北京化工大学：《材料导论》课程阅读材料（金属材料）2D_braided_composites_A_review_for_stiness_critical_applications

Available online at www.sciencedirect.com ScienceDirect COMPOSITE STRUCTURES ELSEVIER Composite Structures 85(208)43-58 www.lsevicr.com/locatc/compstruct 2D braided composites:A review for stiffness critical applications Cagri Ayranci,Jason Carey" Availableonine 10October 2007 Abstract Composite materials offer numerous advantages over conventional engineering metals.Over the years.the use of composite materials of the proce 贴 er Braided composit:2D braiding Preform impregation:Fibr reinfored composites:Elastic constants of braided composites 1.Introduction he fih Braiding has been used since 1800s to produce textile Brad ange:The angle between the longitudinal direc. omposite the braided prefom a the eptdr mate Relative am has fiber carriers moving in a circular pattern Half of e constituent of the composite to the remaining constituents. the carriers move clockwise,the others counterclockwise. Unit cell:Smallest repeating element of a braided com- posite,Fig.Ib brad pattern,such re d The braiding process competes with other composite The reonwere berduate ite preform manufacturing techniques from one crossover region to the other,Fig.Ib. g parts o cussed in the following sections Fig.Ib. 2.Common terminology 3.Braid architecture Braiding:a composite material preform (Fig.la)manu Braiding is a composite material preform manufacturins facturing technique.A braiding machine is used to inter- technique where a braiding machine deposits continuous used braid ) Hercules braid,regular braid,diamond braid.Hercules

2D braided composites: A review for stiffness critical applications Cagri Ayranci, Jason Carey * Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2G8 Available online 10 October 2007 Abstract Composite materials offer numerous advantages over conventional engineering metals. Over the years, the use of composite materials has increased significantly. Braiding is a promising and already very commonly used method to form continuous fiber reinforced com￾posite materials. Braided structures are used in a broad range of applications including, but not limited to, medical, aerospace, and auto￾motive. This paper reviews studies published in the field of 2D braiding in order to outline advantages and disadvantages of the process, common preform impregnation techniques, and common stiffness critical applications. Furthermore, elastic property prediction models published in the field are presented for the purpose of stiffness critical designs and applications. 2007 Elsevier Ltd. All rights reserved. Keywords: Braided composites; 2D braiding; Preform impregnation; Fiber reinforced composites; Elastic constants of braided composites 1. Introduction Braiding has been used since 1800s to produce textile fabrics. New demands for high production rate manufac￾turing of high quality composite materials have focused attention on braiding. A conventional braiding machine has fiber carriers moving in a circular pattern [1]. Half of the carriers move clockwise, the others counterclockwise, in an intertwining serpentine motion producing a desired braid pattern, such as 2-dimensional tubular and flat braids. The braiding process competes with other composite material or composite preform manufacturing techniques such as filament winding, pultrusion, and tape lay-up. The advantages and disadvantages of 2D braiding are dis￾cussed in the following sections. 2. Common terminology Braiding: A composite material preform (Fig. 1a) manu￾facturing technique. A braiding machine is used to inter￾twine fibers to create desired braid architecture before or during the impregnation of the fibers. Braid angle: The angle between the longitudinal direc￾tion of the braided preform and the deposited fiber, Fig. 1b. Volume fraction: Relative amount of one constituent of the composite to the remaining constituents. Unit cell: Smallest repeating element of a braided com￾posite, Fig. 1b. Crossover regions: Regions where intertwining fiber tows are deposited on top of each other in a unit cell. Undulation region: The region where fiber tows undulate from one crossover region to the other, Fig. 1b. Matrix only region: Remaining parts of the unit cell where fiber undulations or fiber crossovers do not exist, Fig. 1b. 3. Braid architecture Braiding is a composite material preform manufacturing technique where a braiding machine deposits continuous, intertwined, fiber tows to create desired reinforcing braid architecture before or during the impregnation of the fibers. There are three commonly used braid architectures: Hercules braid, regular braid, diamond braid. Hercules 0263-8223/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2007.10.004 * Corresponding author. Tel.: +1 780 492 7168. E-mail address: jason.carey@ualberta.ca (J. Carey). www.elsevier.com/locate/compstruct Available online at www.sciencedirect.com Composite Structures 85 (2008) 43–58

