3D textile-reinforced composites are also used in various applications such as floors and floor beams in trains and fast ferries; flat load trays in trucks; crash members in cars, buses, and trucks; shipping containers; and other container transport applications. 3D composites reinforced with spacer fabrics made of two parallel skins of 2D glass fabrics connected by glass yarns are used in car and truck spoilers/fairings and luggage floors of automobiles [84]. Another example of 3D textile composites is the oil pan produced using 3D woven interlock fabrics. Three different 3D woven structures were used for this purpose such as layer-to-layer, orthogonal, and through-the-thickness woven fabrics [99].

In the US, several government/private sector projects made use of composite materials in vehicles. These include Ford Motor's "all composite car," the Automotive Composites Consortium (ACC), the Partnership for the New Generation of Vehicles (PNGV) program [103], and the Sunrise™ electric vehicle (EV) program. Among these projects, Sunrise™ electric vehicle (EV) program in 1996 made the most extensive use of textile composites in a wellintegrated program. This program is co-funded by the National Institute of Standards and Technology (NIST) together with a consortium of eight industry partners. Nearly all types of textile preforms such as woven, knitted, braided, and nonwoven fabrics were used for reinforcement (**Figure 15**) [104].

Other automotive applications of composites include car noses and monocoques of Formula One car bodies from carbon textile structures, aprons and spoilers of sport cars, braided carbon composites for car bumpers (e.g., BMW M6, Lotus Elise), the crash beams of the McLaren SLR which consist of foam cores overbraided with carbon rovings, and the car roof of the BMW M6 which consists of carbon-woven fabrics [105].

### **6.4. Applications in medicine**

**Figure 14.** Strengthening of existing concrete structural members using unidirectional carbon and aramid sheets [98].

woven glass on the other side, and an epoxy glass microsphere core) The resulting composite was compared with an existing stamped steel component for mechanical properties, weight

on the surface of the structure through a technique similar to hand lay-up. Alternatively, composite strips consisting of unidirectional fibers embedded in an epoxy matrix can be directly

Other applications include the I-beams made with a 3D woven composite which is used in the roof of a ski chair-lift building as a replacement of heavy steel beams. 3D woven composite beams demonstrated lower cost and enhanced performance compared with steel and conven-

In recent years, the depletion of petroleum resources and strict environmental regulations forced the scientists and engineers in automotive industry to search for new ways of reducing

stant struggle to reduce the weight of the vehicles in order to decrease the fuel consumption without sacrificing passenger safety and comfort. Lightweight and strong textile composites offer a solution to this problem. Replacing cast iron, steel, and aluminum components with composites can decrease component weight by 10–75%. It is estimated that a 10% reduction in vehicle weight corresponds to a 6–8% reduction in fuel consumption [99]. Composites are gradually replacing steel for several body parts such as bumpers, hatch doors, cabin components, spare wheel containers, and so on. Other applications of composites include underbody panels, instrument panel carriers, battery trays, front-end modules, sunroof beams, door modules, seat structures, convertible header bows, door plate carriers, roof and trunk lids, exterior claddings, skid plates, running boards, step assists, front-end carriers, bumper beams, lift gates, spare wheel tubs, and other structural parts [100]. For example, Turner et al. investigated carbon fiber composites for automotive body panel applications. They produced a full-scale front wing-fender component using two different composite manufacturing processes such as a semi-impregnated system and a novel directed fiber preforming RTM process. The semi-preg system consisted of a surface film (thin woven glass either side of an

emission. Therefore, the automotive industry is in a con-

carbon fiber on one side, 400 g/m2

bonded on the surface of the structure by using an epoxy adhesive (**Figure 14**) [93].

tional composite beams [97].

120 Textiles for Advanced Applications

**6.3. Automotive applications**

the fuel consumption and also CO2

epoxy film) and a bulk ply (woven 3000 filament, 300 g/m2

Composite materials are extensively used in medicine owing to their numerous advantages. Among the most important applications of composite materials in medicine is bone repair. Bone fractures can be treated by two main methods such as external fixation and internal fixation. The purpose of external fixation is to hold the bone fragments in alignment by using various materials such as splints, casts, braces, and external fixator systems. Plaster of Paris (calcium sulfate) reinforced with cotton-woven fabrics is still the most commonly used casting

**Figure 15.** Composite parts breakdown of Sunrise™ BIW according to textile preforming processes and composite manufacturing processes [104].

material, but it has a high failure rate, high density, and low specific strength/stiffness and is sensitive to water. Recently, casts made of glass or polyester fiber fabrics and water-activated polyurethanes are being used to overcome these problems. An ideal splinting material must be lightweight, stiff, strong, and also comfortable. It must be also fit to the complex contours of the limbs. The fabric must be open structured to allow impregnation with a large quantity of plaster. Leno-woven structures as well as warp and weft knitted fabrics can be used [106]. In the internal fixation method, the bone fragments are held together by using wires, pins, screws, plates, and intramedullary nails. Bone plates made of stainless steel and Ti alloy are conventionally used. The stiffness of these materials is way higher than that of the bone, and this stiffness mismatch causes much of the load to be carried by the plate. This causes increased bone porosity (also known as bone atrophy), and the bone becomes less dense and weak. Less rigid plates that are more bone-like in mechanical properties can be used to overcome this problem. Various composite bone plates were developed for the usage of such as CF/epoxy, GF/epoxy, CF/PMMA, CF/PP, CF/PE, CF/nylon, and CF/PEEK [107]. **Figure 16** shows composite bone plates made of various textile composites [107].

Joint replacements such as total hip replacement (THR) and total knee replacement (TKR) also employ composite materials. Conventional THRs use stainless steel, Co-Cr, and Ti alloys for the femoral shaft and neck and Co-Cr alloy or ceramics such as alumina and zirconia materials for the head or ball [107]. CF/PEEK and CF/epoxy systems and UHMWPE-based composites were used for THR and TKR with successful results (**Figure 17**) [108]. Other applications of composites include bone cement, bone grafts, dental post, dental implant and bridge, bracket and archwire, ureter prosthesis, catheters, tendons and ligaments, prosthetic limbs, and medical equipment such as walking support frames and sticks.

**Figure 16.** (a) A typical composite bone plate made using braided carbon fiber fabric and epoxy matrix and (b) composite bone plate made of carbon/PEEK material system [107].

**Figure 15.** Composite parts breakdown of Sunrise™ BIW according to textile preforming processes and composite

material, but it has a high failure rate, high density, and low specific strength/stiffness and is sensitive to water. Recently, casts made of glass or polyester fiber fabrics and water-activated polyurethanes are being used to overcome these problems. An ideal splinting material must be lightweight, stiff, strong, and also comfortable. It must be also fit to the complex contours of the limbs. The fabric must be open structured to allow impregnation with a large quantity of plaster. Leno-woven structures as well as warp and weft knitted fabrics can be used [106]. In the internal fixation method, the bone fragments are held together by using wires, pins, screws, plates, and intramedullary nails. Bone plates made of stainless steel and Ti alloy are conventionally used. The stiffness of these materials is way higher than that of the bone, and this stiffness mismatch causes much of the load to be carried by the plate. This causes increased bone porosity (also known as bone atrophy), and the bone becomes less dense and weak. Less rigid plates that are more bone-like in mechanical properties can be used to overcome this problem. Various composite bone plates were developed for the usage of such as CF/epoxy, GF/epoxy, CF/PMMA, CF/PP, CF/PE, CF/nylon, and CF/PEEK [107]. **Figure 16**

Joint replacements such as total hip replacement (THR) and total knee replacement (TKR) also employ composite materials. Conventional THRs use stainless steel, Co-Cr, and Ti alloys for the femoral shaft and neck and Co-Cr alloy or ceramics such as alumina and zirconia materials for the head or ball [107]. CF/PEEK and CF/epoxy systems and UHMWPE-based composites were used for THR and TKR with successful results (**Figure 17**) [108]. Other applications of composites include bone cement, bone grafts, dental post, dental implant and bridge, bracket and archwire, ureter prosthesis, catheters, tendons and ligaments, prosthetic limbs, and medi-

shows composite bone plates made of various textile composites [107].

cal equipment such as walking support frames and sticks.

manufacturing processes [104].

122 Textiles for Advanced Applications

**Figure 17.** Carbon fiber-reinforced thermoplastic hip prosthesis, with and without hydroxyapatite coating, shown alongside conventional titanium equivalent [108].

#### **6.5. Sports and leisure applications**

Composite materials allow for the directional design of mechanical properties which is a great advantage in various sports equipments. Lighter and stronger golf clubs made of graphite fiber-reinforced epoxy are in common use. Carbon fiber composites are used for the production of poles used in pole vaulting. The pole must be lightweight, flexible yet stiff, and torsion resistant. In order to meet these demands, a layered design is used [109].  Carbon/ epoxy composite layer provides maximum stiffness, while glass fiber composites ensure high torsion resistance [109]. Other applications of carbon fiber composites include bicycle frames, front forks, and seat posts. Carbon fiber composites are lightweight and provide good bending stiffness and fatigue resistance. In addition, glass fiber-reinforced nylon wheels are used as good shock absorbers. Carbon fiber composites are also used to produce tennis racket frames for high strength and stiffness. In addition, the handles can be made by wrapping multiple composite layers around a soft core such as PUR for the purpose of vibration damping [110]. Other applications include kayaks made of carbon and kevlar fibers with epoxy resin, skis and snowboards made of a soft core, and composite layers of various constructions [111].

### **7. Future scope**

Future investigations will focus on novel fiber and matrix systems, fiber architectures and processing techniques, as well as improving the existing technologies. The successful implementation of 3D textile composites requires more work on the production economies and engineering design of these materials in order to create a cost-effective and sustainable production technology. Fabric geometry model (FGM) coupled with CAD-CAM technologies and analyzing systems such as the finite element method (FEM) can create a useful framework which can help integrate fabric design and processing parameters into structural analysis and ultimately efficiently design the required properties for a specific end use. Another interesting topic for the future research is the design of fiber-matrix interface in composites. The quality of the fiber-matrix interface is crucially important for high-standard composite properties. Increasing the fiber-matrix adhesion by using suitable coupling agents and interface modification techniques is the all-time hot topic in composite industry, and it is apparent that this trend will continue in the future. More research is also necessary on the dynamics of matrix infiltration into textile materials during composite processing as well as on the characteristics of curing process. The use of nanofibers and nanotextile structures for the reinforcement of composite materials is another area which is full of potential for future applications.

#### **8. Summary**

Composites reinforced with textile materials have attracted great attention as lightweight and strong materials for various advanced applications such as aerospace, construction, automotive, medicine, and sports. Traditionally, multilayered structures consisting of unidirectional prepregs have been used for the production of advanced composite materials. However, these material systems lack through-the-thickness fibers and consequently exhibit poor out-of-plane properties such as interlaminar strength and damage tolerance. In addition, the layering process is labor intensive and time consuming increasing the overall cost. Textile materials in the form of short and continuous fibers as well as 2D and 3D fabric preforms offer enormous design possibilities through the proper manipulation of fiber architecture. 2D fabrics can be produced at a much lower cost compared with unidirectional prepregs and are easy to handle during composite manufacturing. However, they also require the timeconsuming layering procedure similar to unidirectional laminates, and they also have poor out-of-plane properties due to lack of z-fibers. 3D woven, braided, stitched, and non-crimp fabrics possess through-the-thickness reinforcement and thus have good out-of-plane properties. In addition, the costly layering step is eliminated with these structures. They are suitable for net-shape manufacturing and inclusion of a wide range of structural details such as holes, bifurcations, and junctions which significantly reduce the production time and cost as well as eliminating the weaknesses in the resulting structures originating from these modifications. The major limitation of 3D fabric manufacture is the high production costs due to poorly developed machine technologies and economies of scale issues. These limitations can be eliminated with the implementation of more efficient production technologies and effective engineering design of 3D textile materials. New developments in fiber and matrix systems, interface modification methods, as well as in nanotechnology will increase the use of textile composites in various applications. It is expected that textile materials will continue to play an important role for the reinforcement of advanced composite materials in the future.

