20 3D Fibre Reinforced Polymer Composites Radiol Circumterental Figure 2.8 Illustration of Aerospatiale method for producing 3D orthogonal non-woven preforms and an example of a consolidated preform Unlike multiaxial weaving,orthogonal non-woven processes are more capable of producing yarn architectures close to the idealised view,although they are generally a slower production method than those utilising more conventional weaving technology. Although the processes described here can produce a very wide variety of preforms that are generally more complex than those produced via multilayer weaving,the commercial use of these processes has been extremely limited.Most of the equipment that has been developed is highly specialised and generally not suited for large volume production,thus its commercial use has been primarily in the production of expensive carbon/carbon or ceramic composite structures
20 30 Fibre Reinforced Polymer Composites Radial Figure 2.8 Illustration of Aerospatiale method for producing 3D orthogonal non-woven preforms and an example of a consolidated preform Unlike multiaxial weaving, orthogonal non-woven processes are more capable of producing yam architectures close to the idealised view, although they are generally a slower production method than those utilising more conventional weaving technology. Although the processes described here can produce a very wide variety of preforms that are generally more complex than those produced via multilayer weaving, the commercial use of these processes has been extremely limited. Most of the equipment that has been developed is highly specialised and generally not suited for large volume production, thus its commercial use has been primarily in the production of expensive carbodcarbon or ceramic composite structures
Manufacture of 3D Fibre Preforms 21 Z Yars X Yarns Y Yarns Figure 2.9 Illustration of Fukuta's et al.(1974)equipment for the manufacture of 3D non-woven preforms
Manufacture of 30 Fibre Preforms 21 Figure 2.9 Illustration of Fukuta’s et al. (1974) equipment for the manufacture of 3D non-woven preforms
22 3D Fibre Reinforced Polymer Composites 2.2.4 Multiaxial Weaving One of the main problems facing the use of multilayer woven fabrics is the difficulty in producing a fabric that contains fibres orientated at t45 in the plane of the preform. Standard industry looms,which are capable of producing multilayer fabric,cannot manufacture this fabric with fibres at angles other than 0 and 90.It is possible to orient the through-thickness binder yarns at angles such as t45 but this will not significantly affect the in-plane,off-axis properties of the composite.Although some orthogonal non-woven preforms can be produced with yarn architectures of this type, the equipment and processes used in their production are generally not suited for large volume production.This restricts the potential components that can be made using multilayer fabric as the necessity to add +45 fabric will often negate the advantages that can be gained in using a single,integrally woven preform that contains fibres in the thickness direction.The more recent machinery developments have therefore tended to concentrate upon the formation of preforms with multiaxial yarns. Curiskis et al (1997)have reviewed and described the techniques that are being employed to produce multiaxial preforms.Process such as Triaxial Weaving,Lappet Weaving and Split Reed Systems have been used by a number of researchers to develop equipment capable of producing multiaxial,multilayer preforms and a number of patents have been filed relating to the development of this equipment (Ruzand and Guenot,1994;Farley,1993;Anahara et al.,1991;Addis,1996;Mohamed and Bilisik, 1995).Although promising results have been demonstrated,the current reported technology still appears to be in the development stage and preforms seem limited to having the t45 yarns only towards the outer surfaces and not at other levels within the thickness of the preform(see Figure 2.10) 2.2.5 Distance Fabrics A final subset of the weaving technologies relates to the production of a preform style known generally as Distance Fabric.This family of preforms is produced by the use of the traditional textile technique known as Velvet Weaving.In this multilayer weaving process two sets of warp yarns,spaced by a fixed distance,are woven as separate fabrics but are also interlinked by the transfer of specific warp yarns from one fabric layer to the other.These warp yarns,known as pile yarns,are woven into each face fabric thus forming a strong linkage between the two faces and creating a sandwich structure as shown in Figure 2.11.The spacing between the face fabrics can be adjusted by controlling the separation of the warp yarns in the weaving loom and the angle of the pile yarns can be varied from vertical(90)to bias angles (e.g.45)although currently these bias angles can be only produced in the warp direction.Distance Fabric material is commercially available and comes in a range of heights up to ~23 mm.Due to the strong linkage between the face fabrics it is highly suited for the production of peel- resistant and delamination resistant sandwich structures(Bannister et al.,1999). 2.3 BRAIDING The braiding process is familiar to many fields of engineering as standard two- dimensionally braided carbon and glass fabric has been used for a number of years in a
22 30 Fibre Reinforced Polymer Composites 2.2.4 Multiaxial Weaving One of the main problems facing the use of multilayer woven fabrics is the difficulty in producing a fabric that contains fibres orientated at k45" in the plane of the preform. Standard industry looms, which are capable of producing multilayer fabric, cannot manufacture this fabric with fibres at angles other than 0" and 90". It is possible to orient the through-thickness binder yarns at angles such as +45" but this will not significantly affect the in-plane, off-axis properties of the composite. Although some orthogonal non-woven preforms can be produced with yarn architectures of this type, the equipment and processes used in their production are generally not suited for large volume production. This restricts the potential components that can be made using multilayer fabric as the necessity to add +45" fabric will often negate the advantages that can be gained in using a single, integrally woven preform that contains fibres in the thickness direction. The more recent machinery developments have therefore tended to concentrate upon the formation of preforms with multiaxial yams. Curiskis et a1 (1997) have reviewed and described the techniques that are being employed to produce multiaxial preforms. Process such as Triaxial Weaving, Lappet Weaving and Split Reed Systems have been used by a number of researchers to develop equipment capable of producing multiaxial, multilayer preforms and a number of patents have been filed relating to the development of this equipment (Ruzand and Guenot, 1994; Farley, 1993; Anahara et al., 1991; Addis, 1996; Mohamed and Bilisik, 1995). Although promising results have been demonstrated, the current reported technology still appears to be in the development stage and preforms seem limited to having the +45" yarns only towards the outer surfaces and not at other levels within the thickness of the preform (see Figure 2.10). 