C.Ayramel.J.CareyI Compaslte Smructures 85(2008)43-58 b Unit Cell Undulating regior sites (first three from the left),diferent preform sizes (last two on the right):(b)braid architecture (ie.,unit cell,braid only region】 and ther path by crosses over and below two yarns,and finally if each yarn motion at the end of the track and form a flat braid instead ove and elow on oth 3car trac the ma ine to form a increases bending and tension strength and also stiffness of braided Triaxial braids need to braiding process compete well with filamen on a man tape ing compare duce a biaxial braided preform without the use of a bility.damage tolerance.repair ability,and low manufac turing cost [4 Braiding advantages are high rate of strand braid on mandr forcements in cost 31.The most in tant hraiding s disadvantage is the producing preforms. 4.Introduction to 2D braids Munro et al. 5]presented a di gto one o ect comp The most common com nd disa h hig rate reinforced composite manufacturing techniques were highlighted with respect to design anc tural er po applic ology a nng asp since both have tages and disadvantages either vertically or horizontally.Most braiding machines compared to the other and the selection of the manufactur- are said to be Ma entin ing tec hnique would argely be proc ct dependent 01 D nd Po higher production rates than Maypole braiders,they can detailed time dependent model that predicts not produce flat braids.Flat braids must be produced by carrers following two intersecting serpentine paths;how mandrel in terms or the rel

braid is a braid where each yarn passes over and then above three other yarns, where in regular braid each yarn crosses over and below two yarns, and finally if each yarn crosses over and below one other yarn in a repeating man￾ner, it is called a diamond braid [2,3]. Adding axial fibers along the mandrel axis is called a triaxial braid, and it increases bending and tension strength and also stiffness of braided composite materials. Triaxial braids need to be formed/braided on a mandrel due to the geometric nat￾ure of the process, whereas it is sometimes possible to pro￾duce a biaxial braided preform without the use of a mandrel. Tubular triaxial braids resist to radial shrinkage, and flat triaxial braids resist to shrinkage in width under tensile loads. Hence, these preforms are compatible as rein￾forcements in pultrusion process [3]. 4. Introduction to 2D braids The most common commercial applications of braided composites are, but not limited to, over-braided fuel lines, braided air ducts, rocket launch tubes, and aircraft struc￾tural parts [1]. Other possible applications are catheters, automotive shaft reinforcement, sporting equipment, etc. Conventional braiding machines produce preforms either vertically or horizontally. Most braiding machines are said to be Maypole-type machines due to the serpentine or maypole strand carrier path. There are also Rotary braiders which use two rotating tables. Although they have higher production rates than Maypole braiders, they can not produce flat braids. Flat braids must be produced by carriers following two intersecting serpentine paths; how￾ever the intersecting paths form a single path by removal of the horn-gear. This forces the carriers to reverse their motion at the end of the track and form a flat braid instead of completing a circular track on the machine to form a tubular braid [2,3]. Maypole and Rotary tubular braid pre￾forms are the same in terms of their architectures [2]. Fibers used to produce braided preforms can be dry or prepreg [1]. The braiding process competes well with filament winding, pultrusion, and tape lay-up. Braiding compares favorably in terms of structural integrity of components, design flex￾ibility, damage tolerance, repair ability, and low manufac￾turing cost [4]. Braiding advantages are high rate of strand deposition on the mandrel, ability to produce complex shapes, low capital investment cost [1], and minimal labor cost [3]. The most important braiding process disadvantage is the difficulty in producing low braid angle preforms. Munro et al. [5] presented a direct comparison of braid￾ing to one of its major competitors, filament winding. Advantages and disadvantages of both high production rate reinforced composite manufacturing techniques were highlighted with respect to design and manufacturing methodology and manufacturing aspects. They emphasized that it was not possible to determine the better process since both have similarities, advantages and disadvantages compared to the other and the selection of the manufactur￾ing technique would largely be product dependent [5]. The kinematic analysis of the braiding process has been studied since 1950s [6–9]. Du and Popper [7] proposed a detailed time dependent model that predicts the microge￾ometry of a fiber preform braided on an axisymmetric mandrel in terms of the relationship between braid angle, Fig. 1. (a) various braided composites (first three from the left), different preform sizes (last two on the right); (b) braid architecture (i.e., unit cell, braid angle, undulating region, matrix only region). 44 C. Ayranci, J. Carey / Composite Structures 85 (2008) 43–58