### **Author details**

**6.5. Sports and leisure applications**

124 Textiles for Advanced Applications

**7. Future scope**

**8. Summary**

Composite materials allow for the directional design of mechanical properties which is a great advantage in various sports equipments. Lighter and stronger golf clubs made of graphite fiber-reinforced epoxy are in common use. Carbon fiber composites are used for the production of poles used in pole vaulting. The pole must be lightweight, flexible yet stiff, and torsion resistant. In order to meet these demands, a layered design is used [109].  Carbon/ epoxy composite layer provides maximum stiffness, while glass fiber composites ensure high torsion resistance [109]. Other applications of carbon fiber composites include bicycle frames, front forks, and seat posts. Carbon fiber composites are lightweight and provide good bending stiffness and fatigue resistance. In addition, glass fiber-reinforced nylon wheels are used as good shock absorbers. Carbon fiber composites are also used to produce tennis racket frames for high strength and stiffness. In addition, the handles can be made by wrapping multiple composite layers around a soft core such as PUR for the purpose of vibration damping [110]. Other applications include kayaks made of carbon and kevlar fibers with epoxy resin, skis and snowboards made of a soft core, and composite layers of various constructions [111].

Future investigations will focus on novel fiber and matrix systems, fiber architectures and processing techniques, as well as improving the existing technologies. The successful implementation of 3D textile composites requires more work on the production economies and engineering design of these materials in order to create a cost-effective and sustainable production technology. Fabric geometry model (FGM) coupled with CAD-CAM technologies and analyzing systems such as the finite element method (FEM) can create a useful framework which can help integrate fabric design and processing parameters into structural analysis and ultimately efficiently design the required properties for a specific end use. Another interesting topic for the future research is the design of fiber-matrix interface in composites. The quality of the fiber-matrix interface is crucially important for high-standard composite properties. Increasing the fiber-matrix adhesion by using suitable coupling agents and interface modification techniques is the all-time hot topic in composite industry, and it is apparent that this trend will continue in the future. More research is also necessary on the dynamics of matrix infiltration into textile materials during composite processing as well as on the characteristics of curing process. The use of nanofibers and nanotextile structures for the reinforcement of composite materials is another area which is full of potential for future applications.

Composites reinforced with textile materials have attracted great attention as lightweight and strong materials for various advanced applications such as aerospace, construction, Nesrin Sahbaz Karaduman1 \*, Yekta Karaduman1 , Huseyin Ozdemir2 and Gokce Ozdemir3

\*Address all correspondence to<EMAIL_ADDRESS>
1 Department of Textile, Clothing, Footwear and Leather, Akdagmadeni Vocational High School, Bozok University, Akdagmadeni, Yozgat, Turkey

2 Department of Textile, Clothing, Footwear and Leather, Vocational High School of Technical Sciences, Gaziantep University, Gaziantep, Turkey

3 Department of Fashion and Textile Design, Faculty of Fine Arts, Gaziantep University, Gaziantep, Turkey

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## **Hybrid Yarn Composites for Construction**

Mutlu Kurban, Osman Babaarslan and İsmail Hakkı Çağatay

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69034

#### **Abstract**

Textile-reinforced concrete (TRC) is a new innovative construction material that leads to light-weight and cost-effective construction. TRC consists of a finely grained cement-based matrix and high-performance, continuous multifilament yarns made of alkali-resistant glass, carbon, or polymer. Using these fibers provides superior mechanical properties and corrosion resistance in comparison with ferroconcrete. The application of epoxy resin coating to the textile materials improves the utilization of mechanical performance and handling properties as well. In recent years, researchers have studied alternative methods because coating process is very detailed and epoxy resin is of high cost. The experimental part of this chapter focuses on the experimental investigation carried out on high-strength concrete reinforced with hybrid yarns. Braiding technology was used to manufacture hybrid yarn from alkali-resistant glass fiber (ARG) and polypropylene (PP) filament. Next step, thermoplastic part of braided yarn was melted on press heating. Finally, TRC was produced from ARG, coated ARG, carbon fiber, coated carbon fiber, and heated hybrid yarns. Although the contribution of the heated hybrid yarn is limited, it is expected that the desired results will be obtained by changes in braiding yarn production and yarn composition ratios.

**Keywords:** technical textiles, hybrid yarn, composites, buildtech, textile-reinforced concrete

### **1. Introduction to textile composites for construction**

The principal necessities of human are nutrition, clothing, and shelter. The clothing comes after nutrition and has got many selection factors such as social, economic, environmental, and physiological. The main material of clothing is textile. Textiles always have played an important role in protecting from different environmental conditions and making feel comfortable. Nowadays, the textile industry has to accelerate research on innovative and

attractive products in many fields from agriculture to space. Recently, construction sector is one of the fields that used these innovative textile materials, and these textile materials are named "Buildtech." Buildtech products are defined as membrane, lightweight and massive construction materials, etc. for engineering and industrial buildings [1].

Construction is improving from the earliest times. At ancient times, people built kinds of buildings to shelter. To reduce cracking and to increase bearing capacity of buildings, they added hairs and vegetables in the mortar. Later with technology, construction materials changed. Different materials were used for each period. In the early period, mortar was used, but later various materials such as wood, stone, marble, and steel were used. Finally, with the discovery of concrete, its use in the construction industry has become widespread [2, 3].

Since 1800s, quick developments in construction materials technology have allowed civil engineers to achieve impressive gains in the safety, economy, and functionality of structures built to serve the common needs of the community [4]. Today, in the construction sector, steelreinforced concrete is most important, and it is used widely for structural applications. For several decades, textile-reinforced concrete (TRC) has been innovative material for constructions. TRC can be used instead of conventional composite-building materials for many new applications [5]. TRC is a new composite material consisting of a fine-grained concrete matrix and corrosion-resistant high-performance multifilament yarns such as alkali-resistant glass, carbon, basalt, and polymer [6]. These raw materials are used to produce different textile forms for TRC. Those suited for the reinforcement of concrete matrix are yarns, warp knits (plain, circular or three-dimensional), multi-plies (plain or circular), and woven [7]. Thanks to these textile materials, production of TRC leads to thin structural elements with high strength, high durability, and corrosion resistance [8].

In the present architectures and constructions, there is a specific trend toward innovative structures of high-quality materials such as carbon, glass fibers, basalt, and aramid that continuously increase the requirements placed on the construction materials and that demand a continuous development of their properties. Using nonmetallic high-performance fibers as concrete reinforcement allows for the production of thin and light-weight elements with high durability and the potential of economic savings. These advantages together with the high scope of design options given to the architects have made glass-fiber–reinforced concrete (GFRC) a widespread construction material around the world. A disadvantage of the reinforcement with chopped strands (for example, AR-glass or PP) is the partial unorientated distribution of the fibers over the total cross-section, reducing their effectiveness. In contrast to steel reinforcement, AR glass or carbon fibers in the textile can be positioned in almost any direction and afterward nearly perfectly adopted to the orientation of the applied load. It is thus possible to create an extremely effective reinforcement. The use of corrosion-resistant technical textiles reduces concrete covers significantly and thus allows for light weight and thin concrete structures [9, 10].

Glass fiber is widely used in construction since 1950s. The cementitious matrix has highly alkaline environment (pH-value > 12.5), and glass fiber has poor corrosion resistance in a highly alkaline environment. Despite the glass fiber being considered as a reinforcement of cementitious materials for several decades, because of poor alkaline resistance, the limitation of structural applications still remains. For this reason, the alkali-resistant glass fiber (ARG) was preferably designed to reinforce cementitious matrices. Enhanced mainly by a high percentage of zirconia (ZrO2 > 15% by weight) content, the alkali-resistant glass fiber (ARG) was designed to reinforce cementitious matrices that have been used in construction and civil engineering since the late 1960s. Despite ARG being more resistant to highly alkaline environment than normal glass fiber, many attempts have been made to modify either matrix or fiber by adding fillers or by surface coatings of polymer and carbon layers. In the composites sector, a coating is known as a widespread method of providing corrosion protection in order to improve the durability of engineering structures. For alkali-resistant glass fibers (ARGs), multifunctional sizings are required to provide the surface protection, abrasion resistance, and strength maintenance in the concrete. However, both durability in alkali environment and economic considerations have limited the commercial use of these materials. For enhancing the long-term resistance of glass-fiber–reinforced cement products, it is thus very important to develop an inexpensive and applicable coating to modify the ARG fiber surface and examine how the coatings interact with the surrounding cementitious matrix [11–13].

In the production of TRC, the application of polymer coating to the textile materials improves the utilization of mechanical performance and handling properties as well. Generally, thermoset resin is used as a coating material. Coating process is very long term and tough, and also, cost of coating materials is very expensive. Hence, researchers have searched for alternative methods to provide the surface protection, abrasion resistance, and strength maintenance for textile materials in the concrete.

In this study, hybrid yarn was used in the production of TRC as a reinforcement material. First of all, hybrid yarn was produced with braiding technology. In the hybrid yarn production, while alkali-resistant glass fibers (ARGs) were used as a reinforcement material, polypropylene filament (PP) is used as a matrix material. After production of hybrid yarn was heated in the oven, melted polymer covered alkali-resistant glass fibers (ARGs). Melted hybrid yarns were used in the production of TRC. All TRC samples were tested to see the effect of the hybrid yarn on the strength of the concrete. Information about hybrid yarn technology and braiding technology will be mentioned in the following sections.

