《纺织复合材料》课程参考文献（3-D textile reinforcements in composite materials）08 3-D forming of continuous fibre reinforcements for composites

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8 3-D forming of continuous fibre reinforcements for composites O.K.BERGSMA,F.VAN KEULEN,A.BEUKERS, H.DE BOER AND A.A.POLYNKINE 8.1 Introduction 8.1.1 The earliest fibres,fabrics and composite structures The control of fire and the spinning of continuous strands of fibres are prob- ably the most important discoveries humans ever made.Both inventions made it possible for a naked human to survive in non-tropical conditions. Yarns and derivatives,like robes and textile fabrics,provided humans with a portable and personal tropical microclimate by clothes and structures so that they could withstand most climatological conditions.It made humans able to migrate from the crowded and unhealthy tropical zones to the large, cool plains and mountainous areas,free of diseases,but rich in animals,veg- etables,minerals and water.Compared with animal skin,flexible textile was 豆 a big step forward.The usage of light fabrics that were adjustable to local conditions made a big and relatively fast migration of hunters and gather- ers possible over all continents,except Antarctica [1].Humans could only use local natural growing fibres.They differ from modern artificial synthetic fibres in length.Instead of the continuous filaments,nature offers only short fibres,like animal hair.These protein-based fibres are provided by animals, such as sheep,goats,camels,llamas and rabbits.Various forms of vegetable cellulose-based fibres were available as well:in a hairy form taken from seeds(cotton)and fruits(coir)or as fibres extracted from basts and leaves, like jute,sisal,hemp,flax,yucca,palm,rice,grass,ramie and rattan. Several of these materials could instantly be used to make basket-like structures or to wattle hedges and walls.However,to handle and to make the staple fibres suitable for knitting and weaving,as shown in Fig.8.1,the spinning and intertwining of yarns was essential.A distaff,a small portable wooden spinning wheel on a vertical axle(Fig.8.2),had already been known in prehistoric times,far before the wooden wheel on the horizontal axle was invented to make wheeled transport possible.Depending on the local climate,people started to use ropes,felt (paper-like textile)and woven 241

8.1 Introduction 8.1.1 The earliest fibres, fabrics and composite structures The control of fire and the spinning of continuous strands of fibres are probably the most important discoveries humans ever made. Both inventions made it possible for a naked human to survive in non-tropical conditions. Yarns and derivatives, like robes and textile fabrics, provided humans with a portable and personal tropical microclimate by clothes and structures so that they could withstand most climatological conditions. It made humans able to migrate from the crowded and unhealthy tropical zones to the large, cool plains and mountainous areas, free of diseases, but rich in animals, vegetables, minerals and water. Compared with animal skin, flexible textile was a big step forward. The usage of light fabrics that were adjustable to local conditions made a big and relatively fast migration of hunters and gatherers possible over all continents, except Antarctica [1]. Humans could only use local natural growing fibres.They differ from modern artificial synthetic fibres in length. Instead of the continuous filaments, nature offers only short fibres, like animal hair. These protein-based fibres are provided by animals, such as sheep, goats, camels, llamas and rabbits. Various forms of vegetable cellulose-based fibres were available as well: in a hairy form taken from seeds (cotton) and fruits (coir) or as fibres extracted from basts and leaves, like jute, sisal, hemp, flax, yucca, palm, rice, grass, ramie and rattan. Several of these materials could instantly be used to make basket-like structures or to wattle hedges and walls. However, to handle and to make the staple fibres suitable for knitting and weaving, as shown in Fig. 8.1, the spinning and intertwining of yarns was essential. A distaff, a small portable wooden spinning wheel on a vertical axle (Fig. 8.2), had already been known in prehistoric times, far before the wooden wheel on the horizontal axle was invented to make wheeled transport possible. Depending on the local climate, people started to use ropes, felt (paper-like textile) and woven 8 3-D forming of continuous fibre reinforcements for composites O.K. BERGSMA, F. VAN KEULEN, A. BEUKERS, H. DE BOER AND A.A. POLYNKINE 241 RIC8 7/10/99 8:26 PM Page 241 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:31:28 AM IP Address: 158.132.122.9

