Adv. Composite Mater, Vol 15, No 1, Pp 3-37(2006) VSP 2006 Alsoavailableonline-www.vsppub R Overview of trends in advanced composite research and applications in Japan TAKASHI ISHIKAWA* Aviation Program Director, Japan Aerospace Exploration Agency, 7-44-, Jindaiji-Higashi-Machi Chofu, Tokyo 182-8522, Japan Received 28 November 2005; accepted 22 December 2005 Abstract-Recent research activities in advanced composites technologies conducted in Japan are reviewed and introduced. New research topics in reinforcing fibers described are low modulus pitch-based carbon fiber and PBO fiber. The second of these is very topical at the present time nano-technology based composites use materials such as carbon nanotube, or carbon nano-fiber, or nanoclay. Because the Composites Technology Center in the Japan Aerospace Exploration Agency (AXA) leads many new research fields in composites, the present review paper shows a slight bias towards the outputs of JAXA. The most remarkable outcome in this field at present is a compression ength improvement by loading cup-stack type carbon nano-fiber (CSCNF). Prepreg containing this CsCNF has been developed and has already been released into the market. The third topic is related to newly developed high performance polymers including heat resistant polyimide, Tri A-Pl and its family. The most recent product is a heat resistant polyimide that is highly soluble in some organic solvents; this material is suitable for preparation of imide wet prepreg. Composit fabricated through this prepreg route exhibit no voids and defects compared to the traditional amid id polyimide prepreg route. Another new topic in polymers is related to Japan's national project, radiation cure polymers and their processing. Electron beam cure, ultra-violet cure and visual light cure resins and their processing technologies have been developed in this national project. The next topic is a development of the low cost composites technology mainly for aircraft components. JAXA's activities related to this field are introduced first based on two new key technologies-Z-anchors and stitching. New findings about the mechanism of interlaminar reinforcement by stitching ar lightly focused. Finally, remarkable theoretical findings about composite mechanics in recent years are described. A clarification of mechanics of compression after impact behavior by using a newly developed cohesive zone element is reviewed first in this category. Matrix crack growth theories in the laminae adjacent to the initially cracked layer are introduced next where a motivation of this esearch is a cryogenic composite tank for future space transportation systems. The final topic is a development of the theory of structural health monitoring by using small diameter FBG sensor. By an evolution of these theories structural health monitoring has almost reached the level of practical Edited by the JSCM E-mail: isikawa@ chofu jaxa. jp
Adv. Composite Mater., Vol. 15, No. 1, pp. 3–37 (2006) VSP 2006. Also available online - www.vsppub.com Review Overview of trends in advanced composite research and applications in Japan TAKASHI ISHIKAWA ∗ Aviation Program Director, Japan Aerospace Exploration Agency, 7-44-1, Jindaiji-Higashi-Machi, Chofu, Tokyo 182-8522, Japan Received 28 November 2005; accepted 22 December 2005 Abstract—Recent research activities in advanced composites technologies conducted in Japan are reviewed and introduced. New research topics in reinforcing fibers described are low modulus pitch-based carbon fiber and PBO fiber. The second of these is very topical at the present time: nano-technology based composites use materials such as carbon nanotube, or carbon nano-fiber, or nanoclay. Because the Composites Technology Center in the Japan Aerospace Exploration Agency (JAXA) leads many new research fields in composites, the present review paper shows a slight bias towards the outputs of JAXA. The most remarkable outcome in this field at present is a compression strength improvement by loading cup-stack type carbon nano-fiber (CSCNF). Prepreg containing this CSCNF has been developed and has already been rerleased into the market. The third topic is related to newly developed high performance polymers including heat resistant polyimide, Tri A-PI and its family. The most recent product is a heat resistant polyimide that is highly soluble in some organic solvents; this material is suitable for preparation of imide wet prepreg. Composites fabricated through this prepreg route exhibit no voids and defects compared to the traditional amidacid polyimide prepreg route. Another new topic in polymers is related to Japan’s national project, radiation cure polymers and their processing. Electron beam cure, ultra-violet