### **2. Hybrid yarn technology**

attractive products in many fields from agriculture to space. Recently, construction sector is one of the fields that used these innovative textile materials, and these textile materials are named "Buildtech." Buildtech products are defined as membrane, lightweight and massive

Construction is improving from the earliest times. At ancient times, people built kinds of buildings to shelter. To reduce cracking and to increase bearing capacity of buildings, they added hairs and vegetables in the mortar. Later with technology, construction materials changed. Different materials were used for each period. In the early period, mortar was used, but later various materials such as wood, stone, marble, and steel were used. Finally, with the discovery of concrete, its use in the construction industry has become widespread [2, 3]. Since 1800s, quick developments in construction materials technology have allowed civil engineers to achieve impressive gains in the safety, economy, and functionality of structures built to serve the common needs of the community [4]. Today, in the construction sector, steelreinforced concrete is most important, and it is used widely for structural applications. For several decades, textile-reinforced concrete (TRC) has been innovative material for constructions. TRC can be used instead of conventional composite-building materials for many new applications [5]. TRC is a new composite material consisting of a fine-grained concrete matrix and corrosion-resistant high-performance multifilament yarns such as alkali-resistant glass, carbon, basalt, and polymer [6]. These raw materials are used to produce different textile forms for TRC. Those suited for the reinforcement of concrete matrix are yarns, warp knits (plain, circular or three-dimensional), multi-plies (plain or circular), and woven [7]. Thanks to these textile materials, production of TRC leads to thin structural elements with high strength,

In the present architectures and constructions, there is a specific trend toward innovative structures of high-quality materials such as carbon, glass fibers, basalt, and aramid that continuously increase the requirements placed on the construction materials and that demand a continuous development of their properties. Using nonmetallic high-performance fibers as concrete reinforcement allows for the production of thin and light-weight elements with high durability and the potential of economic savings. These advantages together with the high scope of design options given to the architects have made glass-fiber–reinforced concrete (GFRC) a widespread construction material around the world. A disadvantage of the reinforcement with chopped strands (for example, AR-glass or PP) is the partial unorientated distribution of the fibers over the total cross-section, reducing their effectiveness. In contrast to steel reinforcement, AR glass or carbon fibers in the textile can be positioned in almost any direction and afterward nearly perfectly adopted to the orientation of the applied load. It is thus possible to create an extremely effective reinforcement. The use of corrosion-resistant technical textiles reduces concrete covers significantly and thus allows for light weight and

Glass fiber is widely used in construction since 1950s. The cementitious matrix has highly alkaline environment (pH-value > 12.5), and glass fiber has poor corrosion resistance in a highly alkaline environment. Despite the glass fiber being considered as a reinforcement of cementitious materials for several decades, because of poor alkaline resistance, the limitation

construction materials, etc. for engineering and industrial buildings [1].

high durability, and corrosion resistance [8].

136 Textiles for Advanced Applications

thin concrete structures [9, 10].

For many years, thermoset and thermoplastic composites are often used to produce advanced lightweight structures. Thermoset prepregs, which were previously a combination of resin and fiber, as preformed materials must be kept refrigerated to interrupt the ongoing curing reaction [14]. Generally, in many composite processing methods, the matrix is added to the fibers at the time of manufacture. By using additives and fillers, it improves the surface quality of the part, alleviates some processing problems and reduces the total cost [15, 16].

In the thermoset composite materials, the curing process requires heat and pressure. To improve its usability, the prepreg is typically stored in a freezer and then cured at a high temperature. In the 1960s prepregs produced necessitated quite high cure temperatures and had very short out-lives; nowadays, it is possible for them to be stored in a freezer, have an out-life of possibly several months and a cure temperature of between 50 and 200°C. Prepregs tend to be epoxy resins reinforced with carbon, glass, or aramid fibers. High-temperature polymer composites are occasionally used as other matrix materials [16].

In thermoplastic polymers, the organic molecular units are bonded together. They differ from thermoset polymers in this way. Thermoplastic composites are preferred for their ability to be formed by heat at low pressure. While thermosets are produced with manual production, the thermoplastic processing techniques are machine friendly and enable short processing cycles [14, 17].

Thermoplastic polymers are divided into two groups of amorphous and semicrystalline polymers according to their molecular structure. While amorphous polymers have randomly oriented molecular chains, in semicrystalline polymers, the chains are symmetric enough to be fitted into an ordered crystalline state. Because of the large molecular chain length, complete crystallinity cannot be obtained, and both crystalline and amorphous regions coexist in the solid. When a polymer is cooled, there are some changes. From above, the melt temperature (*Tm*) to glass transition (*Tg* ), the chains lose mobility and begin to interact segment by segment. At *Tg* , the molecular chains are locked in place, and the polymer assumes a "glassy" state. In this case, the molecular orientation is random due to the irregular chain structure. At semicrystalline state, polymers crystallize at temperatures so high from the *Tg* , regions of amorphous, and crystalline phase coexist [17].

When a thermoplastic polymer is heated above the *Tm*, polymer melt viscosity reduces, and it melts. Many thermoplastic polymers can be used as matrix materials in textile composites. Generally, polymers having a lower melting temperature are preferred due to their ease in processing and drying. There are many approaches such as co-woven yarns, inter-dispersed fabrics, plied matrix, powder impregnation, and commingled materials, and they are used to impregnate the reinforcing textile structure with the matrix polymer [17]. In this techniques, the formability is improved. The first three techniques require direct flow of the polymer melt into the fiber bed. Powder impregnated and commingled materials have fiber and matrix constituents intimately mingled before the melt impregnation process. This reduces the distance that the resin must flow to achieve impregnation, offering the possibility of a fast wet-out during consolidation [18]. Nevertheless, the production of thermoplastic composites has some technical processing problems. For example, as thermoplastic melt has much higher viscosity than common thermoset resins, it is difficult to obtain homogeneous composite structure. There are some methods to produce homogeneous composite structure, and they are the following:

Although there are novel thermoplastic composite manufacturing methods such as co-compression molding of textile preforms with a flowable core and overinjection molding of stamped preforms, close contact between the fiber and the matrix is widely used in textile composites [17].

### **2.1. Types of hybrid yarns**

had very short out-lives; nowadays, it is possible for them to be stored in a freezer, have an out-life of possibly several months and a cure temperature of between 50 and 200°C. Prepregs tend to be epoxy resins reinforced with carbon, glass, or aramid fibers. High-temperature

In thermoplastic polymers, the organic molecular units are bonded together. They differ from thermoset polymers in this way. Thermoplastic composites are preferred for their ability to be formed by heat at low pressure. While thermosets are produced with manual production, the thermoplastic processing techniques are machine friendly and enable short processing

Thermoplastic polymers are divided into two groups of amorphous and semicrystalline polymers according to their molecular structure. While amorphous polymers have randomly oriented molecular chains, in semicrystalline polymers, the chains are symmetric enough to be fitted into an ordered crystalline state. Because of the large molecular chain length, complete crystallinity cannot be obtained, and both crystalline and amorphous regions coexist in the solid. When a polymer is cooled, there are some changes. From above, the melt temperature

, the molecular chains are locked in place, and the polymer assumes a "glassy" state. In this case, the molecular orientation is random due to the irregular chain structure. At semicrys-

When a thermoplastic polymer is heated above the *Tm*, polymer melt viscosity reduces, and it melts. Many thermoplastic polymers can be used as matrix materials in textile composites. Generally, polymers having a lower melting temperature are preferred due to their ease in processing and drying. There are many approaches such as co-woven yarns, inter-dispersed fabrics, plied matrix, powder impregnation, and commingled materials, and they are used to impregnate the reinforcing textile structure with the matrix polymer [17]. In this techniques, the formability is improved. The first three techniques require direct flow of the polymer melt into the fiber bed. Powder impregnated and commingled materials have fiber and matrix constituents intimately mingled before the melt impregnation process. This reduces the distance that the resin must flow to achieve impregnation, offering the possibility of a fast wet-out during consolidation [18]. Nevertheless, the production of thermoplastic composites has some technical processing problems. For example, as thermoplastic melt has much higher viscosity than common thermoset resins, it is difficult to obtain homogeneous composite structure. There are some methods to produce homogeneous composite structure, and they are the following: • Polymer direct melt extrusion or pultrusion that reinforce fibers are pulled through a resin;

Although there are novel thermoplastic composite manufacturing methods such as co-compression molding of textile preforms with a flowable core and overinjection molding of stamped preforms, close contact between the fiber and the matrix is widely used in textile

), the chains lose mobility and begin to interact segment by segment.

, regions of amorphous,

polymer composites are occasionally used as other matrix materials [16].

talline state, polymers crystallize at temperatures so high from the *Tg*

cycles [14, 17].

138 Textiles for Advanced Applications

At *Tg*

(*Tm*) to glass transition (*Tg*

and crystalline phase coexist [17].

• Solvents or low viscosity precursors; and

composites [17].

• Close contact between the fiber and the matrix [14].

Hybrid yarns can be produced with many methods such as ring spinning, commingling, and braiding. These methods provide uniform distribution of matrix and reinforcement fibers as well as reduce the damage to reinforcing fibers [19]. The information on methods will be given following sections.

### *2.1.1. Ring spinning*

Classical ring spinning machines have a pair of rollers for the drafting, twisting, and winding mechanism and can use only one type of fiber to manufacture spun yarns. Present ring spinning machines need some modifications to manufacture hybrid yarns. Generally, core ring spinning on a modified ring frame needs with it special guiding devices and feeder rollers (**Figure 1**). With slight modifications and little investment, this technique can be used to produce hybrid yarns by the core spinning system, and these machines are most commonly used to produce core-spun yarns containing elastane as a core. While one type of fiber is used in classical ring spinning, staple fibers and filaments can be used in core ring spinning [19–21].

**Figure 1.** Modified core spinning system [21].

### *2.1.2. Rotor spinning*

As in ring spinning, rotor spinning needs some modifications to manufacture hybrid yarns. In the modified rotor spinning machine, hybrid yarns can be produced by combining staple fibers with filament yarns under varying filament overfeeds. **Figure 2** shows the modified rotor and the diagram of spinning process. In this machine, the staple fiber and the continuous filament were fed into the rotor to produce hybrid yarn. This technology has a tendency to introduce filament misalignment in the core yarn, which is not desirable for composite application [19, 22].

### *2.1.3. DREF spinning*

This spinning system can be used to manufacture core-spun hybrid yarns for thermoplastic composites. In classical DREF spinning, the completely opened fiber strand is brought into engagement with the rotating open end of the yarn by a perforated drum. Attachment and strengthening of the fibers are accomplished by continuously rotating the yarn in the converging region of the two drums. The spinning of the yarn takes place with the help of the rotational movement of the two cylinders, and the friction on the cylinder surface contributes to this [19].

This system can be used to fabricate a hybrid yarn consisting of reinforcement filaments of high-performance fibers in the core and staple fibers of the thermoplastic matrix material such as polyester, poly-ether-etherketone or liquid crystal polymers in the sheath. Hasan et al. studied the application of carbon filament yarn (CFY)–based conductive hybrid yarn as the heating element in a textile-reinforced concrete structure. In order to manufacture this hybrid yarn, they used DREF-2000 spinning technique. Carbon fiber was used as a core, and a mixture of short glass and polypropylene fibers was used as a sheath. **Figure 3** shows friction spinning machine and cross-section of hybrid yarn [19, 23].

**Figure 2.** (a) Diagram of spinning process (b) Modified rotor [22].

### *2.1.4. Wrap spinning*

*2.1.2. Rotor spinning*

140 Textiles for Advanced Applications

*2.1.3. DREF spinning*

machine and cross-section of hybrid yarn [19, 23].

**Figure 2.** (a) Diagram of spinning process (b) Modified rotor [22].

As in ring spinning, rotor spinning needs some modifications to manufacture hybrid yarns. In the modified rotor spinning machine, hybrid yarns can be produced by combining staple fibers with filament yarns under varying filament overfeeds. **Figure 2** shows the modified rotor and the diagram of spinning process. In this machine, the staple fiber and the continuous filament were fed into the rotor to produce hybrid yarn. This technology has a tendency to introduce filament misalignment in the core yarn, which is not desirable for composite application [19, 22].

