2 3-D textile reinforced composites for the transportation industry K.DRECHSLER 2.1 Introduction Composites with directionally oriented long-fibre reinforcement have proven their potential for realizing high-performance,low-mass structural components in the aerospace industry over the past 40 years.Starting from the German glider 'Phonix',which was designed and manufactured using glass fibre reinforced resin,right to the Airbus carbon fibre fin,the mater- ial has helped to extend the limits of the performance and efficiency of planes,helicopters and space structures further and further.The benefits are reductions in fuel consumption and emission,improved payloads and extended service lives due to higher mass-specific stiffness,strength and energy absorption,as well as better fatigue and corrosion performance than metals. n As a consequence,it is not very surprising that other fields of application outside the aerospace sector have an increasing interest in applying this kind of material,too.In the automotive industry,the need for cars with higher efficiency and no losses in terms of safety and comfort has become more and more important because of interest in improved environmental compatibility-low mass is one of the key factors in reaching this goal. Nevertheless,there are significant differences in the requirements for manufacturing methods and structural performance which prevent an easy transfer of know-how from aerospace to automotive applications.One of the most crucial differences is that of production rates.While aerospace components are usually manufactured at a rate of no more than a few hundred,the high-volume automotive market has a need for some hundred thousand components a year.Another difference is the costs allowed for weight reductions.While the space industry spends up to some US$10,000 just to save 1kg of mass in a satellite,the automotive market currently accepts no more than some US$10-20. Thus,the big challenge for the next few years will be developing materi- als,processing methods and structural concepts which allow cost-effective, 43
2.1 Introduction Composites with directionally oriented long-fibre reinforcement have proven their potential for realizing high-performance, low-mass structural components in the aerospace industry over the past 40 years. Starting from the German glider ‘Phönix’, which was designed and manufactured using glass fibre reinforced resin, right to the Airbus carbon fibre fin, the material has helped to extend the limits of the performance and efficiency of planes, helicopters and space structures further and further.The benefits are reductions in fuel consumption and emission, improved payloads and extended service lives due to higher mass-specific stiffness, strength and energy absorption, as well as better fatigue and corrosion performance than metals. As a consequence, it is not very surprising that other fields of application outside the aerospace sector have an increasing interest in applying this kind of material, too. In the automotive industry, the need for cars with higher efficiency and no losses in terms of safety and comfort has become more and more important because of interest in improved environmental compatibility – low mass is one of the key factors in reaching this goal. Nevertheless, there are significant differences in the requirements for manufacturing methods and structural performance which prevent an easy transfer of know-how from aerospace to automotive applications. One of the most crucial differences is that of production rates. While aerospace components are usually manufactured at a rate of no more than a few hundred, the high-volume automotive market has a need for some hundred thousand components a year. Another difference is the costs allowed for weight reductions. While the space industry spends up to some US$10,000 just to save 1kg of mass in a satellite, the automotive market currently accepts no more than some US$10–20. Thus, the big challenge for the next few years will be developing materials, processing methods and structural concepts which allow cost-effective, 2 3-D textile reinforced composites for the transportation industry K. DRECHSLER 43 RIC2 7/10/99 7:24 PM Page 43 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
