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About this book

This book addresses the emerging needs of the aerospace industry by discussing recent developments and future trends of aeronautic materials. It is aimed at advancing existing materials and fostering the ability to develop novel materials with less weight, increased mechanical properties, more functionality, diverse manufacturing methods, and recyclability. The development of novel materials and multifunctional materials has helped to increase efficiency and safety, reduce costs, and decrease the environmental foot print of the aeronautical industry. In this book, integral metallic structures designed by disruptive concepts, including topology optimization and additive manufacturing, are highlighted.

Table of Contents

Frontmatter

Chapter 1. Historical Development of Aeronautical Materials

Abstract
In the present chapter, the evolution of aeronautical materials is presented. The chapter focuses on the historical development of aeronautical materials from the first usage of metals, for the aerospace purpose, to the massive aeronautical implementation of composite materials nowadays. Also described in this chapter are the European policies which are driven by the needs of the global economy and the environmental protection in order to reduce the fuel consumption and the CO2 emissions. Additionally, innovative materials and modern manufacturing techniques are shown so as to achieve the aforementioned environmental and economic goals.
Spiros Pantelakis

Chapter 2. Aircraft Aluminum Alloys: Applications and Future Trends

Abstract
Within the last century aluminum alloys have played a strategic role in the manufacturing and development of lightweight aircraft structures. Years of continuous research has led to significant improvement in mechanical properties in the form of advanced 2xxx and 7xxx series alloys and the opportunity to produce more lightweight materials with advanced properties such as the last-generation Al–Li alloys. An overview of the evolution of aircraft aluminum alloys from the original Al–Cu alloys to modern nanocrystalline and hybrid aluminum alloys is presented. Basic properties and processes are featured, that define the material performance and determine their main applications in aircraft industry. Finally, novel trends in the design of aluminum alloys are considered in order to meet the future challenges of modern aircraft applications.
Alexis T. Kermanidis

Chapter 3. Thermosetting Composite Materials in Aerostructures

Abstract
Thermosetting composites in aircraft structures are typically based on high-performance reinforcing materials, such as carbon fibre, held together by polymer resins, such as epoxies, which undergo an irreversible curing reaction to form the desired structural components. Compared to conventional metallic materials used in aerostructures, thermosetting composites offer superior specific strength and stiffness, along with improved corrosion and fatigue resistance. This can lead to significant gains in performance and fuel efficiency, along with reduced maintenance requirements. Consequently, these materials continue to gain favour in aircraft construction. The drive towards lower production costs, partly facilitated through the development of larger integrated structural components at higher production rates, is leading to new innovations in manufacturing. Advances in liquid resin infusion methodologies are helping to produce such large structural components more economically, while the development of automated fibre placement technologies is enhancing production quality and minimising conventional labour costs. However, a lack of maturity and experience in the analysis, design, manufacture, and maintenance of composite aerostructures continue to necessitate the need for greater research. For example, improvements in non-destructive inspection and adhesively bonded repairs are required to make composite maintenance more efficient and reliable. Further weight savings and performance benefits could also be achieved by integrating essential systems within composite structures, imbuing them with ‘multifunctionality’. Composite waste is another significant issue, given the projected increase in demand for these materials. In particular, thermoset composite recycling is expected to be a key technology requirement.
Brian G. Falzon, Robert S. Pierce

Chapter 4. Thermoplastic Composites for Aerospace Applications

Abstract
Composites world is in continuous evolution and there has been a progressive change in terms of manufacturing processes, passing from standard wet or prepreg manual layup to automated (preforming) technologies, with the objective to increase production rates and make cheaper manufacturing processes. This chapter deals with most recent advancements and applications of thermoplastic composites, focusing on the reasons why for aerospace sector, they are increasingly representing a more viable manufacturing solution for structural components. Starting from thermoplastic polymer structures and difference with respect to thermoset matrix based composites, the standard consolidation processes (autoclave/thermoforming) together with most promising automated and continuous out-of- autoclave manufacturing concepts and processes (Automated Fiber Placement/Automated Tape Laying, In Situ Consolidation, Continuous Compression Molding, Pultrusion), including assembling methods (Fusion/Welding), are illustrated. Furthermore, an overview on different recycling concepts related to thermoplastics and thermosets composites is provided. At last, an overview on the European thermoplastic development roadmap, supported by the EU’s Horizon 2020 Research and Innovation program (2014–2021) for the next generation of aircrafts, is illustrated.
Marco Barile, Leonardo Lecce, Michele Iannone, Silvio Pappadà, Pierluca Roberti

