lightweighting using textiles and fibres

Report for the International Fibre Centre, Industry Association Consortium

Lightweighting using Textiles and Fibres

Dr Tony Pierlot and Dr Niall Finn

March 2013

FUTURE MANUFACTURING FLAGSHIPwww.csiro.au

2 Lightweighting using Textiles and Fibres

CSIRO Future Manufacturing Flagship

Copyright and disclaimer© 2013 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO.

Important disclaimerCSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.

AcknowledgmentFunding support for the preparation of this report from the International Fibre Centre through the Industry Association Consortium is greatly appreciated.

We would also like to thank Ms Kerryn Caulfield of the Technical Textiles & Nonwoven Association and Composites Australia for inviting CSIRO to undertake this analysis.

Lightweighting using Textiles and Fibres 3

Executive summary Achieving more with less resource usage will be increasingly important in the future. Reductions in input materials, labour to manufacture, energy use through a product’s lifecycle, and designing for recycling or sustainable disposal are key requirements to achieve this goal. This lifecycle thinking is being applied to all forms of manufactured products and services. Lightweighting is often an effective strategy to achieve this outcome. Reducing the weight of a product or structure usually reduces material consumption, and often but not always reduces the amount of energy, chemicals or water consumed during manufacture. Less weight requires less energy to transport the final product and requires less energy throughout a products life if it needs to move, e.g. an aircraft, motor vehicle, or robot. Direct material costs represent a significant fraction of most products; representing as much as 70% of the cost of nonwoven roll goods. Achieving similar or better functionality and performance while using less input materials can significantly alter the economics of production and use.

Lightweighting often requires the redesign of the product. This provides an opportunity to improve the design, manufacturability, and usability, to reduce labour inputs and improve the performance requirements of the end product. Textiles and fibres are essential materials in this paradigm. As an example, carbon fibre composites are increasingly used to replace parts of aircraft traditionally constructed from aluminium or steel. This replacement makes the aircraft lighter and therefore significantly reduces the fuel use during flight.

This report provides an overview of lightweighting using textiles and fibres. It is not exhaustive nor is it pitched at experts in the field; it is intended as an introduction to the field of lightweighting using textiles and fibres to bridge the gap and open the field for discussion and interaction between the various palyers along a product’s lifecycle enabling better response to the changing marketplace. Whilst some application may require the development of new materials, many lightweight solutions can be achieved using existing textile and fibre products in innovative ways.


ContentsExecutive summary 3

1 Introduction 6

1.1 Global megatrends 6

1.2 Lightweighting 8

1.3 Role of fibres and textiles in lightweighting 9

2 Lightweighting applications & examples 14

2.1 Auto and aero 18

2.2 Major infrastructure 20

2.3 Pressure vessels and piping 22

2.4 Air supported and inflated structures 23

2.5 Airbeams 25

2.6 Nanofibrous membranes 26

2.7 Auxetic textiles 26

3 Concluding remarks 27

Appendix A Fibre reinforced composites 28

References 32


Figure 1: Interlinked global megatrends 6

Figure 2: Examples of bicomponent fibres 9

Figure 3: Nanofibres generated from a rotating electrode 10

Figure 4: Example of a force extension curve for a fibre 11

Figure 5: Indicative specific strength and specific modulus of materials 13

Figure 6: Image of a rowing scull showing multi-fabric layer composite 14

Figure 7: Burj Al Arab hotel, Dubai 15

Figure 8: Wimbledon roof 15

Figure 9: Fuel bladder located in Antarctica 15

Figure 10: Silver coated nylon fibres 17

Figure 11: Athlete training using interactive sleeve 17

Figure 12: One-piece carbon fibre composite wheel 19

Figure 13: Knitted seat frame cured in desired shape 19

Figure 14: Typical stress-strain curves for glass and carbon fibre 21

Figure 15: Burswood dome at Burswood casino 23

Figure 16: Kite for kitesurfing showing airbeams used in structure 24

Figure 17: Lightweight beam design 25

Figure 18: An example of an auxetic textile structure 26

Figure 19: Impact of megatrends on textile and fibre industry 27

Figure 20: Composite modulus as a function of fibre volume 27

Figure 21: Indicative composite properties 29

Figure 22: Composite tensile strength 29

Figures

TablesTable 1: Indicative properties of materials 12

Table 2: Demand for carbon fibre (1000 tonnes) 18

Table 3: Properties of thermosetting resins 28

Table 4: Properties of thermoplastic resins 28

Table 5: Fibre orientation factor 30

Table 6: Various methods used to form fibre reinforced composites 31

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This report provides an overview of lightweighting using textiles and fibres. It is not comprehensive nor is it pitched at experts in the field. This report is intended as an introduction to the field of lightweighting using textiles and fibres to help bridge the gap between the various players along a product’s lifecycle enabling better response to the changing marketplace. Whilst some applications may require the development of new materials, many lightweight solutions can be achieved using existing textile and fibre products in innovative ways.

1.1 Global megatrends

When thinking about the future, “probable”, “plausible” and “possible” may be used to describe the increasing uncertainty surrounding the occurrence of forecast scenarios with the former descriptor being a subset of the latter. “Possible” captures every conceivable or speculative event but may lack credibility due to the absence of evidence to support and to substantiate such forecast scenarios. Decision makers may be reluctant to make important decisions based on these scenarios due to lack of strong supporting evidence. A “probable” forecast has little uncertainty as it is well supported by empirical evidence, such as historical data. However, given the often limited time series data of emerging important trends, probable scenarios are unlikely to provide insightful or novel descriptions of the future. A “plausible” forecast resides between the two extremes of “possible” and “probable”.

CSIRO recently released its Global megatrends 2012 revision, Our Future World: Global megatrends that will change the way we live”1. This document provides a plausible forcast, a balance of evidence and imagination and presents a narrative of the future constructed from six interlinked megatrends that are anticipated to play out over the next 20 years. A megatrend is defined as a significant shift

in environmental, economic and social conditions that will substantially change the way people live in the future. Megatrends are therefore important to contemporary decision making and may require a change in business processes, business and governance models, and social systems.

The six interlinked megatrends identified by CSIRO are given in Figure 1 and summarised below.

1 Introduction

Figure 1: Interlinked global megatrends


More from less: The earth has limited supplies of natural minerals, energy, water and food resources that are essential for human survival and maintaining lifestyles. Many of these resources are being depleted at sometimes alarming rates. Climate change will place pressure on water and food production systems. At the same time population growth and economic growth are placing upward pressure on demand. For some natural resources, demand is going up and supply is going down. Many other resources are under pressure.

Humanity has an incredible ability to innovate and adapt. Through science and technology, companies, governments, and communities will discover new ways of ensuring quality of life for current and future generations within the confines of the natural world’s limited resources.

Going, going…gone?: Coming decades will see billions of people added to the world population and the continued rapid industrialisation of the emerging economies. Many habitats, plant species and animal species are in decline or are on the brink of extinction. Greenhouse gas emissions and climate change herald potentially unforeseen consequences on our natural and human systems. The Going, going… gone? megatrend explores the perilous situation of the world’s ecological habitats and biodiversity.

As these natural assets are not directly traded in the market place it is often difficult to assign a monetary value to them. However in cultural terms, they have enormous value and are at risk of being lost. Whilst biodiversity is in decline, pressure to respond is mounting. Governments, companies and societies are accepting the challenge, more than ever before, to protect habitats and reduce greenhouse gas emissions. Future decades are our chance to make a difference.

The silk highway: Coming decades will see the world economy shift from west to east and north to south. Rapid income growth in Asia and to a lesser extent, South America and Africa will see billions of people transition out of poverty and into the middle income classes.

China and India have continued to rapidly grow their economies, with strong growth forecast by many analysts over the coming decades. This will build new export markets, business models and cultural ties to Australia. From these countries will flow tourists, funds, ideas and people with Asian ancestry to create

a more culturally diverse Australia. Australia is well positioned culturally, economically and geographically to be part of this new world as the ancient Silk Road becomes the Silk Highway.

Forever young: The aging population is an asset. Australia and many other countries that make up the OECD have an aging population. Elderly citizens provide a wealth of skills, knowledge, wisdom and mentorship. This resource is not fully utilised by governments, companies, communities and families. This megatrend could have been called “hidden treasure”.

This asset is not without its challenges such as escalating healthcare expenditure and the widening retirement savings gap. This megatrend explores the likelihood that people will retire later and in a tapered manner with increasing spend to combat age related illness.

Virtually here: The world is becoming more connected. People, businesses and governments are increasingly moving into the virtual world to deliver and access services, obtain information, perform transactions, shop, work, and interact with each other.

Online retail and teleworking in Australia are forecast to grow rapidly and have the ability to change labour markets, retail business models, city design and transportation. Increasing digital connectivity between people, institutions and gadgets will lead to new meta-level functionality, and changed societal, organisational, and individual behaviours.