This spinning system can be used to manufacture core-spun hybrid yarns for thermoplastic composites. In classical DREF spinning, the completely opened fiber strand is brought into engagement with the rotating open end of the yarn by a perforated drum. Attachment and strengthening of the fibers are accomplished by continuously rotating the yarn in the converging region of the two drums. The spinning of the yarn takes place with the help of the rotational movement of the two cylinders, and the friction on the cylinder surface contributes to this [19]. This system can be used to fabricate a hybrid yarn consisting of reinforcement filaments of high-performance fibers in the core and staple fibers of the thermoplastic matrix material such as polyester, poly-ether-etherketone or liquid crystal polymers in the sheath. Hasan et al. studied the application of carbon filament yarn (CFY)–based conductive hybrid yarn as the heating element in a textile-reinforced concrete structure. In order to manufacture this hybrid yarn, they used DREF-2000 spinning technique. Carbon fiber was used as a core, and a mixture of short glass and polypropylene fibers was used as a sheath. **Figure 3** shows friction spinning In this system, a roving or a sliver feedstock passes through a hollow spindle without receiving true twist. The continuous filament yarn, which is mounted on the hollow shaft, is passed through the hollow spindle as shown and is wound on the central component (**Figure 4**). Hence, this filament strand is wound around the twistless strand in the core. With some modifications, this system can manufacture hybrid yarn using filament for both core and wrapping. When thermoplastic filament is used as a wrap yarn, during the consolidation process, this component will melt and it becomes part of the matrix [19, 24].

### *2.1.5. Air-jet texturing*

Air-jet texturing is completely a mechanical process, and reinforcing and matrix filaments are combined by air. In this process, the air nozzle is the heart of the air-jet texturing process. Supply yarn is overfed into the turbulent zone, and here, compressed air is guided mainly parallel to the yarn path. This compressed air flow opens up filament bundles and then builds mingling sections (**Figure 5**), as a result, mixed filament yarn is manufactured, but, while filaments mix, some loops occur [19, 25].

### *2.1.6. Commingling*

Like air-jet texturing, in the commingling process, compressed air is used to generate entanglements in and among filaments. In this process, two or more yarns, such as carbon or glass, and a thermoplastic matrix yarn are converted to a single strand. Commingled yarn consists

**Figure 3.** (a) DREF-2000 friction spinning machine (Fehrer AG, Linz, Austria), (b) Sketch and (c) Microscopic image of the cross-section and (d) Longitudinal view of the FS hybrid yarn produced to be used as the heating element [23].

**Figure 4.** Filament wrap spinning [19].

**Figure 5.** Air-jet yarn texturing [25].

of blended two parts combination, reinforcing filament yarn and filament yarn spun from thermoplastic polymers. In the beginning, the multifilament yarns are scattered by compressed air, and then they are often mixed with each other in parallel. Unlike air-jet texturing, loops do not occur, and generally, filaments are parallel to each other (**Figure 6**). Thanks to the changes in main production parameters such as degree of overfeeding, production speed, and air pressure, it can be manufactured as a hybrid yarn in the desired filament distribution. It is possible to obtain a homogenous distribution of reinforcement and matrix, and this reduces the mass transfer distance of the matrix during processing. In this way, a fast and complete impregnation of the reinforcement filaments is possible [19, 25, 26].

### *2.1.7. Parallel winding*

In this simple process, the two components of the hybrid yarns are brought together side by side, as shown in **Figure 7**. Parallel winding is also called tape winding or the side-by-side technique. In this process, the continuous reinforcement filaments and the thermoplastic filaments are combined in the form of a band. Then, after the heating process, this tape is converted to a composite material [19, 24].

### *2.1.8. Stretch breaking*

In this process, hybrid yarns consist of discontinuous thermoplastic fibers and filaments. They are brought together into a well-oriented coherent bundle by the insertion of a degree of twist. Thanks to this technology, a broken fiber feed on one or two tows of high-modulus filaments such as carbon or glass and also produces highly consistent yarns with minimal fiber damage. When heating is applied, the composite structure is formed by melting the thermoplastic structure [19, 24].

#### *2.1.9. KEMAFIL technology*

This technology has been developed in Germany for geotextiles. In this technology, a type of circular knitting machine is used to manufacture hybrid yarn. In this machine, a parallel

**Figure 6.** Hybrid yarn by commingling process [19].

**Figure 5.** Air-jet yarn texturing [25].

**Figure 4.** Filament wrap spinning [19].

142 Textiles for Advanced Applications

**Figure 7.** Structure of side-by-side hybrid yarn [19].

arrangement of matrix fibers is surrounded by parallel reinforcing filaments. In this hybrid yarn, while the core consists of matrix and reinforcing filaments, the knitted sheath consists of only matrix fibers [19, 24].

#### *2.1.10. Schappe technology*

Schappe technology is same as stretch breaking. This technology is used to obtain more bulky and higher tenacity hybrid yarn from long fibers. These types of hybrid yarns are composed of a mixture of discontinuous reinforcing and matrix filaments surrounded by continuous matrix filaments. As this consists of transforming the continuous filaments put on top of long fibers, this technique removes the weak points of the fibers [19, 24].

#### *2.1.11. Braided yarn*

Braiding has been used since 1800s to produce textile fabrics and is generally used for producing narrow rope-like materials. In this technology, three or more strands of filaments or yarns are interlaced diagonally like in a Maypole dance. The filament bundles forming the braid are combined in a manner similar to the formation of the ribbon to form the braided yarn. In this way, tubular woven structure occurs. Researchers have focused braiding technology to meet new demands in composite production [27, 28]. Details of braided yarn and its production are discussed in Section 3.

#### **2.2. Fiber distribution in hybrid yarns**

The type of hybrid yarn production technique is very important on the fiber distribution in the hybrid yarn. The homogeneity of component fiber distribution within the matrix is strongly dependent on the hybrid yarn structure. Fiber distribution is influential in the quality of the composites, as it will affect the flow distance of thermoplastic polymer when heat is applied. When they are ranked according to the flow distance, the flow distance increased in the order of Schappe yarn, commingled yarn, Kemafil yarn, side-by-side yarn, and lastly, friction spun yarn. This means that the best degree of mixing of reinforcing and matrix are Schappe and commingled hybrid yarns fibers. Hybrid yarn structures are shown in **Table 1** [19].

arrangement of matrix fibers is surrounded by parallel reinforcing filaments. In this hybrid yarn, while the core consists of matrix and reinforcing filaments, the knitted sheath consists

Schappe technology is same as stretch breaking. This technology is used to obtain more bulky and higher tenacity hybrid yarn from long fibers. These types of hybrid yarns are composed of a mixture of discontinuous reinforcing and matrix filaments surrounded by continuous matrix filaments. As this consists of transforming the continuous filaments put on top of long

Braiding has been used since 1800s to produce textile fabrics and is generally used for producing narrow rope-like materials. In this technology, three or more strands of filaments or yarns are interlaced diagonally like in a Maypole dance. The filament bundles forming the braid are combined in a manner similar to the formation of the ribbon to form the braided yarn. In this way, tubular woven structure occurs. Researchers have focused braiding technology to meet new demands in composite production [27, 28]. Details of braided yarn and its production are

The type of hybrid yarn production technique is very important on the fiber distribution in the hybrid yarn. The homogeneity of component fiber distribution within the matrix is strongly dependent on the hybrid yarn structure. Fiber distribution is influential in the quality of the composites, as it will affect the flow distance of thermoplastic polymer when heat is applied. When they are ranked according to the flow distance, the flow distance increased in the order of Schappe yarn, commingled yarn, Kemafil yarn, side-by-side yarn, and lastly, friction spun yarn. This means that the best degree of mixing of reinforcing and matrix are Schappe and commingled hybrid yarns fibers. Hybrid yarn structures are shown

fibers, this technique removes the weak points of the fibers [19, 24].

of only matrix fibers [19, 24].

**Figure 7.** Structure of side-by-side hybrid yarn [19].

*2.1.10. Schappe technology*

144 Textiles for Advanced Applications

*2.1.11. Braided yarn*

discussed in Section 3.

in **Table 1** [19].

**2.2. Fiber distribution in hybrid yarns**

#### **Hybrid yarn structure Position of performance filaments**

#### **Ring core-spun yarn (RS)**

Performance filaments in core and covered spun fibers in a twisted form

#### **Rotor core-spun yarn (ROS)**

Performance filaments in core and covered spun fibers in a wrapped form

#### **DREF core-spun yarn (DF)**

Parallel arrangement of performance filaments in core and covered spun fibers

#### **Wrap yarn (WS)**

Parallel laid fibers in core and covered by performance filaments

#### **Air-jet textured yarn (AT)**

Thermoplastic filament and performance filaments are interlaced forming loop structure

#### **Commingled (COM)**

Thermoplastic filaments and performance filaments in a mingled form

#### **Parallel winding (SBS)**

Parallel arrangement of performance filaments and thermoplastic filaments

#### **Stretch break (SB)**

Stretched break thermoplastic filaments covered by performance filaments

#### **Kemafil technology (KEM)**

Parallel arrangement of thermoplastic filaments surrounded by parallel performance filaments in the core, sheath in continuous filament in a knitted form

**Table 1.** Hybrid yarn structures based on production method [19, 24].

### **3. Braiding technology**

In composites manufacturing, the molten thermoplastic must flow through the capillaries between the reinforcement filaments. Theoretically, this can be achieved with a commingling method. In our previous studies, this method was tried, and some results were realized. It produced hybrid yarns approximately 1100 tex from 640 tex AR-glass roving and 400 tex polypropylene (PP) filament. In textile reinforcement concrete, generally 2400 tex or more linear density is used as a reinforcement material. In our study with approximately 1100 tex, it could not get a good homogeneity of fiber distribution. A further development of higher linear density with homogeneous fiber content is necessary. Therefore, the braiding yarn was used in this study as a new approach in order to obtain hybrid yarn for TRC production. Also, braiding technology offers minimum or no damage to the reinforcement fiber bundles, when compared to using commingled yarns.

### **3.1. Introduction to braiding technology**

Braiding has been used for 200 years to produce textile fabrics. In this process, three or more threads are interlaced diagonally to the product axis [28, 29].

As the threads pass diagonally, they make an angle between 1 and 89° with the product axis of the yarns, usually within the range of 30–80° (**Figure 8**). This angle is called the braiding angle and is the most important geometric parameter of braided structures [29].

It is possible to produce a thicker, wider, or stronger product or cover some profiles in braiding technology. These products can be linear products (ropes), curved or plane shell, or solid structures (one, two, or three-dimensional (3D) fabrics) with constant or variable cross-section and of closed or open appearance. Researchers have focused braiding technology to meet new demands in composite production [28, 29].

**Figure 8.** Structure of braided yarn [29].

### **3.2. Machine and product classification**

There are several different classifications of the braided processes, machines, and products. Generally, braided products of maypole braiding machines are divided into two main groups: Braids with constant cross-section and variable cross-section form. While there is flat braiding, tubular braiding, and form braiding for braids with constant cross-section, there are only 3D Braids for variable cross-section form. Each group has normal or biaxial braiding and triaxial braiding types. The classical and mainly used braiding machines are known as maypole braiding machines. This name will always be used where these machines have to be distinguished from the other (spiral, lace) braiding machines. Details of these classification are mentioned in the following sections. In the future, it is expected that with the increasing speed of electromechanical drives, maypole braiding machines with switches (3D braiding) will be able to work continuously [29].

