can also be built into the composite equipment for applications such as solvent extraction.
Thermally insulatingWhere high temperature fluids are stored in vessels or pipes, thermal insulation is critical for safety. The use of composites in these applications can reduce or eliminate the need for insulation with external temperatures typically being less than 60°C for fluids and liquors up to 100°C. Furthermore, being an insulator, the transfer of heat from composite materials to any body part is very much less than that from a conductive material such as stainless steel.
Flexible in design and manufactureComposite materials offer solutions to many manufacturing problems due to the vast array of resins, reinforcements and unique manufacturing methods used to produce them. Such flexibility in design and manufacture can result in cost and time savings. For example, it is relatively simple for composite materials to create compound curves in metallic materials. Also, while large covers usually require large support structures, the light weight nature of composites means it is possible to design covers that are supported on the edge of a vessel without the requirement for intermediate supports. Composites manufacturing processes, such as hand lay up, also enable unique designs to be manufactured at relatively
All FRP (handrails, stair treads, landing and support structure) stair platform
Image courtesy of Exel Composites
6
low cost. The ability of composites to conform to any shape and bond with steel and concrete enables rehabilitation and retrofit. For example, composite materials are well used in the lining of process vessels. Composite materials’ flexibility in design and manufacture also means on-site manufacture of very large vessels, such as filament winding of large tanks, is possible
2.3 Productapplications
2.3.1 Current applications
Composites can be used in many applications in the mining and process industries, including:
Mining
ducts for ventilation, chilling and cooling in underground operations•
cuttable rock bolts (used in reinforcement), rib bolts and brackets•
mobile and stationery containers for water, diesel and other liquid •storage on site
bore casings and insulation in underground structures•
theodolites and legs for survey equipment.•
Mineral and chemical processing
tanks for storage of corrosive and non-corrosive materials•
process vessels including gas cooler condensers, electrostatic mist •precipitators, leach tanks, reactor tanks, thickeners, electrolytic cells, cell bearers, mixer settlers, spent tanks, crystallisers, solvent extraction and electrowinning cells, and pulse columns
mineral sands separation equipment including spirals, cone concentrators •and hydrocyclones
cooling towers•
linings for concrete and steel tanks and equipment•
claustra walls and panels•
fans, blades, baffles, agitators, bottom scrapers and mixing tools•
pipes, fittings and launders including products for abrasive (e.g. slurry) •and non-abrasive materials
nozzles, flanges, elbows, reducers, branches, tees and joints•
ducts for transporting process gases and fume extraction•
scrubbers and waste gas towers, quench towers and demisters•
dampeners/valves•
gratings, ladders, walkways, handrails, steps and platforms•
inspection hatches, hoods and covers•
structural applications such as support beams, channels and angles•
froth crowders for flotation tanks•
protective guards on machines•
consoles•
telescopic handles for sampling and testing•
stacks, flues and other large structures•
use of composites to repair failed plant components.•
Chemical resistant FRP piping system with coupling for use in highly
corrosive environments
Image courtesy of A.C.Whalan Composites
The ability of composites
to conform to any shape
and bond with steel
and concrete enables
rehabilitation and retrofit.
7
Mine site infrastructure
guards, grating, walkways, platforms, kick rails, stairs and ladders•
rebar and stay-in-place formwork for concrete•
polymer concrete•
concrete floor and bund coatings and lining•
cable supports, trays and ladders•
pumps•
power poles including cross-arms•
wall and roof sheeting as well as purlins in site buildings•
window and door frames•
water treatment and supply•
bridges•
trusses•
manhole covers•
railway sleepers•
drains and sumps•
poles to remove high voltage lines.•
Port infrastructure
guards and inspection hatches•
gratings, ladders, walkways, handrails, steps and platforms•
structural panelling, sheet piling and other applications in marine environments.•
2.3.2 Future applications
The advantages of composites described above have led to investigations into new applications for composites, including:
truck bodies, cabs, panels and engine casings (fully fibreglass cabs have been •used by Leader trucks and Mack trucks since the 1970s)
access ladders, hand rails and steps attached to major mining and •earth moving equipment
wear blocks•
long and short conveyors including supports, covers and hoods, guards •and rollers
wash plant pipes and air receivers•
port loading infrastructure•
gag ducts for fire suppression in underground mines.•
2.3.3 Pipes and ducts
From pipes carrying sulphuric acid in leaching of copper bearing ore, to waste water, composite pipes have widespread use in the chemical and minerals processing industries in Australia. Key benefits include resistance to corrosion in chemical environments, increased hydraulic flow and reduced operating costs through comparatively low friction compared to steel. Conductive composite pipes are much safer than plastic pipes in solvent extraction plants, and have been found to be more cost effective and durable than the alternative SAF2507 stainless steel.
21 mm solid FRP rods supplied to customer as concrete rebar to eliminate any electrostatic interference with its equipment
Image courtesy of Exel Composites
8
In underground mining, composite ducts are used for ventilation as its light weight nature enables much easier installation and lighter supports than other products. In the chemical and minerals processing industries, composite ducts are used for applications like transporting sulphur dioxide in plants manufacturing sulphuric acid, and in minerals processing plants to extract fumes.