cure and visual light cure resins and their processing technologies have been developed in this national project. The next topic is a development of the low cost composites technology mainly for aircraft components. JAXA’s activities related to this field are introduced first based on two new key technologies — Z-anchor® and stitching. New findings about the mechanism of interlaminar reinforcement by stitching are slightly focused. Finally, remarkable theoretical findings about composite mechanics in recent years are described. A clarification of mechanics of compression after impact behavior by using a newly developed cohesive zone element is reviewed first in this category. Matrix crack growth theories in the laminae adjacent to the initially cracked layer are introduced next where a motivation of this research is a cryogenic composite tank for future space transportation systems. The final topic is a development of the theory of structural health monitoring by using small diameter FBG sensor. By an evolution of these theories structural health monitoring has almost reached the level of practical applications. Edited by the JSCM. *E-mail: isikawa@chofu.jaxa.jp
T Ishikawa Keywords: New fiber; nanotube; new polymer; low cost technologies: new theoretical findings 1 INTRODUCTION It is a very fortunate situation that Advanced Composite Materials, which used to be the official journal of the Japan Society for Composite Materials (SCM) has become the official publication controlled equally by the Korean Society for Composite Materials(KSCM) and JSCM. In order to celebrate this re-inauguration of the journal, the joint editorial board has decided to publish two review papers about composite research trends in each country. The author representing the Japanese side(ti) is very pleased and honored to be given such a great opportunity So, this article is not only a scientific review of the composite research trends but also a proof of the friendship in composite research and development fields between two countries which has been fostered for a long time This review article covers wide aspects of advanced composites research trends conducted in Japan. However, an emphasis is naturally placed on aerospace related research subjects reflecting the author's interest and affiliation (Japan Aerospace Exploration Agency: JAXA). Moreover, the referred topics will be biased slightly into jaXa in-house research because he is familiar with the recent interesting results there. The author would like to apologize to the reader about this bias first Df course, the fact that the length of the article is limited is another constraint on the content coverage. Thus, he tries to concentrate on new, topical, fascinating and important topics in composite research and development in various engineering fields as much as possible. If this article can stimulate many brilliant young composite researchers in both countries, the author fully accomplishes his aim for blication 2. FIBERS AND REINFORCEMENTS The most important reinforcing fiber in advanced composites is, of course, carbon fiber which is roughly classified into two groups- high strength fiber and high modulus fiber. Japan dominates in commercial production of carbon fibers on the woria wide scale, as shown in Fig. 1. Development directions of carbon fiber have been clearly split corresponding to the above two groups in these past twenty years, as shown in Fig. 2 [1]. However, growth in the fiber properties towards high strength(moving upwards on the graph) and high modulus(moving right on the graph) directions seems to have become saturated in recent years. Among such trends, a newcomer is a group of low modulus fibers based on pitch as indicated in Fig. 2 by solid circle symbols. This type of carbon fiber is an invention of Nihon Graphite Fiber Co. Ltd [2] in Japan. One unique feature of these fibers is high strain-to-failure in compression in unidirectional composites made of these fibers [2] as shown in Table 1. Due to this unique feature, these fibers can be applied