### **3.3. Basic principle**

**3. Braiding technology**

146 Textiles for Advanced Applications

**Table 1.** Hybrid yarn structures based on production method [19, 24].

compared to using commingled yarns.

**3.1. Introduction to braiding technology**

demands in composite production [28, 29].

threads are interlaced diagonally to the product axis [28, 29].

and is the most important geometric parameter of braided structures [29].

In composites manufacturing, the molten thermoplastic must flow through the capillaries between the reinforcement filaments. Theoretically, this can be achieved with a commingling method. In our previous studies, this method was tried, and some results were realized. It produced hybrid yarns approximately 1100 tex from 640 tex AR-glass roving and 400 tex polypropylene (PP) filament. In textile reinforcement concrete, generally 2400 tex or more linear density is used as a reinforcement material. In our study with approximately 1100 tex, it could not get a good homogeneity of fiber distribution. A further development of higher linear density with homogeneous fiber content is necessary. Therefore, the braiding yarn was used in this study as a new approach in order to obtain hybrid yarn for TRC production. Also, braiding technology offers minimum or no damage to the reinforcement fiber bundles, when

**Schappe technology (SCH)**

**Braiding technology**

filaments

Mixture of discontinuous performance material and fibers surrounded by thermoplastic filaments

Filament or yarns in core and covered by performance

**Hybrid yarn structure Position of performance filaments**

Braiding has been used for 200 years to produce textile fabrics. In this process, three or more

As the threads pass diagonally, they make an angle between 1 and 89° with the product axis of the yarns, usually within the range of 30–80° (**Figure 8**). This angle is called the braiding angle

It is possible to produce a thicker, wider, or stronger product or cover some profiles in braiding technology. These products can be linear products (ropes), curved or plane shell, or solid structures (one, two, or three-dimensional (3D) fabrics) with constant or variable cross-section and of closed or open appearance. Researchers have focused braiding technology to meet new Braiding has been used for many years in different application areas such as braiding of yarns, flowers, and hair. The application areas for braided products are widespread such as medical items, electric cables, ropes, laces, the huge ropes, and tubes used in the marine oilfield sector. Also, use of braids is growing in the production of fiber-reinforced composites. All the products are manufactured in the same way, i.e., by the interlacing of yarns at an angle of about 40–60° to the main product axis. **Figure 9** shows the principle of hand braiding for a simple braid of three yarns. Initial structure (**Figure 9(a)**) is transformed to the interlacement in two steps:

#### **3.4. Flat braiding**

Flat braiding structures can be obtained when basic braiding is applied to more yarns, e.g. 5, 7. Flat braiding principle is seen in **Figure 10(a,b)**. In this case, at the first step, all left pairs interlace

**Figure 9.** Principle of hand braiding with three yarns [29].

**Figure 10.** Hand braiding of odd (here seven) yarns (a,b) and of even (here six) yarns(c,d) [29].

so that the left goes over the right, and in the second step, all right pairs interlace so that the right yarn goes over the left [29].

Flat braiding is possible for both odd and even numbers of yarns. **Figure 10(c,d)** shows the sequence in the case of six yarns: at every second step, yarns from both the left and right sides stay and wait, while when using an odd number of yarns, only one yarn per cycle stays unused during the interlacement [29].

#### **3.5. Tubular braiding**

In this system, even number of yarns arranged around a circle interlace for production of tubular braids or ropes (**Figure 11**). The sequence of steps in this case is the same as for the flat yarn. In order to produce a regular structure, all yarns have to be kept under constant tension during the braiding process [29].

The interlacing sequence in the case of tubular braiding is same in flat braiding, but unlike flat braiding, all the yarn ends are located around a circle (**Figure 12**). The process can be described as follows:

**Figure 11.** Tubular braids (rope). (a) Geometrical model and (b) Single (upper part) and Tripple (over-) braided part [29].

**Figure 12.** Sequence for tubular braiding [29].

**Figure 10.** Hand braiding of odd (here seven) yarns (a,b) and of even (here six) yarns(c,d) [29].

yarn goes over the left [29].

**3.5. Tubular braiding**

described as follows:

unused during the interlacement [29].

**Figure 9.** Principle of hand braiding with three yarns [29].

148 Textiles for Advanced Applications

during the braiding process [29].

so that the left goes over the right, and in the second step, all right pairs interlace so that the right

Flat braiding is possible for both odd and even numbers of yarns. **Figure 10(c,d)** shows the sequence in the case of six yarns: at every second step, yarns from both the left and right sides stay and wait, while when using an odd number of yarns, only one yarn per cycle stays

In this system, even number of yarns arranged around a circle interlace for production of tubular braids or ropes (**Figure 11**). The sequence of steps in this case is the same as for the flat yarn. In order to produce a regular structure, all yarns have to be kept under constant tension

The interlacing sequence in the case of tubular braiding is same in flat braiding, but unlike flat braiding, all the yarn ends are located around a circle (**Figure 12**). The process can be

In tubular braiding, the beam is slowly covered from the top down. In braiding terminology, the beam is called the core (if it had a regular form) or the mandrel (if it had a more complex geometry), and this braiding system is used today for overbraiding of profiles with carbon or glass fiber composites for aerospace, cables, high pressure ropes, etc., for automotive and other applications [29].

#### **3.6. Biaxial and triaxial braids, inlay yarns**

Inlay yarns can be put in between the core and the yarns. These are named differently in each every different application areas, e.g., middle ends, inlays, and triaxial braids (**Figure 13**) [29].

Inlay yarns can be inserted into all kinds of braided structures; however, the core or the mandrel requires a hollow structure and is mainly used in tubular braids (**Figure 14**) [29].

#### **3.7. Industrial maypole braiding**

In industrial braiding, the machine dancer element is called a carrier, and the path of the carrier is called the track. If the motion of the dancers/carriers is analyzed carefully, it can be seen that all dancers/carriers in one direction are following the same track, while the dancers/

**Figure 13.** (a) Normal (biaxial) braids and (b) Braids with inlay yarns (triaxial) [29].

**Figure 14.** Tubular braid with core and inlay yarns (triaxial) [29].

carriers in the opposite direction follow the opposite track. Hence, for tubular braiding, there are two tracks and two systems of carriers [29].

The path of the motion is determined by the track, but the carriers are moved forward by the horn gears (**Figure 15**). At the beginning of the process, all outer ends of the yarns are connected together at the braiding point. When the carriers start their motions, the yarns interlace together. With this move, the next piece of braid is built at the braiding point. Finally, the braid produced is finally pulled out with the help of a take-off system [29].

### **3.8. Form braiding and 3D braiding**

For different applications, such as thicker braided products of square or other cross-sectional type is required. For example, gaskets or fiber-reinforced composites can be manufactured with these products. In this case, the braiding process is called packing braiding, or 2.5D braiding (2.5D means more than the two dimensions of length and width, but less than

**Figure 15.** Principal construction of maypole braiding machine [29].

three dimensions), or alternatively, 3D braiding (due to the braided product having thickness in all three directions). However, according to some classifications, they may also be named 3D, 4D, etc., braiding, but D means "diagonal" here. In the new generation of braiding machines, they are controlled by a computer, and the track is not constant. The carrier can change its motion and can travel along a set of connected curves, and the selection of the next curve can change dynamically during the braiding process. Thanks to diversity, the braids do not have a constant cross-section, they are called 3D braids, and the process itself is 3D braiding [3, 29].

#### **3.9. Applications of braiding yarns**

**Figure 14.** Tubular braid with core and inlay yarns (triaxial) [29].

**Figure 13.** (a) Normal (biaxial) braids and (b) Braids with inlay yarns (triaxial) [29].

150 Textiles for Advanced Applications

are two tracks and two systems of carriers [29].

**3.8. Form braiding and 3D braiding**

is finally pulled out with the help of a take-off system [29].

carriers in the opposite direction follow the opposite track. Hence, for tubular braiding, there

The path of the motion is determined by the track, but the carriers are moved forward by the horn gears (**Figure 15**). At the beginning of the process, all outer ends of the yarns are connected together at the braiding point. When the carriers start their motions, the yarns interlace together. With this move, the next piece of braid is built at the braiding point. Finally, the braid produced

For different applications, such as thicker braided products of square or other cross-sectional type is required. For example, gaskets or fiber-reinforced composites can be manufactured with these products. In this case, the braiding process is called packing braiding, or 2.5D braiding (2.5D means more than the two dimensions of length and width, but less than The application of braids is various from medical items to electric cable. Also, use of braids is growing in the production of fiber-reinforced composites [3, 29].

If we summarize, we can classify the application fields as follows:

#### **3.10. Braiding technology in future**

### **4. Experimental**

Experimental study is focused on use of braiding yarn for textile-reinforced concrete. Hybrid yarn was produced with using braiding method. Hybrid yarn to be used as reinforcement has a unique combination of reinforcement and matrix component that was produced using a tubular braiding machine consisting of 16 spindles (**Figure 16**). Hybrid yarn can be thought of as a single yarn, although it is composed of two components. Continuous AR-Glass roving was used as the straight inserted axial fibers, and matrix fibers (PP fibers) were braided around the reinforcing AR-Glass roving.

AR-Glass fiber roving (Cem-FIL® 5325 from OCV Reinforcements) and polypropylene (PP) filament yarn (Aker Textile Yarn) were used to produce hybrid yarn with braiding method. The linear density of AR-Glass is 2400 tex, and the linear density of PP filament is 666.6 dtex. To produce hybrid yarn with braiding method, 1-filament AR-Glass and 16-filament PP were used. Yarn linear density was measured according to ISO 2060. The linear density of hybrid yarn, its components, and other reinforcing components are given in **Table 2**.

After the production of hybrid yarn, a hot compression molder was used to fabricate continuous fiber-reinforced thermoplastic composites. Matrix fibers were melted by heating at appropriate molding temperatures and become the matrices for the fiber-reinforced composites that easily wet out the reinforcing AR-glass roving. **Figure 17** shows the view of hybrid yarn before and after heating.

**Figure 16.** Braiding machine.

• Machine engineering: fiber-reinforced materials, package seals.

• Household: packaging, clothesline, do-it-yourself requirements [3, 29, 30].

carriers will surely continue to be used in a large number of applications.

• Traffic: fiber-reinforced materials for aircraft and car construction, track vehicles, and shipping.

• Replacements of mechanical controls of braiding machines by electronic controls will reduce

• In future decades, even if braiding machine by electronic control will be used, mechanical

• Braiding machines for the production of 3-D braids to obtain larger and more complex cross sections will be developed, and they can be used for nearly every application.

• Mathematical models between machine controls and the position of threads in the braid

Experimental study is focused on use of braiding yarn for textile-reinforced concrete. Hybrid yarn was produced with using braiding method. Hybrid yarn to be used as reinforcement has a unique combination of reinforcement and matrix component that was produced using a tubular braiding machine consisting of 16 spindles (**Figure 16**). Hybrid yarn can be thought of as a single yarn, although it is composed of two components. Continuous AR-Glass roving was used as the straight inserted axial fibers, and matrix fibers (PP fibers) were braided

AR-Glass fiber roving (Cem-FIL® 5325 from OCV Reinforcements) and polypropylene (PP) filament yarn (Aker Textile Yarn) were used to produce hybrid yarn with braiding method. The linear density of AR-Glass is 2400 tex, and the linear density of PP filament is 666.6 dtex. To produce hybrid yarn with braiding method, 1-filament AR-Glass and 16-filament PP were used. Yarn linear density was measured according to ISO 2060. The linear density of hybrid yarn, its components, and other reinforcing components are given in **Table 2**.