Great expectations: This is a consumer societal and cultural megatrend that explores the rising demand for services and experiences over products and social relationships. It also captures the expectation of personalised services that meet an individual’s unique needs but are delivered en masse. This megatrend will have implications for the retail sector and government and private sector systems delivering human services. People will expect more personalised, better and faster services and seek higher-end experiences due to income growth and oversupply of mass consumables.

A more comprehensive narrative of these megatrends is provided in the original document1a.


The six megatrends are clearly interconnected with each influencing the other. All will have an impact on the Australian Textile and Fibre industry, from material supply, production and supply chains, product types and functionalities, through to the business models required to deliver products and services including waste disposal and recycling or disassembly.

The Australian Nonwovens Manufacturing Technology Roadmap2, developed with close consultation with industry, identified the lowering of production cost (where input fibre materials represent the most significant cost, e.g. by using recycled fibre), increasing value-add of products and making the industry more eco-efficient as key strategic imperatives.

The European Commission late last year published3 a “Manifesto for a Resource Efficient Europe” that states “In a world with growing pressures on resources and the environment, the EU has no choice but to go for the transition to a resource-efficient and ultimately regenerative circular economy”. A circular economy (as opposed to a linear, “take-make-dispose” economy) is an industrial economy that by design or intention, is restorative and where the two types of material flows are designed to re-enter the biosphere safely (biological nutrients/materials) or circulate at high quality without entering the biosphere (technical nutrients/materials)4. The Manifesto also highlights the need for:

“Creating better market conditions for products and services that have lower impacts across their life-cycles, and that are durable, repairable and recyclable, progressively taking the worst performing products off the market; inspiring sustainable life-styles by informing and incentivising consumers, using the latest insights into behavioural economics and information technology, and encouraging sustainable sourcing, new business models and the use of waste as raw materials.”

“Providing clear signals to all economic actors by adopting policy goals to achieve a resource-efficient economy and society by 2020, setting targets that give a clear direction and indicators to measure progress relating to the use of land, material, water and greenhouse gas emissions, as well as biodiversity. Such indicators must go beyond conventional measures of economic activity, help guide the decisions of all actors, and assist public authorities in

timely action. All organisations above a meaningful size and impact must be held accountable to measure and report key non-financial progress indicators on a comparable basis.”

Achieving more with less resource usage will be increasingly important in the future. For example, reductions in input materials, labour to manufacture, energy use through a product’s lifecycle, and designing for recycling or sustainable disposal are key requirements. This lifecycle thinking is being applied to all forms of manufactured products and services. Lightweighting is often an effective strategy to achieve this outcome. Reducing the weight of a product or structure reduces material consumption, often, but not always, reduces the amount of energy, chemicals or water consumed during manufacture. Less weight requires less energy to transport the final product, throughout its life if the product needs to move e.g. an aircraft, motor vehicle, or robot. Direct material costs represent a significant fraction of most products; e.g. representing as much as 70% of the cost of nonwoven roll goods or 80% of an automobile5. Achieving similar or better functionality and performance while using less input materials can significantly alter the economics of production and use.

Lightweighting often requires the redesign of the product. This provides an opportunity to improve the design, manufacturability, usability, to reduce the labour required for installation or to add new or improved functionality and performance requirements to the end product. Textiles and fibres are essential materials in this paradigm. As an example, carbon fibre composites are increasingly used to replace parts of aircraft traditionally constructed from aluminium or steel. This replacement makes the aircraft lighter and therefore significantly reduces the fuel use during flight. To aid in the development of lightweight solutions and innovations, Centres have been established both in Australia6 and overseas7.

1.2 Lightweighting


1.3.1 FIBRE FORMATION

Fibres used to produce textiles typically have a diameter around 20 µm with a length to diameter ratio greater than 1000. The common natural (staple) fibres are wool, with a diameter between 15-50 µm and length of around 100 mm, and cotton, with a “diameter” of around 15 µm and a length of 30 mm. Synthetic polymer fibres can be produced in a similar range of diameters and lengths but also include continuous filaments. Glass, ceramic, and carbon based fibres are also readily available as staple (short) or continuous fibre lengths. Synthetic fibres are typically produced with circular cross section but can be produced in a variety of shapes for various applications, for example dog bone, triangular, tape, or with a hollow core.

Once fibres have been formed they can be manipulated to produce various higher order textile structures through mechanical processing. These structures include webs, bundles of aligned fibres (tow if continuous filament, roving if staple fibre,) yarns and plied yarns. Further mechanical processing may then be undertaken to produce braided, woven, knitted, or nonwoven fabrics. These fabrics are often processed to add additional functionality (e.g. water proofing by applying a small amount of polymer; usually <5% by mass), or coated or infused with a polymeric resin to produce a composite structure. The resins used to form the composite structure can be thermoplastic (meltable polymer) or thermosetting (hardens through chemical reaction).

Traditionally, synthetic fibres were produced using a homogeneous material, for example polyester, or intimate blends of materials. The need for improved functionality and lightweight products has seen the development of more complex systems of production. An example is extrusion processes that allow different materials or polymers to be brought together and assembled into a fibre with a heterogeneous structure such as bicomponent structures including, core sheath, side by side, segmented, citrus, and islands in the sea (Figure 2).

The two polymer melts are brought together at the spinneret, which is much larger than the desired fibre diameter. Drawing the molten fibre followed by cold drawing reduces the fibre diameter whilst still retaining the original physical structure formed at the spinneret. The core sheath and side by side arrangements are the simplest and allow,

for example, the production of a fibre that has a strong component (e.g. core) with a lower melting temperature component (e.g. sheath). The lower melting temperature component can be melted to glue the fibres together to form a lightweight, lofty and resilient batt or fabric for thermal or acoustic insulation or high liquid absorbency.

Sea-island and citrus fibres are often used to produce fabrics containing microfibres, fibres less than 10 mm in diameter, frequently less than 1µm. These fine fibres are difficult to process economically through conventional textile processing equipment as they are very flexible with low strength, leading to dense entanglements (neps) and high breakage. Production of a bicomponent fibre at conventional diameters allows processing into fabrics followed by a fibre splitting process to produce microfibres. The citrus and segmented fibres are usually mechanically split with water jets or needle punching as the two fibre components are chosen so that adhesion between them is poor. Sea-island fibres are designed so that one component can be removed via dissolution in a solvent, often water. In some cases up to 1000 sub-filaments within each fibre are spun and with multiple drawing stages these sub-filaments can be reduced to submicron-scale dimensions, less than 100 nm8.

Nanosized fibres (less than 100 nm diameter) can also be formed by an electrospinning process. In the simplest form of the process, polymer dissolved in a solvent is pumped through a fine needle to which a high d.c. voltage of between 10 and 30 kV has been applied. A grounded collector surface, placed a few hundred millimetres away, is used to capture the nanofibres. The electric field strength is concentrated at the needle tip so that when a drop of polymer solution emerges from the needle,

1.3 Role of fibres and textiles in lightweighting

Figure 2: Examples of bicomponent fibres. From left to right core sheath, citrus, islands in the sea and side by side.


it becomes highly electrified with charges induced and evenly distributed over the surface. Under these electrostatic forces, repulsion occurs between the surface charges and Coulombic forces from the external electric field so that the droplet becomes distorted in a conical shape known as the Taylor cone. Once the force reaches a threshold that overcomes the surface tension of the polymer solution, a liquid jet is ejected from the needle tip. During transit to the collector electrode, the liquid jet undergoes a whipping and stretching process at the same time as solvent is evaporated to produce long nanometre diameter filaments.

Producing electrospun fibres using a single needle or even multiple needles is an extremely slow process and with production rates of a few mg/hour, products produced are only useful for research purposes. One commercially available system with significantly higher production is from the Elmarco company9 (Czech Republic). This system operates through d.c. voltage being applied to a rotating cylinder electrode partially immersed in a bath of the polymer solution (Figure 3). As the cylinder rotates, a thin film of solution is formed on the cylinder. Under the action of the electric field, any random fluctuations in film thickness are amplified to produce multiple Taylor cones and filaments emanating from the cylinder surface. The collector is usually a fabric that runs above the cylinder to provide a continuous nanofibre membrane coating. Depending on the membrane weight required, machines 1.6 m wide running at up to 10 m/min are available. Electrospinning from polymer melts is also possible.

A melt-blown process can also produce very fine homogenous or bicomponent fibres at reasonable production rates. In this process lower molecular weight polymers are used to provide low viscosity and high flow. The fibres are extruded into a hot, fast air stream that impinges on the fibres immediately they leave the spinnerets and the air flow draws the fibres to great lengths and into very fine filaments. The fibres are not continuous but are long compared to staple fibres and are typically several micrometres in diameter. The fibres are collected on a belt or drum with suction to condense the mat into a fabric held together by fibre entanglement with some melt bonding between the fibres. Hills Inc10 has developed a melt-blown system with very precise dies and well controlled air flow that allows production of fibres around 250 nm diameter at production speeds of 3 kg/hr per metre width. Low molecular weight

polymers with narrow molecular weight distribution and high melt-flow index are required.