Chapter 5. Additive Manufacturing: Design (Topology Optimization), Materials, and Processes

Abstract
Additive Manufacturing is defined as the process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methods. The adoption of AM techniques can offer the ability to design and produce complex and demanding components that have optimal material topology and therefore optimal behavior in terms of functionality, load transfer, strength, and mechanical behavior. In this chapter an introduction to structural optimization is provided and different types of structural optimization techniques are presented, focusing on topology optimization. The basic concepts and techniques used for the topological optimization of structural components are presented and applied in two characteristic aeronautical structural parts of different scale, namely a bracket connection and a commercial aircraft fuselage airframe section. Subsequently, various types of AM manufacturing processes are described, suitable for production of topology optimized aerospace parts; special emphasis is placed in powder bed fusion techniques, which are more commonly applied for the production of aeronautical parts and components. The chapter is completed with an overview of the main active research subjects in the scientific field of additive manufacturing, especially relative to the aerospace sector.
George Lampeas

Chapter 6. Cellular and Sandwich Materials

Abstract
Sandwich structures with cellular cores and metallic or composite skins are novel structural concepts with a high potential for application in modern aerospace structures, due to their high bending stiffness and impact energy absorption capability, combined with thermal insulation and vibration damping. In this chapter, the specific characteristics of cellular materials that act as cores in aeronautical sandwich structures are presented. Several typical types of regular lattice cellular cores are presented, focusing on the open lattice or open micro-truss cores, which offer specific advantages compared to the conventional honeycomb or foam cores for aerospace applications. The main manufacturing technologies applied for the production of cellular cores depending on cellular material type and unit cell size are also described. Consequently, an overview of analysis and simulation approaches of lattice cores is briefly presented and demonstrated in the case of a Body Cantered Cubic (BCC) unit cell. Finally, analysis and simulation techniques suitable for sandwich structures with cellular cores are presented.
George Lampeas

Chapter 7. Integral, Disruptive, and Multifunctional Aircraft Structures

Abstract
The design of composite structures currently employed in commercial aircraft is closely related to their metallic counterparts. Significant changes to the conventional design philosophy are required to provide competitive solutions for next-generation aircraft. Due to the inherently large design freedom associated with composite material, this can be achieved through a rigorous integral and multifunction design approach. Three highly promising concepts are introduced in this chapter:
1.
Disbond-arrest features for adhesively bonded composite joints, which present an enabling technology for integral design solutions.
 
2.
Selective stitching, to enhance the damage tolerance of integral composite structure.
 
3.
Composite sandwich structures that provide the greatest design freedom to integrate structural as well as nonstructural functionalities.
 
Ronny Sachse, Daniel Fernandez, Yves Klett, Peter Middendorf

Chapter 8. Nano-enabled Multifunctional Materials: Mechanical Behavior and Multi-scale Modeling

Abstract
This chapter discusses the status and prospective of the nano-enabled MM developed for aircraft applications by focusing on the mechanical behavior and multi-scale modeling. After a general introduction on MM and a description of the existing aircraft applications, results on the mechanical behavior of four different nano-enabled MM are presented and discussed by exploiting observations from scanning electron microscopy images. The materials discussed in this chapter are the MWCNT/PA6 nanocomposite designed for improved mechanical properties and hydrothermal aging resistance; the MWCNT/RTM6-2/GPOSS nanocomposite and the MWCNT/CFRP/GPOSS composite designed for improved mechanical properties, electrical conductivity, and flame resistance; and the CFRP/microcapsule material designed with self-healing characteristics. In the second part of the chapter, multi-scale models developed to predict the properties of nano-enabled MM as functions of material and processing parameters are described, and the basic results are presented.
Konstantinos Tserpes, Spiros Pantelakis