There are a range of standards and guidelines available for the design and manufacture of composite ducts and pipes. Those most widely used in Australia include:
Composite pipes can be used at low and high pressures. For example, the API 15 HR specification for high pressure fibreglass line pipe covers pipes rated for 3.45 MPa to 34.5 MPa.
For above ground pipes and ducts, BS 6464 contains information on installation including supports, guides and anchors. Pipe support spacing is important and the ratio of the vertical deflection of a pipe to the horizontal span between supports is often limited to 1:300. For pipe supports, a minimum contact arc of 120° under the pipe is typical and rubber packers between the support and the pipe can help reduce point loads.
For buried pipes, AWWA C950 contains information on design whilst AS 2566 and BS 6464 can be used for installation. Information on trench preparation, backfilling material and installation procedures are given in these standards.
It is possible to make continuous radius bends, including elbows and long radius bends, as a single unit with no longitudinal joints in composites.
2.3.4 Tanks and process vessels
In the chemical and minerals processing industries, composite tanks and process vessels have a long history of successful use in chemical environments which readily corrode steel and attack concrete.
Sulphuric and hydrochloric acids are widely used in processing copper, lead, nickel and zinc. In these manufacturing plants, composites are used to construct leach tanks, thickeners, electrolytic cells mixer settlers, spent tanks and pulse columns. In sulphuric acid manufacturing plants, composites are widely used in radial flow scrubbers, gas cooler condensers and electrostatic mist precipitators.
AS 3571 Plastics piping systems—Glass-reinforced thermoplastics (GRP) systems based on unsaturated polyester (UP) resin—pressure and non-pressure drainage and sewerage; and pressure and non-pressure water supply
AS 2634 (obsolescent) Chemical plant equipment made from glass-fibre reinforced plastic (GRP), based on thermosetting resins
AS/NZS 2566 Buried flexible pipelines
BS 7159 Code of practice for design and construction of glass-reinforced plastics (GRP) piping systems for individual plants or sites
BS 6464 Specification for reinforced plastic pipes, fittings and joints for process plants
BS EN ISO 14692 Petroleum and natural gas industries—glass-reinforced plastics (GRP) piping
ISO 10467 Plastics piping systems for pressure and non-pressure drainage and sewerage—glass-reinforced thermosetting plastics (GRP) systems based on unsaturated polyester (UP) resin
ISO 10639 Plastics piping systems for pressure and non-pressure water supply—glass-reinforced thermosetting plastics (GRP) systems based on unsaturated polyester (UP) resin
ANSI/AWWA C950 Standard for fiberglass pressure pipe
ISO 10639 Plastics piping systems for pressure and non-pressure water supply using GRP systems based on unsaturated polyester (UP) resin.
FRP Fuel tanks
9
While the corrosion resistance of composites is a key benefit, the relatively low cost of composites compared to alternative materials such as stainless steel, duplex and other alloys has also accelerated their acceptance.
The following standards and guides are applicable to composite tanks and vessels:
As well as storage tanks and process vessels, composites can also make internal components such as baffles and weirs. For example, composite flanges, manways and other fixtures can be built into the composite tank or vessel.
It is important to reinforce areas of composite tanks and vessels subject to higher loads. Shells should be reinforced with external circumferential reinforcing ribs to provide rigidity, particularly where agitators are not independently supported. Floors should be reinforced where intermediate supports are needed for tank roofs. Roofs should be reinforced where personnel and/or other equipment need to be supported.
Information on supports for tanks and process vessels is given in the standards. It is standard practice to use concrete slabs as supports, however, concrete ring beams filled with compacted sand finished with a layer of sand and oil mixture can also be used.
2.3.5 Launders
There is no design standard specifically for composite launders, although BS 6464 contains some applicable information. The stiffness of the launder should be sufficient to prevent sag, twist, camber or spreading without full length supports or restraints while the launder is operating. It is advisable to reinforce off-take areas of launders.
2.3.6 Joints and fittings
The type of joints affects the durability and cost of pipelines. Common methods of joining composite pipes are butt and strap; rubber ring type and flanged joins. Restrained joints eliminate the need for and thus cost of thrust blocks etc. Butt and strap joints used with composite pipes are restrained, have similar chemical resistance to the parent pipe material and are less susceptible to leaks. However, in terms of installation butt and strap joints are slow and costly and do not tolerate misalignment or movement well. Whilst rubber ring type joints are not restrained, they are quick to install and tolerate some degree of misalignment and movement. Thus rubber ring type joints are particularly useful for buried pipelines.
There are a number of requirements for durable butt and strap joints. The strength of the joint must be at least equivalent to that of the parent material. The required widths of pipe joints are given in the standards, and where accessible, the internal surface of the joint should be laminated. Since joints are hand laid, their thickness must be that of a hand laid pipe, even for joints in a filament wound pipe. To prevent ingress of fluids into the laminate, all cut ends must be sealed with resin. Tees, branches and other similar joints can be prepared using similar techniques to those employed for standard composite butt and strap joints.
AS 2634 (obsolescent) Chemical plant equipment made from glass-fibre reinforced plastic (GRP), based on thermosetting resins
BS 4994 (superseded) Specification for design and construction of vessels and tanks in reinforced plastics
BS EN 13121 GRP tanks and vessels for use above ground. Design and workmanship
BS EN 13923 Filament-wound FRP pressure vessels. Materials, design, manufacturing and testing
ASME RTP-1 Reinforced thermoset plastic corrosion resistant equipment
ASTM D3299 Standard specification for filament-wound glass-fiber-reinforced thermoset resin corrosion-resistant tanks.