44 3-D textile reinforcements in composite materials high-volume manufacturing of low-mass composite components.A very promising approach to achieving this goal is the development and applica- tion of advanced textile technologies,such as 3-D weaving,3-D braiding, knitting or stitching,offering the potential for automated manufacturing of near net shaped fibre preforms with optimized fibre reinforcement in 3-D space according to structural requirements. In combination with appropriate impregnation or consolidation tech- niques,a significant reduction of manual work can be realized compared with state-of-the-art aerospace technologies based on unidirectional fibre tapes or 2-D weavings.In this way,one of the most important requirements for cost reduction in aerospace and the introduction of composites in high- volume automotive applications can be fulfilled.Another very interesting feature is the possibility to produce a 3-D fibre reinforcement in the com- posite material.It has been shown that this results in significantly improved damage tolerance and structural integrity. 9 The focal points in this chapter are the description of benefits and draw- backs involved in composite materials with conventional and textile rein- forcement compared with metals,the requirements for the material with regard to aerospace and automotive applications,and discussion of first 容t exemplary applications demonstrating the potential of textile structural composites for improving mechanical performance and reducing manufac- turing costs. 2.2 The mechanical performance of conventional and 3-D reinforced composites 8 The mechanical performance of composites is mainly determined by the fibre type and the reinforcing fibre geometry.The most important fibre types are glass,carbon and aramide fibres.It has been shown that carbon fibres offer by far the best potential in terms of stiffness.Therefore,they represent the most important material for aerospace applications.They have so far not been considered as a structural material for high-volume automotive applications because prices are very high,ranging from $20 to 500/kg.In this field,glass fibres,which are priced at approximately $3/kg, represent the most important material. In the near future it can be expected that much cheaper carbon fibres will be launched on the market.Nevertheless,the mechanical performance and the textile processability of this new fibre class have to be proven, because it may be necessary to use much thicker fibre bundles to reach the cost reduction goal.The second factor of influence is the reinforcing fibre geometry,whereby composites can be broken down into two classes: material with non-directional (short)fibre reinforcement (mats,injection
high-volume manufacturing of low-mass composite components. A very promising approach to achieving this goal is the development and application of advanced textile technologies, such as 3-D weaving, 3-D braiding, knitting or stitching, offering the potential for automated manufacturing of near net shaped fibre preforms with optimized fibre reinforcement in 3-D space according to structural requirements. In combination with appropriate impregnation or consolidation techniques, a significant reduction of manual work can be realized compared with state-of-the-art aerospace technologies based on unidirectional fibre tapes or 2-D weavings. In this way, one of the most important requirements for cost reduction in aerospace and the introduction of composites in highvolume automotive applications can be fulfilled. Another very interesting feature is the possibility to produce a 3-D fibre reinforcement in the composite material. It has been shown that this results in significantly improved damage tolerance and structural integrity. The focal points in this chapter are the description of benefits and drawbacks involved in composite materials with conventional and textile reinforcement compared with metals, the requirements for the material with regard to aerospace and automotive applications, and discussion of first exemplary applications demonstrating the potential of textile structural composites for improving mechanical performance and reducing manufacturing costs. 2.2 The mechanical performance of conventional and 3-D reinforced composites The mechanical performance of composites is mainly determined by the fibre type and the reinforcing fibre geometry. The most important fibre types are glass, carbon and aramide fibres. It has been shown that carbon fibres offer by far the best potential in terms of stiffness. Therefore, they represent the most important material for aerospace applications. They have so far not been considered as a structural material for high-volume automotive applications because prices are very high, ranging from $20 to 500/kg. In this field, glass fibres, which are priced at approximately $3/kg, represent the most important material. In the near future it can be expected that much cheaper carbon fibres will be launched on the market. Nevertheless, the mechanical performance and the textile processability of this new fibre class have to be proven, because it may be necessary to use much thicker fibre bundles to reach the cost reduction goal. The second factor of influence is the reinforcing fibre geometry, whereby composites can be broken down into two classes: material with non-directional (short) fibre reinforcement (mats, injection 44 3-D textile reinforcements in composite materials RIC2 7/10/99 7:24 PM Page 44 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
