introduction to aerospace engineering - tu delft ocw · pdf file22-11-2011 challengethe future...
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1 Challenge the future
Introduction to Aerospace Engineering
Lecture slides
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22-11-2011
Challenge the future
DelftUniversity ofTechnology
StructuresAircraft & spacecraft shell structures
Faculty of Aerospace Engineering
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2Structures | 25
• 15/11 Material physics & properties / environment• 22/11 Structures• 29/11 Loads• 6/12 Materials & manufacturing• 13/12 Selection of materials & structures / space• 20/12 Design & certification / fatigue & durability
• 6/1 Manufacturing & joining
• Lecturer• Name: R.C. Alderliesten (Structural Integrity)
• Room: NB0.45
• Email: [email protected]
IntroductionOutline of lectures/lecturer
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3Structures | 25
Learning objectives
• Give definition of• Airframe
• Principal structural elements
• Secondary structural elements
• List typical structural elements for aircraft and spacecraft
• Explain the function of sheets• Explain the difference between material stiffness and structural(geometrical) stiffness
Student should be able to…
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4Structures | 25
Aircraft & spacecraft structures
• Aircraft/spacecraft without installed equipment and furnishing
• Consists of load bearing parts: parts that take up forces during• normal flight
• maneuvers
• take-off
• Landing, etc.
• Consists of skin and framework (skeleton) that provide aerodynamic shape
• Protects contents from environment
Definition of airframe
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5Structures | 25
Aircraft structures
• Skin and framework
Examples
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6Structures | 25
Spacecraft structures
• Skin and framework
Examples
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7Structures | 25
Aircraft & spacecraft structures
• Primary structure• Critical load bearing structure of an aircraft/spacecraft that in case of
severe damage will fail the entire aircraft/spacecraft
• Secondary structure• Structural elements of an aircraft/spacecraft that carry only air and
inertial loads generated on or in the secondary structure
Definition of primary/secondary structure
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8Structures | 25
Aircraft & spacecraft structures
• Fuselage shells• Skin
• Frames
• Stringers
• Bulkheads
• Splices
• Wing structure• Wing skin panels
• Ribs
• Spars
• Assembly of spars & skin
Typical elements
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9Structures | 25
Shell structuresRecall: from truss to shell structures
• Function of diagonal elements (tension & compression)
• Replacement by sheet (compression causes buckling)
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10Structures | 25
Shell structures
• Buckling of sheet
Examples of buckling
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11Structures | 25
• A sheet has more capabilities than reinforcing a structure!
• Tension
• Compression
• Diagonal function: shear
• Sealing function (air tight, fuel tight)
Shell structuresSheet material
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12Structures | 25
Shell structuresStiffness of sheet material
• A sheet in compression bends out• Sheet in tension is not a problem
• Structural solutions• Fold the sheet ⇒ stiffening effect
• Support sheet with stiffener
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13Structures | 25
Shell structuresExample of folding/corrugating sheet
• Junker 52 - 1932
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14Structures | 25
Shell structuresSelection of stiffening configuration
• Comparison of stiffener geometry
• Stiffening spacing
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15Structures | 25
Shell structuresStiffener geometry
• Preferred shape depends on type of load
• Preferred shape depends on manufacturing method• Sheet metal work (brake press forming, rolling, drawing)
• Extrusion
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16Structures | 25
Shell structuresStiffener geometry
Z-stringer J-stringer Y-stringer I-stringer
hat-stringer Z-stringer hat-stringer hat-stringer
(Lower wing) (Upper wing)
or adhesive bonding
stiffening effect
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17Structures | 25
Shell structures
• Sheet geometrically reinforced by stiffeners
• Example stiffeners• Stringers
• Longerons
• Frames
Stiffener geometry
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18Structures | 25
Shell structures
• Stringers in combination with thickness steps (joggling)• Butt-joints
• Doublers
• Intersection of stiffening elements
Stiffener intersections
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19Structures | 25
Shell structuresOther stiffening concepts
• Integral structure by machining
• Sandwich structure
face sheet
• Skin core
face sheet
Extra material milled away
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20Structures | 25
Shell structuresOther stiffening concepts
• Integral structure by machining• low cost
• low part count
• simple blade stiffening
• thickness continuously adaptable
• lot of scrap (90%)
• rapid crack growth
• thick skin ⇒ large aircraft
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21Structures | 25
Monocoque structuresStiffening concept
• Sandwich structure• No stringers needed
• Smooth structure
• Difficult to repair
• Difficult to join
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22Structures | 25
Monocoque structuresStiffening concept
• Sandwich structure• No stringers needed
• Smooth structure
• Difficult to repair
• Difficult to join
• Excellent structural concept, however..• complex and expensive details
• corrosion (metal) and delamination (composites) problems
Bending
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23Structures | 25
Monocoque structuresStiffening concept
• Sandwich: Excellent structural concept, however..• Corrosion (metal) and delamination (composites) problems
• 1970s: Bréguet Atlantic
• Problem: Moisture ingress in honeycomb → corrosion
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24Structures | 25
Monocoque structuresStiffening concept
• Sandwich: Excellent structural concept, however..• Corrosion (metal) and delamination (composites) problems
• March 6, 2005: Airbus A310-308 - Air Transat Flight 961
• Problem: In-flight separation of composite rudder
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25Structures | 25
Summary
• Shell structures• provide function as diagonal element
• Can be geometrically stiffened
• Stiffeners• Have different shapes depending on load and manufacturing
• Can be attached to skin sheet or milled from thick plate
• Sandwich panels• Face sheets carry tension/compression loads
• Core carries the shear load
Aircraft & spacecraft structures