FRP flange installed at a fertilizer (phosphates) manufacturing facility in Australia
Image courtesy of Lucy Cranitch, GHD
10
Flanged joints are also widely used and flanges can be made from composite materials. The thicknesses of composite flanges depend on the design, but are generally greater than that of metal flanges. ANSI dimensions are commonly used for bolt patterns, and composite flanges can be manufactured to be compatible with most existing flanges made of PVC, steel and ductile iron. It is important to ensure composite flanges are flat to provide a good seal, so full flat-faced flanges with steel backing rings are often used. It is important to never mix full face composite flanges and raised face flanges as this readily results in leaks and failures. To avoid point loads caused by nuts directly in contact with the composite flange face, washers should be used under nuts, reliefs can be cut into the face of the flange and care must be taken with bolt torque. All cut outs for bolt holes must be sealed with resin to enhance durability. A number of standards are applicable to flanges.
2.3.7 Coatings and linings
Composites can be used in conjunction with concrete or steel to provide a corrosion-resistant lining or coating. This may be in the form of an internal corrosion protection to steel or concrete tanks, or as a protective layer on concrete floors or bunds. The following standards and guides are applicable to composite coatings and linings:
The following steps are typical in applying a bonded composite layer to concrete:
1. The concrete should be left 28 days to cure prior to application of any coating or lining.
2. Surface preparation of the substrate is important. Abrasive grit blasting (high pressure water or grit blasting) of the surface is required to improve bonding of the coating or lining.
3. Remove dust or grit by vacuuming and/or sweeping.
4. Wash the surface to remove oils, greases and other contaminants.
5. Dry the substrate.
6. Test for suitability of the coating or lining. Various tests are required depending on the substrate, for example pH, moisture and surface pull-off tests are required for concrete.
7. Fill voids with a resin-based filler.
8. Prime.
9. Apply the basecoat, consisting of resin reinforced with fibre mats or with fillers.
10. Apply the top coat, and if required spread silica aggregate to provide slip resistance.
Quality control during the coating or lining process is important. This should include wet film thickness tests, adhesion tests, coating sensitivity tests and resin gel time tests. If an additional conductive primer coat is applied, spark testing can be conducted once the basecoat is applied.
BS 6374-4 Lining of equipment with polymeric materials for the process industries. Part 4: Specification for lining with cold curing thermosetting resins
ACI 515.1R Guide to the use of waterproofing, damp-proofing, protection and decorative barrier systems for concrete.
AS 4087 Metallic flanges for waterworks purposes
AS 2129 Flanges for pipes, valves and fittings
AS 4331.1 (ISO 7005) Metallic flanges (steel flanges)
11
3 Composite product manufacturing
3.1 Components
Each component contributes to the overall properties, performance and appearance of the composite product. The precise type of materials and manufacturing process used are determined by the specific properties required for the final product. The following principles are essential for the production of good-quality composite products:
quality of materials—resins, glass fibres, additives and cores•
quality of design—quantity, orientation and suitability of fibres, suitability and •volume of resins, suitability and volume of additives, and suitability of cores
quality of manufacturing—consistency and control of the manufacturing and •curing processes. Full curing of the product is essential to attain optimum mechanical properties, prevent heat softening, limit creep and reduce fluid diffusion
quality of transport and installation practices.•
As the composite material itself is made at the same time as the part, quality assurance and inspection throughout these processes are essential.
3.2 Fibrereinforcement
The role of the reinforcement in a composite part is to carry the applied load. The factors which affect the contribution of the reinforcement to the composite properties are:
the type of reinforcement •
the form of reinforcement •
the quantity of reinforcement (resin-to-reinforcement ratio)•
the orientation of the reinforcement.•
Type: Many different types of reinforcement are available, including E glass, ECR glass, C glass, carbon, aramid (Kevlar) and many other less common fibres. Carbon fibre is used in the mining industry primarily to provide conductivity. The bulk of the reinforcements are made of glass. E glass is the most widely used fibre type due to its high strength and relatively low cost. C glass is used where excellent chemical resistance is required, usually in the form of a tissue as described in the table below. ECR glass is sometimes used to provide better resistance to chemicals.
The following table, taken from the Eurocomp Design Code, compares typical glass fibre properties. Compared to steel, glass fibres have approximately 2.5 times the strength with only one third of the density, and higher dimensional stability.
Table 2 Comparison of properties of glass fibre types and steel
Composite products consist
of a combination of fibres,
resins, additives, and in
some cases, cores.
Fibreglass borehole liner
Image courtesy of Teakle Composites
Property Eglass Cglass Steel
Specific gravity 2.54 2.50 7.8
Tensile strength (MPa) 3400 3000 1350
Tensile modulus (GPa) 72 69 200
Elongation (%) 4.8 4.8 10–32
Coefficient of thermal expansion (10–6/°C) 5.0 7.2 11.5
12
Form: Fibres are available in many forms, as described in the following table.