The melt-blown process is often used to form a finer web on top of a spunbond web in a single process. Additional spunbond or melt-blown layers can be added through further processing of the composite web, e.g. to protect the fine melt-blown layer by sandwiching it between two spunbond layers. Melt-blown nanofibres are relatively weak and have low abrasion resistance but they provide small pores and good barrier properties with minimal use of material while the spunbond layers provide strength and abrasion resistance. Fabrics containing a melt-blown web are mainly used for filtration and breathable barrier applications as the pore size of a spunbond fabric is too large to act as a barrier layer to prevent the passage of small particles such as viruses and bacteria. The melt-blown layer provides the barrier layer whilst still allowing the passage of gas or water vapour for comfort or sterilisation. Example products include disposable medical gowns, surgery drapes and wrappings. The pore size may still be too large to act as a barrier against viruses and spores in coarser diameter, melt-blown fabrics.

Fabrics made from nanofibres generally have a nonwoven structure and appear more like a polymer film or membrane unless viewed under an electron microscope. Similar to nano-sized particles, nano sized fibres also have high surface area to volume or mass ratio and may display different properties compared to macroscopic fibres. The surface area to

Figure 3: Nanofibres generated from a rotating electrode. Image with permission from Elmarco


mass ratio of fibres with a circular cross-section is 2/3 that of spherical particles with the same diameter. For a given mass, the surface area of both increase with reduced diameter as 1/d, where d is the fibre or particle diameter. Hence 1 kg of material with a density of 1,000 kg/m3 will have a surface area of 200 m2 when formed into 20µm diameter fibres compared to 200,000 m2 when formed into 20 nm diameter fibres. Hence in applications where surface area is important, e.g. as a support for a (heterogeneous) catalyst, a reduced weight of material is required to achieve the same surface area if converted into smaller diameter fibres.

1.3.2 MATERIAL AND FIBRE PROPERTIES

Tensile Properties

Textile fibres generally have maximum strength under tensile load in the axial or length direction. An example of a load or force extension curve for a material is shown in Figure 4 along with the mechanical properties that can be determined from this type of test.

Identified in Figure 4 are the maximum force or strength, extension to break and the initial, linear slope. The energy required to break the material can be determined from the area under the curve. To normalise this type of curve to the properties of a particular material it is convenient to convert the force applied to a stress and the extension to a strain. The nominal or engineering stress, s(N/m2), generated by the applied force, F (N), is given by s = F/A0 where A0 (m2) is the initial material cross sectional area normal to the applied force. The strain e (dimensionless) is derived from the ratio of the extension (Δl) to the initial length l, i.e. Δl/l. The elastic (Young’s) modulus, E (N/m2 ≡ Pa), of the material is given by the initial, linear slope of the stress/strain curve; that is E= s/e. The maximum stress experienced by the material is known as the (ultimate) tensile strength (N/m2≡ Pa) while the energy/unit volume required to rupture the material is given by the area under the stress/strain curve.

Specific Strength

Lightweight materials providing strength or stiffness without weight are often a key requirement in lightweighting. In this case the specific modulus or specific strength of a material, which relates the modulus or strength to material density, is a more useful parameter. The specific strength, also known as the strength-to-weight ratio for the material, is derived from the stress at failure divided by the material density, r, giving units of (N/m2)/(kg/m3) or more commonly simplified to Nm/kg. . This may also be used to determine the material self-supporting length. That is, for a material of fixed cross section, the vertical length under the influence of gravity that can be supported when fixed at the top. Dense materials that are strong when expressed in terms of stress (force/cross-sectional area) may not be the best choice when weight is important as alternative low density materials may provide higher strength for a given mass but increased volume.

Specification of material properties based on cross-sectional area are useful when the material is solid, for example a single fibre, but less useful when the material is a yarn or rope. The cross-sectional area is no longer continuous but contains voids as the fibres do not occupy 100% of the volume. Theoretically, the maximum occupied volume that closely packed fibres of the same diameter can occupy is 91%. Twisted or spun yarns will typically have significantly

Figure 4: Example of a force extension curve for a fibre


lower occupied volume, around 50%. Hence for textile materials it is more common to specify the material dimensions in terms of its linear density or mass per unit length. The linear density of yarns can be specified in units of Tex (g/km) and to obtain convenient sized numbers for fibres in deciTex (dTex ≡g/10km). Fibres made from a material with low density will have a larger cross-sectional area than fibres of higher density material at the same fibre linear density.

Tenacity

The term used to describe the strength of fibres or yarns is tenacity. This is analogous to the specific strength of materials and is obtained by dividing the breaking force, F (N), by the yarn linear density to give units of N/Tex (≡106N.m/kg). Other units often quoted are centi-Newtons per Tex (cN/Tex) or centi-Newtons per dTex (cN/dTex), where 100cN = 1N and 10dTex = 1Tex.

Specific Modulus

The specific modulus is also derived by dividing the modulus by the material density (E/r) to give units of N/kg (≡ m2/s2). High specific modulus materials find applications where the design limitation is deflection

or physical deformation rather than breaking strength, for example aeroplane wings, bridges, masts and bike frames11. In tension applications, for example a beam in tension, both stiffness and mass/unit length are directly proportional to the cross-sectional area. Hence performance can be selected based on specific modulus. For beams subjected to bending or Euler buckling, if weight reduction for a beam of constrained cross sectional dimensions is the objective, then performance (deflection) will also be related to E/r. However if weight is fixed and the cross sectional dimensions are unconstrained then resistance to Euler buckling, when subjected to an axial load, will be proportional to the modulus and the area moment of inertia. Hence stiffness will be related to either E/r2 (e.g. for solid round or square beams) or E/r3 (e.g. thin-walled round beam).

Examples of properties of materials in tension are given in Table 111-12 and shown graphically in Figure 5 . The breaking length (km) can be calculated by dividing the specific strength (kN.m/kg) by the acceleration due to gravity (~10 m/s2). The last three columns in Table 1 are the specific modulus derived from the modulus divided by the density, density squared or density cubed respectively.

Material Density kg/m3

Strength MPa

Specific Strength kN.m/kg

Specific Strength

N/tex

Young’s Modulus

GPa

Specific Modulus

E/ρ 106.m2s-2

Specific Modulus

E/ρ2 103.m5kg-1s-2

Specific Modulus

E/ρ3 m5kg-2s-2

Aluminium 2700 600 220 0.22 70 26 9.6 3.6 Brass 8550 580 68 0.068 110 13 1.5 0.18 Copper 8920 220 25 0.025 120 13 1.5 0.17 Steel 7860 2000 250 0.25 200 25 3.2 0.41 Concrete 2300 10 4.4 0.004 40 17 7.6 3.3 Rubber 920 15 16 0.02 0.06 0.07 0.07 0.08 Oak 690 60 90 0.09 10 14 21 30 Nylon 1130 78 70 0.07 3.0 2.6 2.3 2.1 Polypropylene 900 80 90 0.09 1.2 1.3 1.5 1.7 Carbon fibre 1750 4300 2500 2.5 230 130 74 42 E-glass fibre 2600 3400 1300 1.3 75 31 12 4.6 Dyneema (UHMPE) 970 3600 3700 3.7 120 120 130 130 Kevlar (p-aramid) 1440 3600 2500 2.5 110 76 53 37 Vectran 1400 2900 2100 2.1 100 70 50 36 Carbon-epoxy composite 1580 2500 1600 1.6 180 110 72 46 E-glass fibre-epoxy composite 1990 1500 750 0.75 45 23 11 5.7 p-aramid fibre-epoxy composite 1350 1300 960 0.96 75 56 41 30

Table 1: Indicative properties of materials and unidirectional fibre composites (~60% fibre volume fraction)


Aluminium

Carbon fibre

E-glass fibre

Dyneema (UHMPE)

Kevlar (p-aramid)

Vectran

Carbon-epoxy composite

E-glass fibre-epoxy composite

p-aramid fibre-epoxy composite

Steel

0

500

1000

1500

2000

2500

3000

3500

4000

0 20 40 60 80 100 120 140

Spec

ific S

tren

gth/

kNm

kg-1

Specific Modulus /106m2s-2

It is readily apparent that a number of fibrous materials have specific strength exceeding common engineering materials, like concrete, steel and wood (oak). It is for this reason that textile and fibre materials are increasingly displacing traditional engineering materials. Textiles and fibre structures may be utilised essentially as stand-alone materials or incorporated into a fibre reinforced composite structure.