3-D textile reinforced composites for the transportation industry 45 moulding)and with directionally oriented long fibres(unidirectional tapes, fabrics). For aerospace components,only directionally oriented long fibres are used,as this configuration alone allows full utilization of the fibre proper- ties,and an optimal anisotropic design according to the structural require- ments concerned.So far,use of this material in high-volume manufacturing has been limited to easily shaped components,because the manufacturing process requires a lot of manual work. In Fig.2.1,the most important mechanical properties of the composites are compared with light metals and steel.It is shown that the most signifi- cant mass reductions can be achieved using carbon fibres and a non- isotropic fibre reinforcement,as required by the respective loads.When comparing quasi-isotropic composites with metals,one will find that mass savings of more than 30%compared with aluminium,and 60%compared with steel are feasible. 15650t Nevertheless,this comparison is based on 'idealized'laboratory-scale values determined under the following conditions:unidirectional rein- forcement,high fibre volume fraction (60%),tensile load,no fibre undula- tion and no delaminations.In realistic applications several additional udmau'praypoon//:dny Aq ■steel ZIEI'85I :dl Aluminium 图CFRP-UD 6 weight spec. weight spec weight spec. residual strength damping stiffness strength energy absorption after fatigue Potential for weight reduction 70%compared to steel 40%compared to aluminium 2.1 Comparison between mechanical performance of metals and composite materials
moulding) and with directionally oriented long fibres (unidirectional tapes, fabrics). For aerospace components, only directionally oriented long fibres are used, as this configuration alone allows full utilization of the fibre properties, and an optimal anisotropic design according to the structural requirements concerned. So far, use of this material in high-volume manufacturing has been limited to easily shaped components, because the manufacturing process requires a lot of manual work. In Fig. 2.1, the most important mechanical properties of the composites are compared with light metals and steel. It is shown that the most signifi- cant mass reductions can be achieved using carbon fibres and a nonisotropic fibre reinforcement, as required by the respective loads. When comparing quasi-isotropic composites with metals, one will find that mass savings of more than 30% compared with aluminium, and 60% compared with steel are feasible. Nevertheless, this comparison is based on ‘idealized’ laboratory-scale values determined under the following conditions: unidirectional reinforcement, high fibre volume fraction (60%), tensile load, no fibre undulation and no delaminations. In realistic applications several additional 3-D textile reinforced composites for the transportation industry 45 2.1 Comparison between mechanical performance of metals and composite materials. RIC2 7/10/99 7:25 PM Page 45 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
46 3-D textile reinforcements in composite materials 100% 60% 20% ud-rein- fibre ud quasi- ud quasi. forcement misalignment 中=60% isotropic isotropic mat,knitting 0=60% 中=50% 0=60% compression◆=60% =60% φ=50% tensile load tensile load load compression tensile tensile load tensile load load after impact 2.2 Degradation of composite performance due to manufacturing and UDOSJdEPUDOPOOMdiN WV St:6t in-service effects. 2102 factors of influence have to be taken into consideration which can be caused by the series manufacturing process,the structural service conditions,the 网 component geometry and the fibre reinforcement.Figure 2.2 gives an idea of the magnitude of the various factors of influence. It is obvious that unidirectional tape-based composites offer the highest 是69 utilization of fibre properties and therefore the highest in-plane stiffness and strength,because the fibres are aligned without any curvature exactly in the loading direction and no resin-rich areas cause strain inhomo- geneities within the material. All textile structures show a more or less high degree of fibre undulation. In 2-D weavings this effect is caused by the mutual crosslinking of weft and warp fibres,and weft knittings consist more or less of a mesh system with curved fibres.Additional degradations of in-plane properties are caused principally by a 3-D reinforcement,because the z-directional fibre fraction reduces the share of load-carrying fibres and generates resin-rich areas. Optimizing these effects is very important especially for aerospace appli- cations:despite the growing need for cost savings,low weight is still the driving force for research and development in this field of application. In the past years,significant improvements have been realized for example in the field of 3-D weaving.In Fig.2.3 2-D weavings,'conventional' 3-D weavings and advanced 3-D weavings,manufactured by a process recently developed by the North Carolina State University,are compared. It is shown that,owing to reduced fibre undulation and fibre damage,the
