Aircraft Composite Structures - Research Paper Example

Running Head: Aircraft Composite Structures Aircraft Composite Structures Aircraft Composite Structures Introduction Fibre Reinforced Polymer or FRP composite materials are one of the most common types of composite materials used in industrial manufacturing. Aircrafts and other aerospace applications call for lighter but tougher building material. In aerospace engineering and research, composite materials are aimed at replacing traditional materials like steel and aluminium. In the sphere of aircraft structure manufacturing, FRP composite airframes have been widely experimented with. According to Composites Overview (2002, section 1): “The first commercial composites were called glass fibre reinforced plastics and, remarkably, they still dominate the market today, comprising about 90% of the composites market.” FRP composites, in fact, provide a general matrix-based polymeric interface for interweaving different kinds of fibres, particles, materials, and additives. Examples of glass fibre reinforced polymer (GFRP), carbon fibre reinforced polymer (CFRP), etc. can be illustrated to establish utility of composite materials for aircraft structure manufacturing and design. According to Kalanchiam and Chinnasamy (2012), it can be concluded that metal alloy based and composite materials based aircraft structures have their specific advantages and disadvantages. “Metallic structure is superior to composite in strength and cost aspects. Composite structure is superior to metallic structure in weight aspect which will influence in airplane performance.” (Kalanchiam and Chinnasamy 2012, p. 1010) Advantages, Disadvantages, and Manufacturing Methods There are several advantages of using composite materials to manufacture aircraft structures. The most striking advantage is that the composite materials are easy to mould and give novel shapes. Per se, aircraft designers can enjoy more flexibility and room for their imagination. Special shapes of fuselage and wings are necessary for special purposes. For example, specially designed wings are necessary to accomplish the airframe structure of a stealth bomber. Likewise, long distance jet aircrafts may need corrosion resistant and aerodynamic drag resistant designs. Composite materials are easier to use for giving variety of desired shapes and sizes. Generally, composite materials are preferred for building tougher airframes. But several manufacturers are attempting to build even the internal parts of an aircraft with the help of composite materials. The main advantages of composite materials are explained below with special emphasis on FRP variety. 1. Composite materials provide high specific strength. This attributes to resistance towards deformity due to stress or strain. This resistance is due to certain elastic and coherent properties of the composite material molecule. The polymer bases in which the various fibrous materials are interwoven provide shock absorbent properties to the overall lamella. The final matrix of composite molecules becomes stronger per unit square area for offering resistance towards permanent deformities. (Staszewski, Mahzan, and Traynor 2009) 2. Despite higher specific strength, composite materials have less weight. In the case of FRP composites, the polymeric base has less density. While in materials like aluminium the molecules are heavily packed, molecules in composite material matrix have more coherence than closer packing. (Staszewski, Mahzan, and Traynor 2009) 3. Due to relative flexibility and brittle nature, composite materials are hard to be subjected to chronic abrasion (Abe 2011). The main advantage of this feature is that composite frames have more durability. Since corrosion causes physical damage to the aircraft, composite materials help in developing protection against corrosion with the help of its higher specific strength and molecular coherence (Staszewski, Mahzan, and Traynor 2009). The same reason helps in minimisation of fatigue too. 4. Due to polymeric base, FRP composites can be subjected to varied degree of heat, pressure, chemical intervention, etc. So the moulding process of composite airframe may turn out to be easier. Since bending and moulding are easier with plastic-based fibrous matrix, composite airframes can be prepared and presented in various shapes and sizes (Staszewski, Mahzan, and Traynor 2009). For example, aluminium sheets may not prove to be enough supple and elastic for manufacturing an oval shaped aerodynamic structure. But composite materials give rise to highly elastic frames that can be moulded into a variety of structural shapes, especially in which rounded edges and welded fittings are needed most. However, there are various disadvantages too for putting composite materials in use to manufacture aircraft structures