Fibre Reinforced Composites

Fibre reinforced composites are produced from two or more different materials that have significantly different chemical or physical properties. One component is fibre which is usually strong and stiff and acts as the reinforcement. Both short fibres and continuous fibre/filaments may be used in fibre reinforced composite materials. The other component is referred to as the matrix and this usually has lower strength and modulus and higher extensibility than the fibre component. The matrix can often be a polymer or resin and it infiltrates and surrounds the fibres so that they maintain their relative position. This allows the matrix to transfer stress between fibres so that each fibre takes up the load simultaneously. The interaction between fibre and matrix is critical as without stress transfer between fibre and matrix,

each fibre may take the applied load sequentially and then fail so that the material fails at a much lower load than if all the fibres take the load simultaneously. Composite materials display properties that cannot be achieved from the individual materials that make up the composite, in particular strength or stiffness with reduced weight. Numerous matrix and fibre combinations are possible allowing designers and engineers to develop products and structures with optimum combination of properties.

To summarise, textile fibres such as glass, carbon, polyester, nylon, UHMPE and p-aramid have low density compared to many other materials e.g. many metals and ceramics. The maximum strength of fibrous and textile structures is achieved under tensile load in the fibre direction. As fibres have low density and high strength, they have high specific strength and specific stiffness and these properties are essential when designing and developing structures and products with reduced weight. To achieve strength and stiffness in bending or compression, the fibres need to be incorporated into a matrix material. Continuous fibres are often used in preference to long staple fibres due to their ease of handling and to maximise the volume of fibres included in the composite. See Appendix A for further information on fibre reinforced composites.

Figure 5: Indicative specific strength and specific modulus of materials and unidirectional fibre composites (~60% fibre volume fraction)


Examples of lightweight structures and applications are presented to provide an overview of various approaches that may be used to achieve lightweight structures utilising textile and fibrous materials. Textile and fibre structures may be used as stand-alone materials, used in a composite, or as coated or laminated fabrics. Reducing the amount of material may require substitution with higher performing materials and sometimes an increase in the cost of production. However, often this increase in cost is more than offset by other advantages, e.g. ease of transport, improved assembly or installation, or greater design flexibility.

Applications utilising fibre reinforced composites include transportation, sporting equipment, construction, and infrastructure. Typically, continuous carbon fibre composites are used where low weight, high strength, and high stiffness are necessary while

lower cost fibreglass composites are used in less demanding situations where weight is less critical. Helicopter rotor blades, wind turbine blades and the hulls of small fishing boats and large racing yachts are routinely manufactured using glass fibre reinforced composites. Jet skis and boat trailers often contain parts manufactured from glass fibre composites to reduce weight and corrosion. Pultruded fibreglass is used to produce rebar to strengthen concrete or to produce electrical towers and light poles. Sporting goods such as tennis racquets, golf clubs, fishing rods and bicycle frames contain carbon fibres to reduce weight and improve performance. Multiple fibre types may be used in a composite construction to optimise properties of strength, stiffness and toughness. An example is shown in Figure 6 where glass, aramid and carbon fibre fabrics have been used to construct a rowing scull13.

2 Lightweighting applications & examples

Figure 6: Rowing scull showing multi-fabric layer composite (white- gelcoat over fibreglass; yellow- aramid; black-carbon fibre.Image courtesy of Sykes Racing.


Fabrics constructed from a fibrous scrim laminated between two impervious layers have found widespread applications as lightweight flexible covering and containment materials. These fabrics can be joined together through various welding techniques (e.g. hot air or hot wedge, radio frequency) to create large impervious barriers. The strength of the fabric is primarily controlled by the properties of the fibre scrim and when welded correctly there is little reduction in fabric strength at the join. Examples include roofing materials, tarpaulins, truck sidings, awnings, pool liners, rubbish and liquid containment, dam liners and bulk storage grain covers. For critical containment applications, doubled welded seams separated by a small unwelded air channel can be formed and the channel pressurised and monitored for pressure reduction (leaks) to ensure strong, leak-free joins have been formed.

Examples where these types of fabrics have been included in large buildings include the retractable roof over Wimbledon centre court and the sail façade of the Burj Al Arab hotel in Dubai (Figure 7). The sail facade of the Burj Al Arab hotel contains 15,000 m2 (200 m high) of PTFE coated glass fabric as 12 individually tensioned, 2 layer membrane panels. The translucent facade is also used as a giant projection screen for creating lighting effects.

Figure 7: Burj Al Arab hotel, DubaiImage by Gryffindor: source Wikipedia14

The retractable Wimbledon roof is stored as accordion folds when not in use and covers 5,200 m2 when deployed. The roof fabric is waterproof, translucent and constructed from expanded PTFE fibres.

Figure 8: Wimbledon roofImage by Daniel (UK): source Wikipedia15

Tanks or bladders constructed in the shape of an onion or pillow are available for lightweight, foldable and readily transportable water and fuel storage systems16. Bladder sizes in excess of 1 million litres are possible, manufactured from fibre reinforced polyvinyl chloride or thermoplastic polyurethane membranes. These systems are particularly suited to the military and remote or temporary installations e.g. mining sites where transportation infrastructure is minimal Figure 9.

Figure 9: Fuel bladder located in AntarcticaImage by Eli Duke: source Wikipedia17


Bladders are also used to ship wine from Australia to the UK18. A 6 m container can accommodate around 9,900 litres of bottled wine whereas a bladder holds 24,000 litres and cost little extra to transport. Glass bottles are eliminated and the extra volume of wine stays cooler during a typical 40-day trip, reducing the need for refrigeration. Whilst the bladders have been in use for a number of decades, improvements in construction and membrane materials have reduced the risk of spoilage. Bladders are also used to transport fruit juice concentrate, paint and chemicals.

Similar types of fabrics are used to line old, large fuel tanks. Aging fluid containment infrastructure within the petrochemical industry has resulted in the need to implement cost effective solutions to refurbish and prevent leakage of these tanks as an alternative to the high capital cost of replacement. One option is to render the tank with an impervious layer to patch any leaks or refurbish the entire interior of the tank e.g. a glass fibre reinforced resin. Whilst potentially offering an acceptable solution, this approach requires significant down-time and the need for good adhesion between the existing walls and render. An alternative lightweight solution is the use of fabric based (prefabricated) impervious membranes in the form of bladders or liners19. This approach reduces down-time, eliminates the problem of adhesion and allows the spanning of gaps where the tank walls have reduced mechanical integrity. Depending on the specific requirements, a number of different fabric layers are used to solve specific problems. For example, a geo-textile layer can be incorporated between the liner membrane and inner wall of the tank to prevent abrasion and puncturing. Leak detection can be achieved through the use of double liners to collect and monitor any leakage. In this case a geo-textile is incorporated between the two liners to allow wicking of any fluid leaking from the innermost liner to a dip stick tube, sump detection system or sight glass.

Ballistic body armour in the form of vests and helmets has long been used to protect personnel from bullets or shrapnel from exploding devices. An ongoing challenge is to reduce weight, improve comfort and manoeuvrability whilst at the same time improving ballistic performance. Weight reductions do not necessarily reduce the total burden carried by a solider as the lower weight body armour is often replaced by additional ammunition, water or communication equipment. Since the “steel pot” helmet of the 1940’s weighing 11.7 kg/m2, improvements in design and the

use of lightweight composite materials like UHMPE, the weight of the latest helmet due for release in 2014 has been reduce to 9.0 kg/m2 but offers double the ballistic performance. The entire body armour system consisting of helmet, ballistic fibre vest and ceramic plates has been reduced from 150 kg/m2 in WW II to 32 kg/m2 through the use of new, lightweight, high performance ceramics and fibre materials20.

High performance fibres (e.g. aramid, UHMWPE, Vectran21, PBO22) have replaced traditional materials used to construct ropes, lines and nettings in many applications as they offer reduced weight with improved performance. Braided fishing line produced from UHMPE fibre has become popular with recreational fishermen, as for a given breaking load, longer lengths can be added to the reel. The braid is also more abrasion resistant than monofilament nylon but is difficult to knot and is visible in water; hence it is often used with a monofilament leader.

Flexible, intermediate bulk containers (big bags) are manufactured from woven fabrics and are used to transport dry flowable products, for example, fertiliser, grains, plastic granules, stock feed and chemicals. These can be recycled and are transported on pallets or on their own with lifting done through attached loops.

The weight of clothing fabric per unit area (g/m2) has been progressively decreasing over many decades. This has been made possible through developments in both fibre technology (finer fibres) and fabric processing equipment (e.g. finer gauge knitting machines). This trend has seen the emergence of “garment layering”, the wearing of multiple layers of garments on top of each other, as the preferred approach to both fashion and technical or functional clothing. Layering allows each layer to be developed with different functional attributes that can be optimised for the specific demands of the layer. Layering also allows greater flexibility. Outdoor and active sportswear manufactures in particular favour this approach. Two thin layers of clothing can be lighter and provide greater warmth than a single thick layer as the air trapped between the layers acts as a thermal barrier. Three layers are often utilised. A base or inner layer designed to keep the skin dry and transport moisture away from the skin where it can evaporate. A mid layer is used to provide additional thermal insulation. An outer shell layer is used to provide wind and (liquid) water resistance whilst preferably still allowing water vapour from perspiration to pass through to the outside


environment. Layered technical fabrics and garments are utilised by the military and in demanding environments as improved performance at reduced weight can be achieved.