Chapter 9. Biopolymers and Biocomposites

Abstract
This chapter gives a comprehensive review on R&D efforts to develop bio-based thermosetting resins and biocomposites for use in critical applications such as aircraft fabrication, rail transportation, and construction by a Chinese research consortium in collaboration with international teams. This work was initially motivated by the fact that, on one hand, environmental and resource-related benefits of bio-sourced materials are still compromised by limited standards of technical performance and material life. On the other hand, in the air and ground transportation sectors, new environmental regulations and societal concerns have triggered a search for new products and processes that complement not only environment but also resources. To address this issue, novel bio-sourced materials, including bio-sourced epoxies, continuous plant fibers, textiles and prepregs, and neat and hybrid biocomposite laminates, were developed. These materials were characterized, modified, and evaluated in terms of their interfacial properties, flammability, and hydrothermal stability levels. Quasi-structural and structural damping biocomposite structures were finally designed and manufactured using technologies that have been fully adapted to state-of-the-art industrial composite processes. It is also found that developing function-integrated plant-fiber-fabric-reinforced biocomposites and corresponding hybrid structures appears to be more essential and feasible than the mere development of “high-performance” biocomposites for applications. At the end of the chapter, structural damping and decorative quasi-structural composites for use in aircraft, rail transportation, and civil engineering sectors are presented.
Xiaosu Yi, Jianfeng Tong, Xvfeng Zhang, Jin Zhu, Xiaoqing Liu, Guijun Xian, Yan Li, Fangbo Ding, Chris Rudd, Xiaoling Liu, Pooria Khalili

Chapter 10. Self-Healing Mechanisms in Multifunctional Structural Materials

Abstract
This chapter is focused on current shortcomings of self-healing materials for their applications in aeronautics. In particular, the critical points, which prevented the application and the widespread use of these materials in aircraft structures, will be discussed. After “the state of the art” on the design of current developed structural self-healing materials and their drawbacks for application as aircraft materials, recent achievements in this field, able to overcome current drawbacks, will be described. The possibility to simultaneously impart other specific functions, which can be integrated in the material together with the auto-repair function, will be considered.
L. Guadagno, C. Naddeo, L. Vertuccio, E. Calabrese, G. Barra, M. Raimondo

Chapter 11. Laser Joining Processes for Lightweight Aircraft Structures

Abstract
This chapter deals with laser-based processes for joining light metals and lightweight structures. At the beginning, a short introduction concerning the tool laser beam is given. A subsequent focus will be on laser welding of aluminum, in particular deep penetration laser welding (keyhole welding). A section addresses the specific challenges of this process and the current solution approaches from research and development. Hereby, the increase in the gap bridging ability, the increase in the seam surface quality, the reduction in the susceptibility to hot cracking, the prevention of spatters and pores, and the increase in process reliability are highlighted. Especially, the laser welding of thin sheets up to thicknesses of a few millimeters is covered. Alongside the joining of aluminum alloys, the joining of dissimilar materials in particular plays a key role in aircraft construction in order to transfer the advantages of a targeted eco- and cost-efficient material mix into an efficient multi-material design of lightweight structures. A further subchapter is therefore dedicated to laser-based joining of aluminum and titanium components by deep penetration as well as heat conduction laser processes. The focus here is on the process technology approaches and the strength of the joints achieved. An outlook into the future is given by the consideration of aluminum-titanium-carbon fiber-reinforced plastic (CFRP) transition structures. However, laser irradiation has a high potential not only as a direct joining tool but also for preprocessing or post processing or as a supplementary process. Therefore, laser-based adhesive surface pretreatment processes as well as the production of novel hybrid laminar flow control (HLFC) structures based on the combination of several laser machining processes as an aerodynamic approach to reduce the kerosene consumption are demonstrated.
Peer Woizeschke

Chapter 12. Adhesive Bonding of Aircraft Structures

Abstract
In the present chapter, the evolution of adhesive bonding technology in aircraft structures is described. The chapter focuses on materials and processes, while it neglects modeling and structural analysis aspects. Also described in the chapter are the nondestructive methods used to assess the quality of the bondline, the extended nondestructive methods developed to analyze surface contamination and to detect kissing bonds, the main destructive methods used to evaluate the mechanical performance of bonded joints, some design aspects related to the implementation of joining profiles made from advanced composite materials, and the status of research performed toward certification of adhesive bonding for primary composite structures.
Konstantinos Tserpes

Chapter 13. Bonded Repair of Composite Structures

Abstract
The recent venue of all-composite fuselage aircraft (A350, B787), together with the expansion of older aircraft fleets, introduces new requirements in bonded composite repair. These contemporary repair challenges and the latest innovations in equipment and methodologies to address them need to be disseminated towards the aeronautical community in an efficient and comprehensive manner, in order to support reliable application of bonded composite repairs and further business development of repair organizations (MROs—airlines’ workshops). This chapter has been structured in a way to address engineers and technicians with knowledge of composite repairs, who want to receive complementary theoretical and technical knowledge, in order to address new challenges in their field of operations.
Georgios Kanterakis, Roland Chemama, Konstantinos Kitsianos

Backmatter

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