After the production of hybrid yarn, a hot compression molder was used to fabricate continuous fiber-reinforced thermoplastic composites. Matrix fibers were melted by heating at appropriate molding temperatures and become the matrices for the fiber-reinforced composites that easily wet out the reinforcing AR-glass roving. **Figure 17** shows the view of hybrid yarn

• Civil engineering: fiber-reinforced concrete.

• Electrical terotechnology: cables, insulation.

**3.10. Braiding technology in future**

setup times.

152 Textiles for Advanced Applications

will be defined [3].

before and after heating.

around the reinforcing AR-Glass roving.

**4. Experimental**

**Table 2.** Linear density of hybrid yarn and its component.

Before and after heating, the cross-section of hybrid yarn was investigated on a microscope with 40× (**Figure 18**). It was observed that while structure of hybrid yarn was a bit loose before heating (a, b), it turned into compact structure after heating (c, d).

After hybrid yarns were prepared, coated AR-glass fibers were prepared to compare with hybrid yarn and uncoated AR-glass fibers. Epoxy resin (SR 8500/ SD 8605 from Sicomin) was applied to AR-glass fibers with roller coater. After coating, all samples were preheated and fixed at appropriate temperature and time. **Figure 19** shows the view of AR-glass fibers before and after coating.

**Figure 17.** (a) Hybrid yarn before heating (b) Hybrid yarn after heating.

**Figure 18.** Cross-section of hybrid yarn before heating (a, b), Cross-section of hybrid yarn after heating (c, d).

**Figure 19.** (a) Uncoated AR-Glass fibers (b) Coated AR-Glass fibers.

Prepared textile materials were placed in the mold for flexural test. For each sample, five yarns were placed in the mold along the long edge, and the distance between each yarn was set to 1 cm. The yarns were placed at a distance of 3 mm from bottom of the sample (**Figure 20**).

After all the textile components were prepared, second component for TRC which is concrete was prepared as shown in the mix proportions in **Table 3**.

The mixtures were batched in the vertical axis concrete mixer (**Figure 21**). The cement and fly ash were dry mixed for 1 min. This was followed by the addition of fine-grained aggregate, water, and the superplasticiser, with a mixing time of 5 min. After pouring the mix into oiled molds, a vibrator was used to decrease the amount of air bubbles. The specimens were demolded after 1 day and then placed in a curing room in the special pool which its water temperature is 20°C for 27 days of curing according to TS EN 12390-2 standard. For 12 h prior to the tests, the specimens were allowed to air dry in the laboratory.

**Figure 20.** Yarn position in the TRC sample.

**Figure 17.** (a) Hybrid yarn before heating (b) Hybrid yarn after heating.

154 Textiles for Advanced Applications

**Figure 18.** Cross-section of hybrid yarn before heating (a, b), Cross-section of hybrid yarn after heating (c, d).

Prepared textile materials were placed in the mold for flexural test. For each sample, five yarns were placed in the mold along the long edge, and the distance between each yarn was set to 1 cm. The yarns were placed at a distance of 3 mm from bottom of the sample (**Figure 20**).

After all the textile components were prepared, second component for TRC which is concrete

The mixtures were batched in the vertical axis concrete mixer (**Figure 21**). The cement and fly ash were dry mixed for 1 min. This was followed by the addition of fine-grained aggregate, water, and the superplasticiser, with a mixing time of 5 min. After pouring the mix into oiled molds, a vibrator was used to decrease the amount of air bubbles. The specimens were demolded after 1 day and then placed in a curing room in the special pool which its water temperature is 20°C for 27 days of curing according to TS EN 12390-2 standard. For 12 h prior to the tests, the specimens

was prepared as shown in the mix proportions in **Table 3**.

**Figure 19.** (a) Uncoated AR-Glass fibers (b) Coated AR-Glass fibers.

were allowed to air dry in the laboratory.

**Table 3.** Mix proportions of fine grained concrete.

**Figure 21.** Concrete mixer.

**Figure 22.** (a) Compression test machine (b) Flexural strenght test machine.

For the prepared mixture, eight specimens (three 150 × 150 × 150 mm cubes for compression test and five 325 × 50 × 20 mm beams for three-point loading flexural test) were prepared. The compression tests were carried out in the UTEST compression test machine (Type UTC-5750) (**Figure 22(a)**) at a loading rate of 4 kN/s on the 150 × 150 × 150 mm cubes according to the requirements of TS EN 12390-3 standard. The three-point loading flexural tests were carried out in ELE flexural test machine (Model 37-6330; **Figure 22(b)**) at a loading rate of 0.4 kN/s on the 325 × 50 × 20 mm beams according to the requirements of TS EN 12390-5 standard. The mean values of the test results were shown in table at next section.

### **5. Results and discussion**

The mechanical properties of the concrete were measured with a compression test to see the strength of concrete used in the TRC production. The average compressive strength (28 days) of a cube specimen (150 × 150 × 150 mm) was taken as 52.3 MPa. This result is good for conventional concrete. This concrete mix was used in the production of all TRC samples, and different materials were used as a reinforcing component.

In this study, only AR-glass roving was used to manufacture hybrid yarn with braiding technology. There is only AR-glass roving inside the braided yarn, and it is covered with PP filaments. To see the effectiveness of coating, carbon fiber (1600 tex from DOWAKSA) was used to produce TRC. The results of 3-point loading flexural test can be seen in **Table 4**.

As seen in **Table 4**, each reinforcement material contributes to the flexural strength of the concrete. Commonly used AR-glass roving and carbon filaments in concrete reinforcement have contributed to flexural strength, 41.19 and 146.57%, respectively, according to without reinforcement. As expected, the epoxy resin coating also has contributed to flexural strength

**Table 4.** Results of 3-point loading flexural test.

according to reinforcement with AR-glass roving and carbon filament, respectively, 78.44 and 64.69%. Heat-treated hybrid yarn reinforcement has contributed to a flexural strength of 57.71% according to without reinforcement. While reinforcement with epoxy resin coating has contributed to the flexural strength of 78.44%, reinforcement with heated hybrid yarn has contributed to flexural strength of 11.70% according to reinforced with AR-Glass roving. In this study, as it is known, it was seen that the epoxy resin coating provides a significant contribution. It is possible to evaluate the use of heated hybrid yarns produced by braiding technology in the production of TRC though it has contributed less than epoxy resin, since the epoxy resin cost is high and epoxy resin coating process is long and difficult.

### **6. Conclusion**

For the prepared mixture, eight specimens (three 150 × 150 × 150 mm cubes for compression test and five 325 × 50 × 20 mm beams for three-point loading flexural test) were prepared. The compression tests were carried out in the UTEST compression test machine (Type UTC-5750) (**Figure 22(a)**) at a loading rate of 4 kN/s on the 150 × 150 × 150 mm cubes according to the requirements of TS EN 12390-3 standard. The three-point loading flexural tests were carried out in ELE flexural test machine (Model 37-6330; **Figure 22(b)**) at a loading rate of 0.4 kN/s on the 325 × 50 × 20 mm beams according to the requirements of TS EN 12390-5 standard. The

The mechanical properties of the concrete were measured with a compression test to see the strength of concrete used in the TRC production. The average compressive strength (28 days) of a cube specimen (150 × 150 × 150 mm) was taken as 52.3 MPa. This result is good for conventional concrete. This concrete mix was used in the production of all TRC samples, and

In this study, only AR-glass roving was used to manufacture hybrid yarn with braiding technology. There is only AR-glass roving inside the braided yarn, and it is covered with PP filaments. To see the effectiveness of coating, carbon fiber (1600 tex from DOWAKSA) was used

As seen in **Table 4**, each reinforcement material contributes to the flexural strength of the concrete. Commonly used AR-glass roving and carbon filaments in concrete reinforcement have contributed to flexural strength, 41.19 and 146.57%, respectively, according to without reinforcement. As expected, the epoxy resin coating also has contributed to flexural strength

to produce TRC. The results of 3-point loading flexural test can be seen in **Table 4**.

mean values of the test results were shown in table at next section.

**Figure 22.** (a) Compression test machine (b) Flexural strenght test machine.

different materials were used as a reinforcing component.

**5. Results and discussion**

156 Textiles for Advanced Applications

In the experimental part of this study, the braiding method for using of TRC was investigated. Tubular braiding technique was applied to produce hybrid yarns using AR-glass roving as the core reinforcement fibers and PP fibers as the matrices around AR-glass roving. At the next step, these hybrid yarns were heated, and they were used for TRC production. All prepared samples used flexural strength test. When all test results were examined:

### **Acknowledgements**

This research is supported by "Scientific Research Projects Governing Unit of Çukurova University" with project number FDK-2016-6682. We would also like to thank KORD Industrial Rope and Yarn Industry and Trade Inc.—for hybrid yarn production; ÇİMSA Cement Industry and Trade Inc.—for their materials and laboratory; and Çukurova University Civil Engineering Department—for their laboratory.

### **Author details**

Mutlu Kurban1 \*, Osman Babaarslan2 and İsmail Hakkı Çağatay3

\*Address all correspondence to<EMAIL_ADDRESS>
1 Çukurova University, Vocational School of Technical Sciences, Textile Technology, Sarıçam, Adana, Turkey

2 Çukurova University, Faculty of Engineering and Architecture, Department of Textile Engineering, Balcalı, Sarıçam, Adana, Turkey

3 Çukurova University, Faculty of Engineering and Architecture, Department of Civil Engineering, Balcalı, Sarıçam, Adana, Turkey

### **References**

[6] Brameshuber W, editor. Textile Reinforced Concrete. 1st ed. RILEM Publications: Stateof-the-Art Report of RILEM Technical Committee 201-TRC. RILEM Report 36; 2006. 273 p. ISBN: 2-912413-99-3, Bagneux, France

**Acknowledgements**

158 Textiles for Advanced Applications

**Author details**

Mutlu Kurban1

Adana, Turkey

**References**

Department—for their laboratory.

\*, Osman Babaarslan2

\*Address all correspondence to<EMAIL_ADDRESS>
Engineering, Balcalı, Sarıçam, Adana, Turkey

Engineering, Balcalı, Sarıçam, Adana, Turkey

ISBN 978-1-56990-565-4, München, Germany

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This research is supported by "Scientific Research Projects Governing Unit of Çukurova University" with project number FDK-2016-6682. We would also like to thank KORD Industrial Rope and Yarn Industry and Trade Inc.—for hybrid yarn production; ÇİMSA Cement Industry and Trade Inc.—for their materials and laboratory; and Çukurova University Civil Engineering

and İsmail Hakkı Çağatay3

1 Çukurova University, Vocational School of Technical Sciences, Textile Technology, Sarıçam,

2 Çukurova University, Faculty of Engineering and Architecture, Department of Textile

3 Çukurova University, Faculty of Engineering and Architecture, Department of Civil

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## **Three-Dimentional Textile Preform Using Advanced Textile Technologies for Composite Manufacturing**

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### **Abstract**

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Textile reinforcement structure plays an important role in the reinforcement/composite performances during the composite manufacturing and in-service life of the composite material. Structures with a three-dimensional (3D) fiber topology are desired due to their superior multiaxial performance and efforts have been made to modify 2D textile technologies to produce complex 3D shapes. Most of these 3D solutions are based on the principle of adding out-of-plane reinforcements to a planar 2D fabric. Well-established 3D textile methods such as braiding and knitting have also been demonstrated to directly produce near net-shape structures. To understand these potentialities, the first section of this chapter will present the several textile technologies with strengths and weaknesses of these processes to manufacture technical reinforcements for composite applications. In the following sections, several applications with specific textile architectures will be given, in particular, the applications of the through-the-thickness reinforcement and 3D textile ply during the composite manufacturing.