Table 3 Forms of reinforcement
Quantity: The manufacturing process has a large effect on the quantity of reinforcement in composites. Fabrics with closely packed fibres will give a higher volume fraction of reinforcement than those fabrics with large gaps between fibre bundles. The weight per unit area of reinforcement varies greatly from as low as 20 g/m2 for tissues, to 300 or 450 g/m2 for chopped strand mat, to 800 g/m2 for woven rovings, and to well over 1600 g/m2 for filament wound rovings. As a general rule, the strength and stiffness of a composite are proportionate to the quantity of reinforcement present. However, the laminate strength peaks at an optimum fibre volume of about 70 per cent, above which the strength declines due to a lack of resin to hold the fibres together.
Orientation: The tensile strength of fibres is greatest in longitudinal direction rather than width. Fibres must therefore be oriented in the direction of the load, and orientation can be designed to suit the particular loading requirements of the
Reinforcementform Description
Filament Individual fibres as initially drawn from the raw materials. Filaments are processed further before use.
Continuous strand Filaments gathered in continuous bundle. Continuous strands are processed further before use.
Milled fibre Continuous strands hammer-milled into lengths of 0.8 to 3 mm. Milled fibres are used as fillers and additives to control heat distortion and improve surface quality in compounding and casting.
Chopped strand Strands chopped to 5 to 60 mm lengths.
Roving Strands bundled together without twist. Rovings are used in various manufacturing processes including filament winding and pultrusion to give high strength in the direction of the fibres.
Yarn Twisted strands. Yarns are processed further before use such as in the manufacture of cloths.
Chopped strand mat Non-woven mat of chopped strands in random orientations. This reinforcement is widely used to give strength in all directions and good inter-laminar adhesion.
Continuous strand mat Non-woven mat of continuous strands in random orientations.
Tissue/veil Fine non-woven mat of continuous filaments that are uniformly distributed over the surface in random orientations. Tissues have relatively low strength. Their purpose is to support a resin-rich layer which protects the composite from moisture and chemicals, through preventing these fluids entering the laminate along the fibres.
Unidirectional fabric Rovings in one direction held together by a small amount of fibres woven or stitched at 90°. Unidirectional fabrics give strength in one direction.
Woven roving Rovings woven into a fabric in a particular pattern, usually a plain weave. Woven rovings give strength in two directions.
Cloth Fabric made from yarns woven in a particular pattern. Cloths give strength predominantly in two directions.
Stitched fabric Layers of fibres held together by stitching. Stitched fabrics give strength predominantly in two directions and have higher interlaminar strength than cloths.
Multi axial fabrics Fabric made from yarns or rovings in more than two directions. Multi axial fabrics give strength in three or more directions.
Needle punched and combi-mats
Fibreglass cloth composed in a swirl pattern
13
part. Unidirectional fibres run in one direction only, whereas fabrics have fibres in predominantly two directions, and chopped strands are oriented in all directions. The combination of reinforcements results in an anisotropic material, where its properties vary with direction.
3.3 Resins
While the fibres are the principal load-carrying members, the surrounding matrix of resin maintains them in the desired orientation and location. It also allows the applied load to be transferred between the reinforcing fibres. Another very important function of the resin is to provide a barrier to the environment, which protects the composite from the elements, such as water and chemicals.
Resins are also referred to as ‘polymers’ as they are made up of many (poly) long-chain molecules (mers). It is helpful to distinguish between two broad groups of polymers—thermoplastic and thermosetting. Thermoplastic polymers melt when heat is applied. This is because their long chains are not chemically bound together (i.e. they are not cross-linked). Thermosetting polymers, on the other hand, do not melt when heated because their long chains are chemically bound together (i.e. they are cross-linked). The resins used in composites (and those described here) are all thermosetting polymers.
There are a great variety of resins. The most common groups are polyester, vinyl ester and epoxy. Whilst fire retardant versions of these resins are available, phenolic resins are also used in situations where fire retardant properties are required. Resins are supplied to composite manufacturers in a liquid state, and during the manufacture of the composite part the resin is cured to form a solid. This process of curing the resin is a chemical reaction in which the cross-links are formed between the polymer chains. Before curing, the resin is in a liquid state as the polymer chains can flow easily. Once the polymer chains are linked together, the polymer chains can no longer flow and the resin becomes a hard solid.
Polyester and vinyl ester resins supplied to the composite industry are dissolved in styrene monomer. This reduces the viscosity, so that the resin flows more readily to allow ease of spreading and ensures full fibre-wetting, complete impregnation and minimal voids. The styrene monomer is also a key component in the curing process of polyester and vinyl ester resins, forming the cross-links between the polymer chains.
Polyesterresins provide good strength at a relatively low cost and are used widely in the marine industry, and in pools, spas, transport, casting, infrastructure and automotive applications. Various types of polyester resins provide a wide variety of properties relating to water and chemical resistance, weathering and shrinkage during curing.
Vinylesterresins are used primarily where improved water and chemical resistance, heat resistance or improved flexibility is required. Standard and high performance vinyl ester resins are widely used in the mining and chemical industries due to their high resistance to acids, alkalis and solvents.
Epoxyresins have a different structure to polyester and vinyl ester resins. They are usually sold as a two-pack system—Part A and Part B and these two parts must be mixed strictly in the ratios given by the supplier. The part A is the resin and the part B is the hardener and there are a number of different types of each. Epoxy resins are not dissolved in styrene monomer and do not shrink as much as polyester or vinyl ester resins when they cure.