2.2.5 Distance Fabrics A final subset of the weaving technologies relates to the production of a preform style known generally as Distance Fabric. This family of preforms is produced by the use of the traditional textile technique known as Velvet Weaving. In this multilayer weaving process two sets of warp yarns, spaced by a fixed distance, are woven as separate fabrics but are also interlinked by the transfer of specific warp yarns from one fabric layer to the other. These warp yarns, known as pile yarns, are woven into each face fabric thus forming a strong linkage between the two faces and creating a sandwich structure as shown in Figure 2.11. The spacing between the face fabrics can be adjusted by controlling the separation of the warp yams in the weaving loom and the angle of the pile yarns can be varied from vertical (90") to bias angles (e.g. k45") although currently these bias angles can be only produced in the warp direction. Distance Fabric material is commercially available and comes in a range of heights up to - 23 mm. Due to the strong linkage between the face fabrics it is highly suited for the production of peelresistant and delamination resistant sandwich structures (Bannister et al., 1999). 2.3 BRAIDING The braiding process is familiar to many fields of engineering as standard twodimensionally braided carbon and glass fabric has been used for a number of years in a
Manufacture of 3D Fibre Preforms 23 variety of high technology items,such as:golf clubs,aircraft propellers,yacht masts and light weight bridge structures (Popper,1991).Thick,multilayered preforms can be manufactured through traditional 2D braiding,but the processes of 2D and 3D braiding and the variety of possible preforms that can be manufactured using these techniques are generally very different 3。 3b 3d- 3c A Figure2.l0 Example of multilayer woven fabric containing0°，90°and±45°yarns (courtesy of CTMI)
Manufacture of 30 Fibre Preforms 23 variety of high technology items, such as: golf clubs, aircraft propellers, yacht masts and light weight bridge structures (Popper, 199 1). Thick, multilayered preforms can be manufactured through traditional 2D braiding, but the processes of 2D and 3D braiding and the variety of possible preforms that can be manufactured using these techniques are generally very different. 1' 3c 2 'I I JA 1 Figure 2.10 Example of multilayer woven fabric containing Oo, 90' and +45" yarns (courtesy of CTMI)
24 3D Fibre Reinforced Polymer Composites Figure 2.11 Illustration of Distance Fabric material 2.3.1 2D Braiding The standard 2D braiding technique is illustrated in Figure 2.12,which demonstrates how the counter-rotation of two sets of yarn carriers around a circular frame forms the braided fabric.This movement of the yarn carriers is accomplished through the use of "horn gears"which allow the transfer of the carriers from one gear to the next.The fabric architecture produced by this process is highly interlinked and normally in a flat or tubular form,as shown in Figure 2.13.The style and size of the braided fabric and its production rate are dependent upon a number of variables (Soebroto et al.,1990), amongst which are the number of braiding yarns,their size and the required braid angle. The equations that relate these variables dictate the range of braided fabric that can be produced on any one machine.Generally though,braiding is more suited to the manufacture of narrow width flat or tubular fabric and not as capable as weaving in the production of large volumes of wide fabrics.Typical large braiding machines tend to have 144 yarn carriers,however,larger braiding machines,up to 800 carriers (A&P Technology,1997),are now coming into commercial operation and this will allow braided fabric to be produced in larger diameters and at a faster throughput. The braiding process can also be used with mandrels to make quite intricate preform shapes (see Figure 2.14).By suitable design of the mandrel and selection of the braiding parameters,braided fabric can be produced over the top of mandrels that vary in cross- sectional shape or dimension along their length.Attachment points or holes can also be braided into the preform,thus saving extra steps in the component finishing,and improving the mechanical performance of the component by retaining an unbroken fibre reinforcement at the attachment site.Thus,within the limitations of fabric size and production rate,braiding is seen to be a very flexible process in the range of products
24 30 Fibre Reinforced Polymer Composites Figure 2.11 Illustration of Distance Fabric material 2.3.1 2D Braiding The standard 2D braiding technique is illustrated in Figure 2.12, which demonstrates how the counter-rotation of two sets of yarn carriers around a circular frame forms the braided fabric. This movement of the yarn carriers is accomplished through the use of “horn gears” which allow the transfer of the carriers from one gear to the next. The fabric architecture produced by this process is highly interlinked and normally in a flat or tubular form, as shown in Figure 2.13. The style and size of the braided fabric and its production rate are dependent upon a number of variables (Soebroto et al., 1990), amongst which are the number of braiding yarns, their size and the required braid angle. The equations that relate these variables dictate the range of braided fabric that can be produced on any one machine. Generally though, braiding is more suited to the manufacture of narrow width flat or tubular fabric and not as capable as weaving in the production of large volumes of wide fabrics. Typical large braiding machines tend to have 144 yarn carriers, however, larger braiding machines, up to 800 carriers (A&P Technology, 1997), are now coming into commercial operation and this will allow braided fabric to be produced in larger diameters and at a faster throughput. The braiding process can also be used with mandrels to make quite intricate preform shapes (see Figure 2.14). By suitable design of the mandrel and selection of the braiding parameters, braided fabric can be produced over the top of mandrels that vary in crosssectional shape or dimension along their length. Attachment points or holes can also be braided into the preform, thus saving extra steps in the component finishing, and improving the mechanical performance of the component by retaining an unbroken fibre reinforcement at the attachment site. Thus, within the limitations of fabric size and production rate, braiding is seen to be a very flexible process in the range of products