C.Ayrancl.J.Carey/Composite Structures 85(2008)43-58 45 fabric cover factor,yarn volume fraction,convergence zone in the materials as a result of non-homogeneous impregna- tion of nbers the mng proces Ding the manufacturing process s of the braided com Early studies showed that the crimp angle and braid angle duction. Manual impregnation of the preform.such as affect the strength and stiffness of the braided composites brushing or massaging resin into the preform,is the sim and st expen e metho but has its decrease in the str the praided composite [1o Smith resins with longg and Swanson [1]investigated the stiffness and strength more,product quality depends highly on the skill level of the operator applying ther resin ont and thi me 17 18 the baid re fihe ntage h Kruesi et al [19]suggested use of an impregnation ring that preimpregna es fibers prior to their deposition onto the nand lone by con led am 3.121 They also through the pro posed impregnation ring It wa reported that very low void content,ranging from 3.71% near net henanfactimgcapebites 01.74% volume fraction ented fibers.Damage tolerance results from the locking decreasing production uime. mechanism between the intertwined fibers the brai tha pre yarn 5.2.Commingled fibers nated comosites has ong ben and methods In some applications thermoplastic (TP)resins may be of further thermosetting resins.One of the reasons or using I s is to decr e c as the thermose resins.Fujita et a 20 investigated com properties.Jackson [15]and Kuykendall [16]reported on mingled and un-commingled yarns as impregnating sys. tems to increase the unif s.In used to orms as one manulacturing tec for un-commingled yarn,the reinforcing fibers and matrix They technique makes ssible to s are placed next to each other.Specimens were man um ons afactured by compr sion molding.Th of r parts Lack of imes compared to un-commingled specimens 201 Addi through the thickness tows and long manufacturing times tional advantage of thermoplastic resins is the greater frac were listed as ture toughness comp ared to therm osetting resins [211 Ine au ded tu the high cost of the 3d braiding machinery was a maio braiding preimpregnated thermoplastic powder uthors ind d or commingled】 s were use Braided com 2D ighty above was chosen as the manufacturing technique [15]. pultrusion die.The complete melting process of the ther. moplastic and subsequent impregnation of the fibers occurs 5.Resin impregnation of 2D braided fibers 5.1.Manual impregnation 5.3.Resin transfer molding based processes One from inconfc that orig

fabric cover factor, yarn volume fraction, convergence zone length and rate of braid formation. The model also outlines limits of the braiding process as a result of jamming of yarns [7]. Early studies showed that the crimp angle and braid angle affect the strength and stiffness of the braided composites. Phoenix [10] presented experimental findings that verify that an increase in the crimp angle or the braid angle causes decrease in the strength of the braided composite [10]. Smith and Swanson [11] investigated the stiffness and strength properties of 2D braided carbon/epoxy composites under biaxial tension and compression loading. Influential factors on stiffness were fiber volume, braid angle, percentage of fibers in the braid and axial directions [11]. Braided composites are usually used in applications that require high shear and torsional strength and stiffness. A ±45 braid angle was proven suitable for such applications [3,12]. They also offer increased transverse moduli, trans￾verse strength, damage tolerance, dimensional stability and near net shape manufacturing capabilities [13]. The transverse moduli and strength, and dimensional stability of braided composites arise from off-longitudinal-axis ori￾ented fibers. Damage tolerance results from the locking mechanism between the intertwined fibers of the braid architecture that prevents or limits yarn delamination. Low velocity impact damage tolerance capability of lami￾nated composites has long been recognized and methods of further improving the damage tolerance of the compos￾ites have been studied [14]. Braiding is listed as one of the manufacturing techniques to produce aircraft primary structures at lower cost and with better damage tolerant properties. Jackson [15] and Kuykendall [16] reported on studies investigating resin transfer molding (RTM) impreg￾nated 2D braided preforms as one manufacturing tech￾nique used to produce aircraft primary structures at lower cost and with better damage tolerant properties. They indicated that RTM technique makes possible to achieve up to 60% fiber volume fractions. Thicker parts can be achieved by adding any desired number of braided layers; this is an advantage of 2D braiding. Lack of through the thickness tows and long manufacturing times for multi-lamina stacking procedures were listed as the dis￾advantages of the 2D braids [15,16]. The authors indicated that 3D braiding addressed these disadvantages; however, the high cost of the 3D braiding machinery was a major disadvantage. As an example, for their study, authors indi￾cated that the 2D braided components cost 10% less than that of the 3D braided components, and hence 2D braiding was chosen as the manufacturing technique [15]. 