4 T. Ishikawa Keywords: New fiber; nanotube; new polymer; low cost technologies; new theoretical findings. 1. INTRODUCTION It is a very fortunate situation that Advanced Composite Materials, which used to be the official journal of the Japan Society for Composite Materials (JSCM), has become the official publication controlled equally by the Korean Society for Composite Materials (KSCM) and JSCM. In order to celebrate this re-inauguration of the journal, the joint editorial board has decided to publish two review papers about composite research trends in each country. The author representing the Japanese side (TI) is very pleased and honored to be given such a great opportunity. So, this article is not only a scientific review of the composite research trends but also a proof of the friendship in composite research and development fields between two countries which has been fostered for a long time. This review article covers wide aspects of advanced composites research trends conducted in Japan. However, an emphasis is naturally placed on aerospace related research subjects reflecting the author’s interest and affiliation (Japan Aerospace Exploration Agency: JAXA). Moreover, the referred topics will be biased slightly into JAXA in-house research because he is familiar with the recent interesting results there. The author would like to apologize to the reader about this bias first. Of course, the fact that the length of the article is limited is another constraint on the content coverage. Thus, he tries to concentrate on new, topical, fascinating and important topics in composite research and development in various engineering fields as much as possible. If this article can stimulate many brilliant young composite researchers in both countries, the author fully accomplishes his aim for the publication. 2. FIBERS AND REINFORCEMENTS The most important reinforcing fiber in advanced composites is, of course, carbon fiber which is roughly classified into two groups — high strength fiber and high modulus fiber. Japan dominates in commercial production of carbon fibers on the world wide scale, as shown in Fig. 1. Development directions of carbon fiber have been clearly split corresponding to the above two groups in these past twenty years, as shown in Fig. 2 [1]. However, growth in the fiber properties towards high strength (moving upwards on the graph) and high modulus (moving right on the graph) directions seems to have become saturated in recent years. Among such trends, a newcomer is a group of low modulus fibers based on pitch as indicated in Fig. 2 by solid circle symbols. This type of carbon fiber is an invention of Nihon Graphite Fiber Co. Ltd. [2] in Japan. One unique feature of these fibers is a high strain-to-failure in compression in unidirectional composites made of these fibers [2] as shown in Table 1. Due to this unique feature, these fibers can be applied
Trends in composite research in Japa 2000oTon/Year Japans Product 10000 1973197819831988199319982003 Figure 1. Worldwide production of carbon fiber and Japan's domination GP ◆ PAN High Strength Glass Fiber ■ PAN High Modulus H。 o Pitch Low Modulus Aluminum alloy High-Ten. Steel 01002003004005006007008009001000GPa Figure 2. Development trends in carbon fiber properties to unexpected components. An example of application of low modulus pitch fiber the shafts of golf clubs in order to increase bending failure load [2] is shown here A schematic view of the shaft, its lamina stacking sequence and results of three point bending impact [2] are shown in Fig 3, where T700S pipe or 'XN-05 pipe indicates that the outer reinforcing layer consists of each nominated unidirectional lamina, respectively(3 plies or 4 plies corresponding to lamina thickness). The other lamina arrangement is as follows: the inner bias layers consist of Toray M40J 4 plies and the middle and load-carrying straight layer consists of Toray T800H 3 plies, where all matrices are epoxy resin. It is very clear that XN-05 pipe shows quite higher bending load, bending deflection and stored energy before failure, which is the most important for the golf club shaft, although the compression strength of T700S is much higher than XN-05 according to Table 1. This phenomenon is
Trends in composite research in Japan 5 Figure 1. Worldwide production of carbon fiber and Japan’s domination. Figure 2. Development trends in carbon fiber properties. to unexpected components. An example of application of low modulus pitch fiber to the shafts of golf clubs in order to increase bending failure load [2] is shown here. A schematic view of the shaft, its lamina stacking sequence and results of three point bending impact [2] are shown in Fig. 3, where ‘T700S pipe’ or ‘XN-05 pipe’ indicates that the outer reinforcing layer consists of each nominated unidirectional lamina, respectively (3 plies or 4 plies corresponding to lamina thickness). The other lamina arrangement is as follows: the inner bias layers consist of Toray M40J 4 plies and the middle and load-carrying straight layer consists of Toray T800H 3 plies, where all matrices are epoxy resin. It is very clear that XN-05 pipe shows quite higher bending load, bending deflection and stored energy before failure, which is the most important for the golf club shaft, although the compression strength of T700S is much higher than XN-05 according to Table 1. This phenomenon is