factors of influence have to be taken into consideration which can be caused by the series manufacturing process, the structural service conditions, the component geometry and the fibre reinforcement. Figure 2.2 gives an idea of the magnitude of the various factors of influence. It is obvious that unidirectional tape-based composites offer the highest utilization of fibre properties and therefore the highest in-plane stiffness and strength, because the fibres are aligned without any curvature exactly in the loading direction and no resin-rich areas cause strain inhomogeneities within the material. All textile structures show a more or less high degree of fibre undulation. In 2-D weavings this effect is caused by the mutual crosslinking of weft and warp fibres, and weft knittings consist more or less of a mesh system with curved fibres. Additional degradations of in-plane properties are caused principally by a 3-D reinforcement, because the z-directional fibre fraction reduces the share of load-carrying fibres and generates resin-rich areas. Optimizing these effects is very important especially for aerospace applications: despite the growing need for cost savings, low weight is still the driving force for research and development in this field of application. In the past years, significant improvements have been realized for example in the field of 3-D weaving. In Fig. 2.3 2-D weavings,‘conventional’ 3-D weavings and advanced 3-D weavings, manufactured by a process recently developed by the North Carolina State University, are compared. It is shown that, owing to reduced fibre undulation and fibre damage, the 46 3-D textile reinforcements in composite materials 2.2 Degradation of composite performance due to manufacturing and in-service effects. RIC2 7/10/99 7:25 PM Page 46 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
3-D textile reinforced composites for the transportation industry 47 Tensile strength Compression strength 700 Compression strength after impact传7JWmm 600 500 400 300 200 100 0 2-D 3-D 3-D advanced wo'ssaudmau'peaupoo/ WV St:6Z 2.3 Mechanical performance of various 2-D and 3-D woven composites. 2102 effect of the 3-D reinforcement can be compensated and the stiffness and strength of 2-D weavings can be achieved. Naturally,no problems with fibre curvature occur in multiaxial warp knit- tings,because the fibre layers are placed on top of each other without crosslinking.Nevertheless,the stitching fibres,holding the single layers together,can lead to a reduction of mechanical performance owing to fibre damage or to disturbance of the reinforcing fibre alignment.The mechani- cal performance of weft knittings can be improved by prestretching the meshes before curing or by an additional fibre system running straight through the mesh system. High stiffness and strength are just two criteria for the evaluation and selection of a structural material for automotive and aerospace applications. In particular,components that are susceptible to impact or crash loads have to be designed according to their mechanical performance after a first failure.This can lead to the necessity of high safety factors,reducing the weight reduction potential.Therefore,the 'damage tolerance'can be an important material property. Conventional 2-D reinforced composites based on tapes or weavings tend to delaminate owing to impact loads,because the bonding between the single layers is relatively poor,which leads to poor interlaminar per- formance.A significant improvement is possible by a 3-D through-the- thickness fibre reinforcement,which can be realized by 3-D-weaving, 3-D-braiding or stitching
effect of the 3-D reinforcement can be compensated and the stiffness and strength of 2-D weavings can be achieved. Naturally, no problems with fibre curvature occur in multiaxial warp knittings, because the fibre layers are placed on top of each other without crosslinking. Nevertheless, the stitching fibres, holding the single layers together, can lead to a reduction of mechanical performance owing to fibre damage or to disturbance of the reinforcing fibre alignment. The mechanical performance of weft knittings can be improved by prestretching the meshes before curing or by an additional fibre system running straight through the mesh system. High stiffness and strength are just two criteria for the evaluation and selection of a structural material for automotive and aerospace applications. In particular, components that are susceptible to impact or crash loads have to be designed according to their mechanical performance after a first failure. This can lead to the necessity of high safety factors, reducing the weight reduction potential. Therefore, the ‘damage tolerance’ can be an important material property. Conventional 2-D reinforced composites based on tapes or weavings tend to delaminate owing to impact loads, because the bonding between the single layers is relatively poor, which leads to poor interlaminar performance. A significant improvement is possible by a 3-D through-thethickness fibre reinforcement, which can be realized by 3-D-weaving, 3-D-braiding or stitching. 3-D textile reinforced composites for the transportation industry 47 700 600 500 400 300 200 100 0 Tensile strength Compression strength Compression strength after impact (6.7 J/mm) 2-D 3-D 3-D advanced MPa 2.3 Mechanical performance of various 2-D and 3-D woven composites. RIC2 7/10/99 7:25 PM Page 47 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