5. Resin impregnation of 2D braided fibers 5.1. Manual impregnation One of the limiting factors of broader use of composite materials is from inconsistent mechanical properties due to stress concentrations originating from the voids that occur in the materials as a result of non-homogeneous impregna￾tion of fibers. During the manufacturing process of the braided com￾posites, fiber impregnation is as important as preform pro￾duction. Manual impregnation of the preform, such as brushing or massaging resin into the preform, is the sim￾plest and least expensive method but has its limitations [17,18]. In this type of impregnation, to avoid premature cure, resins with long gel time must be selected. Further￾more, product quality depends highly on the skill level of the operator applying the resin onto the preform, and this can lead to inconsistent mechanical properties. This can be addressed by using preimpregnated (prepreg) fibers [17,18]. Kruesi et al. [19] suggested use of an impregnation ring that preimpregnates fibers prior to their deposition onto the mandrel. This is done by a controlled amount of resin applied to the fibers through small pores while they are passing through the proposed impregnation ring. It was reported that very low void content, ranging from 3.71% to 1.74%, was achieved. Also high fiber volume fractions in excess of 60% were achieved [19]. This process may pro￾vide consistent specimen fiber volume fraction while also decreasing production time. 5.2. Commingled fibers In some applications thermoplastic (TP) resins may be preferred over thermosetting resins. One of the reasons for using TP resins is to decrease composite manufacturing time, because TP resins do not need chemical reaction time as the thermoset resins. Fujita et al. [20] investigated com￾mingled and un-commingled yarns as impregnating sys￾tems to increase the uniformity of mechanical properties of braided composites. In commingled yarns, reinforcing fibers and matrix fibers are commingled together, while for un-commingled yarn, the reinforcing fibers and matrix fibers are placed next to each other. Specimens were man￾ufactured by compression molding. The commingled yarn specimens required lower pressures and shorter holding times compared to un-commingled specimens [20]. Addi￾tional advantage of thermoplastic resins is the greater frac￾ture toughness compared to thermosetting resins [21]. Bechtold et al. [22] modeled the impregnation process for braided and pultruded tubes. Due to the difficulty in braiding preimpregnated thermoplastic tapes, powder impregnated or commingled yarns were used. Braided com￾mingled yarns are preheated slightly above the thermoplas￾tic melting temperature prior to entering the heated pultrusion die. The complete melting process of the ther￾moplastic and subsequent impregnation of the fibers occurs in the heated die, which is followed by a pressurized cool￾ing stage through a die for calibration purposes [22]. 5.3. Resin transfer molding based processes Brookstein [17,18] underlined that consistency in fiber volume fractions and hence mechanical properties may also C. Ayranci, J. Carey / Composite Structures 85 (2008) 43–58 45

46 C.Ayranci,J.Carey/Composite Structures 85(2008)43-58 be achieved by using other automated impregnation tech- used in the prepreg materials had to be manufactured in niques such as resin transfer molding (RTM)[17,18]. a fiber form and directly braided into the preform along RTM creates high fiber volume composites with very low with the reinforcing fibers (without compromising braid void content.This leads to homogeneous products.In structural integrity).Experimental results demonstrated addition,near net shape products are possible to produce. similar mechanical properties between proposed RTM Circumferential frames,keel frames,and window frames and conventional prepreg autoclave manufactured com- are some examples of RTM manufactured braided com- posites [28]. posites [23,24]. Uozumi et al.[32]proposed a new technique to manu- In RTM,a completed preform is put in a tool or mold. facture near-net-shaped composites using RTM impreg- The part and the resin are heated to optimal temperature nated 2D braiding,followed by a forging process to for the resin to have minimal viscosity.Resin is then minimize cost as compared to3 D braiding.“T”,“J' applied to the preform under pressure.Later the necessary “T”,“Z”shaped composites are listed as producible.. curing procedure for the specific resin is followed [25].Min- Authors found superior tensile properties with the braided imal machining requirement of these products decrease the specimens compared to equivalent aluminum specimens, end cost.It also avoids the negative effects of machined suggesting possible aircraft applications for weight savings. composite parts,such as stress concentration factors intro- Also,the braiding/RTM process was reported to have duced at the machined location of the part.Also due to the approximately 34%cost savings compared to the hand- damage of matrix in the machined region,environmental lay-up/autoclave process [32]. effects such as moisture and other existing chemicals effect the fibers,matrix,and the interface and hence this effect the 6.Applications strength and elastic properties of the machined composites. Michaeli et al.[26]used RTM to manufacture a braid Braid reinforced composite materials have a broad reinforced tubular composite where the reinforcement range of industrial applications.Based on the aforemen- was placed over a flexible tubing and inserted into the tioned advantages,such as the specific strength,these mate- RTM mold.The tube was pressurized and resin injected. rials are preferred increasingly over the conventional Good fiber placement and controlled impregnation as well engineering metals.This section outlines some of the broad as good surface finish were achieved. applications of braided composites. However,resin permeability through the preform plays Brookstein [17,18]listed structural columns,rods, a major role in the quality of products manufactured by shafts,pressure vessels,and plates as some classical appli- RTM.Charlebois et al.