**Keywords:** textile reinforcement, 3D fabric, tufting, 3D surface weaving, forming

### **1. Introduction**

The definition of textile reinforcement is an essential factor during composite manufacturing and for the performance of composite material. The step of the impregnation of the reinforcement is governed by its porosity (size and distribution) [1]. Porosities can be controlled by the permeability defined as the ability of the reinforcement to transmit fluids [2]. Permeability behavior of reinforcing textiles is a strong function of the textile's complex architecture [3] and depends on the fiber volume fraction. For the specifications of composite materials, load transfer from the matrix to the reinforcement is governed by the fiber orientation, which plays a paramount role

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

in the composite stiffness [4]. Fiber direction and fiber volume fraction must be managed during the manufacturing process of composite materials. Resin transfer molding (RTM) [5] is one of the main manufacturing processes to produce composite parts for the transport industries [6].

A lot of experimental and numerical studies [7–11] concerning the draping stage of dry reinforcement, the first step of RTM process, were carried out to analyze the deformability of different reinforcements on specific tools. Research works have been published about the textile composite forming of hemispherical [12, 13], double-dome [14], tetrahedral shapes [15], and also with square box [16]. On these complex shapes, this preforming stage modifies the main parameters as fiber direction and fiber volume fraction and consequently has a significant influence on the resin flow impregnation and on the characteristics of the final composite part. The behavior of highly aligned reinforcements (woven, braided knitted, etc.) during the preforming step is characterized by complex coupled tensile, in-plane shear, and bending, but also by compaction deformations. Criteria to define the feasibility to realize a particular shape are based on limits of these deformations, such as the locking angle [17] for the in-plane shear behavior. All these studies have shown that the reinforcement architecture is a main parameter to predict the feasibility forming conditions and to prevent the manufacturing defects.

During the manufacturing of composite parts, defects may be introduced in their structure. Potter et al. [18] have presented a taxonomy of defect states that may have adverse impacts on the performance of composite parts. During the first step of the RTM process (preforming stage), with the use of full-field optical measurements of strains, the detection of defects is possible, as wrinkles [19], nonhomogeneity of the fiber density, and if the discontinuity of the preform due to sliding of tows takes place. The quantification of different level of strains in tension or in-plane shear can be also analyzed for the mechanical state of the preform. At mesoscopic scale, tows misalignment in the plane of the fabric or tow buckles that are defined as out-of-plane misalignment [20, 21] can be investigated. This presentation of defects could not be complete without mentioning the difficulties associated to the preforming of multilayer dry textile reinforcement, or thick as preforms as those used in high-tech industrial domains, such as automotive and aerospace industries, for instance, fan blades developed by Snecma [22]. In the literature, the preforming of multilayer dry textile reinforcements has been one of the main subjects [10, 11, 23]. In the considered forming parameters of multilayers, the number and the orientation of each ply must be taken into account. The study presented in Ref. [8] shows that preforming of multilayer is not yet controlled and demonstrate the influence of the layer orientations especially on the draw-in and finally on the final shape. The interply behavior is used, for example, with the identification of friction laws, through numerical and experimental studies [24, 25]. However, these studies estimated criteria of forming only on the top or bottom ply and did not measure the quantities in each ply of the multilayer. When these defects manifest during forming applications (and also thermostamping [23, 26]), it can be controlled by the addition of lateral restraint (e.g., matched die) or modification of forming temperature, tooling velocity, contact-to-free edge distance (e.g., blank size), and pretensioning (e.g., binder pressure) [27, 28]. Parametric studies are developed to study independently the effect of each of these parameters on final part quality; especially, experimental approaches lead to well understand the influence of the processing conditions to fabricate defect-free preform, as for example, the effect of blank-holder [29]. The development of numerical tools, by finite element simulation, can be an effective approach to take into account whole coupling parameters, to avoid experimental trial and error, and finally define optimal configurations of these parameters. If research works were concerned the efficiency of the modification of forming process parameters to avoid/reduce these defects, the influence of specifically the nature and the architecture of dry preform during the preforming is less analyzed.

in the composite stiffness [4]. Fiber direction and fiber volume fraction must be managed during the manufacturing process of composite materials. Resin transfer molding (RTM) [5] is one of the main manufacturing processes to produce composite parts for the transport industries [6]. A lot of experimental and numerical studies [7–11] concerning the draping stage of dry reinforcement, the first step of RTM process, were carried out to analyze the deformability of different reinforcements on specific tools. Research works have been published about the textile composite forming of hemispherical [12, 13], double-dome [14], tetrahedral shapes [15], and also with square box [16]. On these complex shapes, this preforming stage modifies the main parameters as fiber direction and fiber volume fraction and consequently has a significant influence on the resin flow impregnation and on the characteristics of the final composite part. The behavior of highly aligned reinforcements (woven, braided knitted, etc.) during the preforming step is characterized by complex coupled tensile, in-plane shear, and bending, but also by compaction deformations. Criteria to define the feasibility to realize a particular shape are based on limits of these deformations, such as the locking angle [17] for the in-plane shear behavior. All these studies have shown that the reinforcement architecture is a main parameter to predict the feasibility forming conditions and to prevent the manufacturing defects.

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During the manufacturing of composite parts, defects may be introduced in their structure. Potter et al. [18] have presented a taxonomy of defect states that may have adverse impacts on the performance of composite parts. During the first step of the RTM process (preforming stage), with the use of full-field optical measurements of strains, the detection of defects is possible, as wrinkles [19], nonhomogeneity of the fiber density, and if the discontinuity of the preform due to sliding of tows takes place. The quantification of different level of strains in tension or in-plane shear can be also analyzed for the mechanical state of the preform. At mesoscopic scale, tows misalignment in the plane of the fabric or tow buckles that are defined as out-of-plane misalignment [20, 21] can be investigated. This presentation of defects could not be complete without mentioning the difficulties associated to the preforming of multilayer dry textile reinforcement, or thick as preforms as those used in high-tech industrial domains, such as automotive and aerospace industries, for instance, fan blades developed by Snecma [22]. In the literature, the preforming of multilayer dry textile reinforcements has been one of the main subjects [10, 11, 23]. In the considered forming parameters of multilayers, the number and the orientation of each ply must be taken into account. The study presented in Ref. [8] shows that preforming of multilayer is not yet controlled and demonstrate the influence of the layer orientations especially on the draw-in and finally on the final shape. The interply behavior is used, for example, with the identification of friction laws, through numerical and experimental studies [24, 25]. However, these studies estimated criteria of forming only on the top or bottom ply and did not measure the quantities in each ply of the multilayer. When these defects manifest during forming applications (and also thermostamping [23, 26]), it can be controlled by the addition of lateral restraint (e.g., matched die) or modification of forming temperature, tooling velocity, contact-to-free edge distance (e.g., blank size), and pretensioning (e.g., binder pressure) [27, 28]. Parametric studies are developed to study independently the effect of each of these parameters on final part quality; especially, experimental approaches lead to well understand the influence of the processing conditions to fabricate defect-free preform, as for example, the effect of blank-holder [29]. The development of numerical tools, by finite element simulation, can be an effective approach to take into account whole coupling parameters, to avoid experimental trial and error, and finally define optimal Studies concerning, separately, the preforming of carbon, glass, and also natural fiber textiles in woven fabrics [12], nonwoven fabrics [30], noncrimp fabrics [24, 31], three-dimensional (3D) interlock [12, 32], weft-knitted fabric [25], UD [33], or also braided reinforcements [34] can be found in the literature. These studies show that there is a very wide range of types of reinforcements from high performance fibers such as carbon, glass, or aramid fibers to natural or hybrid (as comingled [35]) fibers, which can be used to manufacture composite materials [36]. These reinforcements are developed from textile technologies, as weaving, knitting, breading, or nonwoven manufacturing processes, and have different mechanical properties, especially during the preforming step. The classification of these reinforcement architectures, in the textile literature, is based first on the technologies used but also on the fiber topology, e.g., the number of fiber directions [37, 38], but conventional laminated composite has fibers oriented only in the plane of the laminate and is therefore vulnerable to delamination. Due to the inclusion of the throughthickness yarns, three-dimensional (3D) fiber reinforced composites have several advantages over traditional two-dimensional (2D) composites such as elevated fracture toughness, better interlaminar fracture toughness, higher damage tolerance, impact resistance, and tensile strainto-failure [39]. Due to the complexity and diversity [40] of these 3D composite architectures [41], the performance and efficacy of these 3D composite in service are predicted early from numerical computational work. In order to validate the computational results and gauge the influence of the through-thickness fibers on the in-plane and out-plane mechanical properties, numerous authors have worked on the identification of the mechanical properties of 3D reinforced composites [42]. Transverse cracking and propagation of delamination have been studied earlier with the help of digital image correlation (DIC), which maps the surface strain distribution [43]. Moreover, to describe the complex 3D preform architecture, X-ray microcomputed tomography has also been used [44]. Consequently, efforts have been made to modify 2D textile technologies to manufacture complex 3D preform [37, 38]. Most of these 3D solutions are based on the principle of adding out-of-plane reinforcements to a planar 2D fabrics, examples include *z*-pinning [45], interlockweaving [46], stitching [47], or tufting [48].Well-established 3D textile methods such as braiding [49], weaving [40, 46], and knitting [50] have also been demonstrated to directly produce near net-shape structures. The control of these textile technologies that are able to manufacture 3D preform is absolutely necessary to avoid damage occurring by the insertion of the through-thethickness reinforcement and consequently decreasing mechanical properties of 3D composites.

To describe potentialities of 3D preform reinforcement especially during manufacturing steps of composite materials, this chapter focused on applications. In the second section, the several textile technologies will be presented in fact to understand architecture of reinforcements and its influences on their properties. Strengths and weaknesses of these processes will be given. In the third section of this chapter, an example of through-the-thickness reinforcement by tufting will be described specifically for the preforming step of the RTM process. Experimental comparisons between untufted and tufted samples subjected to hemispherical preforming will be compared to minimize defects as interlayer sliding or excessive draw-in. In the latest section, concerning the manufacturing of a square box part, two methods are compared: the classical preforming realized experimentally by a specific preforming device and the surface 3D weaving able to deposit the warp and weft yarns perfectly perpendicular on all of the surfaces of the final 3D ply. Fiber orientations as well as wrinkles and in-plane shear angles are analyzed and compared for each preform obtained. Conclusions and prospects finish this chapter.

