Introduction 5 greatest drawback with most of the methods is the higb cost.For example,toughened resins are usually at least 5-10 times more expensive than standard resins.In the case of interleaving it is necessary to cut and individually arrange the interleaf films between the fabric plies before infusing the resin.The inclusion of the interleaf films is a laborious and slow process that can add considerably to the manufacturing cost of a composite.Another problem is the difficultly in manufacturing high-quality laminates using some of the methods.For example,in the manufacture of composites with rubber toughened resin,the fine rubber particles can become trapped within the fabric reinforcement and may not be evenly distributed through the material. 0.8 0.6 0.4 0.2 0.0 6 810 12 IMPACT ENERGY(J) (a) 0.8 0.6 0.4 0.2 0.0 3 IMPACT ENERGY(J) (b) Figure 1.3 Effect of impact energy on the(a)residual tensile strength and (b)residual compressive strength of 2D carbon/epoxy laminate.The post-impact strength values are normalised to the strength of the laminate without impact damage (The tensile and compressive strength data are from Dorey (1989)and Caprino(1984).respectively)
6 3D Fibre Reinforced Polymer Composites 1.2 INTRODUCTION TO 3D FRP COMPOSITES Since the late-1960s,various types of composite materials with three-dimensional(3D) fibre structures (incorporating z-direction fibres)have been developed to overcome the shortcomings of 2D laminates.That is,the development of 3D composites has been driven by the needs to reduce fabrication cost,increase through-thickness mechanical properties and improve impact damage tolerance.The development of 3D composites has been undertaken largely by the aerospace industry due to increasing demands on FRP materials in load-bearing structures to aircraft,helicopters and space-craft.The marine,construction and automotive industries have supported the developments.3D composites are made using the textile processing techniques of weaving,knitting, braiding and stitching.3D composites are also made using a novel process known as z- pinning. Braiding was the first textile process used to manufacture 3D fibre preforms for composite.Braiding was used in the late 1960s to produce 3D carbon-carbon composites to replace high temperature metallic alloys in rocket motor components in order to reduce the weight by 30-50%(Stover et al.,1971).An example of a modern rocket nozzle fabricated by 3D braiding is shown in Figure 1.4.At the time only a few motor components were made,although it did demonstrate the capability of the braiding process to produce intricately shaped components from advanced 3D composites. Shortly afterwards,weaving was used for the first time to produce 3D carbon-carbon composites for brake components to jet aircraft (Mullen and Roy,1972).3D woven composites were made to replace high-temperature metal alloys in aircraft brakes to improve durability and reduce heat distortion. Figure 1.4 3D braided preform for a rocket nozzle(Courtesy of the Atlantic Research Corporation)
6 30 Fibre Reinforced Polymer Composites 1.2 INTRODUCTION TO 3D FRF' COMPOSITES Since the late-l960s, various types of composite materials with three-dimensional (3D) fibre structures (incorporating z-direction fibres) have been developed to overcome the shortcomings of 2D laminates. That is, the development of 3D composites has been driven by the needs to reduce fabrication cost, increase through-thickness mechanical properties and improve impact damage tolerance. The development of 3D composites has been undertaken largely by the aerospace industry due to increasing demands on FRP materials in load-bearing structures to aircraft, helicopters and space-craft. The marine, construction and automotive industries have supported the developments. 3D composites are made using the textile processing techniques of weaving, knitting, braiding and stitching. 3D composites are also made using a novel process known as zpinning. Braiding was the first textile process used to manufacture 3D fibre preforms for composite. Braiding was used in the late 1960s to produce 3D carbon-carbon composites to replace high temperature metallic alloys in rocket motor components in order to reduce the weight by 30-5096 (Stover et al., 1971). An example of a modern rocket nozzle fabricated by 3D braiding is shown in Figure 1.4. At the time only a few motor components were made, although it did demonstrate the capability of the braiding process to produce intricately shaped components from advanced 3D composites. Shortly afterwards, weaving was used for the first time to produce 3D carbon-carbon composites for brake components to jet aircraft (Mullen and Roy, 1972). 3D woven composites were made to replace high-temperature metal alloys in aircraft brakes to improve durability and reduce heat distortion. Figure 1.4 3D braided preform for a rocket nozzle (Courtesy of the Atlantic Research Corporation)
