Introduction to Aerospace Structures and Materials

1 Introduction to Aerospace Structures and MaterialsDr. ir. (Ren ) AlderliestenIntroduction to Aerospace Structuresand MaterialsIntroduction to Aerospace Structuresand University of TechnologyDelft, The NetherlandsIntroduction to Aerospace Structures and Materials by Alderliesten, Delft University of Technology islicensed under aCreative Commons Attribution-NonCommercial-ShareAlike International License,except where otherwise image CC-BY TU Delft is a derivation of two images by:Christopher Boffoli,Big Appetites Studio, Seattle,Washington, USA, ( ), who graciously agreed for us to use his Public Domain photographof the Boeing 787 fuselage in high resolution, and by Gillian Saunders-Smits, Delft University of Technology withher photograph of a Fokker F100 Cockpit Structure (CC-BY-SA ).

2 The final cover design was made by MarcoNeeleman, Delft University of Technology attempt has been made to ensure the correct source of images and other potentially copyrighted materialwas ascertained, and that all Materials included in this book has been attributed and used according to itslicense. If you believe that a portion of the material infringes someone else s copyright, please the authordirectly on: funded by the TU Delft Extension School( )as part of the development of aMassive Open Online Course in Introduction to Aerospace Structures and E-Pub: 978-94-6366-077-8 ISBN hardcopy: 978-94-6366-074-7 ISBN PDF: & spacecraft IntroductionTobeabletodesignandanalyseai rcraftorspacecraftstructures, ,butwillbefurtherexploredinthechapter6an d7,whereloadsactinguponthesestructuralel ements are discussed and the stresses that they , ,these elements are often referred to are several definitions that can be given for the airframe.

3 An airframe is the aircraft or spacecraft without installed equipment and furnishing the skin and framework (skeleton) that provide aerodynamic shapes the load bearing parts that take up forces duringnormal flight,manoeuvres,take-off, landing etcetera. the parts that together protect the contents from the , ,iscompletelydifferentinappearancethanth emilitaryaircraftthatareoperatedtheseday s, ,butishardlyapplicabletotheFokkerSpin,wh erethepilotisonlyprotectedfromtheenviron ment by elements that are not part of the of the Fokker Spin or Fokker Spider. (Anon., , Public Domain.)Figure of a Sukhoi SU-25T Fighter Jet. (Altoing, 2011, ) calledsecondary of the shell structure of the cockpit section of the Fokker 100 aircraft (component located in the collection ofthe Delft Aerospace Structures & Materials Laboratory TU Delft, , Own Work.)

4 Structural conceptsInthepastcentury, these concepts will be described Truss ,forexample,(railway) ,tubesandwires(wire-bracingofastructure) .Afamousexampleofwire-bracingofastructur eistheFokkerSpinshownin Figure , the load bearing , . (onlyintension),rodsandtubes(tensionandc ompression) structural concept that will be discussed of truss structure concept: diagonal function with wire-bracing (a-c), with rods (d), and with sheet (e-h).(TU Delft, , Own Work.)Althoughtrussstructureswerethefirs tstructuralconceptintroducedinairframes, ,theintroductionoftailoredtrussstructure shasledtosignificantweight of truss Structures , left: Ribs in the centre fuselage section of the Space Shuttle using boron-aluminiumtubes, (Rawal 2001), and right:deployable truss concept for space applications.

5 Derivative from NASA (2001,2010), Public ,wheretheribsinthecentrefuselagesectiono ftheSpaceShuttlehavebeenconstructedpartl yfromatrussstructureusingboron-aluminium tubesleadingtoa45% for space Shell ,thesheetperformsthediagonalfunctioninsh ear, , ,withtheintroductionofsheetmaterialinthe structure,itisnolongerconsideredatrussst ructure, (alsowithtubesandwires),sheetmaterialcan carryloadinshear(diagonalfunction), (includingtheabilitytocarrymembranestres ses)andfortheapplicationofintegralfuel functions of sheet : tension, compression, diagonal/shear, sealing (air/fuel tight). (Alderliesten, 2011, Work.)Tofullyexploitthebenefitsofsheetma terial, , ,asheetincompressionwillbulgeoutwithoutb eingabletocarrysignificantcompressiveloa ds, (a).

6 Onlywhenthesheetisreinforcedorgeometrica llystiffened,asillustratedinFigure (b,c), it is able to carry more compressive ,thesheetstiffnesscannotbeusedwhenitbulg es, , (c)illustratesthatthesheetofexample(a)ca nbestiffenedbyanothersheetthatisformedin toaprofile,wherethecombinationofthetwosh eetsbecomesaloadcarryingstructureinwhich theflatsheetcarriesasignificant part of the applied of sheet material versus geometrical stiffness. (Alderliesten, 2011, Own Work.) ,whereatcertaincompressiveloadstheflange willbulgeout, (a),butonlyattheunsupported of stiffener geometry on deformation induced by panel compression. (Alderliesten, 2011, Own Work.)

7 ,suchas,forexample,theupperwingpanels(up wardwingbendingcausescompressionintheupp ershellstructure) (lowerwingpanels), , ( ) ,spacingbetweenstiffenersmustbechosen in the of stiffener spacing on stability of panel under compression. (TU Delft, , Own Work.)Whereinitiallyabeamstructurewasdes ignedastrussstructure,wherebendingwastak enupbynormalforcesintheupperandlowertube sandthediagonalfunctionperformedbythedia gonallyplacedelements, ,whereastheelementstakingupthe(bending)l oadsbynormalforces are called the girders. This beam concept is illustrated in Figure of a beam based on sheet web with girders. (Alderliesten, 2011, Own Work.)

8 ,clipsandstringersallutilizethecharacter isticbeamconcept with web plate and and stringers based upon the beam concept. (TU Delft, , Own Work.) Sandwich , ,thesandwichstructurecarriestheloadsin two directions. This similarity in concept is illustrated in Figure , ,polymerhoneycombsarebeingused,whileinth epast(seeBr guetAtlanticexampleonthenextpage) cores is the low weight due to the high percentage of empty of similarity of concept between beam and sandwich; the girders and face sheets carry the normalforces, while the web plate and core provide the diagonal function. (TU Delft, , Own Work.) cores can either be made of polymers or of sandwich concept utilizing the honeycomb core.

9 (TU Delft, , Own Work.) , , , ,theweightisonlyslightlyincreased, : Sandwich panel conceptThe sandwich structure may be considered an excellent structural concept,because it requires no additional stiffening elements providing a smoothsurface. However, examples from the (recent) past have also put the emphasison the drawback of this 1970 the Br guet Atlantic, shown in (a) revealed substantial corrosion issues related to moisture absorbed bythe sandwich structure. One may assume that the sandwich structure is aclosed system, but nonetheless, moisture is being picked up by the sandwichIntroductiontoAerospaceStructure sandMaterials85structure, and the moisture remains subsequentially trapped inside, see the X-ray photo in Figure (b).

10 To illustrate that this is not a particular problem related to metallic sandwichstructures, but to sandwich Structures in general, another example is shown inFigure (c). On March 6, 2005, an Airbus A310-308 operated by Air Transatdesignated Flight 961 had to perform an emergency landing after it lost in-flighta composite sandwich rudder of several meters revealed that moisture absorbed by the sandwich panel trappedbetween core and face sheets caused rapid delamination of the face sheetsfrom the core, as a result of volumetric increase of the frozen of detrimental environmental influence on sandwich concept: corrosion in metallicsandwich (a,b) and rapid delamination in composite sandwich (c).