T Ishikawa very interesting and is worth being studied. The authors of ref. [2] conducted 31 finite element analysis and concluded that the compression stress in the thickness direction at the loading point in the 3-point bending may increase the compression strength of load carrying T800H lamina if the outer layer compression failure does not happen due to its large strain-to-failure. Although some further study might be needed because the actual situations in golf club shafts or fishing rods are cantilever Table 1 Tensile and compressive properties of unidirectional carbon fiber/epoxy laminate Pitch-based low modulus CF PAN-based CI XN-05 XN-10 T700sT800H CFRP CFRP CFRP CFRP CFRP Tensile properties MPa 650 1050 1400 2845 Tensile modulu 150 Strain to failure 1.5 14 8 1.6 Compressive properties MPa 1070 1150 1470 1570 Compressive mo 123 Strain to failure % 2.1 l.8 14 LO Note: The strength and modulus were normalized to a fiber volume fraction of 60% Outer reinfor ang layer Higer feno Riaslayers XN-05 pipe z 500F T700S pipe Deflection mm Figure 3. Schematic of golf club shaft wrapped by low modulus pitch fiber and its impact response
6 T. Ishikawa very interesting and is worth being studied. The authors of ref. [2] conducted 3D finite element analysis and concluded that the compression stress in the thickness direction at the loading point in the 3-point bending may increase the compression strength of load carrying T800H lamina if the outer layer compression failure does not happen due to its large strain-to-failure. Although some further study might be needed because the actual situations in golf club shafts or fishing rods are cantilever Table 1. Tensile and compressive properties of unidirectional carbon fiber/epoxy laminate Pitch-based low modulus CF PAN-based CF XN-05 XN-10 XN-15 T700S T800H CFRP CFRP CFRP CFRP CFRP Tensile properties Tensile strength MPa 650 1050 1400 2650 2845 Tensile modulus GPa 34 72 93 127 150 Strain to failure % 1.8 1.5 1.4 1.8 1.6 Compressive properties Compressive strength MPa 880 1070 1150 1470 1570 Compressive modulus GPa 32 64 85 123 147 Strain to failure % 2.9 2.1 1.8 1.4 1.0 Note: The strength and modulus were normalized to a fiber volume fraction of 60%. Figure 3. Schematic of golf club shaft wrapped by low modulus pitch fiber and its impact response
in composite research in Japa end loading instead of three point bending, the experimental findings and analysis are very encouraging. In the case of components based on cylindrical geometry of a small diameter and predominantly bending loads, similar situations can be expected according to this discovery. The phenomenon might be referred to as'structural hybrid effect'in a cylinder. Due to such a property, this fiber will be highly enhanced in the sporting goods market Another new trend in long fibrous reinforcement is 'PBO fiber where PBO an abbreviation of poly(p-phenylene benzo-bis-oxazole). Although this fiber was originally invented in the USA, a Japanese company, Toyobo Co. Ltd, bought the license and produces it commercially in Japan. A feature of this fiber is the very strong tensile strength. which is better than Kevlar@ fiber as the organic material as shown in Fig. 4 [3], although the stress-strain plot of high strength carbon fiber in this figure is quite intentionally low. Other features of this fiber are resistance to re and fame with a lol Limited Oxygen Index) value of 68 in comparison to value of 58 for carbon fiber and 30 for aramid fiber and great impact tolerance due to high energy absorption capacity. So, possible application fields of this fiber are tension structures, such as membrane of airships or civil structures for retrofitting. An example of applications to civil field components is introduced here An upper portion of Fig. 5 [4] indicates the schematic of strengthening technique of a concrete beam by pre-stressed PFRP(PBO Fiber Reinforced Plastic) sheets The PBO fiber sheets are first stretched to a percentage of pre-stress, then coated with epoxy resin on-site and bonded to the structural concrete surface. After curing, the tensile load is released and the pre-stress is transferred to the concrete beam structure. The key technology responsible for the success of this material is the bond at the interface. To achieve a perfect bond, an air bag system with vacuum facility is developed for construction site applications. Moreover, the shear stress oncentrations at two ends are usually the cause of debonding, and attributed to the high loads due to pre-stressing forces. Therefore, reduction of shear stress concentration can be accomplished by gradually releasing the pre-stressing forces PBO Fiber High Modulus High Strength Carbon Fiber 3.000 Carbon fib Dyneema Fib H-Aramidifiber 2,000 Glass: Fiber 1000 1.5 Strain (%) Figure 4. Stress-strain relationships of various fibers