Introduction 7 It is worth noting that these early 3D composites were made of carbon-carbon materials and not fibre reinforced polymers.The need for 3D FRP composites was not fully appreciated in the 1960s,and it was not until the mid-1980s that development commenced on these materials.From 1985 to 1997 a NASA-lead study known as the 'Advanced Composite Technology Program'(ACTP),that included participants from aircraft companies,composite suppliers and the textiles industry,was instrumental in the research and development of 3D FRP composites (Dow and Dexter,1997).The program examined the potential of the textile processes of weaving,braiding,knitting and stitching to produce advanced 3D composites for aircraft components. Developmental work from the ACTP,combined with studies performed by other research institutions,has produced an impressive variety of components and structures made using 3D composites,and some of these are described below.However,due to the commercial sensitivity of some components only those reported in the open literature will be described. 1.2.1 Applications of 3D Woven Composites Weaving is a process that has been used for over 50 years to produce single-layer, broad-cloth fabric for use as fibre reinforcement to composites.It is only relatively recently,however,that weaving techniques have been modified to produce 3D woven materials that contain through-thickness fibres binding together the in-plane fabrics.A variety of 3D woven composites have been manufactured using modified weaving looms with different amounts of x-,y-and z-direction fibres so that the properties can be tailored to a specific application.The great flexibility of the 3D weaving process means that a wide variety of composite components have been developed for aerospace, marine,civil infrastructure and medical applications (Mouritz et al.,1999).However, only a few 3D woven components are currently used;most of the components have been manufactured as demonstration items to showcase the potential applications of 3D woven composites.A list of applications for 3D woven composites is given in Table 1.1 and some woven preform structures are shown in Figure 1.5.It is seen that a range of intricate shapes can be integrally woven for possible applications as flanges,turbine rotors,beams and cylinders.In the production of these demonstration items it has been proven in many cases that it is faster and cheaper to manufacture 3D woven components than 2D laminates,particularly for complex shapes.Furthermore,3D woven components have superior delamination resistance and impact damage tolerance Table 1.1 Demonstrator components made with 3D woven composite Turbine engine thrust reversers,rotors,rotor blades,insulation,structural reinforcement and heat exchangers Nose cones and nozzles for rockets Engine mounts T-section elements for aircraft fuselage frame structures Rib,cross-blade and multi-blade stiffened aircraft panels T-and X-shape elements for filling the gap at the base of stiffeners when manufacturing stiffened panels Leading edges and connectors to aircraft wings I-beams for civil infrastructure Manhole covers
Introduction 7 It is worth noting that these early 3D composites were made of carbon-carbon materials and not fibre reinforced polymers. The need for 3D FRP composites was not fully appreciated in the 1960s, and it was not until the mid-1980s that development commenced on these materials. From 1985 to 1997 a NASA-lead study known as the ‘Advanced Composite Technology Program’ (ACTP), that included participants from aircraft companies, composite suppliers and the textiles industry, was instrumental in the research and development of 3D FRP composites (Dow and Dexter, 1997). The program examined the potential of the textile processes of weaving, braiding, knitting and stitching to produce advanced 3D composites for aircraft components. Developmental work from the ACTP, combined with studies performed by other research institutions, has produced an impressive variety of components and structures made using 3D composites, and some of these are described below. However, due to the commercial sensitivity of some components only those reported in the open literature will be described. 1.2.1 Applications of 3D Woven Composites Weaving is a process that has been used for over 50 years to produce single-layer, broad-cloth fabric for use as fibre reinforcement to composites. It is only relatively recently, however, that weaving techniques have been modified to produce 3D woven materials that contain through-thickness fibres binding together the in-plane fabrics. A variety of 3D woven composites have been manufactured using modified weaving looms with different amounts of x-, y- and z-direction fibres so that the properties can be tailored to a specific application. The great flexibility of the 3D weaving process means that a wide variety of composite components have been developed for aerospace, marine, civil infrastructure and medical applications (Mouritz et al., 1999). However, only a few 3D woven components are currently used; most of the components have been manufactured as demonstration items to showcase the potential applications of 3D woven composites. A list of applications for 3D woven composites is given in Table 1.1 and some woven preform structures are shown in Figure 1.5. It is seen that a range of intricate shapes can be integrally woven for possible applications as flanges, turbine rotors, beams and cylinders. In the production of these demonstration items it has been proven in many cases that it is faster and cheaper to manufacture 3D woven components than 2D laminates, particularly for complex shapes. Furthermore, 3D woven components have superior delamination resistance and impact damage tolerance. Table 1.1 Demonstrator components made with 3D woven composite Turbine engine thrust reversers, rotors, rotor blades, insulation, structural reinforcement and heat exchangers Nose cones and nozzles for rockets Engine mounts T-section elements for aircraft fuselage frame structures Rib, cross-blade and multi-blade stiffened aircraft panels T- and X-shape elements for filling the gap at the base of stiffeners when manufacturing stiffened panels Leading edges and connectors to aircraft wings I-beams for civil infrastructure Manhole covers
8 3D Fibre Reinforced Polymer Composites (a) (b) Figure 1.5 Examples of 3D woven preforms.(a)Cylinder and flange,(b)egg crate structures and (c)turbine rotors woven by the Techniweave Inc.(Photographs courtesy of the Techniweave Inc.)