obtain improved or modified properties. The earliest laminated composite structures, like composite bows and chariots, were glued layered structures of natural composites such as wood, bone, sinew and horn [2]. They were all fibrous materials, based on cellulose, collagen and keratin, which had very specific capabilities, already discovered and understood by the prehistoric craftsman (Table 8.1). All applications mentioned in this part of the Introduction, from textile structures more than 50 to 8 millennia ago to the composite shelters, bows and chariots from 12 to 5 millennia ago were not developed overnight, the structures were sometimes very complex and took probably centuries 3-D forming of continuous fibre reinforcements for composites 243 Table 8.1. Elastic properties of some natural composites compared with steel Material Density Young’s Yield stress Yield Elastic (kg/m3 ¥ 103 ) modulus (N/m2 ¥ 106 ) strain energy/ (N/m2 ¥ 109 ) (%) weight (J/kg) Steel 0.2 carbon 7.8 210 773 0.2 99 quenched Piano wires, 7.8 210 3100 0.8 1590 springs Animal Sinew 1.3 1.24 103 4.1 1620 Buffalo horn 1.3 2.65 -124 -3.2 1530 Bovine bone 2.1 22.6 -254 -1.4 846 Ivory 1.9 17.5 217 1.2 685 Hardwood Ash 0.69 13.4 165 1.0 1196 Birch 0.65 16.5 137 1.0 1050 Elm 0.46 7.0 68 1.0 740 Wych elm 0.55 10.9 105 1.0 950 Oak 0.69 13.0 97 1.0 703 Softwood Scots pine 0.46 9.9 89 0.9 870 Taxus brevifolia 0.63 10.0 116 1.3 1100 Notes: 1 Northern hardwoods, sinew and horn were the basic structural materials for the laminated composite bows and chariots from Mesopotamia and Egypt. 2 Taxus baccata was used for medieval longbows. 3 Horn, a natural thermoplastic polymer was especially applied in the compression loaded areas. 4 Sinew, superior in tension, was employed for strings and bow-reinforcement; more in general it was used as a shrinking (smart) robe to encapsulate and to connect different components. RIC8 7/10/99 8:26 PM Page 243 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:31:28 AM IP Address: 158.132.122.9

244 3-D textile reinforcements in composite materials of experimentation and evolution.The results are still striking for the craftsmanship,knowledge of materials and the sophisticated manu- facturing processes [2].For a successful introduction of modern artificial composites,equal understanding must be developed and supported by modern mathematical modelling and computers.Besides the application of new synthetic materials,the biggest break with the past will be the introduction of low-cost and fast manufacturing and simulation equipment to replace the time-consuming,high-priced and mystic skills of craftsmen. 8.1.2 The renaissance of fibre reinforced composites During the second half of this century,the last decade in particular,a true revival started of using light-weight composite structures for many techni- cal applications.In the beginning,the introduction of fibre reinforced poly- 酒 mers was only driven by particular electromagnetic characteristics.More pooM than a century ago,cotton reinforced rubbers and phenolics were used for insulators.Later,glass fibre reinforced polyesters were applied for radomes, minehunters and minesweepers.In the 1980s,high-technology composites based on carbon-and aramid-fibre reinforced epoxies became popular to 2-0 improve the structure performance of spacecraft,military aircraft,heli- copters and all kinds of sports and racing equipment.Initially,the sky was A the limit as far as the price was concerned.Nowadays,cost reduction during manufacturing and operation is the technology driver,and examples are large structures in civil applications(carbon fibre reinforcement of bridges 二一8、 and buildings)or in corrosive chemical or marine environments(glass fibre reinforced bridges,piers,pipes,tanks,etc.).One of the latest developments is the application of continuous fibre reinforced polymers to protect people against impact and fire and a more general tendency to design means of transport which are less damaging to our environment.Some typical exam- ples are shown in Fig.8.3. Like in prehistoric times,the reinforcing fibrous materials are applied in different forms;short or continuous,as tapes,mats or plain weaves. Although the vegetable fibres mentioned earlier are gaining renewed inter- est,most structural applications are now reinforced with synthetic fibres with constant quality.Inorganic fibres are applied such as glass,metal and silica,organic fibres based on natural cellulose and protein polymers or syn- thetic fibres based on condensation or addition polymers.There are innu- merable types of synthetic fibres,such as single filaments or tows,neat or post-treated,stretched or carbonized.Nowadays,the most popular rein- forcing fibres with respect to price-performance are the low-cost(E)glass fibres and the high modulus(HM)aramid-and high-tenacity (HT)carbon fibres (Table 8.2)