Trends in composite research in Japan 7 end loading instead of three point bending, the experimental findings and analysis are very encouraging. In the case of components based on cylindrical geometry of a small diameter and predominantly bending loads, similar situations can be expected according to this discovery. The phenomenon might be referred to as ‘structural hybrid effect’ in a cylinder. Due to such a property, this fiber will be highly enhanced in the sporting goods market. Another new trend in long fibrous reinforcement is ‘PBO’ fiber where PBO is an abbreviation of poly(p-phenylene benzo-bis-oxazole). Although this fiber was originally invented in the USA, a Japanese company, Toyobo Co. Ltd., bought the license and produces it commercially in Japan. A feature of this fiber is the very strong tensile strength, which is better than Kevlar® fiber as the organic material, as shown in Fig. 4 [3], although the stress–strain plot of high strength carbon fiber in this figure is quite intentionally low. Other features of this fiber are resistance to fire and flame with a LOI (Limited Oxygen Index) value of 68 in comparison to the value of 58 for carbon fiber and 30 for aramid fiber and great impact tolerance due to high energy absorption capacity. So, possible application fields of this fiber are tension structures, such as membrane of airships or civil structures for retrofitting. An example of applications to civil field components is introduced here. An upper portion of Fig. 5 [4] indicates the schematic of strengthening technique of a concrete beam by pre-stressed PFRP (PBO Fiber Reinforced Plastic) sheets. The PBO fiber sheets are first stretched to a percentage of pre-stress, then coated with epoxy resin on-site and bonded to the structural concrete surface. After curing, the tensile load is released and the pre-stress is transferred to the concrete beam structure. The key technology responsible for the success of this material is the bond at the interface. To achieve a perfect bond, an air bag system with vacuum facility is developed for construction site applications. Moreover, the shear stress concentrations at two ends are usually the cause of debonding, and attributed to the high loads due to pre-stressing forces. Therefore, reduction of shear stress concentration can be accomplished by gradually releasing the pre-stressing forces Figure 4. Stress–strain relationships of various fibers
T Ishikawa at both ends and by reducing the number of layers in composites used at the ends together with FRP U-anchors or bolt anchorage with bonded steel plates. The lower portion of Fig. 5 [4] shows typical load-deflection curves of 10 m long concrete girders with pre-stressed PBO fiber sheets at different pre-stress levels. The control girder without external reinforcement failed due to yielding of tensile steel followed by concrete crushing. The girder strengthened by three-layer PBO sheets without pre-stressing exhibited the similar bend-over point to the control, but gained significant strain hardening after the yielding of steel. With pre-stressing, he linear proportional limit was increased by 45% and the ultimate load by 65%0 a high percentage of pre-stressing could effectively change the failure mode from debonding to PBO tensile rupture, leading to a significant increase in load-carrying capacity. This technology and PBO fiber show high potential of increasing load- arrying capacity of civil structures such as the bridge girders Concrete structures a Prestress I Pretension of pfrp sheets PFRP sheets 2. Bonding and curing Release and cutting of PPRP Stress distribution in a structural section 60 PFRP sheets rupt 500 PFRP sheets debor propagation 300 ………"- 200 --·· Without reinforcement Without prestressing(3 layers PFRP sheets) 33% prestressing layers PFRPsheets) 45%prestressing( layers PFRPsheets 0 40 80100120 Displacement(mm) Figure 5. Load-deflection curve of concrete girder of 10 m span with pre-stressed PFRP
8 T. Ishikawa at both ends and by reducing the number of layers in composites used at the ends together with FRP U-anchors or bolt anchorage with bonded steel plates. The lower portion of Fig. 5 [4] shows typical load–deflection curves of 10 m long concrete girders with pre-stressed PBO fiber sheets at different pre-stress levels. The control girder without external reinforcement failed due to yielding of tensile steel followed by concrete crushing. The girder strengthened by three-layer PBO sheets without pre-stressing exhibited the similar bend-over point to the control, but gained significant strain hardening after the yielding of steel. With pre-stressing, the linear proportional limit was increased by 45% and the ultimate load by 65%. A high percentage of pre-stressing could effectively change the failure mode from debonding to PBO tensile rupture, leading to a significant increase in load-carrying capacity. This technology and PBO fiber show high potential of increasing loadcarrying capacity of civil structures such as the bridge girders. Figure 5. Load–deflection curve of concrete girder of 10 m span with pre-stressed PFRP
