《纺织复合材料》课程参考文献（3-D textile reinforcements in composite materials）02 3-D textile reinforced composites for the transportation industry

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 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. 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, 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 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. 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 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 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 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. 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 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 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 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 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. 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