[27]reported on permeability char- cations where braid reinforcement had replaced conven- acteristics and mechanical properties of braided fabrics. tional materials.Brookstein suggested,with no Authors investigated permeability of 2D biaxial braided theoretical or experimental evidence to support the claims, glass fibers at three braid angles±35°，±45°，±50°，and the structural limits of braided structure.It was stated that found that change in braid angle effect the fiber volume braided structure could be used for tensile load carrying fraction and thus permeability.Permeability of +45 and applications if the braid angle did not exceed 15.In the +50 angles decreased as the fiber volume fraction was cases of compression loading and thin-wall buckling, increased.However,permeability of +35 angle was not delamination could be overcome by the circumferential affected from the fiber volume fraction change [27. reinforcing nature of braided fabrics (if 20%of the fiber Vacuum assisted resin transfer molding(VARTM)has placement was at a +45 braid angle).Shafts were listed also been used to manufacture braided composites [28]. as ideal components manufactured using composite materi- VARTM offers low cost for high volume production,large als,where axially placed fibers provide stiffness,and 145 and complex shapes capabilities and high fiber volume braid provided torque transmission reinforcement.He fractions compared to hand lay up [29].VARTM process showed,through modeling,that 54.74 braided pressure requires that a dry preform be placed in a mold (or tool), vessels are also good candidates for braided composite low viscosity resin be transferred to the preform under vac- applications [17,18]. uum,followed by the resin curing procedure.It is used by 2D braiding may be used to manufacture structural many industries [30].Some other advantages of VARTM components as well.Kobayashi et al.[33]reported manu- and RTM are their low volatile organic chemical (VOC) facturing a T-shape braided graphite epoxy composite truss emission and good part surface quality production ability joint.Authors proposed a different continuous production [31] manufacturing method for structural components such as RTM and VARTM provide cost reductions in compos- T-shaped trusses.At the end of the process the whole T- ite materials compared to using prepregs.Prepreg materials shape had two layers of continuous triaxial braiding.In offer good toughness to the composites;however,the resins this study EPIKOTE 828 epoxy resin with an amine system used have high viscosities that can not be used with the hardener(KC1118)was used.Fibers were impregnated in a RTM/VARTM techniques.Pederson et al.[28]addressed vacuum and an autoclave was used for curing.It was this issue and proposed to achieve better toughness using reported that the braided T-shaped truss joint had higher RTM.For this,the resin system toughening agent that is strength than a similar cloth tape component [33]

be achieved by using other automated impregnation tech￾niques such as resin transfer molding (RTM) [17,18]. RTM creates high fiber volume composites with very low void content. This leads to homogeneous products. In addition, near net shape products are possible to produce. Circumferential frames, keel frames, and window frames are some examples of RTM manufactured braided com￾posites [23,24]. In RTM, a completed preform is put in a tool or mold. The part and the resin are heated to optimal temperature for the resin to have minimal viscosity. Resin is then applied to the preform under pressure. Later the necessary curing procedure for the specific resin is followed [25]. Min￾imal machining requirement of these products decrease the end cost. It also avoids the negative effects of machined composite parts, such as stress concentration factors intro￾duced at the machined location of the part. Also due to the damage of matrix in the machined region, environmental effects such as moisture and other existing chemicals effect the fibers, matrix, and the interface and hence this effect the strength and elastic properties of the machined composites. Michaeli et al. [26] used RTM to manufacture a braid reinforced tubular composite where the reinforcement was placed over a flexible tubing and inserted into the RTM mold. The tube was pressurized and resin injected. Good fiber placement and controlled impregnation as well as good surface finish were achieved. However, resin permeability through the preform plays a major role in the quality of products manufactured by RTM. Charlebois et al. [27] reported on permeability char￾acteristics and mechanical properties of braided fabrics. Authors investigated permeability of 2D biaxial braided glass fibers at three braid angles ±35, ±45, ±50, and found that change in braid angle effect the fiber volume fraction and thus permeability. Permeability of ±45 and ±50 angles decreased as the fiber volume fraction was increased. However, permeability of ±35 angle was not affected from the fiber volume fraction change [27]. Vacuum assisted resin transfer molding (VARTM) has also been used to manufacture braided composites [28]. VARTM offers low cost for high volume production, large and complex shapes capabilities and high fiber volume fractions compared to hand lay up [29]. VARTM process requires that a dry preform be placed in a mold (or tool), low viscosity resin be transferred to the preform under