Trends in composite research in Japa 3. NANO-TUBES NANO-FIBERS AND NANO-FILLERS a big boom of nanocomposites research has landed also in Japan. As a virtual center of excellence' in composites technology there, ACE TeC of JAXA has led pioneering sections of nanocomposites research, particularly in mechanica properties oriented applications. An overview of research activities related nanocomposites in ACE TeC will be given first and some remarkable results will be introduced briefly The first example is a Carbon Fiber Reinforced Composite(CFRP) laminate using epoxy resin stiffened by carbon nanotubes (CNT). It is well known that CNT exhibits extremely high elastic modulus and strengths. One trend in CNT application as composite reinforcement is direct dispersion like chopped fiber in polymer with an alignment as parallel as possible, which is considered as two-phase material of CNT and polymer. Although it looks like a proper way of obtaining CNT-reinforced composites, alignment of CNT with uniform spatial dispersion in resin is not an easy task. ACE TeC pursues another route for CNT reinforced composites of three-phase material-CNT, polymer and conventional carbon fiber (CF. In this idea, CNT can be regarded as a modifier of matrix resin for increasing its mechanical properties. In this trial, the CNt used is unique, and should be referred to as carbon nanofiber(CNF): Carbere, made by GSI CREOS Corporation in Japan [5]. They refer to this product as cup-stack nanofiber(CSNF). A schematic llustration [5] of such CSNF is shown in Fig. 6 where conical graphene sheets are accumulated like a stack of paper cups and their outer diameter is in the range of 80 to 100 nm with 15 nm wall thickness, which is rather larger than usual CNT. The mechanical properties of this CSNF are compared in Fig. 7 where common carbon fiber data are plotted [5]. Two types of CSNF were employed in the difference of aspect ratios, i.e. fiber length of 500 nm to I um(AR1O)and fiber length of 2.5 to 10.0 um(AR50), respectively. These two types of CSNF are dispersed to Epikote 827 epoxy resin by the company and they can supply the dispersed \15nm\50nm CARBERE Figure 6. Schematic illustration of cup-stack type carbon nanofiber and its dim
Trends in composite research in Japan 9 3. NANO-TUBES, NANO-FIBERS AND NANO-FILLERS A big boom of nanocomposites research has landed also in Japan. As a virtual ‘center of excellence’ in composites technology there, ACE TeC of JAXA has led pioneering sections of nanocomposites research, particularly in mechanical properties oriented applications. An overview of research activities related to nanocomposites in ACE TeC will be given first and some remarkable results will be introduced briefly. The first example is a Carbon Fiber Reinforced Composite (CFRP) laminate using epoxy resin stiffened by carbon nanotubes (CNT). It is well known that CNT exhibits extremely high elastic modulus and strengths. One trend in CNT application as composite reinforcement is direct dispersion like chopped fiber in polymer with an alignment as parallel as possible, which is considered as two-phase material of CNT and polymer. Although it looks like a proper way of obtaining CNT-reinforced composites, alignment of CNT with uniform spatial dispersion in resin is not an easy task. ACE TeC pursues another route for CNT reinforced composites of three-phase material — CNT, polymer and conventional carbon fiber (CF). In this idea, CNT can be regarded as a modifier of matrix resin for increasing its mechanical properties. In this trial, the CNT used is unique, and should be referred to as carbon nanofiber (CNF): Carbere®, made by GSI CREOS Corporation in Japan [5]. They refer to this product as cup-stack nanofiber (CSNF). A schematic illustration [5] of such CSNF is shown in Fig. 6 where conical graphene sheets are accumulated like a stack of paper cups and their outer diameter is in the range of 80 to 100 nm with 15 nm wall thickness, which is rather larger than usual CNT. The mechanical properties of this CSNF are compared in Fig. 7 where common carbon fiber data are plotted [5]. Two types of CSNF were employed in the difference of aspect ratios, i.e. fiber length of 500 nm to 1 µm (AR10) and fiber length of 2.5 to 10.0 µm (AR50), respectively. These two types of CSNF are dispersed to Epikote® 827 epoxy resin by the company and they can supply the dispersed Figure 6. Schematic illustration of cup-stack type carbon nanofiber and its dimensions