48 3-D textile reinforcements in composite materials Compression after Impact 6,7 [J/mm] 07 Customer Requirement 0,6 V 0.5 0.65 0,4 0.55 0.3 0,5 0.36 0,35 0.2 0.1 十 Tape Laminate Tape Laminate Tape Laminate 2-D woven 3-D woven Thermoset Interleaved Thermoplast Thermoset Thermoset 2.4 Damage tolerance of different composite materials. WV St:6Z 210e In Fig.2.4,the damage tolerances of various composite materials,char- acterized by the compression after impact test,are compared.In this test, 网 composite plates are impacted and afterwards compression tested accord- ing to exactly defined specifications.The remaining strength and breaking elongation represents a value for the damage tolerance evaluation and the design of impact-susceptible structures. It is shown that performance after impact can be improved significantly by the 3-D fibre reinforcement.With a fibre share of below 5%,the design goal of 0.5%after impact that is required in aerospace can be reached even with brittle resin systems.The parameters that influence performance are type,thickness and distance of z-fibres as well as the reinforcing geometry.Figure 2.5 illustrates the reason for higher impregnation speed.Compared with 2-D composites,the z-fibres lead to a significant improvement in bonding of the single layers,as demonstrated by the peel strength. The structural integrity is of major importance,especially for automotive applications.After a crash,the structures have to maintain a minimum mechanical performance.Complete debonding of component parts has to be avoided.These criteria can be realized easily by metals owing to their plastic deformation characteristics.The more or less brittle crush behaviour of conventional,especially carbon fibre reinforced composites is much more critical in this respect. This performance can also be improved by a 3-D fibre reinforcement
In Fig. 2.4, the damage tolerances of various composite materials, characterized by the compression after impact test, are compared. In this test, composite plates are impacted and afterwards compression tested according to exactly defined specifications. The remaining strength and breaking elongation represents a value for the damage tolerance evaluation and the design of impact-susceptible structures. It is shown that performance after impact can be improved significantly by the 3-D fibre reinforcement. With a fibre share of below 5%, the design goal of 0.5% after impact that is required in aerospace can be reached even with brittle resin systems. The parameters that influence performance are type, thickness and distance of z-fibres as well as the reinforcing geometry. Figure 2.5 illustrates the reason for higher impregnation speed. Compared with 2-D composites, the z-fibres lead to a significant improvement in bonding of the single layers, as demonstrated by the peel strength. The structural integrity is of major importance, especially for automotive applications. After a crash, the structures have to maintain a minimum mechanical performance. Complete debonding of component parts has to be avoided. These criteria can be realized easily by metals owing to their plastic deformation characteristics. The more or less brittle crush behaviour of conventional, especially carbon fibre reinforced composites is much more critical in this respect. This performance can also be improved by a 3-D fibre reinforcement. 48 3-D textile reinforcements in composite materials 2.4 Damage tolerance of different composite materials. RIC2 7/10/99 7:25 PM Page 48 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
3-D textile reinforced composites for the transportation industry 49 800 700 3-d 600 500 三 400 300 2-d 200 Thermoplast 100 Toughened Thermoset Thermoset 10 15 20 25 Notch Length (mm) 2.5 Notch growth in 2-D and 3-D reinforced composites. WV St:6 202 Figure 2.6 shows double T-shaped beams,typical structural components in automotive and aerospace design,after longitudinal and transversal crash tests.The preforms for the composite structures are integrally 3-D braided by a new'n-step'braiding process in an optimum configuration according to the loads.The integral fibre reinforcement guarantees high structural 具 integrity with locally restricted damage area and high after-crash perfor- mance.An additional feature is the high mass-specific energy absorption owing to the complex,exactly controllable failure modes in the 3-D fibre structure. More complex preforms for composites with high structural integrity which cannot be made by one textile technology can be realized by stitch- ing several basic preforms together.A stiffened panel is discussed in Chapter 5 as an example.It has been made by stitching the warp-knitted skin to a 3-D braided profile. 2.3 Manufacturing textile structural composites The diverse textile processes,such as advanced weaving,braiding,knitting or stitching,allow the production of more or less complex fibre preforms. While weavings and warp knittings are predestined for flat panels,braid- ings allow the manufacture of profiles.The most complex preforms can be realized where warp-knitting is used.Tables 2.1 and 2.2 summarize the most important features of textile process and composites as well as the