vac￾uum, followed by the resin curing procedure. It is used by many industries [30]. Some other advantages of VARTM and RTM are their low volatile organic chemical (VOC) emission and good part surface quality production ability [31]. RTM and VARTM provide cost reductions in compos￾ite materials compared to using prepregs. Prepreg materials offer good toughness to the composites; however, the resins used have high viscosities that can not be used with the RTM/VARTM techniques. Pederson et al. [28] addressed this issue and proposed to achieve better toughness using RTM. For this, the resin system toughening agent that is used in the prepreg materials had to be manufactured in a fiber form and directly braided into the preform along with the reinforcing fibers (without compromising braid structural integrity). Experimental results demonstrated similar mechanical properties between proposed RTM and conventional prepreg autoclave manufactured com￾posites [28]. Uozumi et al. [32] proposed a new technique to manu￾facture near-net-shaped composites using RTM impreg￾nated 2D braiding, followed by a forging process to minimize cost as compared to 3D braiding. ‘‘I”, ‘‘J”, ‘‘T”, ‘‘Z” shaped composites are listed as producible. Authors found superior tensile properties with the braided specimens compared to equivalent aluminum specimens, suggesting possible aircraft applications for weight savings. Also, the braiding/RTM process was reported to have approximately 34% cost savings compared to the hand￾lay-up/ autoclave process [32]. 6. Applications Braid reinforced composite materials have a broad range of industrial applications. Based on the aforemen￾tioned advantages, such as the specific strength, these mate￾rials are preferred increasingly over the conventional engineering metals. This section outlines some of the broad applications of braided composites. Brookstein [17,18] listed structural columns, rods, shafts, pressure vessels, and plates as some classical appli￾cations where braid reinforcement had replaced conven￾tional materials. Brookstein suggested, with no theoretical or experimental evidence to support the claims, the structural limits of braided structure. It was stated that braided structure could be used for tensile load carrying applications if the braid angle did not exceed 15. In the cases of compression loading and thin-wall buckling, delamination could be overcome by the circumferential reinforcing nature of braided fabrics (if 20% of the fiber placement was at a ±45 braid angle). Shafts were listed as ideal components manufactured using composite materi￾als, where axially placed fibers provide stiffness, and ±45 braid provided torque transmission reinforcement. He showed, through modeling, that 54.74 braided pressure vessels are also good candidates for braided composite applications [17,18]. 2D braiding may be used to manufacture structural components as well. Kobayashi et al. [33] reported manu￾facturing a T-shape braided graphite epoxy composite truss joint. Authors proposed a different continuous production manufacturing method for structural components such as T-shaped trusses. At the end of the process the whole T￾shape had two layers of continuous triaxial braiding. In this study EPIKOTE 828 epoxy resin with an amine system hardener (KC1118) was used. Fibers were impregnated in a vacuum and an autoclave was used for curing. It was reported that the braided T-shaped truss joint had higher strength than a similar cloth tape component [33]. 46 C. Ayranci, J. Carey / Composite Structures 85 (2008) 43–58

C.Ayranci,J.Carey/Composite Structures 85 (2008)43-58 47 Hamada et al.[34,35]reported a new technique to pro- antennas and tent frames as other possible applications of duce tubular braided products that are more resistant to deployable structures [40,41]. interlaminar delamination,also referred to as through- Braided composites have also been suggested for use the-thickness toughness.The technique uses a conventional with structural reinforced concrete components since flex- 2D braider in a multireciprocal fashion to produce a multi- ural strength and ductility of reinforced concrete members layer braided laminate.Through-the-thickness fibers were can be improved with braided composite jackets [42].Life simultaneously added to the braid through a three track spans of reinforced concrete structures can be improved system where the spindles travel from one track to the by using corrosion resistant and high specific strength other creating a three-dimensional structural network of braided fiber reinforced polymer(FRP)rebars instead of strands.It was observed that propagation of interlaminar conventional steel rebars.The non-ductile behavior of delamination was impeded during lateral compression tests braid reinforced FRP rebars were also addressed by of said manufactured tubular braided specimens [34,35. researchers:Hampton et al.[43],and Lam et al.[44] Due to their specific strength and tailorable mechanical reported on hybrid Kevlar-Carbon FRP rebars manufac- properties,composites have long been the preferred mate- tured using a braiding/pultrusion process exhibiting desir- rials for aviation [15,23,24,32,36].White [36]reported on able ductile behavior similar to conventional steel rebars manufacturing,testing,and cost analysis of a Kevlar [43.441. 490/epoxy blade spar.Ballistic tests were done to evaluate Karbhari et al.