Epoxy Resins provide particularly good mechanical strength and adhesion and have good stiffness, toughness, heat resistance and water resistance. Epoxy resins tend to be more expensive than polyester resins. Epoxy resins are widely used in piping and infrastructure.
It is helpful to distinguish
between two broad groups
of polymers—thermoplastic
and thermosetting.
Spent Electrolyte Tank installed at Cause Nickel, Kalgoorlie
Image courtesy of Marky Industries Pty Ltd
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3.4 Additives
The following additives can be incorporated into the resin:
Fillers are powders used to add bulk to the resin, which reduces costs and enhances the compressive strength of the composite material. Fillers can also reduce the exotherm (heat build-up) and shrinkage during curing. Fillers may be added to the resin at up to 50 per cent by weight (for dense fillers) or 35 per cent by volume. Addition of filler over these amounts should be avoided as it reduces the flexural and tensile strengths, as well as the chemical resistance of the composite.
Thixotropes are powders added to the resin to allow it to hold up onto a vertical surface. The addition of thixotropes is required when the resin must not run or sag when it is applied to steep moulds or to vertical walls (such a lining of a tank). Thixotropes allow the resin to flow when a shear force is applied (i.e. when resin is forced through a spray gun), and prevent the resin from flowing when the force is removed.
Pigments can be incorporated into the resin to produce a specific colour and to provide UV resistance.
UVinhibitorsandabsorbers can be added to the resin to improve its UV resistance.
Flameretardants can be added to the resin to improve its resistance to fire.
Inhibitors are chemicals added to the resin to slow down the curing reaction, so more time is available to work with the resin during manufacture before it cures. As resins can cure in storage, inhibitors help to extend the resin’s storage life.
Promotersandaccelerators are chemicals added to the resin to speed up the curing reaction to enable manufacture in a reasonable timeframe.
While additives improve many properties of composites, they can also impair other properties at the same time. For example, some fire retardants can reduce the composite’s resistance to weathering and chemicals. Additives should therefore be carefully selected.
3.5 Cores
Some composite parts incorporate core materials, primarily to impart stiffness without increasing weight. Cores may also be used to increase the impact strength, fatigue resistance, thermal insulation and sound deadening effect. For a panel, the flexural stiffness is proportional to its thickness cubed, which means as thickness increases, stiffness increases dramatically. Cores can be used in specific areas of a structure where extra stiffness is required (e.g. stiffening ribs) or throughout the area of a laminate as a sandwich panel.
A sandwich panel consists of a core with reinforcement and resin on either side (skin). In a sandwich panel, the adhesive layers between the skins and the core must be able to transfer the loads and therefore be at least as strong as the core material. Without a good bond, the three components work as separate beams and the stiffness is lost.
Figure 1 shows a sandwich panel under a bending load. As a result of the bending, the upper section is placed under compression, the lower section in tension and the core in shear. Shear strength and stiffness of a core material are important.
Fibreglass drill rod joint assembly in Instron testing machine
Image courtesy of Teakle Composites
Figure 1. Bending a sandwich panel
Compression
Shear
Tension
Skin
Core
Skin
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3.6 Exampleofacompositelaminate
Figure 2 shows the wall of a composite tank or pipe to illustrate the layers that make up the composite material.
The reinforcement sequence is often given on drawings in the format below, in order from the internal surface to the outer surface:
C/2M/4(MW)/M/C*
Reinforcements: C = 40 g/m2 C glass or synthetic tissue such as Nexus tissue.M = 450 g/m2 E glass powder bound chopped strand mat. W = 800 g/m2 E glass woven roving. C* = 40 g/m2 C glass or synthetic tissue such as Nexus tissue with
resin containing wax and UV inhibitors or pigment.
3.7 Manufacturingprocesses
Formation of a composite product involves combining layers of reinforcement with resin. A chemical reaction of the resin then converts it from a liquid to a solid to bind everything together as a whole. This chemical reaction is called curing, and is activated by catalysts for polyester and vinyl ester resin and a hardener for epoxy resins. The catalyst or hardener must be added to the resin prior to combining the resin with the reinforcement. It is important to achieve good cure of resins in a timely manner. This can be achieved through adjusting the chemicals involved in curing, including the inhibitors, accelerators and catalyst or hardener, and through taking account of the temperature during manufacture. There are a number of different manufacturing processes.
Handlayupinvolves the manufacture of a part in a mould. Resin is first applied to the mould surface, then layers of glass which are wet by the resin and consolidated with rollers.
VacuumInfusionProcessing(VIP) involves the lay up of dry glass on a mould. A flexible film (‘bag’) is then laid over the glass and sealed to airtight and then the resin is pulled through the glass under the force of a vacuum.
ResinTransferMoulding(RTM) uses two matched moulds – a bottom mould and a top mould. This process therefore produces parts with two finished surfaces.
Filamentwinding is performed on a machine that winds glass fibres onto a cylindrical mandrel in a prescribed pattern to form the desired finished shape (e.g. a pipe). Fibres in the form of continuous rovings are routed through a bath of resin before reaching the mandrel. After curing, the tube is removed from the mandrel.
Pultrusion is used for the manufacture of products of a constant cross-section. The glass fibres are pulled through a die (as compared to ‘extrusion’ where the material is ‘forced’ through a die) in a continuous process, injected with resin, shaped by the die and then cured.
