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Aircraft Materials

Aircraft Materials, for Aeroespace Engineers
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  Student Notes Materials forAeronautical Engineering Tristan Burg and Alan Crosky  School of Materials Science and EngineeringUniversity of New South Wales © 2001  Aerospace Materials – Student ©  2001 Materials Science and Engineering - UNSW2 NOTICE: All referenced images in these notes are copied under the following act. COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969WARNINGThis material has been reproduced and communicated to youby or on behalf of the University of New South Wales pursuantto Part VB of the Copyright Act 1968 ( the Act ).The material in this communication may be subject to copyrightunder the Act. Any further reproduction or communication of this material by you may be the subject of copyright protectionunder the Act.Do not remove this notice.  Aerospace Materials – Student ©  2001 Materials Science and Engineering - UNSW3 INTRODUCTION The materials used for aircraft construction can be split into two broad categories;airframe materials and engine materials, and these will be considered separately.However, selection of materials for both applications is based on the designconstraints. These are defined by the mechanical, chemical and thermal propertyrequirements of each component. Typical design constraints include weight, stiffness,strength, fatigue performance (high/low cycle), corrosion resistance and cost. THE AIRFRAME The airframe consists of components such as the: wing upper, wing lower, fuselage,spars, frames, ribs, landing gear and control surfaces. Essentially, the airframe isrequired to resist applied loads, provide an aerodynamic shape and protect passengers, payload and equipment from the external environmental conditions. Each componenthas different specific constraints, resulting in different material selection for eachcomponent. Wings Overall, the wings are subjected to the most complex and highest levels of stress.However, due to the nature of the wing loading the upper and lower wings are loadeddifferently (compression and tension respectively) and thus will be treated separately.Wing upper The wing upper is loaded in bending and is under compression stresses. Thus, to resistthe applied stresses and minimise weight it requires high ratios of stiffness to densityand yield strength (compression) to density. The upper wing also requires goodresistance to stress corrosion cracking fracture.Wing lower The wing lower is loaded in bending and is under tension stresses. Thus to resist theapplied stresses and minimise weight, it requires high stiffness to density and yieldstrength to density ratios. The lower wing also requires good resistance to stresscorrosion cracking fracture and good corrosion resistance. Due to the tensile nature of the stresses it also requires good fatigue strength and low fatigue crack growth rates. Fuselage The fuselage carries the whole of the payload and is stressed under tension,compression, torsion, bending and pressurisation forces. Most of these forces placethe fuselage under tension. Thus to minimise weight it requires high stiffness andstrength to density ratios. It requires good corrosion resistance and, due to the tensileforces, requires high fatigue strength and low fatigue crack growth rates. Spars, Frames and Ribs These lie under the skin and are used to distribute loads, retain the aerodynamicshape, and increase the buckling strength of the structure. These components areloaded in bending and thus their requirements are similar to those of the wing upper and lower.  Aerospace Materials – Student ©  2001 Materials Science and Engineering - UNSW4 Landing Gears The landing gears, as shown in Figure 1, are subjected to high static and cyclicloading. Thus they must be stiff and strong enough to withstand this loading and haveacceptable fatigue and fracture resistance. The components must also be resistant tostress corrosion cracking failure. In addition there is a volume constraint on the size of the components. Figure 1:    Landing gears  [1] Control Surfaces These consist of the rudder, elevators, ailerons and flaps and are, in general, lightlyloaded. Thus they require structural stiffness and light weight. Skin materials These require good corrosion resistance as they are under continuous atmosphericexposure. In supersonic aircraft skin heating becomes an important factor and is most pronounced on the nose and leading edges of the aircraft as shown in Figure 2. Figure 2:   Skin heating across the airframe [2]
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