and parts. The disadvantages are summarised below: 1. Composite materials are light weight. They are also durable in the sense that they can resist corrosive effects of airstreams as well as mechanical abrasions. However, structures made of composite materials are susceptible to damage due to impacts. This may result into a huge drawback especially when even mid-velocity impacts develop cracks and holes in the composite airframe. (Abe 2011) 2. Although composite airframes are flexible and can be given various shapes, their structural integrity must be questioned. Difficulty in detecting small cracks and notches in the composite sheets complicate this problem. Despite composite materials show sufficient flexibility, they are brittle. Therefore, only “minor permanent deformation” may take place before a sudden failure or disintegration (Abe 2011, slide 13). Consequently, it is difficult to prepare for a suspected or possible failure well in advance. 3. Composite materials are costly. Creating the sturdy and stable polymeric matrix may prove to be time consuming and costly because of the scientific process complications involved. However, one time spending to manufacture or buy a composite airframe can be compensated if the airframe is sufficiently light weight and leads to less fuel consumption when put to use. But according to the experts like Abe (2011), Ariffin et al (2009), etc., composite airframes may prove to be too costly in the long run. Even if these relatively durable materials ensure reduction in fuel consumption, they may become easy victims of chronic impact damages leading to sudden failure. Figure – 1: Usage of different materials in the aircraft structure of Boeing 787 (Abe 2011, slide 4) Manufacturing of FRP Composites One of the main challenges to manufacture and design of composite aircraft structures is drilling process. Small-scale impacts exploit the susceptibility and brittleness of composite aircraft structures. And drilling processes may lead to intermittent or regular small to medium impacts, which may result into fissures in the surface or cracks inside the dorsal areas of the structure (Ariffin et al 2009). However, FRP composites are ideal for creating complex matrices. In these polymer-based matrix structures, glass or carbon fibres can also be embedded or admixed in an organised way. For example, development of glass fibre mixed FRP composites is described as the following: “Pre-impregnated sheets of glass fibres in a partially-cured resin, or pre-pregs, made manufacturing of components easier. By placing the fibres on a plastic film in a preferred orientation, adding the resin, pressing, and then partially curing the resin, flexible sheets of a precursor material could be produced. Pre-pregs eliminated the early production steps for manufacturers trying to avoid the resin and glass fibre raw materials. These sheets could be cut to shape, stacked, and consolidated into a single piece by pressure and heat.” (Composites Overview 2002, section 1) So the internal flexibility of composite matrix layers (wherein various fibre-based structures can be created and embedded) allows prospective scope of mimicking biomechanical structures and functions such as micro-vascular systems. What is more, FRP matrices provide ample engineering scopes for further utilising and admixing carbon fibres, ceramic fibres, metallic additives, glass particles and fibres, etc. Discussion on Failure, Repairing, and Recycling Failure Generally, failure of an aircraft structure takes place under two conditions. First, a sudden and big impact may lead to disintegration and failure. Second, continuous wear and tear may lead to chronic damages developing into major ones and subsequent failure. In the second case, composite aircraft structures are particularly worrisome. Most importantly, composite structures show only diminutive structural deformation before catastrophic failures (Abe 2011). Moreover, it is very hard to detect the minor deformations that could be warning for a major impending catastrophe (Staszewski, Mahzan, and Traynor 2009). Repairing Although the composite materials are susceptible to medium to heavy impacts, they can withstand effects of heat, vibration, etc. better than metallic materials. General aircraft maintenance regimen can be followed to manage the effects of erosion, abrasion, vibration, thermodynamic strain, etc. However, a prominent feature of composite structures in the context of repairing and maintenance is its durability. Durability and strength are relatively different concepts here. Composite airframes can tolerate wear and tear for a longer time. One of the main reasons behind this is that composite materials are easy to mould and develop innovative designs. Now aerodynamic drag is a big problem during flight. With the help of more innovative