In the fashion industry, layering allows flexibility in attire as garments can be mixed and matched and are often designed so that parts of inner layers are still visible under outer layers. Warmth without weight is an important requirement of many garments and the development of polarfleece fabrics and their widespread adoption created a major disruption to traditional fabrics used in garments and bedding products.

Conducting textiles and electronic textiles (e-textiles) are formed when electrically conducting wires or fibres are included as part of a fabric structure (e.g. weave structure). In applications with low power requirements, the metallic wires can be replaced by traditional lightweight synthetic fibres coated with a thin metallic layer (e.g. silver coated nylon).

In simplest form, conducting materials embedded within the textile, can be used to link textile based switches and sensors with various conventional electronic components, for example, battery, light emitting diodes (LED) and integrated circuits to produce, fabric displays, light based fashion garments (LED), allow connectivity to a phone or music player, to form sensors e.g. to monitor heart rate, for heating or electromagnetic radiation shielding. Levis have developed a jacket that has an inbuilt computer and keyboard allowing the wearer to play their favourite songs. Researchers are developing garments that

allow soldiers or hikers to generate their own electricity from body movement23. Sensors embedded in garments can also be used to provide feedback to the wearer regarding work rate or skill and technique. Jogging suits have been developed and configured to play certain types of music and with adapted rhythm, encourage the wearer to increase or decrease work rate23. An interactive sleeve has also been developed to assist Australian Olympic athletes with their training. The sleeve provides interactive feedback to assist with attaining preferred movement. Low weight and bulk of any interactive device is essential in retaining an athlete’s natural movement.

Figure 10: Silver coated nylon fibres (grey) embedded within fabric to identify punches during boxingImage by Reg Ryan

Figure 11: Athlete training using interactive sleeve

Flexible and lightweight super capacitors based on carbon applied to fabrics are being studied for integration as an energy source into smart garments as batteries or conventional capacitors are considered too heavy and bulky to be wearable24. Photovoltaic solar cells can integrated with fabric structures for energy production, shading or as architectural features25.

Research is ongoing to embed electronic components within or on textile fibres. This field of research is sometimes called fibertronics with examples of organic fibre transistors and organic solar cells on fibres demonstrated in the laboratory. This can be achieved through printing of special inks and pigments or through the formation of a larger fibre pre-form that is then drawn down into a much finer diameter fibre. The challenge is to achieve good manufacturability and to retain the aesthetics and the properties of the textile substrate.


2.1 Auto and aeroThe use of carbon fibre composites as a means of achieving lightweight structures is growing rapidly. Over the last decade demand has increased at approximately 10% per annum and is expected to increase at an even greater rate over the next decade as usage increases in traditional and expanding industrial markets26 (Table 2). It is estimated that most uses of carbon fibre are early in the product development lifecycle.

Table 2: Demand for carbon fibre (1000 tonnes)

The major attractiveness of carbon fibre composites is reducing weight (Table 1). For a given weight, carbon fibre composite is significantly stronger than steel and stiffer than aluminium. In some structures, for example an aeroplane wing, (specific) bending stiffness is most important, making carbon fibre composites even more appealing for these applications over traditional metal components.

These improved mechanical properties (weight basis) and weight reduction offers the transport sector (e.g. aerospace and automobile) a significant improvement in fuel efficiency. In aerospace, the improved mechanical properties of carbon fibre composites also enable a significant reduction in drag through a reduction in the wing cross-sectional area. By volume, 80% of the Boeing 787 Dreamliner airframe is composite materials (50% composite by weight, 20% aluminium, 15% titanium). This leads to a 20% reduction in fuel consumption compared to similarly sized conventional aircraft27. In this sector, fuel costs

represent a significant portion of the operating costs, with every kilogram reduction in weight of the aircraft saving ~$3,000/year in fuel or $90,000 over the lifetime of the aircraft. The use of a composite primary structure also reduces the scheduled and non-routine maintenance of the aircraft due to reduced risk of corrosion and fatigue of composites compared with metallic components.

Fan blades in jet engines are sometimes manufactured from carbon fibre reinforced composites rather than metal (e.g. titanium) to offer substantial weight savings. The engine containment case, that is designed to contain and prevent high-speed debris from any blade separation event impacting the airframe or aircraft systems, is typically aluminium over-wrapped with aramid fibre. These weight savings enable other components such as shafts and bearings, pylons attaching the engine to the wing and the associated wing structure also to be constructed from lighter materials28. Half a tonne or more can be saved per engine.

Similar economic and environmental pressures (reduction in CO2 emissions) are appearing in the auto industry with two decades of strong growth predicted for carbon fibre in the auto industry 29. A recent cradle-to-grave study of energy usage by an Audi A3 with a 200,000 km lifetime identified energy use as 6% material production, 6% manufacture, 84% fuel during use, 3% parts and servicing and 1% for recycling at end of life. Fuel consumption during usage, highly dependent on vehicle weight, is by far the major contributor to total energy consumption and car manufacturers are developing carbon fibre composites to achieve energy savings. In the transition to electric vehicles it is even more important. BMW i series (electric) cars contain a lightweight passenger cell made entirely of a carbon fibre composite30. This is the first volume produced vehicle to use carbon fibre composite for the passenger cell with mass rollout of the BMW i3 anticipated in late 2013. The use of carbon fibre composite also enabled more complex design features to improve aerodynamics and improve the sense of space. This weight saving helped compensate for the additional weight of the battery and lowered the car’s centre of gravity to make it a more dynamic vehicle to drive.

Category/Year 2006 2010 2020

Confirmed Scenario

2023

Forecast Scenario

Aerospace 5.1 11.9 31.5

Wind Energy 3.8 7.5 78.0

Automotive 1.8 2.1 96.0

Sport 5.4 6.7 8.3

Industrial 9.9 14.6 25.8

Other (inc anti-ballistic & medical)

1.0 1.0 1.0

Total 27.0 43.8 240.6 1,500 -1,800


Carbon Revolution, an Australian manufacturer, has recently developed a one-piece carbon fibre composite wheel leading to a 40-50% reduction in unsprung mass31 (Figure 12). This reduction in unsprung mass leads to improved acceleration and deceleration, better steering, handling and response, and reduced fuel consumption.

Futuris Automotive Interiors32, an Australian automotive component supplier, is developing car seatback frames from a textile composite as a lightweight alternative to the steel frames typically used33. High performance fibres/yarns, most likely aramid, are knitted on industrial 3D knitting machines to produce a seatback frame made of fabric. The

Figure 12: One-piece carbon fibre composite wheelImage with permission from Carbon Revolution31

Figure 13: Knitted seat frame cured in desired shapeImage with permission from Futuris Automotive Interiors (Australia) 32

knitted fabric is then inflated in a mould, infused with resin and cured in the desired shape to produce a hollow frame that can be covered with seat padding (Figure 12). Claimed advantages of this approach are reduced labour and energy during manufacture and low capital investment. With seat sets weighing around 50 kg/vehicle, weight savings of around 10 kg are anticipated. The other advantage of the textile composite is the ability to manufacture the seat at any location, ship as a flat pack and then mould into shape where it is to be installed in the vehicle.


2.2 Major infrastructureWhen Melbourne’s 2.5 km long West Gate Bridge opened in 1978 linking the inner city with the western suburbs and Geelong it was designed to carry loads arising from 25 tonne per truck and 40,000 vehicles a day. Traffic volume has increased to around 160,000 vehicles a day and with loads from B-double trucks up to 70 tonnes. The bridge has recently been strengthened and the number of lanes increased from 8 to 1034. The bridge is a cable-stayed, steel box girder construction and was strengthened using carbon fibre composite materials. The West Gate Bridge is believed to be the largest bridge ever strengthened using this approach. Carbon fibre composite was chosen because of its tensile strength, light weight, durability and resistance to corrosion as well as during application, minimal labour cost and traffic disturbance. More than 10,000 m2 of carbon fibre fabric and 76,000 litres of epoxy resin (40,000 lineal metres of carbon fibre laminate) were used35 to strengthen the top and underside of the bridge deck, central spine girder, cantilever bridge deck support beams and the bridge deck infill panels.