T Ishikawa Usual SW-CNT Modulus: 1 TPa Strength: 600 GPa 20%15%10 0.5% 098 CARBERETM 品 T1000 ★CSNF 0 O PITCH 2000 Modulus(GPa) Figure 7. Strength and modulus plot of cup-stack type carbon nanofiber ompound of high CSNF weight content and this epoxy. At the first trial stage, a manual fabrication process of the composite plates by impregnation of the diluted compound by the same epoxy into dry carbon fiber fabrics(Torayca CO6343 T300/plain weave) was employed followed by the hot-press curing. Compression strength improvements around 15%o in the three-phase composites by a loading of CSNF in comparison with the control case of no CSNF are shown Fig. 8 as the typical example of this stage [5] where all strength data are normalized by the control data. The most efficient case, 5% loading of the weight of the resin with AR 50 CSNF, is marked by a circle in this figure. By stimulating such promising results, the supplier company of CSNf, GSI-Creos, decided to develop prepreg systems containing dispersed CsnF [6] in order to obtain more stable mechanical properties than manual fabrication processes. Another key issue in the prepreg development is an optimization of the aspect ratio of CSNF. Although the details of this process belong to the company and cannot be disclosed, one advantage for a good dispersion is many numbers of edges of graphene sheets appearing on the CSNF surface. Such edges may help to increase interaction between CSNF and polymer due to this cup-stack nature. A good dispersion of CsnF is suggested in oscopic sectional view of Fig. 9 for the three phase composites through the prepreg route 16]. Compression strength improvement in these three phase composites by the prepreg is more remarkable than manually impregnated cases as shown in Fig. 10 [6]. In this T-700 CF Ud prepreg case, the compression strength in the fiber direction is improved by some 25% in comparison with the contre (no CSNF) case. However as shown there, the elastic modulus in compression of
10 T. Ishikawa Figure 7. Strength and modulus plot of cup-stack type carbon nanofiber. compound of high CSNF weight content and this epoxy. At the first trial stage, a manual fabrication process of the composite plates by impregnation of the diluted compound by the same epoxy into dry carbon fiber fabrics (Torayca CO6343: T300/plain weave) was employed followed by the hot-press curing. Compression strength improvements around 15% in the three-phase composites by a loading of CSNF in comparison with the control case of no CSNF are shown in Fig. 8 as the typical example of this stage [5] where all strength data are normalized by the control data. The most efficient case, 5% loading of the weight of the resin with AR 50 CSNF, is marked by a circle in this figure. By stimulating such promising results, the supplier company of CSNF, GSI-Creos, decided to develop prepreg systems containing dispersed CSNF [6] in order to obtain more stable mechanical properties than manual fabrication processes. Another key issue in the prepreg development is an optimization of the aspect ratio of CSNF. Although the details of this process belong to the company and cannot be disclosed, one advantage for a good dispersion is many numbers of edges of graphene sheets appearing on the CSNF surface. Such edges may help to increase interaction between CSNF and polymer due to this cup-stack nature. A good dispersion of CSNF is suggested in the microscopic sectional view of Fig. 9 for the three phase composites through the prepreg route [6]. Compression strength improvement in these three phase composites by the prepreg is more remarkable than manually impregnated cases as shown in Fig. 10 [6]. In this T–700 CF UD prepreg case, the compression strength in the fiber direction is improved by some 25% in comparison with the control (no CSNF) case. However as shown there, the elastic modulus in compression of
Trends in composite research in Japan ■ Tension Compression .10H Fle xure 090 080 06 CoNTROL AR10-5wt% AR10-10wt AR50-5wt% AR50-10wt% Figure 8. Compression strength increase in CSNF/epoxy/CF three-phase composites. Satisfactory Dispersion Figure 9. SEM view of CSNF/epoxy/CF three phase composites by prepreg route his composite is not affected as naturally expected. These prepreg systems are considered to be very potential and they are now available in the composite raw material market. Moreover, their applications have been started to the sporting goods in Japan
