[Technical Tips] Detailed Explanation of Advanced Fiber Structures For Aerospace Composites (IV): Examples Of Fiber Structures in Aerospace Applications

 

Abstract

 

To achieve structural reinforcement in the aerospace field, the reinforcing fibers need to have very high performance in terms of strength, stiffness, heat resistance or chemical resistance. Textile structural composites are materials containing rigid fabrics designed for structural or load-bearing applications. Specific combinations of flexible fiber materials (fibers, yarns and fabrics) are called textile composite preforms. Textile preforms vary greatly in fiber orientation, entanglement and geometry.

 

The structures and properties of various high-performance fibers: toughness, modulus, heat resistance, chemical resistance, etc. must be transferred to yarn and fabric structures to produce preforms with the required properties. In the case of mechanical properties, the efficiency of this transfer will largely depend on the degree of orientation of the fibers in the yarn and fabric structures.

 

In this special article, the fiber structure of composite materials used in the aerospace field will be introduced in detail. After the previous three articles have successively structured 2D and 3D fiber structures, this article will continue to introduce the typical applications of the above structures in the aerospace field.

 

Appendix: Special articles on advanced fiber structures for aerospace composites: “Characteristics and performance of fiber 1D, 2D and 3D structures”

“2D woven, knitted, oriented and braided structures”, “3D braided and knitted fiber structures”

 

Over the past few decades, the driving force in the field of aerospace composites has been to reduce costs, improve component performance and reduce component weight. Due to its excellent specific strength, specific stiffness, and its overall design potential, the application of textile structural composites in aerospace is increasing.

 

Composite structures account for approximately 17%, 25% and 50% of the Airbus A340, A380 and A350 XWB respectively, and are growing rapidly. The in-plane mechanical properties of textile composites prepared by liquid molding (vacuum assisted resin transfer molding VARTM, resin transfer molding (RTM) or resin film infusion (RFI)) are almost equal to those of composites prepared by prepreg method.

However, the out-of-plane impact resistance of textile structural composites manufactured by liquid molding is lower than that of fabric structural composites developed by prepreg method.

It is also important to note that the use of glass fiber and aramid fiber in aerospace is relatively limited due to the higher density and lower stiffness of glass fiber and the high hygroscopicity of aramid fiber.

Therefore, most composite parts used in the aerospace industry are produced using carbon fiber fabrics pre-impregnated with thermosetting matrix. Woven, knitted, oriented structure (DOS), braided and other fabric structures have been used to develop composite parts for aerospace applications, with the most commonly used fabric structure being DOS.

 

Woven Structures

An example of the use of woven structures in the aerospace field was achieved by Kawasaki Heavy Industries, Japan, which used Teijin Tenax HTS 5631 12K fiber to manufacture a 380 g/m2 2×2 twill carbon fiber fabric through a special weaving technology. Prepregs developed using this fabric have been used in a variety of applications, including the Embraer ERJ 170 inboard flap, the ERJ190 outboard flap and wing tip, and the Boeing 737-300 winglet (Figure 1).

 

Figure 1 Boeing 737-300 Winglet

 

Knitted Structure

Daimler-Benz has developed aerospace composite parts with knitted structures. Figure 2 shows a stiffened panel made of warp-knitted skins and 3D-woven reinforcements sewn together to form a complex preform. The fiber structure was subsequently impregnated by DLR Braunschweig using the RTM process.

 

Figure 2 Reinforced Panel Consisting Of Woven Profile And Warp Knitted Outer Skin

 

Directed Structure

 

Directed structure (DOS) using 12K carbon fiber is the most commonly used structure in aerospace applications. There are two main typical application examples: Airbus A380 rear pressure bulkhead (RPB) and Airbus A400M cargo door. The A380 RPB is produced at the Airbus plant in Stade near Hamburg using preforms made of multiaxial carbon fiber DOS supplied by Saertex.

 

This preform is draped over the positive mold and then laminated using the RFI process (Figure 3). After initial curing of the 3 mm thick base laminate and the attachment of the stringers, the part is finally cured in an autoclave. The finished bulkhead weighs approximately 240 kg and measures 6.2 m by 5.5 m.

 

Figure 3 DOS Fabric in Production of Airbus A380 Rear Pressure Bulkhead

 

The Airbus A400M cargo door is mainly composed of multiaxial carbon fiber DOS and additional uniaxial DOS fabric for local reinforcement and skin laying. The A400M cargo door is processed using EADS/Premium Aerotec’s patented vacuum assisted process (VAP) infusion technology (Figure 4). The A400M cabin door is manufactured at the Premium Aerotecs factory in Augsburg.

 

Figure 4 Airbus A400M Cargo Door Manufactured by Premium Aerotec

 

In addition to the large structures mentioned above, DOS has some additional aerospace applications at the substructure level, such as Airbus A380 flap track partitions, side shells and belts.

 

Braided Structures

Large braiding machines open up interesting applications of braided structures in the aerospace industry. A&P developed a Vectron sock with a diameter of 2 meters and a length of 3 meters using an 800 carrier braiding machine. Figure 5 shows a braided sock produced by A&P mainly used in a prototype airlock developed by NASA.

 

Figure 5 Braided airlock developed by NASA

 

Future Applications

 

At present, the application of textile structures in the aerospace industry is mainly based on 2D structures using prepreg technology, because 2D textile reinforcements are stronger in plane than 3D fabric reinforcements. Out-of-plane impact resistance is another important load case consideration in the development of aerospace composite parts.

 

3D fabric structures with oriented yarns in the thickness direction can give composites very strong out-of-plane properties. Therefore, the use of 3D fabric structures is conducive to avoiding delamination and fracture of aerospace composite parts.

 

However, in parts such as stiffeners and stringers, not all loads are in-plane, which makes prepreg laminates less suitable. It can be foreseen that in the near future, three-dimensional woven, knitted and woven fiber structures will attract great attention in the aerospace industry.

 

Carbon Fiber And Its Composite Material Technology

 

Introducing the latest progress of the Carbon Fiber and Composite Material Team of Ningbo Institute of Materials, Chinese Academy of Sciences (formerly the Special Fiber Division of Ningbo Institute of Materials, Chinese Academy of Sciences), reviewing the key technologies and application technologies in the field of carbon fiber and composite materials, and sharing the latest information in the field of carbon fiber and composite materials at home and abroad