This approach to strengthening or repairing major infrastructure or buildings using fibre reinforced polymer composite is an established technology and is becoming increasingly widespread due to degradation or the need to upgrade service requirements or capacity beyond initial design requirements. Common fibres used in fibre reinforced polymers (FRP) include glass, aramid and carbon with resins of epoxy, polyester and vinyl ester. FRP has high strength to weight ratio and excellent corrosion resistance and the properties in a particular direction can be tailored for specific applications. The high strength to weight ratio also leads to ease and speed of transportation and installation, minimising disturbance to services and traffic. FRP formed by the wet lay-up process can be used to follow the contours of complex shapes, something that cannot be easily done if using steel plates as reinforcing or strengthening elements. The high tensile strength of FRP means that it can be used to greatest advantage when combined with concrete, a material that is strong in compression but poor in tension36. Applications include the external bonding of FRP to concrete structures for strengthening, concrete structures reinforced or prestressed with FRP, FRP tubes filled with concrete for columns or piles as well as FRP/concrete beams or bridge decks. Concrete slabs and beams may be strengthened

by applying FRP strips (fibres oriented similarly to the internal flexural steel reinforcement) to their tension face to improve flexural performance. Shear strengthening of beams is achieved by applying FRP on the side faces with fibre orientation transverse to the longitudinal beam direction. Shear strengthening by U–wraps around the sides and tension face or the use of closed wraps around the entire beam are preferable depending on accessibility to the beam faces. Closed wraps with overlaps means that failure will typically require rupture of the fibres. The bonding between the FRP and slab or beam is important for flexural strengthening and particularly for shear strengthening if achieved through side bonding or U-wraps. Column strengthening is usually achieved through closed or complete perimeter wrapping to increase shear resistance and compressive strength under axial loading.

Steel structures are also strengthened through bonding to or wrapping the steel structure with FRP36. Not surprisingly weight reduction is the main advantage leading to speed and ease of transportation, installation and reduced disturbances to services. Steel plates may also be bonded to the steel structure. However as a steel plate has a much larger bending stiffness compared to FRP, for a given tensile capacity, it leads to higher peeling stresses at the interface between the steel structure and plate. Additional advantages of using FRP for strengthening rather than welding of steel plates include less introduction of residual stresses, particularly important for enhancing fatigue resistance, reduced risk of fire (e.g. fuel storage tanks or chemical plants) or local strength reduction in heat affected zones in high strength steel. Carbon fibre reinforced polymer (CFRP) is preferred over glass fibre reinforced polymer (GFRP) in the strengthening of steel structures due to its much higher elastic modulus. Typical stress-strain curves are shown in Figure 13 for mild steel and carbon and glass fibre reinforced polymer36.


New materials are often introduced into the construction industry as replacements for traditional materials. This allows familiarity to develop but is often limited to the current designs and building systems developed for the traditional materials. These new materials offer the opportunity for new designs and innovations.

A cable stayed bridge across the Straits of Gibraltar manufactured from carbon fibre reinforced composites was proposed and designed in 198737. Compared to steel, the use of carbon fibre reinforced composite tripled the limiting span, the span at which the structural system will just support itself. Whilst this bridge has not been built there are many examples of bridges (e.g. in western Europe38) that have been designed and constructed using FRP.

The first carbon fibre composite bridge constructed in Spain, the 46 m Autovia del Cantabrico highway bridge, contains three parallel, 0.8 m deep hollow trapezoidal composite sections (two sections each spanning 10 and 13 m). The beams were manufactured with epoxy/carbon fibre laminated on polyurethane preforms. The lightweight composite structure, at 100 kg/m (supporting 2500 kg/m of concrete road deck) was installed using a 50 tonne crane compared to a 400 tonne crane if constructed of concrete.

The bridge elements of the Garstang Mount Pleasant M6 Bridge in the UK were fabricated at the roadside from glass and carbon FRP and then lifted into place. The new bridge is half the weight of the bridge it replaced but twice as strong.

The Cuenca Parque de los Moralejos in Spain is claimed to be the world’s longest stress ribbon bridge using pretensioned cables as the main load bearing elements. Eighty, 40 m long carbon fibre reinforced polymer cables pretensioned to 70 tonne run the entire length of the bridge.

A rotating platform, capable of hold 54 cows for milking, has been manufactured from glass and aramid fibre composite material to achieve a weight reduction of 80% compared to traditional concrete platforms39. The composite platform is expected to have a 25% longer lifespan as the reduced weight means there is less friction on the drives and running gear resulting in less wear and tear.

Figure 14: Typical stress-strain curves for glass and carbon fibre reinforced polymer and mild steel


2.3 Pressure vessels and pipingHigh performance organic fibres such as p-aramid, ultra high molecular weight polyethylene and liquid crystal polymers are increasingly used in applications where strength without weight is important. Other advantages may also be gained by replacing traditional materials with fibres. Textiles composed of glass, p-aramid or carbon fibres can be used to produce lightweight pressure vessels (composite overwrapped pressure vessel). These vessels consist of a structural fibre composite wrapped around a thin non-structural liner40. The liner provides a barrier to the gas or fluid so that it does not come in contact with the fibre composite. A protective shell is also often applied to the fibre composite to protect it from the external environment and impact damage. The use of high strength fibre significantly reduces the weight of the cylinder compared to a metal cylinder. Weight reduction is particularly advantages in reducing the load carried (air cylinder) by firefighters or in storing oxygen in aircraft.

Flexible pipes and hoses can be produced in a similar way where a thin, non-structural liner is reinforced by wrappings of high strength fibres (e.g. p-aramid) 41. The composition of the inner liner is selected based on the medium to be transported (e.g. gas, water, oil, solvent) while a thin flexible outer covering of the high strength fibre provides wear resistance. The mid layer or layers of high strength fibres in woven, braided or filament-wound wrappings provides the load bearing capacity for the pipe. These thin walled, flexible, lightweight pipes can be flattened for spooling and ease of transport and produced in lengths greater than 1 km. Old, deteriorating metal or concrete pipes do not need to be replaced as the flattened pipe can be inserted and pulled through the old pipe work and around bends from small construction pits. Once filled, the pipe expands to its operating dimension and pressure leaving a small annular gap between the new and host pipe.

For new pipe installations, hard, thermoplastic pipes reinforced with high strength fibres are available that are significantly lighter and stronger than steel pipes42. Some flexibility is retained so that they can be spooled in long lengths (~500 m) and trenched into place rather than digging ditches and pipe laying; reducing the cost of installation. The reduced weight of the pipe aids transportation particularly to remote locations where light vehicles and low grade roads can be used.

Fibre reinforced thermoplastic polymers have been used to produce a material that can be rolled into a stable reel and when the material unrolls from the reel it automatically adopts a tube like structure (overlapping or C cross-section depending on the desired application) 43. The tube can be rolled up with minimal amount of force for ease of storage and redeployment when required. This product offers a lightweight, compact method for producing tubes that can be used for mounting sensors, communication devices or as lightweight structural elements. Simple on-site welding or bonding of the seam can be used to produce pipes and conduits that can be stored and shipped in compact form. The material and structures can be optimised for stiffness, as pressure pipes or for use in compression or tension.


2.4 Air supported and inflated structuresAir supported or air inflated structures44 (e.g. domes or tents) have been in use for a number of decades. The structural integrity of these buildings is derived from the internal pressure that is used to inflate a pliable, fabric based material. Consequently, air (positive pressure) is the main support for the structure and access is necessary via an air lock (e.g. two sets of doors or revolving door). The internal pressure needs to exceed the external pressure applied to the structure from both any loading or from the environment, wind or snow build-up.

Quality structures can withstand wind speeds of 190 km/h and snow weights of 20 kg/m2. The structure does not need to be air tight to maintain structural integrity, provided the pressurisation system can keep up with any air loss. The pressure required to keep the structure inflated is not high, typically around 250 Pa (0.002 bar) and the structure is secured by weights on the ground or ground anchors attached to foundations. Cables may be required for anchoring and stabilisation of large span structures. Modern structures have computer controlled systems that monitor dynamic loads and automatically compensate by adjusting inflation pressure.

Temporary or permanent structures for sports arenas, warehousing and shelters for military and civilian uses can be produced from air inflated structures. The occurrence of sudden collapse should be negligible as the structure gradually deforms or sags under a heavy load but if this warning sign is ignored, rupture leading to sudden deflation may occur. Materials used to produce these structures are typically PVC or Teflon coated fibreglass and polyester fabrics with resistance to deterioration from moisture and ultraviolet radiation.

The Burswood Entertainment Complex (now known as Crown Perth) opened in 1988 and is an example of an air supported structure. The arena is enclosed by a 9,000 m2 dome with seating capacity for around 13,000 people. The arena is pressurised so that the fibreglass roof becomes suspended 35 m above the ground. A further example is the Carrier Dome at Syracuse University (New York) opened in 1980 with seating capacity of nearly 50,000. This dome was constructed with a Teflon coated fibreglass inflatable roof45.

An inflatable, balloon-like room is under development as a replacement for the currently used, solid structures for the space station47. The inflatable room

would be compressed for delivery to the space station and then inflated into a 3 m diameter space room.

