CHAPTER
10
Materials
With this chapter, we begin the purely aeronautical part of the book, where we consider structures
peculiartothefieldofaeronauticalengineering.Thesestructuresaretypifiedbyarrangementsofthin,
load-bearingskins,frames,andstiffeners,fabricatedfromlightweight,high-strengthmaterials,ofwhich
aluminum alloys are the most widely used examples. As a preliminary to the analysis of the basic
aircraftstructuralformspresentedinsubsequentchapters,weshalldiscussthematerialsusedinaircraft
construction.
Several factors influence the selection of the structural material for an aircraft, but among these,
strength allied to lightness is probably the most important. Other properties having varying, though
sometimes critical, significance are stiffness, toughness, resistance to corrosion, fatigue, the effects
of environmental heating, ease of fabrication, availability and consistency of supply, and, not least
important,cost.
Themaingroupsofmaterialsusedinaircraftconstructionhavebeenwood,steel,aluminumalloys
with, more recently, titanium alloys, and fiber-reinforced composites. In the field of engine design,
titaniumalloysareusedintheearlystagesofacompressor,whilenickel-basedalloysorsteelsareused
forthehotterlaterstages.Asweareconcernedprimarilywiththematerialsinvolvedintheconstruction
oftheairframe,discussionofmaterialsusedinenginemanufacturefallsoutsidethescopeofthisbook.
10.1 AluminumAlloys....................................................................................
Purealuminumisarelativelylow-strength,extremelyflexiblemetalwithvirtuallynostructuralapplica-
tions.However,whenalloyedwithothermetals,itspropertiesareimprovedsignificantly.Threegroups
ofaluminumalloyhavebeenusedintheaircraftindustryformanyyearsandstillplayamajorrolein
aircraft construction. In the first of these, aluminum is alloyed with copper, magnesium, manganese,
silicon,andironandhasatypicalcompositionof4%copper,0.5%magnesium,0.5%manganese,0.3%
silicon,and0.2%iron,withtheremainderbeingaluminum.Inthewrought,heat-treated,naturallyaged
condition,thisalloypossessesa0.1percentproofstressnotlessthan230N/mm^2 ,atensilestrengthnot
lessthan390N/mm^2 ,andanelongationatfractureof15percent.Artificialagingataraisedtemperature
of,forexample,170◦Cincreasestheproofstresstonotlessthan370N/mm^2 andthetensilestrengthto
notlessthan460N/mm^2 ,withanelongationof8percent.
Thesecondgroupofalloyscontains,inadditiontothepreceding1to2%ofnickel,ahighercontent
ofmagnesiumandpossiblevariationsintheamountsofcopper,silicon,andiron.Themostimportant
Copyright©2010,T.H.G.Megson. PublishedbyElsevierLtd. Allrightsreserved.
DOI:10.1016/B978-1-85617-932-4.00010-5 327