### **2. Classification of preform architecture**

Several points need to be remembered to introduce textile reinforcement classifications. (1) In a composite material, the fiber contributes mainly to the mechanical performances of the final parts. The positions and orientations of the fibers are critical to the mechanics of final parts. (2) The textile structure and the composite part should be distinguished. The textile structure is so-called dry: it is a semiproduct. The composite part is composed of the impregnated textile structure of polymerized matrix or reconsolidated matrix. (3) Textile structures are fundamentally multiscale materials in which the macroscopic mechanical behavior of the structure is directly inherited behavior at lower scales. Three scales of observation of the reinforcement are generally recognized (**Figure 1**): microscopic scale (scale of fiber), mesoscopic scale (scale of the tow and the structure pattern), and macroscopic scale (scale of the whole part).

The textile structures are very diverse although traditionally classified into the four main technologies: weaving, knitting, braiding, and nonwoven. There are many ways of classifying textile structures:

Different classifications have been suggested for the fiber reinforcement architecture in order to help the designer to select the architecture that respond to the cost and performance requirements. These classifications are based on the structural integrity and fiber linearity and continuity, fiber orientation, or the textile manufacturing technology. The conventional textile technologies have significantly evolved over the last century, especially by using technical fibers as glass or carbon fibers. However, some limitations are associated with the employment of conventional textile processes in technical fiber manufacturing reinforcement preforms, as the high degradation of technical fiber/yarn on the conventional textile machineries are occurring, or either, the fact that conventional machineries allow only the production of planar (2D)

**Figure 1.** The three levels of study woven fibrous reinforcements.

or thin cylindrical preforms. It is possible to sort out the textile structures according to their size, i.e., size determined by fiber orientations.

deposit the warp and weft yarns perfectly perpendicular on all of the surfaces of the final 3D ply. Fiber orientations as well as wrinkles and in-plane shear angles are analyzed and compared for

Several points need to be remembered to introduce textile reinforcement classifications. (1) In a composite material, the fiber contributes mainly to the mechanical performances of the final parts. The positions and orientations of the fibers are critical to the mechanics of final parts. (2) The textile structure and the composite part should be distinguished. The textile structure is so-called dry: it is a semiproduct. The composite part is composed of the impregnated textile structure of polymerized matrix or reconsolidated matrix. (3) Textile structures are fundamentally multiscale materials in which the macroscopic mechanical behavior of the structure is directly inherited behavior at lower scales. Three scales of observation of the reinforcement are generally recognized (**Figure 1**): microscopic scale (scale of fiber), mesoscopic scale (scale

of the tow and the structure pattern), and macroscopic scale (scale of the whole part).

The textile structures are very diverse although traditionally classified into the four main technologies: weaving, knitting, braiding, and nonwoven. There are many ways of classifying

• by construction technology: weaving, knitting, braiding, and nonwovens according to their

Different classifications have been suggested for the fiber reinforcement architecture in order to help the designer to select the architecture that respond to the cost and performance requirements. These classifications are based on the structural integrity and fiber linearity and continuity, fiber orientation, or the textile manufacturing technology. The conventional textile technologies have significantly evolved over the last century, especially by using technical fibers as glass or carbon fibers. However, some limitations are associated with the employment of conventional textile processes in technical fiber manufacturing reinforcement preforms, as the high degradation of technical fiber/yarn on the conventional textile machineries are occurring, or either, the fact that conventional machineries allow only the production of planar (2D)

each preform obtained. Conclusions and prospects finish this chapter.

**2. Classification of preform architecture**

textile structures:

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dimensionality: 1D, 2D, 3D,… [51]

• by number of orientations: monoaxial, biaxial,…

**Figure 1.** The three levels of study woven fibrous reinforcements.

The component of the textile structure is the fiber. It can be presented in the form of tape, roving, or yarn. The textile structure is a tangle of fibers. Let us agree that the twisted yarn or multifilament twisted or not is considered one-dimensional (1D), as in this longitudinal direction, the stiffness is predominant. Therefore, size of textile structure is drawn by mechanical stiffness orientations, i.e., along fibers. Similarly, the fabric that is obtained by nonwoven technology, by weaving, knitting, or by flat braiding is considered in 2D as the fibers are almost oriented into one plane, associated rigidities membrane. A so-called conventional 2D preform comprises fibers oriented in the main plane of the structure. For example, a conventional woven fabric, in the plane (*X, Y*), has fibers oriented along the *X* axe (said at 0° angle) and transverse fibers, along the *Y* axe (said at 90° angle). Therefore, none are along the *Z*-axis, i.e., out of the plane (*X, Y*). The major advantage of a so-called 3D preform is that, having fibers in the "third direction," the structure is generally more efficient because more mechanically efficient mechanically in this "third direction," as explained by Mouritz et al. [37, 47, 52–54].

Recall that the reinforcement into a composite material serves to strengthen, i.e., to provide the mechanical properties of the composite part. Moreover, one possible definition of the "size" of a textile structure is given by the orientation of the fiber bundles that constitute it. In fact, the comparison and classification of textile preforms is a difficult task because of the diversity of 3D structures as shown in **Figure 2**. Fukuta and Aoki have classified textile preforms according to different criteria such as the fiber orientation, the method of manufacture, or the geometry of the final preform (see **Figure 3**). Besides, a growing number of *Z*-reinforcement methods are available. Integral techniques (3D knitting, 3D weaving, or braiding) must be distinguished from insertion of the *Z*-reinforcement. For *Z*-reinforcement techniques, the insertion in *Z*-direction is separate manufacturing steps after the initial preform lay-up. It is the case for the structural stitching, the tufting, the *Z*-pinning or either the *Z*-anchoring. Besides, integral techniques are developed for the manufacture of large-scale 3D reinforced laminates, and *Z*-reinforcement techniques are ideally suited for the localized *Z*-reinforcement of sections in the composite with high out-of-plane stress state. A new class of reinforcements has to be introduced. Let us call it 2D+. A 2D+ structure is a structure where the thickness is greater than that of the 2D structures, but not as much as other dimensions. The 2D+ structures can be defined as structures where the thickness is greater than that of the 2D structures. For example, the woven structure called "interlock Aerotiss 2.5D" [55] is a bonding layer to chain interlock fabric layer having multiple layers in the thickness. A weave derived from the three-layer structure is carbon reinforcement, G1151, from Hexcel. Note that this structure is thicker than a simple fabric that tows bind the layers together. For interlock structures, the thickness is less negligible compared to the other dimensions and some are no longer just in the main plane (*X, Y*) of the structure.

In order to solve the problems associated with traditional laminated structures and especially their low interlaminar properties, much energy has been deployed in the past 50 years to develop composite structures with 3D reinforcements [37]. Many techniques can lead to the production of 3D textile architecture as 3D weaving, 3D braiding, and stitching. All these techniques are designed to obtain complex 3D shapes while providing improved mechanical performance. From all the classifications listed previously, a study of the typology of textile reinforcements is

**Figure 2.** List of textile structures by Ko and Du [56].

**Figure 3.** Classification by Fukuta and Aoki [57].

proposed in **Figure 5** to classify preforms during the various developments. The purpose of this classification with respect to all those present in the literature is to situate new textile reinforcement structures for composites. Moreover, the classification in **Figure 5** also proposes a class for flat thick preforms as woven interlock: the 2D+ class. It makes a case for assembly preforms. These structures are 3D structured using even strengthened by assembly, whether by stitching, but also by tufting or nailing. The classification in **Figure 4** explores unnamed geometric preforms. The main aim of the proposition presented in **Figure 5** is to clarify what is called 3D. It should also help researchers to define where are set their objects.

**Figure 4.** Classification of textile preforms.

**Figure 2.** List of textile structures by Ko and Du [56].

166 Textiles for Advanced Applications

**Figure 3.** Classification by Fukuta and Aoki [57].

**Figure 5.** Tufting process.

### **3. Reinforcement by tufting technology**

In this subdivision, an example of through-the-thickness reinforcement technology is applied and examined for its influences during the preforming stage of the RTM process. For thick composite parts, multilayer dry textile reinforcements are deformed on tools associated with the geometry of the composite part to fabricate. The interply sliding is identified as a major forming defect during this phase of the procedure. Moreover, the manufacturing defects will be presented and especially on the influence of the layer orientations on the sliding and wrinkles, which are not acceptable for the final part.

### **3.1. Tufting process and tufted 3D reinforcements**

Tufting technology has been developed based on the stitching technique (see **Figure 5**). The dry reinforcements are tufted together by yarn loops. **Figure 5** shows a hollow needle passes through one side of dry preform without tension. When the hollow needle retracts, the tuft yarn is kept within the dry preform by friction and forms a loop. Tufting technology applies a formation of loops with a loose and almost stress-free presentation of the threading system that can bring down the stitching effect on the in-plane properties [55, 58]. Compared to the conventional stitching, tufting is much simpler as it does not require a second thread and lock the threads [58].

A specific tufting device developed in GEMTEX Laboratory is shown in **Figure 6**. **Figure 6a** shows the tufting equipment. Four principal parts of this equipment: tufting device,

**Figure 6.** The tufting equipment (a) and zoom of the tufting head (b).

presser foot device, thread feeding device, and framework are illustrated. The tufting needle linked to a pneumatic jack in order to well-control the tuft length. A presser foot situated next to the needle is carried by another pneumatic jack to apply a force per unit area on the preform in tufting process. The thread feeding device provides tufting yarn with a certain length and tautness. These devices are installed along a mobile framework to form the tufting head (see **Figure 6b**). During the tufting, stitch length, tufting density, tufting direction, and pressing of the presser foot can be well-controlled. The maximum tuft length 50 mm is used in the present study, which is decided by the range of the pneumatic jack. A change of needles can be selected according to the yarn performance and the cloth of the preform.

For the presented case, the reinforcement fabric is E-glass plain weave with an area density of 157 ± 5 g/m2 . The tested preforms were first laminated with four plies [±45°, 0°/90°]2 . **Table 1** shows the preforms were tufted by TENAX® carbon yarn with different tufting densities corresponding to a tufting spacing. The tufting spacing is defined by the vertical distance of two neighbor tuft lines. One of the preforms after tufting is shown in **Figure 7**. The dimensions of the tested preforms are 280 × 280 × 1.0 mm3 . As presented in **Figure 7**, the preform is tufted in square spiral pattern to assure that the tufting thread is continuous and uninterrupted and inserted in two directions (warp and weft directions).

**Table 1.** Main properties of the tufted 3D fabric specimens.

**3. Reinforcement by tufting technology**

168 Textiles for Advanced Applications

kles, which are not acceptable for the final part.

the threads [58].

**3.1. Tufting process and tufted 3D reinforcements**

**Figure 6.** The tufting equipment (a) and zoom of the tufting head (b).

In this subdivision, an example of through-the-thickness reinforcement technology is applied and examined for its influences during the preforming stage of the RTM process. For thick composite parts, multilayer dry textile reinforcements are deformed on tools associated with the geometry of the composite part to fabricate. The interply sliding is identified as a major forming defect during this phase of the procedure. Moreover, the manufacturing defects will be presented and especially on the influence of the layer orientations on the sliding and wrin-

Tufting technology has been developed based on the stitching technique (see **Figure 5**). The dry reinforcements are tufted together by yarn loops. **Figure 5** shows a hollow needle passes through one side of dry preform without tension. When the hollow needle retracts, the tuft yarn is kept within the dry preform by friction and forms a loop. Tufting technology applies a formation of loops with a loose and almost stress-free presentation of the threading system that can bring down the stitching effect on the in-plane properties [55, 58]. Compared to the conventional stitching, tufting is much simpler as it does not require a second thread and lock