Researchers in the US are developing a one-tonne balloon like plug from a liquid crystal polymer fabric (Vectran) to protect subway tunnels from floodwaters resulting from storms, terrorist strike or accident48. Rather than retrofit tunnels with metal floodgates or other expensive structures the idea is to develop a cheap inflatable plug to seal the tunnel and holdback floodwater, much like blowing up a balloon inside a tube. The plug needs to be strong, flexible, durable, easy to install and foolproof when deployed. The pliable, lightweight plug needs to be able to withstand the pressure of water behind it and create a seal against the tunnel wall. The plug also needs to be constructed from tough materials as friction between the plug and tunnel wall is what keeps it in place against the water pressure.

Obstructions and protrusions from the tunnel wall like pipes, safety walkways as well as tracks cause gaps between the plug and tunnel walls. Many obstructions can be rectified by modifying short sections of tunnel, rounding sharp corners or allowing protrusion to swing up against the wall e.g. pipes. The plug will be folded inside a container and located against the tunnel wall in strategic locations out of the way of passing trains ready to be inflated by air when the need arises. The objective is to reduce the flood of water to something more manageable rather

Figure 15: Burswood dome at Burswood CasinoImage by Nachoman-au: source Wikipedia46


than completely stop all water. The plugs are initially expected to cost around $400,000 each, significantly less than the $2 billion in damage caused to buildings when a crew sinking bridge pilings breached an abandoned freight tunnel under the Chicago River in 1992.

A lightweight, inflatable dry docking system for boats up to 14 m in length is available49. An inflatable barrier system, flexible waterproof liner and an aerated netting system allows docked boats to remain completely dry in the water. An inflatable tubing system that doubles as a fender system is used to create a berth for the boat. Once inside, the rear is inflated to totally enclose the boat. The water inside the sleeve is evacuated to bring the hull in contact with the aerated netting system. The dry docking system can be deflated and stowed onboard if necessary.

Archways constructed from regolith (dust soil and rocks) have been proposed where there is a need to deploy large, rugged structures including on the surface of the moon. The regolith is held in place by a strong, deployable arch-shaped jacket. During the filling of the jacket, that arch is sported by an inflatable structure. Once filled, the catenary arch is self-supporting and the inflatable structure can be removed. An arch of 3 m thickness is proposed for structures on the moon to resist radiation and the impact of micrometeoroids and high velocity debris50.

Air inflated fabric structures can be stiffened through the use of special coatings51. These coatings are initially pliable but once the structure is inflated and properly erected a change is trigged (e.g. crosslinking reaction) in the coating stiffening the fabric so that the fabric behaves in much the same manner as a fibre reinforced composite. The change can be triggered by elevated temperature, ultraviolet light, or oxygen.

Figure 16: Kite for kitesurfing showing airbeams used in structureImage by Arpingstone: Source Wikipedia52


2.5 AirbeamsAn airbeam is a pressurised inflatable tube that is soft and pliable when deflated but becomes rigid and a structural support when inflated. The stiffness of the structure is primarily a function of the inflation pressure. Airbeams are produced from braided or woven, high strength, dimensionally stable fabrics that cover an air retention bladder or are made from inherently impermeable fabrics. Depending on how the fabric is woven or braided or by incorporating different material into the fabric the airbeam shape can be manipulated for different applications e.g. beams or arches. The internal pressure prestresses the fabric in tension and provides load bearing capacity, particularly when the pressure is high. When overloaded, air beams bend or buckle but usually recover when the load is reduced rather than break. Inflated structures are becoming more common in both military and civilian use due to their light weight, ease of mobilisation and low packed volume. Examples include large tents for military personnel, aircraft and vehicle maintenance, disaster relief shelters, pollution containment barriers, inflatable antennas or load-bearing structures for space application like antenna reflectors, solar sails and wings. Small hiking tents and surf kites also utilise airbeams in their structures.

Large tents may utilise airbeams 1 m in diameter while small tents will use airbeams of 5 mm in diameter. High pressure beams required for large shelters will need a compressor to achieve the required pressure of 3- 6 bar while tents for recreational use can be pressurised to the desired pressure of around 0.5 bar by a manual pump. More complex air filled structures with internal webs and chambers can be used, for example, floors for inflatable boats, energy absorbing walls51 and the inflatable wings of a two seater ultra light or unmanned aircraft53.

Figure 17: Lightweight beam design incorporating airbeam for increased stability against buckling

For large structures the use of large diameter airbeams operating at high pressures may be necessary to obtain the desired stiffness. A solution is to combine an airbeam with conventional cables and struts to improve the load bearing capacity54. A compression strut is tightly connected to the airbeam membrane along the entire length and at least one pair of cables is spiralled around the airbeam and firmly connected to the compression element at both ends of the airbeam (Figure 16).

The loads are carried by the cables and compression element. The pressure in the air beam is typically 0.05 to 0.5 bar and its role is to pretension the cables and stabilise the compression element against buckling. The load bearing capacity of this hybrid combination is claimed to be improved by two orders of magnitude compared to a traditional airbeam. As a demonstration of the concept, an 8 m span bridge with 3.5 tonnes maximal load was produced from two 500 mm diameter airbeams (PVC coated polyester fabric operating at 0.4 bar pressure), 6 mm diameter steel cables and a carbon fibre composite compression element. Each hybrid beam weighed 40 kg compared to 370 kg for a HEB steel girder with the same load bearing capacity. A simple airbeam with the same dimensions would need to be pressurised to 15 bar to achieve the same load bearing capacity.

Light weight artificial muscles with high power to weight ratio that utilise a fabric structure surrounding a pneumatic tube are under development for use in robotics, automation or an exoskeleton55. The fabric needs to be flexible with good recovery properties and anisotropic, that is stiff in one direction but flexible in the other directions, to allow the fabric to deform differently in the radial and longitudinal direction.


2.6 Nanofibrous membranesNanofibrous membranes are under development as barrier materials for protection against chemical and biological contamination56. Traditionally, protective clothing was constructed from impermeable barrier materials to block penetration of any contaminants. This approach, while effective at preventing contamination, comes at the expense of wearer comfort as they were often bulky, heavy and with a high thermal burden due to poor water

vapour transmission. Nanofibrous membranes are a promising approach to overcome these deficiencies as they are lightweight, have an open and porous structure and high surface area to volume ratio. Nanofibrous membranes produced through electro-spinning may be utilised in energy storage and conversion systems such as rechargeable, lithium-ion batteries, fuel and solar cells and super capacitors57.

2.7 Auxetic textilesWhen stretched, most materials contract in the transverse dimensions, or when under compression will expand laterally. The extent of these dimensional changes is governed by a fundamental mechanical property of the material, known as Poisson’s ratio and given the symbol n. Polymers and steel have a n of around 0.3, rubber is nearly 0.5 (the upper limit for isotropic materials) while cork is around 0 resulting in very little lateral expansion under compression (good for inserting into bottles for sealing). A negative n is also possible with a lower limit of -1 for isotropic materials.

Materials having a negative n are termed auxetic or dilatational58. Auxetic materials are not common but include naturally occurring materials such as iron pyrite and cat skin. Auxetic behaviour can be observed in materials at the molecular level (some polymer fibres) and in macroscopic structures (e.g. brick structures, textile structures) spanning all the major classes of materials, ceramics, metals polymers and composites. These materials are of interest because other material properties are enhanced as a result of having a negative n. These include increased indentation resistance, shear stiffness, fracture toughness and energy for fibre pullout from composites. Under impact, material flows away from the impact site of conventional materials whereas it flows to the site for an auxetic material thereby increasing the density. Auxetic materials have an enhanced ability to form doubly curved surfaces e.g. a dome or saddle. Auxetic materials can be used in applications as diverse as press-fit fasteners, curved sandwich panels, flexible impact buffers and sound proof materials.

Auxetic behaviour can be engineered into fibre and textile structures59. As an example, a high stiffness filament helically wrapped around a thicker, elastic filament produces an auxetic textile. When tension is applied to the structure, the stiffer filament straightens and forces the thicker, elastic filament to wrap around it thereby increasing the effective volume of the structure (Figure 17). Woven and knitted structures can also be engineered with auxetic properties. It has been suggested that auxetic fibres within a composite would resist fibre pull out as it would expand rather than contract in diameter. Further application of auxetic fabrics include adaptive and deployable flexible structure, energy absorption and viscoelastic damping components, climbing ropes59b and improved blast protection fabrics60.

Figure 18: An example of an auxetic textile structure


3 Concluding remarksLightweighting is not a fad and has probably been a desire ever since man started making tools and had to carry and use them. Recently designers, manufactures, and consumers have taken more of a whole of life view and included lifecycle thinking in their decision making. Products manufactured with less material usually have less environmental impact since less material needs to be extracted, recycled or ends up going to waste. Less material use can result in a reduction in the amount of energy, chemicals or water consumed during manufacture, the energy required to transport and install the final product, or the energy consumed during use if the product needs to move e.g. an aircraft or motor car. Energy consumption during use typically represents more than 50% of the total energy consumed during the lifetime of a motor car (~200,000 km). Hence reducing the weight of the vehicle significantly reduces running costs and environmental impact.