of experimentation and evolution. The results are still striking for the craftsmanship, knowledge of materials and the sophisticated manufacturing processes [2]. For a successful introduction of modern artificial composites, equal understanding must be developed and supported by modern mathematical modelling and computers. Besides the application of new synthetic materials, the biggest break with the past will be the introduction of low-cost and fast manufacturing and simulation equipment to replace the time-consuming, high-priced and mystic skills of craftsmen. 8.1.2 The renaissance of fibre reinforced composites During the second half of this century, the last decade in particular, a true revival started of using light-weight composite structures for many technical applications. In the beginning, the introduction of fibre reinforced polymers was only driven by particular electromagnetic characteristics. More than a century ago, cotton reinforced rubbers and phenolics were used for insulators. Later, glass fibre reinforced polyesters were applied for radomes, minehunters and minesweepers. In the 1980s, high-technology composites based on carbon- and aramid-fibre reinforced epoxies became popular to improve the structure performance of spacecraft, military aircraft, helicopters and all kinds of sports and racing equipment. Initially, the sky was the limit as far as the price was concerned. Nowadays, cost reduction during manufacturing and operation is the technology driver, and examples are large structures in civil applications (carbon fibre reinforcement of bridges and buildings) or in corrosive chemical or marine environments (glass fibre reinforced bridges, piers, pipes, tanks, etc.). One of the latest developments is the application of continuous fibre reinforced polymers to protect people against impact and fire and a more general tendency to design means of transport which are less damaging to our environment. Some typical examples are shown in Fig. 8.3. Like in prehistoric times, the reinforcing fibrous materials are applied in different forms; short or continuous, as tapes, mats or plain weaves. Although the vegetable fibres mentioned earlier are gaining renewed interest, most structural applications are now reinforced with synthetic fibres with constant quality. Inorganic fibres are applied such as glass, metal and silica, organic fibres based on natural cellulose and protein polymers or synthetic fibres based on condensation or addition polymers. There are innumerable types of synthetic fibres, such as single filaments or tows, neat or post-treated, stretched or carbonized. Nowadays, the most popular reinforcing fibres with respect to price–performance are the low-cost (E) glass fibres and the high modulus (HM) aramid- and high-tenacity (HT) carbon fibres (Table 8.2). 244 3-D textile reinforcements in composite materials RIC8 7/10/99 8:26 PM Page 244 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:31:28 AM IP Address: 158.132.122.9