Figure 2.6 shows double T-shaped beams, typical structural components in automotive and aerospace design, after longitudinal and transversal crash tests. The preforms for the composite structures are integrally 3-D braided by a new ‘n-step’ braiding process in an optimum configuration according to the loads. The integral fibre reinforcement guarantees high structural integrity with locally restricted damage area and high after-crash performance. An additional feature is the high mass-specific energy absorption owing to the complex, exactly controllable failure modes in the 3-D fibre structure. More complex preforms for composites with high structural integrity which cannot be made by one textile technology can be realized by stitching several basic preforms together. A stiffened panel is discussed in Chapter 5 as an example. It has been made by stitching the warp-knitted skin to a 3-D braided profile. 2.3 Manufacturing textile structural composites The diverse textile processes, such as advanced weaving, braiding, knitting or stitching, allow the production of more or less complex fibre preforms. While weavings and warp knittings are predestined for flat panels, braidings allow the manufacture of profiles. The most complex preforms can be realized where warp-knitting is used. Tables 2.1 and 2.2 summarize the most important features of textile process and composites as well as the 3-D textile reinforced composites for the transportation industry 49 2.5 Notch growth in 2-D and 3-D reinforced composites. RIC2 7/10/99 7:25 PM Page 49 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
50 3-D textile reinforcements in composite materials 100 WVst:6Z:ZI I 1OZ ZZ Anutr 'Aupines 80 6'ZZI'ZEI'8SI :dl 60 40 20 0 10 20 30 40 50 60 70 Displacement [mm] 2.6 Structural integrity of 3-D braided profiles after crash
50 3-D textile reinforcements in composite materials 2.6 Structural integrity of 3-D braided profiles after crash. RIC2 7/10/99 7:25 PM Page 50 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
s6u!eaM OE leixeninW enjonns Bununow ewn 6ununow y6!H woo'ssaidmau'peaypoow//:dny Aq paranad WVSt:6Z:ZI I 10Z 'ZZ KIenunr 'Kupines pue yem o1 peuw! eqy-z snole 6'ZZI'ZEI'8SI :ssauppy dl (noZ7 souqej iely (seunjonjis 品 号 51
Table 2.1. Textile processes for composites: an overview Textile Principle – design Preform geometry Fibre orientation Productivity Development goals process mounting 3D Flat fabrics Limited to weft and High productivity Multiaxial 3D weavings weaving Integral stiffeners warp direction (0/90) Very high mounting with integrated 45° Integral sandwich-structure Various z-fibre time fibres Simple profiles reinforcements 3D Open and closed profiles Braiding fibres 10–80° Medium productivity Varying cross-sections braiding (I, L, Z, O, U, ...) Local integration of High mounting time Varying fibre orientation Flat fabrics straight 0° fibres Knitting Very complex preforms Fibres mainly in Medium productivity Integration of straight (weft) (knot-elements, curved mesh structure Short mounting time fibres in the mesh structures) structure 51 RIC2 7/10/99 7:25 PM Page 51 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
auo ul sJeAel senons (azis 'a6ewep)peay 6ununow ewn Bununow joys WVSt:6Z:ZI I 10Z 'ZZ KIenunr 'Kupines ulew u!aldwexe uonloeJip ssens oiseq uo 6u!puadea 6'ZZI'ZEI'8SI :ssappy dl -yoIMpues leJBajul seunjonJis (dieM) 52
Table 2.1. (cont.) Textile Principle – design Preform geometry Fibre orientation Productivity Development goals process mounting Knitting Flat fabrics Multiaxial in-plane High productivity Integration of more (warp) Integral sandwich- orientation High mounting time layers in one structures 0°/90°/±45° production step Up to 7 layers fixed by knitting fibre Embroidery Attaching additional Very complex fibre Slow process Improvement of fibres on basic fabrics orientation, for Short mounting time production speed example in main Optimization of control stress direction program for 3-D structures Stitching Very complex preforms Depending on basic Very quick process Optimization of control by combining several preforms Short mounting time program for 3-D textile structures structures Optimization of stitchhead (damage, size) 52 RIC2 7/10/99 7:25 PM Page 52 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:45 AM IP Address: 158.132.122.9