Lightweighting often requires the redesign of the product and this should be viewed as an opportunity to improve the design and manufacturability, usability or to add features and improved performance to the end product. Textiles and fibres are essential materials to achieve this aim and will become increasingly important as megatrends play out over the next two decades and change the way we live. These megatrends will have an impact on the Australian Textile and Fibre industry, from material supply, production and supply chains through to the business models required to deliver products and services. Examples of these potential impacts are given in Figure 18. Achieving more with less is essential if society is to mitigate the effects of increasing population, depleted resources and a changing climate.

Figure 19: Impact of megatrends on textile and fibre industry


Property/Resin Epoxy Phenolic Polyester Polyimide

Maximum use temperature (⁰C) 95 - 175 150 - 205 80 - 140 205 - 315

Density (kg/m2) 1200 1300 1100 1300

Tensile strength (MPa) 35 - 105 35 - 60 20 - 90 40 - 90

Tensile modulus (GPa) 0.4 - 0.5 0.6 - 1.2 0.2 - 0.4 0.3 - 0.4

Elongation (%) - 0.5 - 0.8 1.4 - 4.0 1.1

Flexural strength (MPa) 310 - 380 50 - 95 55 - 160 105 - 170

Flexural modulus (GPa) 1.4 - 1.7 0.7 0.3 0.3 - 0.6

lzod impact (kJ/m) 3.2 - 4.8 3.0 - 9.6 3.2 - 6.4 15 - 25

Moisture absorption (%) 0.1 - 0.7 - 0.15 - 0.60 1.1 - 1.2

Coefficient of thermal expansion (10-5.K-1) 6 - 7 3 - 5 - 3 - 5

Appendix A Fibre reinforced compositesProperties of typical thermosetting and thermoplastic resins used in fibre reinforced composites are given in Table 361 and Table 461 respectively.

Table 3: Properties of thermosetting resins

Table 4: Properties of thermoplastic resins

Property/Resin

PEEK PES PPS PEI PA6 PC

Crystallinity (%) 35 0 < 65 0 0

Tm (⁰C) 334 - ~270 - 219 -

Tg (⁰C) 143 ~220 88 215 ~50 148

Maximum use temperature (⁰C) 260 170 200 170 180 125

Density (kg/m2) 1300 1370 1350 1340 1130 1200

Yield strength (MPa) 92 83 86 103 82 63

Tensile modulus (GPa) 3.6 2.7 - 2.9 3.1 2.3

Elongation (%) > 60 40 - 80 3 - 6 60 20 - 50 120

Flexural strength (MPa) 170 120 145 142 1.1 90

Flexural modulus (GPa) 4.1 2.7 4.1 3.2 2.8 2.3

lzod impact (kJ/m) no break no break 8 - 16 1.3 - -

Moisture absorption (%) 0.5 0.4 < 0.02 0.28 10 0.35

Coefficient of thermal expansion (10-5.K-1) 0.47 4.9 4.1 5.6 8 7


As a first approximation the properties of the composite tend to follow the “rule of mixtures” which relates the properties of the composite to the volume proportions of the constituent materials (fibre and matrix) that make up the mixture. The density of the composite is given by the following equation;

ρc = ρfVf + ρmVm Equation 1

where ρc, ρf, ρm are the densities of the composite, fibre and matrix respectively and Vf , Vm (=1-Vf ) are the volume fractions of fibre and matrix respectively.

For continuous, perfectly aligned, unidirectional fibres, with ideal bonding between the matrix and fibre, the composite strength, σc, and composite modulus, Ec , in the longitudinal direction are given by;

σc = σfVf + σmVm Equation 2

Ec = EfVf + EmVm Equation 3

while in the transverse direction the fibre and matrix function in series so properties are given by;

1/Ec = Vf /Ef + Vm /Em Equation 4

The change in the composite modulus as a function of fibre volume fraction in both the longitudinal and transverse direction is shown in Figure 19. .

Both short fibres and continuous fibre/filaments may be used in fibre reinforced composite materials. Composites with short fibres may be produced with the fibres reasonably well aligned in a single direction to enhance the properties in this direction or with random orientation so that the properties of the material are similar in all directions. Due to the difficulty in handling, compacting or mixing

short fibres within the matrix, these composites are usually matrix rich. Variations in the distribution of fibres within the matrix may occur resulting in regions of lower fibre concentration leading to stress concentration within the composite.

Fibre reinforced composites produced from continuous fibre filaments are often layered or laminated in structures where each fibrous layer has a different fibre orientation. Tows of continuous filaments can be woven into fabrics or laid as unidirectional tapes free of any crimp. Layering alternate layers at 90o enables the properties of the composite to be matched in the orthogonal direction. Composites produced from continuous fibre filaments are often fibre rich to maximise the properties of the fibre reaching a practical limit of around 70% fibre volume fraction62 (Figure 20).

To account for fibre orientation and fibre length, Equation 2 and Equation 3 need to be modified.

Ec = η0ηLEEfVf + EmVm Equation 5

σc = η0ηLSσfVf + σ’mVm Equation 6

where η0 is a factor accounting for fibre orientation with respect to the load direction and ηLE and ηLS are fibre length factors derived for modulus and strength respectively.

The fibre orientation factor, η0, has the values given in Table 5 for various orientations.

Figure 20: Composite modulus as a function of fibre volume fraction in both the longitudinal and transverse directions for long, unidirectional fibres with ideal bonding between matrix and fibre; Ef =10E m

Figure 21: Indicative composite properties as a function of fibre volume fraction.


Orientation η0

Unidirectional 1.0

Biaxial 0.5

Random (in-plane) 0.38

Biaxial ±45o 0.25

Random 3 dimensional 0.2

From Cox’s shear-lag theory63 an expression can be derived for ηLE Equation 7 where Equation 8

and Gm is the shear modulus of the matrix, R is the fibre spacing (mean fibre centre to centre spacing is 2R) and r and L the fibre radius and length respectively.

( )

−+= ∑ ∑i

j j

cj

c

iif L

LvLvLv

21

2/1LSη Equation 9

In Equation 6, σ’m is the stress in the matrix at the failure strain of the fibre rather than the ultimate strength of the matrix (Figure 21). The composite is considered to have failed when the fibres break and this will typically occur at peak load.

Figure 22: Composite tensile strength as a function of fibre volume fraction

Table 5: Fibre orientation factor

In Equation 10, Lc is the critical fibre length64. The maximum load that can be applied to the fibre via the matrix depends on the area and strength of adhesion of the fibre to the matrix; hence on the length and diameter of the fibre. Fibres shorter than the critical length will debond from the matrix before reaching their breaking stress. The critical fibre length is given by; Lc = σf d/2τ or Lc /d = σf /2τ Equation 10

where σf is fibre strength, d the fibre diameter and τ the lower of either the matrix-fibre interfacial shear strength or the matrix shear strength. In Equation 9, vi is the fibre volume fraction of fibres with length Li less than Lc and vj is the volume fraction of fibres with length Lj greater than Lc. From these equations, adhesion between the fibre and the matrix, the fibre volume fraction, the fibre aspect ratio (L/d), and the fibre orientation influence the strength and modulus of the composite. The critical fibre length equation can be rearranged to give the critical aspect ratio, Lc /d = σf /2τ which indicates that if the fibre to matrix adhesion is poor then the fibres need to be long or very fine to increase the surface area and hence adhesion to achieve maximum strength. For typical fibre/matrix combinations, provided L > 1 mm, the modulus correction factor, ηLE, is greater than 0.9 and to achieve 95% of the strength of a continuous fibre composite for the same volume fraction, the fibre aspect ratio needs to be about 10 times the critical length65.

The various methods typically used to form fibre reinforced composites using either short or continuous fibres in thermosetting or thermoplastic resins are shown in Table 662.

2/)2/tanh(1LE L

Lββη −=

2/1

)/ln(21

=

rREG

r f

mβ


Fibre Reinforced Composite Processing Routes

Thermosetting Resins Thermoplastic Resins

Short Fibre Reinforcing

Long Fibre Reinforcing Short Fibre Reinforcing

Long Fibre Reinforcing

Spray up

Liquid moulding

Compression moulding

Injection moulding

Lay up

Liquid moulding

Filament winding

Pultrusion

Compression moulding

Injection moulding

Lay up

Thermoforming

Compression Moulding

Table 6: Various methods typically used to form fibre reinforced composites


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FOR FURTHER INFORMATION

Materials Science and Engineering

Dr Tony Pierlot t +61 3 5246 4000 e [email protected] w www.csiro.au/en/Organisation-Structure/Flagships/Future-Manufacturing-Flagship

CONTACT USt 1300 363 400 +61 3 9545 2176 e [email protected] w www.csiro.au

YOUR CSIROAustralia is founding its future on science and innovation. Its national science agency, CSIRO, is a powerhouse of ideas, technologies and skills for building prosperity, growth, health and sustainability. It serves governments, industries, business and communities across the nation.