designs, composite airframes can be built such that the factor of aerodynamic drag has minimum effect on them. (Kalanchiam and Chinnasamy 2012) Furthermore, composite materials are less chemically active than metallic or metal alloy structures. Lack of reactivity gives composite surfaces effective protection against damages due to corrosion. During flight, an aircraft can be subject to corrosive damage due to variations of temperature or excessive moisture. However, composite aircraft structures can resist this factor of corrosive damage from creating larger cracks or fissures. So repairing becomes relatively more cost effective. Aircraft maintenance technicians would not need frequent patches and/or replacement of composite aircraft structures. Only careful examination of the structures can effectively result into preventive maintenance and damage controlling mechanism. (Kalanchiam and Chinnasamy 2012) But yet in composite aircraft structures, lack of repair in correct time may lead to sudden disintegration. Consequently, damage detection is the key for preventing disintegration and catastrophe. Thus, Staszewski, Mahzan, and Traynor (2009) state that improvised techniques and advanced instrumentation should be deployed for detecting the small-scale deformations in proper time. This involves implementation of X-ray and ultrasound technologies for aircraft maintenance and fault detection. Recycling In the realm of manufacturing and maintaining composite materials, it is most important to focus on the ongoing research aiming at the development of self-repairing capabilities. According to Saeedipour (2014, paragraph 2): “Fibre-reinforced composite materials are widely used, especially in the aerospace industry. The concept of repair by bleeding of enclosed functional agents serves as the biomimetic inspiration of synthetic self-repair approaches which are mainly depending on advancement in polymeric materials.” In general consideration, this is the process that encourages the prospects pf having self healing fibrous materials inside an FRP composite matrix. Ongoing research for giving rise to biomechanical and self-healing properties has already led to certain important innovations. Although detection of minor faults is difficult, these faults can be healed with the help of fibrous bandaging inside the polymeric matrix of FRP composites. In this way, composites can be effectively recycled even if there are preponderant and chronic damages (Composites Overview 2002). Conclusion Both composite materials and metal alloy aircraft structures have their benefits and drawbacks. While composite materials help in manufacturing lightweight and durable aircraft structures, metal alloys are cost effective. Larger numbers of experienced professionals are available while dealing with metal alloy aircraft structures. Most of the aircraft maintenance engineering curricula in this world are generally based on the study of metal alloy structures. Also, designing a composite airframe would call for best design methods and experienced designers available in the industry. So handling an aircraft structure manufacturing project may prove to be hectic at times when dealing with composite materials and novel aircraft designs. It is true that in commercial usage, working with composite airframes may prove to be problematic due to high spending on research and development. However, in military and aerospace applications, relatively greater monetary allotments are available. So the full potential of composite materials can be understood with the help of military aircrafts and aerospace application development. Aircraft structures built with the help of FRP composites can be highly durable and potentially reusable even after major damages. List of References Abe, T. (2011), Composite Application Challenge in Primary Aircraft Structures, Bonn: International Council of the Aeronautical Sciences Ariffin, M.K.A.M., Ali, M.I.M., Sapuan, S.M., and Ismail, N. (2009), An optimise drilling process for an aircraft composite structure using design of experiments, Scientific Research and Essays, 4, pp. 1109-1116. Composites Overview (2002), Cambridge MA: The Dibner Institute for the history of Science and Technology Kalanchiam, M. and Chinnasamy, M. (2012), Advantages of composite materials in aircraft structures, International Scholarly and Scientific Research & Innovation, 6, pp. 1006-1010 Saeedipour, H. (2014), Self-healing technology for aircraft composite structure repair. In: Singapore Aerospace Technology and Engineering Conference, Singapore: Singapore Institute of Aerospace Engineers and Republic of Singapore Air Force Staszewski, W. J., Mahzan, S., and Traynor, R. (2009), Health monitoring of aerospace composite structures–Active and passive approach, Composites Science and Technology, 69, pp. 1678-1685 Read More