[45,46]studied crush performance and the structural damage.After complete armor penetration. energy absorbing capabilities of braided composites.Braid static retesting of spar section did not show any detectable energy absorbing capabilities could be eventually used in changes in the elastic behavior.which was attributed to the industrial applications such as car bumpers.They reported braided fabric delamination resistance.Also,ultrasonic C- that triaxially braided composites increased the energy scan inspection of the structure was assessed and satisfac- absorbing performance of the braided composites [45], tory results were observed.Finally,the cost evaluation of and the occurrence of damage prior to onset of crushing the braided structure revealed 33%savings compared to fil- affected crush performance [46]. ament wound glass blade spar [361. Braid reinforced composite materials have been exten- The sports equipment industry highly utilizes the bene- sively studied for biomedical applications.Hudgins et al. fits offered by braided composite materials.Casale et al. [47,48]suggested replacing the natural intervertebral disc [37]reported on design and fabrication of a braided bicycle with a prosthetic intervertebral disc.The proposed disc frame using Kevlar/graphite braided hybrid preforms had a core of elastomeric polymer and a braid reinforced impregnated with Epon 828 epoxy resin and D-230 curing outer shell.Braided shells proved to provide compressive agent.The frame was manufactured by braiding the four- strength to the design [47,48].Moutos et al.[49]reported piece frame over a foam core and subsequent joining pro- tubular braided structures with elastomeric cores that were cess.Five prototype bicycles were produced [37]. manufactured and tested to mimic the properties of ante- Production of braid reinforced laminated wood baseball rior cruciate ligaments [49].Reinhardt et al.[50]underlined bats have been reported by Axtell et al.[38,39].Reversed the high numbers of hip replacement surgeries conducted balloon molding was used to manufacture the bats.During every year in the world,and the need for a design that this process an elastomeric tube was inflated and the would have tailorable mechanical properties,enhanced molded component pushed onto it.The tube was subse- fatigue life,and biocompatibility.Authors proposed a quently deflated to wrap the part for the curing process. design that consisted of balsa wood core with six layers Following curing,the tube was again inflated forcing the of braided carbon preforms manufactured by RTM using cured product out. a vinyl ester matrix.The study was designed as a basis Neogi et al.[40,41]published their findings on design for future studies but early mechanical performance of analysis and fabrication of a self deployable structural ele- the design were reported to be excellent;however,resin bio- ment,constructed of a foam core,internal bladder,braided compatibility issues were left for future studies [50. load carrying preform and an outer jacket,which was orig- Another example of biomedical application of braided inally developed to minimize payload volume on space composites,braided carbon/PEEK composite bone plates, shuttle missions.The proposed structure had a minimum were fabricated and tested by Fujihara et al.[51].Braided volume at the onset;using a resistance wire embedded in fabric reinforcement was chosen for this work based on the foam core as a heat source,the structure expanded better in plane properties and out of plane delamination and cured.A carbon/epoxy system was chosen for the resistance.Promising results encouraged researchers to fur- braid because of low coefficient of thermal expansion,high ther investigate the effect of the braid angles and plate longitudinal and torsional stiffness and interlaminar thicknesses on the bending performance of the composite strength.As a result of the study,80%volume savings were plates;braid angle was identified as important for thick achieved compared to original designs.The authors sug- plates.For example,it was suggested that a 2.6 mm thick gested using a triaxial braid structure due to the lower spe- plate with a 10 braid angle was suitable for forearm treat- cific stiffness of the final product compared to aluminum ments [51-53].Finally in dentistry,braided composites structures.They also listed emergency sailboats,deployable were used in dental posts that require varying stiffness

Hamada et al. [34,35] reported a new technique to pro￾duce tubular braided products that are more resistant to interlaminar delamination, also referred to as through￾the-thickness toughness. The technique uses a conventional 2D braider in a multireciprocal fashion to produce a multi￾layer braided laminate. Through-the-thickness fibers were simultaneously added to the braid through a three track system where the spindles travel from one track to the other creating a three-dimensional structural network of strands. It was observed that propagation of interlaminar delamination was impeded during lateral compression tests of said manufactured tubular braided specimens [34,35]. Due to their specific strength and tailorable mechanical properties, composites have long been the preferred mate￾rials for aviation [15,23,24,32,36]. White [36] reported on manufacturing, testing, and cost analysis of a Kevlar 49/epoxy blade spar. Ballistic tests were done to