Trends in composite research in Japan 11 Figure 8. Compression strength increase in CSNF/epoxy/CF three-phase composites. Figure 9. SEM view of CSNF/epoxy/CF three phase composites by prepreg route. this composite is not affected as naturally expected. These prepreg systems are considered to be very potential and they are now available in the composite raw material market. Moreover, their applications have been started to the sporting goods in Japan
T Ishikawa Compression Stength of CNT-CFRP 700 +25 400 300 B30 20 10 CNT 4 5% CNT 4.5% CF: Toray T700 180 gim? RC 38% 180 glm"RC Figure 10. Compression strength and modulus in CSNF/epoxy/CF three-phase composites by prepreg route(T700, 180 g/m- fiber aerial weight, CNT%: volume content The second research topic concerning nanotechnology composites in ACE TeC/ JAXA is an improvement of heat resistance of high temperature polymer [7 by loading of multi-wall carbon nanotube(MW-CNT). In this attempt, a baseline polymer itself is one of the ever-best high temperature polymers, Triple A Polyimide (TriA- PD), which shows much better heat resistance than NASA standard PETI-5 The detail of this resin will be explained in the next section on newly developed polymers. The final purpose here is to increase heat resistance such as glass transition temperature by adding Mw-CNT to this polymer. The Mw-CNT adopted in this attempt is fabricated through CVD technique by Carbon Nanotech Research Institute Inc(CNRD) in Japan [7]. The SeM picture of this MW-CNT is shown in Fig. 11 where its diameter and lengths show the scatter of 20 to 100 nm and several um, respectively. Chosen loading weight fractions of MW-CNT are as follows: 0. 3.3. 7.7 and 14.3%. Because the imid-oligomer is solid room temperature, MW-CNT is added to imid-oligomer powder and mechanically blended by a ball mixer(RouteD). Then the mixture is consolidated by using a hot- press for an hour at 370C. Another processing route is the liquid route in an ami acid/NMP solution with some chemical reactions including imidization(Route (m)) although a description of the details is not given here. The obtained material is a two-phase composite if we follow the previous terminology. Dynamic viscoelastic properties were measured for the obtained composites by a dynamic mechanical analyzer (DMA: Q800 of TA Instruments Corp )in the single cantilever bending method and static tensile properties were measured with a small coupon of 5 mm x 1. I mm x 80 mm(width x thickness x length). Increases in the glass transition temperature(Tg) based on the dynamic mechanical analyzer are shown in Fig 12 where Tg defined by initiation of the storage modulus reduction is 333 C for the
12 T. Ishikawa Figure 10. Compression strength and modulus in CSNF/epoxy/CF three-phase composites by prepreg route (T700, 180 g/m2 fiber aerial weight, CNT%: volume content). The second research topic concerning nanotechnology composites in ACE TeC/ JAXA is an improvement of heat resistance of high temperature polymer [7] by loading of multi-wall carbon nanotube (MW-CNT). In this attempt, a baseline polymer itself is one of the ever-best high temperature polymers, Triple A Polyimide (TriA-PI), which shows much better heat resistance than NASA standard PETI-5. The detail of this resin will be explained in the next section on newly developed polymers. The final purpose here is to increase heat resistance such as glass transition temperature by adding MW-CNT to this polymer. The MW-CNT adopted in this attempt is fabricated through CVD technique by Carbon Nanotech Research Institute Inc. (CNRI) in Japan [7]. The SEM picture of this MW-CNT is shown in Fig. 11 where its diameter and lengths show the scatter of 20 to 100 nm and several µm, respectively. Chosen loading weight fractions of MW-CNT are as follows: 0, 3.3, 7.7 and 14.3%. Because the imid-oligomer is solid at room temperature, MW-CNT is added to imid-oligomer powder and mechanically blended by a ball mixer (Route (I)). Then the mixture is consolidated by using a hotpress for an hour at 370◦C. Another processing route is the liquid route in an amid acid/NMP solution with some chemical reactions including imidization (Route (II)) although a description of the details is not given here. The obtained material is a two-phase composite if we follow the previous terminology. Dynamic viscoelastic properties were measured for the obtained composites by a dynamic mechanical analyzer (DMA: Q800 of TA Instruments Corp.) in the single cantilever bending method and static tensile properties were measured with a small coupon of 5 mm × 1.1 mm × 80 mm (width × thickness × length). Increases in the glass transition temperature (Tg) based on the dynamic mechanical analyzer are shown in Fig. 12, where Tg defined by initiation of the storage modulus reduction is 333◦C for the