246 3-D textile reinforcements in composite materials Table 8.2.Fibre properties of some typical natural and synthetic fibres Density Young's Tensile Strain failure (kg/m3×10) modulus failure (%) (NWm2×10) (N/m2×10) Natural organic polymer base Jute 1.46 10-25 400-800 1-2 Hemp 1.48 26-30 550-900 1-6 Flax 1.54 40-85 800-2000 3-2.4 Sisal 1.33 46 700 2-3 Coir 1.25 6 221 15-40 Cotton 1.51 1-12 400-900 3-10 Synthetic organic polymer base HT carbon (T300) 1.76 230 3530 1.5 HM carbon (M40) 1.83 392 2740 0.7 HM aramide 1.45 133 3500 2.7 Inorganic base E-glass 2.58 73 3450 4.8 S/R-glass 2.48 88 4590 5.4 ssaidmau'peaupoo/ 210 Note:Properties of natural materials are very variable,so the figures shown are averages and collected from a great variety of publications. 周 tance.Decreasing structural weight,often beneficial for performance improvement,not only reduces the quantity and cost of materials but also often reduces the production time,and consequently the cost of manufac- turing.A powerful approach to reach this goal is the matrix reinforcement with proper fibres,to high possible volume fractions,continuous and with a complete control of fibre orientations,in other words to control anisotropy.The success of composite applications,by volume and by number,can be ranked by the success of the applied manufacturing tech- niques (Fig.8.4).For all processes shown,suitable for short to continuous fibres,the introductory (pioneering)period was based on thermosetting polymers,from phenolics,polyesters,vinylesters to epoxies.In the case of injection moulding with short (<10mm)and pressing with longer fibre rein- forcements (<100mm),thermoset polymers are being increasingly replaced by more expensive but technically equivalent or better thermoplastics. However,the main reason for this is the cost reduction by cycle time reduc- tion.Most important among the technologies mentioned is injection mould- ing of generally small and complex parts.The reinforcement by fibres is limited with respect to length,volume percentage (<35%)and orientation control.Flow-moulding of larger thermoset and thermoplastic shell- structures (SMC and GMT)became important as well,especially for car

tance. Decreasing structural weight, often beneficial for performance improvement, not only reduces the quantity and cost of materials but also often reduces the production time, and consequently the cost of manufacturing. A powerful approach to reach this goal is the matrix reinforcement with proper fibres, to high possible volume fractions, continuous and with a complete control of fibre orientations, in other words to control anisotropy. The success of composite applications, by volume and by number, can be ranked by the success of the applied manufacturing techniques (Fig. 8.4). For all processes shown, suitable for short to continuous fibres, the introductory (pioneering) period was based on thermosetting polymers, from phenolics, polyesters, vinylesters to epoxies. In the case of injection moulding with short (<10 mm) and pressing with longer fibre reinforcements (<100 mm), thermoset polymers are being increasingly replaced by more expensive but technically equivalent or better thermoplastics. However, the main reason for this is the cost reduction by cycle time reduction. Most important among the technologies mentioned is injection moulding of generally small and complex parts. The reinforcement by fibres is limited with respect to length, volume percentage (<35%) and orientation control. Flow-moulding of larger thermoset and thermoplastic shellstructures (SMC and GMT) became important as well, especially for car 246 3-D textile reinforcements in composite materials Table 8.2. Fibre properties of some typical natural and synthetic fibres Density Young’s Tensile Strain failure (kg/m3 ¥ 103 ) modulus failure (%) (N/m2 ¥ 109 ) (N/m2 ¥ 106 ) Natural organic polymer base Jute 1.46 10–25 400–800 1–2 Hemp 1.48 26–30 550–900 1–6 Flax 1.54 40–85 800–2000 3–2.4 Sisal 1.33 46 700 2–3 Coir 1.25 6 221 15–40 Cotton 1.51 1–12 400–900 3–10 Synthetic organic polymer base HT carbon (T300) 1.76 230 3530 1.5 HM carbon (M40) 1.83 392 2740 0.7 HM aramide 1.45 133 3500 2.7 Inorganic base E-glass 2.58 73 3450 4.8 S/R-glass 2.48 88 4590 5.4 Note: Properties of natural materials are very variable, so the figures shown are averages and collected from a great variety of publications. RIC8 7/10/99 8:26 PM Page 246 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:31:28 AM IP Address: 158.132.122.9