3.8 Manufacturers
Australia’s composites industry is represented by Composites Australia Inc. Composites Australia is a membership-based, not-for-profit association dedicated to increasing the awareness and general usage of composites in Australia. Composites Australia has access to an extensive database of organisations in the Australian composites industry including raw material suppliers, manufacturers, designers and engineers, research and development agencies and training and education providers. See section 9 of this guide for contact details for a number of Australian composite product manufacturers, or contact Composites Australia at:
Level 15, 10 Queens Road, Melbourne Victoria 3004 Telephone: + 61 3 9866 5586 or 1300 654 254 Facsimile + 61 3 9866 6434 [email protected] www.compositesaustralia.com.au
Figure 2. An example of the makeup of a composite wall
C = TissueM = Chopped Strand MatW = Woven Roving
Alternating chopped mat & woven roving to desired
thickness
Vinyl Ester Resin resin/wax topcoat
C M M W M M M M M C
Primary corrosion
barrier
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4 Australian case stories
The following tables provide examples of where composites have been used in Australia.
Table 4 Current composite components in Australian mining and minerals processing plants
Enduser Industry Location Components
Rio Tinto Aluminium Gladstone, QLD Hoods for fume tanks, pipes, claustra walls in pot rooms
Adelaide Chemical Company
Copper Burra, WA Acid leach tanks (agitated), tank, slurry pipe, grating, gas cooling tower
Xstrata Copper Refineries
Copper Townsville, QLD Electrolyte pipework, polymer concrete Electrolytic cells, galvanizing tank, acid storage tank, grating, wall cladding, roofing
BHP Billiton, Olympic Dam
Copper, uranium, gold, silver
Roxby Downs, SA Mixer settlers, Jameson cells, pipes in solvent extraction and electrowinning, bund linings, ducts, electrolytic cells, stack, tanks, electrostatic mist precipitators
Kanowna Belle Gold Gold WA Roaster stack, fan to stack ducting
Posgold Ltd Gold WA Tanks
Nystar Lead Port Pirie, SA Roof and wall sheeting, cable ladder to support cabling
Heraeus Ltd Metals VIC Fume extraction ducting for precious metals recovery plant
Rennison Mine Mining Burraga, NSW Pump
Centaur Mining — Minproc/Davy JV Cawse Nickel
Nickel WA Settler tank and lids
Kombalda Nickel Smelter Nickel WA Process equipment in the sulphuric acid plant
Kalgoorlie Nickel Smelter Nickel Kalgoorlie, WA Electrostatic mist precipitators, scrubber
BHP Billiton, QNI Nickel Yabulu, QLD Leach tanks, linings in the stage 2 organic running tank and the cobalt sulphate discharge storage tank, lining of gas cooler condensers
Sunmetals Zinc Townsville, QLD Cooling towers, grating
Xstrata Zinc and lead Mt Isa, QLD Froth crowders for flotation tanks
Nyrstar Zinc Hobart, TAS Leach reactor tanks and wash down tanks, electrolytic cells, spent tanks, launders, cooling towers, tank covers, cell bearer, baffles for tank, copper sulphate reactor tanks, mercury removal towers, foreshore stacks, pipework, precipitators, concrete tank linings, tanks, agitator blades, segmented clarifier covers, tank, dampeners, butterfly valve, gas cooling towers and internals.
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Table 5 Current composite components in Australian chemical processing plants
EndUser Industry Component
Ferro Corporation Ammonium and sulphur products
Sieve tray scrubbing tower
Nufarm Chloralkali Plant Chloralkali plants Sodium hypochlorite storage tanks, chlorine headers, chlorine scrubber, anolyte tank
Incitec Pivot Sulphuric acid and fertilizer
Settlers, pipes, radial flow scrubber, 2 gas cooling towers, ducts, drying tower inlet manifold, 8 electrostatic mist precipitators
Alcoa General chemical Tank
Australian Chemical Company
General chemical Mist eliminator vessel for copper roaster
NSW Brickworks General chemical Freestanding insulated fume stack
Chemplex effluent treatment plant
General chemical Pipework
Feld Proctor Gamble General chemical Tank
ICI Operations General chemical Tank
Koka Chrome Ind. Co Ltd General chemical Fume extraction ducting for plating plant
Metalok (S) Pte Ltd General chemical Plating line fume exhaust ducting
Pritcorp Sdn Bhd fatty alcohol plant
General chemical HCl vapour scrubber, glycerine reactor/settler, acidulated soap storage surge tank, tank
SCM Milenium Chemicals General chemical Titanium dioxide stack, chlorine scrubber
Tiwest General chemical Titanium dioxide stack, plant pipework
Toxide Group Services General chemical Ducting (fume extraction), stack (steel supported)
Unizon Singapore General chemical 3600 cfm vertical scrubber
Delta (BHP) EMD Plant Manganese dioxide Electrolytic cells, storage tanks for fresh and spent electrolyte
Cold Rolling Sdn Bhd Steel Pipe (for pickle line), lining of steel preflux tank, lining of steel acid pickling tank
Tubemakers Steel Acid pickling tank
BHP Pellet Plant Steel Waste gas tower, fine scrubber, quench tower, fine scrubber demister, pre-quench scrubber
Minnehasa Sulphuric acid Mercury removal tower.