Introduction 9 (c) Figure 1.5 (continued)Examples of 3D woven preforms.(a)Cylinder and flange,(b) egg crate structures and (c)turbine rotors woven by the Techniweave Inc.(Photographs courtesy of the Techniweave Inc.). While a variety of components have been made to demonstrate the versatility and capabilities of 3D weaving,the reported applications for the material are few.One application is the use of 3D woven composite in H-shaped connectors on the Beech starship (Wong,1992).The woven connectors are used for joining honeycomb wing panels together.3D composite is used to reduce the cost of manufacturing the wing as well as to improve stress transfer and reduce peeling stresses at the joint. 3D woven composite is being used in the construction of stiffeners for the air inlet duct panels to the Joint Strike Fighter(JSF)being produced by Lockheed Martin.The use of 3D woven stiffeners eliminates 95%of the fasteners through the duct,thereby improving aerodynamic and signature performance,eliminating fuel leak paths,and simplifying manufacturing assembly compared with conventional 2D laminate or aluminium alloy.It is estimated the ducts can be produced in half the time and at two- thirds the cost of current inlet ducts,and save 36 kg in weight and at least USS200,000 for each duct. 3D woven composite is also being used in rocket nose cones to provide high temperature properties,delamination and erosion resistance compared with traditional 2D laminates.It is estimated that the 3D woven nose cones are produced at about 15% of the cost of conventional cones,resulting in significant cost saving.3D woven sandwich composites are being used in prototype Scramjet engines capable of speeds up
Introduction 9 Figure 1.5 (continued) Examples of 3D woven preforms. (a) Cylinder and flange, (b) egg crate structures and (c) turbine rotors woven by the Techniweave Inc. (Photographs courtesy of the Techniweave Inc.). While a variety of components have been made to demonstrate the versatility and capabilities of 3D weaving, the reported applications for the material are few. One application is the use of 3D woven composite in H-shaped connectors on the Beech starship (Wong, 1992). The woven connectors are used for joining honeycomb wing panels together. 3D composite is used to reduce the cost of manufacturing the wing as well as to improve stress transfer and reduce peeling stresses at the joint. 3D woven composite is being used in the construction of stiffeners for the air inlet duct panels to the Joint Strike Fighter (JSF) being produced by Lockheed Martin. The use of 3D woven stiffeners eliminates 95% of the fasteners through the duct, thereby improving aerodynamic and signature performance, eliminating fuel leak paths, and simplifying manufacturing assembly compared with conventional 2D laminate or aluminium alloy. It is estimated the ducts can be produced in half the time and at twothirds the cost of current inlet ducts, and save 36 kg in weight and at least US$200,000 for each duct. 3D woven composite is also being used in rocket nose cones to provide high temperature properties, delamination and erosion resistance compared with traditional 2D laminates. It is estimated that the 3D woven nose cones are produced at about 15% of the cost of conventional cones, resulting in significant cost saving. 3D woven sandwich composites are being used in prototype Scramjet engines capable of speeds up