evaluate the structural damage. After complete armor penetration, static retesting of spar section did not show any detectable changes in the elastic behavior, which was attributed to the braided fabric delamination resistance. Also, ultrasonic C￾scan inspection of the structure was assessed and satisfac￾tory results were observed. Finally, the cost evaluation of the braided structure revealed 33% savings compared to fil￾ament wound glass blade spar [36]. The sports equipment industry highly utilizes the bene- fits offered by braided composite materials. Casale et al. [37] reported on design and fabrication of a braided bicycle frame using Kevlar/graphite braided hybrid preforms impregnated with Epon 828 epoxy resin and D-230 curing agent. The frame was manufactured by braiding the four￾piece frame over a foam core and subsequent joining pro￾cess. Five prototype bicycles were produced [37]. Production of braid reinforced laminated wood baseball bats have been reported by Axtell et al. [38,39]. Reversed balloon molding was used to manufacture the bats. During this process an elastomeric tube was inflated and the molded component pushed onto it. The tube was subse￾quently deflated to wrap the part for the curing process. Following curing, the tube was again inflated forcing the cured product out. Neogi et al. [40,41] published their findings on design analysis and fabrication of a self deployable structural ele￾ment, constructed of a foam core, internal bladder, braided load carrying preform and an outer jacket, which was orig￾inally developed to minimize payload volume on space shuttle missions. The proposed structure had a minimum volume at the onset; using a resistance wire embedded in the foam core as a heat source, the structure expanded and cured. A carbon/epoxy system was chosen for the braid because of low coefficient of thermal expansion, high longitudinal and torsional stiffness and interlaminar strength. As a result of the study, 80% volume savings were achieved compared to original designs. The authors sug￾gested using a triaxial braid structure due to the lower spe￾cific stiffness of the final product compared to aluminum structures. They also listed emergency sailboats, deployable antennas and tent frames as other possible applications of deployable structures [40,41]. Braided composites have also been suggested for use with structural reinforced concrete components since flex￾ural strength and ductility of reinforced concrete members can be improved with braided composite jackets [42]. Life spans of reinforced concrete structures can be improved by using corrosion resistant and high specific strength braided fiber reinforced polymer (FRP) rebars instead of conventional steel rebars. The non-ductile behavior of braid reinforced FRP rebars were also addressed by researchers: Hampton et al. [43], and Lam et al. [44] reported on hybrid Kevlar-Carbon FRP rebars manufac￾tured using a braiding/pultrusion process exhibiting desir￾able ductile behavior similar to conventional steel rebars [43,44]. Karbhari et al. [45,46] studied crush performance and energy absorbing capabilities of braided composites. Braid energy absorbing capabilities could be eventually used in industrial applications such as car bumpers. They reported that triaxially braided composites increased the energy absorbing performance of the braided composites [45], and the occurrence of damage prior to onset of crushing affected crush performance [46]. Braid reinforced composite materials have been exten￾sively studied for biomedical applications. Hudgins et al. [47,48] suggested replacing the natural intervertebral disc with a prosthetic intervertebral disc. The proposed disc had a core of elastomeric polymer and a braid reinforced outer shell. Braided shells proved to provide compressive strength to the design [47,48]. Moutos et al. [49] reported tubular braided structures with elastomeric cores that were manufactured and tested to mimic the properties of ante￾rior cruciate ligaments [49]. Reinhardt et al. [50] underlined the high numbers of hip replacement surgeries conducted every year in the world, and the need for a design that would have tailorable mechanical properties, enhanced fatigue life, and biocompatibility. Authors proposed a design that consisted of balsa wood core with six layers of braided carbon preforms manufactured by RTM using a vinyl ester matrix. The study was designed as a basis for future studies but early mechanical performance of the design were reported to be excellent; however, resin bio￾compatibility issues were left for future studies [50]. Another example of biomedical application of braided composites, braided carbon/PEEK composite bone plates, were fabricated and tested by Fujihara et al. [51]. Braided fabric reinforcement was chosen for this work based on better in plane properties and out of plane delamination resistance. Promising results encouraged researchers to fur￾ther investigate the effect of the braid angles and plate thicknesses on the bending performance of the composite plates; braid angle was identified as important for thick plates. For example, it was suggested that a 2.6 mm thick plate with a 10 braid angle was suitable for forearm treat￾ments [51–53]. Finally in dentistry, braided composites were used in dental posts that require varying stiffness C. Ayranci, J. Carey / Composite Structures 85 (2008) 43–58 47