50 m Composite Fibre Conveyor. Modulus design for easy transport, assembly and dismantling.
Capacity: 400 tone per hour Belt speed: 2 m/s Conveyor span: 24 m Number of spans: 2 Incline angle: 20 degrees
Image courtesy of Wagners CFT Manufacturing Pty Ltd
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5 Technical performance
This section is particularly aimed at people who are relatively unfamiliar with composites, and for those who would not normally have considered them for applications. This section aims to raise awareness of the properties of composites and the factors to be considered in their use.
Properties of composites and their raw materials given in this document are typical or average figures. It is important to use the actual product data from the suppliers when designing products with composites.
5.1 Design
Composites are less successful when they are used to replace another material without considering its specific design. For example, composite pipes are less stiff than metallic pipes, and therefore the supports need to the placed more closely together when installing composite pipes. Such factors have been considered in the various design standards for composites.
It is important to engage composite designers and also have 3rd party verification where appropriate. Specialist designers can be contacted directly or through the composite manufacturer. Consideration of the various loads must be performed diligently and by those who have the background and knowledge of the materials and structures.
Section 10 of this guide contains details for a number of Australian composites design and engineering service providers.
5.2 Standards
Standards can be accessed at www.sai-global.com and other online stores.
AS 3571 Plastics piping systems—glass-reinforced thermoplastics (GRP) systems based on unsaturated polyester (UP) resin—pressure and non-pressure drainage and sewerage; and pressure and non-pressure water supply
AS 2634 (obsolescent) Chemical plant equipment made from glass-fibre reinforced plastic (GRP), based on thermosetting resins
AS/NZS 2566 Buried flexible pipelines
AS 2376.2 (superseded) Plastics building sheets—glass fibre reinforced polyester (GRP)
AS 2424 (superseded) Plastics building sheets—general installation requirements and design of roofing systems
AS/NZS 4256.3 Plastic roof and wall cladding materials—glass fibre reinforced polyester (GRP)
AS/NZ 2924 High-pressure decorative laminates—sheets made from thermosetting resins—classification and specifications
AS/NZS 3572 Plastics—glass filament reinforced plastics (GRP)—Methods of Test
BS 4994 (superseded) Specification for design and construction of vessels and tanks in reinforced plastics
BS 6464 Specification for reinforced plastic pipes, fittings and joints for process plants
BS 6374-4 Lining of equipment with polymeric materials for the process industries, Part 4: specification for lining with cold curing thermosetting resins
BS EN 13121 GRP tanks and vessels for use above ground. Design and workmanship
BS EN ISO 14692 Petroleum and natural gas industries—glass-reinforced plastics (GRP) piping.
Finite element buckling analysis of a large fibreglass nozzle under external pressure
Image courtesy of Teakle Composites
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5.3 Guides
5.4 Relativeperformanceofmaterials
Table 6 Composite properties* compared to other materials
* The properties in this table are indicative only
ACI 440.1R-01 Guide for the design and construction of concrete reinforced with FRP bars, Committee 440, American Concrete Institute, Farmington Hills, MI. (May 2001), www.aci-int.org
ACI 515.1R A guide to the use of waterproofing, damp-proofing, protection and decorative barrier systems for concrete.
A guide for Flowtite GRP pressure and non-pressure pipe, engineering design guidelines, Iplex Pipelines Australia, www.iplex.com.au
Material
Randomglass
composite
Bi-directional
glasscomposite
Uni-directional
glasscomposite
Aramidcomposite
Carboncomposite Aluminium Mildsteel
Stainlesssteel
Fibre content by weight (%)
25–50 45–70 50–90 40–55 40–59 0 0 0
Density (g/cm3) 1.4–1.9 1.5–1.9 1.6–2.2 1.4 1.5 2.6–2.8 7.8 7.92
Tensile strength (MPa )
48–170 190–440 410–1730 345–2067 410–2700 80–480 200–800 190–552
Tensile modulus (GPa )
6–18 12–25 21–62 19–80 30–180 70 190–210 193–200
Compressive strength (MPa)
115–170 98–280 210–480 102–172 360 84–338 410–480 220–552
Compressive modulus (GPa)
6–9 8–17 - 16–19 - - - -
Flexural strength (MPa)
90–340 200–450 690–1860 301 378 310 413 551
Flexural modulus (GPa)
5–17 9–23 27–48 15 28 69 207 193
In-plane shear strength (MPa)
62–96 55–83 110–140 - - 276 - -
In-plane shear modulus (GPa)
2.8–3.0 3.0–4.0 4.1–5.2 - - 26–30 75–80 -
Tensile elongation (%)
1.6–2.1 3–4.5 2.4 2–2.6 1–1.5 2.5–23 22–37 40
Thermal conductivity (W/m°C)
0.15–0.52 0.19–0.35 0.3 (in fibre direction)
1.7 (in fibre direction)
1.4 (90° to fibres)
34 (in fibre direction)
0.8 (90° to fibres)
140–200 43–50 110
Coefficient of linear thermal expansion (10–6/mm/°C)
18–33 9–16 9 (in fibre direction)
14 (90° to fibres)
–4 (in fibre direction)
57 (90° to fibres)
–0.5 (in fibre direction)
25 (90° to fibres)
23 11–14 16–18
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Figure 3. Stress strain curves of various materials
5.5 Servicelife
It is typical to specify a minimum design life of 20 years of continuous operation for composite process equipments in the mining industry. In other industries, such as underground water pipelines, a design life of 100 years is more typical.