248 3-D textile reinforcements in composite materials pressure vessels and the pultrusion of composite profiles.Typical for the advanced composite sector is the use of continuous fibres(glass,aramid and carbon)and the high fibre volume percentages(<70%).It is still the domain of thermosetting polymers. Although the application of advanced continuous fibre reinforced com- posites may result in highly satisfactory structural performances [3],the volume and number of applications are still limited.The success of the advanced composites depends completely on the availability of fast and reproducible industrial manufacturing processes. A development of such an industrial process based on 3-D deformation, i.e.draping,of (impregnated)textile fabrics,is the subject of this chapter. The major deformation mechanisms,the geometrical draping-simulation strategies,finite element simulation and the final product optimization, essential for designers and analysts,is outlined in the following sections. The draping process is part of a press-forming cycle,more specifically the press forming of textile fabrics which are impregnated to a certain extent with thermosetting or preferably thermoplastic polymers.Nowadays many industrial impregnation strategies for both thermosetting or thermoplastic 业 polymers are available.Once the fabric has been impregnated and the polymer brought to a deformable state,e.g.by heating,the plain sheet can be formed into a shell structure in seconds by press forming and(re)con- solidation in the last phase by application of matching dies.This technol- ogy can be used to produce high-quality preforms for the (thermosetting) resin injection or transfer moulding (RTM)of advanced aircraft and car components (Fig.8.4).Major successes are,however,achieved in the press 人兰今份 forming of continuous reinforced thermoplastic composite parts (Figs.8.5 and 8.6).Similar to the already-mentioned technologies for advanced com- posites,high fibre volume contents and reproducible fibre orientations are typical for press forming.The speed is comparable with the ordinary injec- tion moulding and flow-moulding of short fibre reinforced parts.The pres- sure levels are relatively low:for forming,1 bar or less;for (re-) consolidation,10-40 bar.When the heating and cooling times are consid- ered as well (for thin-walled structures,a matter of seconds),it is clear that the press forming of advanced composites is not only attractive because of its manufacturing speed,but also because of the light-weight equipment and minimum energy required [4]. 8.1.4 Outline of the simulation and optimization strategy The following sections deal with the simulation and optimization of 3-D formed continuous fibre reinforced components.In the scheme shown in Fig.8.5 the role they play in an integral process of design and analysis is clarified.When automated structural optimization is applied,the scheme

pressure vessels and the pultrusion of composite profiles. Typical for the advanced composite sector is the use of continuous fibres (glass, aramid and carbon) and the high fibre volume percentages (<70%). It is still the domain of thermosetting polymers. Although the application of advanced continuous fibre reinforced composites may result in highly satisfactory structural performances [3], the volume and number of applications are still limited. The success of the advanced composites depends completely on the availability of fast and reproducible industrial manufacturing processes. A development of such an industrial process based on 3-D deformation, i.e. draping, of (impregnated) textile fabrics, is the subject of this chapter. The major deformation mechanisms, the geometrical draping–simulation strategies, finite element simulation and the final product optimization, essential for designers and analysts, is outlined in the following sections. The draping process is part of a press-forming cycle, more specifically the press forming of textile fabrics which are impregnated to a certain extent with thermosetting or preferably thermoplastic polymers. Nowadays many industrial impregnation strategies for both thermosetting or thermoplastic polymers are available. Once the fabric has been impregnated and the polymer brought to a deformable state, e.g. by heating, the plain sheet can be formed into a shell structure in seconds by press forming and (re)consolidation in the last phase by application of matching dies. This technology can be used to produce high-quality preforms for the (thermosetting) resin injection or transfer moulding (RTM) of advanced aircraft and car components (Fig. 8.4). Major successes are, however, achieved in the press forming of continuous reinforced thermoplastic composite parts (Figs. 8.5 and 8.6). Similar to the already-mentioned technologies for advanced composites, high fibre volume contents and reproducible fibre orientations are typical for press forming. The speed is comparable with the ordinary injection moulding and flow-moulding of short fibre reinforced parts. The pressure levels are relatively low: for forming, 1 bar or less; for (re-) consolidation, 10–40 bar. When the heating and cooling times are considered as well (for thin-walled structures, a matter of seconds), it is clear that the press forming of advanced composites is not only attractive because of its manufacturing speed, but also because of the light-weight equipment and minimum energy required [4]. 8.1.4 Outline of the simulation and optimization strategy The following sections deal with the simulation and optimization of 3-D formed continuous fibre reinforced components. In the scheme shown in Fig. 8.5 the role they play in an integral process of design and analysis is clarified. When automated structural optimization is applied, the scheme 248 3-D textile reinforcements in composite materials RIC8 7/10/99 8:26 PM Page 248 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:31:28 AM IP Address: 158.132.122.9

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