5.6 Mechanicalproperties
5.6.1 General
The mechanical properties of composites depend on a number of factors:
resin-to-glass ratio•
orientation of fibres•
method of fabrication.•
Composites are anisotropic, which means their properties vary with direction. For the mechanical properties discussed below, it is important to remember the values will be different in the direction of the fibres to that normal to the fibres. In terms of strength, composites have the greatest strength in the direction of the fibres. In the direction normal to the fibres, the resin and the fibre-resin interface determine the strength, which may be one or two orders of magnitude lower than in the direction of the fibres. Designers must therefore avoid stress systems that result in significant loads normal to the fibres.
Detailed design literature and programs are available to estimate the effect of combinations of fibres in different directions on the overall capacity of the composite. Calculations of the anisotropic properties of composites require the application of the theory of anisotropic elasticity or use of simpler means to obtain reasonable estimates. For this type of work, the reader is referred to the various standards, guides and software programs available.
5.6.2 Strength
The rule of mixtures is used to calculate the strength of composites. This rule takes into account the relative fractions of the strength of both the fibres and resin.
Tensile strengthThe fibres in composites are the principal contributor to the tensile strength of the component. The resin has significantly lower strength and acts to bind the fibres together and transmit the loads between them.
Compressive strengthThe strength of the resin has a much greater influence on the compressive strength of composites than it does on the tensile strength. This is because the resin must have sufficient compressive strength to prevent the fibres from undergoing local buckling or kinking under compression. The resin also helps to prevent failure through longitudinal splitting. The resistance to buckling under compression can be improved at the design stage by incorporating edge flanges, double curvature and troughs.
Anti-static cable tray supplied for the Blacktip Offshore Gas Production Platform
Image courtesy of Exel Composites
Stre
ss
Yeild and ultimate strength can be considered the same. Design is to ultimate using safety factor.
Stre
ss
Strain
A. Composites
Yeild strength lower than ultimate. Design is to yeild using safety factor.
Strain
B. Common metals
Non-linear curves depending on polymer.
Stre
ss
Strain
C. Non-reinforced plastics
21
Shear strengthWhen subject to shear stress, the load-bearing abilities of the fibres and matrix, and the extent to which stresses are transferred between them, affects the stiffness and strength of composites. Most composites contain planes of weakness between the layers which can result in interlaminar failure in shear. The property of interlaminar shear strength describes this behaviour. Composites made from fabrics which have some fibres in the z direction (through-wall thickness), such as stitched cloths or chopped strand mat, are more resistant to interlaminar failure than composites made from fabrics without fibres in the z direction.
Flexural strengthFlexure/bending involves a combination of tensile, compressive and shear forces. At a simple level, the tensile, compressive and shear properties of the materials can be used in the design for flexure. However, flexural strength is seldom the limiting criterion in composites, as stiffness more often dominates the design.
StiffnessThe stiffness of composites is low compared to steel, although carbon fibre-reinforced composites are an exception. Since the tensile strength-to-weight ratio of composites is high and stiffness low compared to steel, stiffness tends to be the key determinant in structural design with composites.
The stiffness of composite parts can be increased by:
selecting fibres with a higher elastic modulus (e.g. carbon fibres) •
sandwich construction. Since stiffness is a function of thickness, cores can be •incorporated into a composite to provide rigidity, while keeping the weight low
localised increase in thickness, for example, progressive thickening along a •local edge or flanging along the edge of a panel
ribs can be incorporated into the reverse side of the part•
compound curves or local corrugations. A folded plate construction can be used •to achieve the required stiffness from the overall geometry of the structure.
For most composites with more than about 50 per cent volume of fibres, the stiffness in tension is dominated by the fibres, and the resin contribution is insignificant.
5.6.3 Fatigue
Fatigue is the progressive damage that occurs when a material is subject to cyclic loading and when the stress values of each cycle are less than the ultimate stress limit. For example, in the mining and chemical industries, tanks and process vessels with internal agitators can be subject to constantly imposed stress cycles and are therefore susceptible to fatigue.
The fatigue behavior of steel tends to involve intermittent propagation of a single crack, while the material close to the crack is virtually unchanged. In contrast to this, cyclic loading of composites results in the formation of many micro-sized cracks. Since the small cracks in composites are spread uniformly in the material rather than concentrated in a single area, a greater area of material is involved in resisting fatigue failure. Furthermore, as the formation of each small crack absorbs energy, composites tend to have good fatigue resistance compared to most metals. However, as damage accumulates, a critical point is eventually reached at which the material can no longer sustain the applied load and failure occurs.
To improve the fatigue resistance of composites, resins which are tougher and have greater resistance to micro-cracking should be used, and the amount of voids and other defects in the laminate should be minimised. It is also important to ensure the load normal to the direction of the fibres is minimised.
Flowtite™ GRP Pipe (Continuous Filament Wound) installed in South-East Queensland’s western corridor recycled water pipeline
Image courtesy of Iplex Pipelines Pty Ltd and Fibrelogic™ Pipe Systems
