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1 Challenge the future
Introduction to Aerospace Engineering
Lecture slides
10-1-2012
Challenge the future
DelftUniversity ofTechnology
Structural jointsWelded, mechanically fastened, bonded
Faculty of Aerospace Engineering
2Structural joints | 27
Learning objectives
• Describe the different joint types
• Mechanically fastened joints
• Explain the difference between tension and shear joints
• Describe the load transfer mechanisms
• Describe the failure modes
• Welded joints
• Adhesive bonded joints
Student should be able to…
3Structural joints | 27
Mechanically fastened joints
• Types of fasteners
• Threaded fasteners
• Rivets
• Blind fasteners
• Nails
Types of joints
4Structural joints | 27
Mechanically fastened joints
• Joints classified by loading mode of fastener
Types of joints
Shear Tension
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Mechanically fastened joints
• Tensile joint
• Mechanical joint (bolts)
• Welding (laser beam, friction stir welding)
• Shear joint
• Mechanical joint (rivets, bolts)
• Welding (laser beam, friction stir, spot welding)
• Adhesive bonding
Types of joints
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Mechanically fastened joints
• Many variations
• T- and angle-clips
• Angle- and channel-fittings
• Flanges
Joining – tensile joint Tension
Fokker F-28 horizontal stabilizer (flange) Channel fitting fromAn MK8 Meteor
7Structural joints | 27
Mechanically fastened joints
• Fuselage skin joints
• Shear clips
• Stringer-to-skin connections
• Lugs
Joining – shear joint
Wing spar connection lug
Fuselage butt joint
Fuselage lap joint
8Structural joints | 27
Mechanically fastened joints
• Low cost
• Installation
• Unit
• Hole filling properties
• Kt reduction
• Residual stress
• Load transfer
• Permanency
• Can not vibrate loose
Benefits of rivets
9Structural joints | 27
Mechanically fastened joints
• Removable
• Assembly/disassembly
• Reusability
• High strength
• Wider range of materials
• Heat treatments
• Case hardening
• Multi-purpose
• Shear bolts
• Tension bolts
• Tension-shear bolts
Benefits of threaded fasteners
10Structural joints | 27
• Solid rivets: squeezing ⇒ Interference
Mechanically fastened jointsJoint characteristics
1 2
3 4
P
Plastic region
Elastic region
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• Open hole loading
• Filled hole (interference) loading
Mechanically fastened jointsJoint characteristics
12Structural joints | 27
• Constrained deformation
• Reduction of stress concentration factor Kt
Mechanically fastened jointsJoint characteristics
Open hole Filled hole
>-S-S
~2S3S
13Structural joints | 27
Mechanically fastened joints
• Secondary bending ⇒ peel stress
Joint characteristics
14Structural joints | 27
Mechanically fastened joints
• Secondary bending ⇒ peel stress
Joint characteristics
15Structural joints | 27
Mechanically fastened joints
Load Transfer
Secondary Loads
BypassBearing Friction
Secondary Bending Interference
Load transfer mechanism
16Structural joints | 27
Mechanically fastened jointsFailure modes
Net Section Tension
BearingShear
Tear OutBolt Shear
17Structural joints | 27
Mechanically fastened joints
• Reinforcing laminate edge for bearing by
• Additional composite plies
• Adding metallic inserts
• Replacing composite by metallic plies
Composites
18Structural joints | 27
• Bolted joint
• Honeycomb inserts: attached
to both facings, surrounded by
filling compound
Mechanically fastened jointsComposites
19Structural joints | 27
Mechanically fastened joints
• Bolted joint
• Taper to laminate
Composites
20Structural joints | 27
Welded joints
• Laser beam welding Friction stir welding
Metals
21Structural joints | 27
Welded joints
• Welding
• Laser beam welding, friction stir welding, spot welding
• Formation of residual stresses
• Stress concentrations
• Elastic ‘spring back’
Metals
22Structural joints | 27
Welded joints
• With multiple components an ‘integral design’ is created; no crack
barriers
Metals
23Structural joints | 27
Welded joints
• Thermoplastic
• Resistance welding
Composites
24Structural joints | 27
• Metallic components
• Anodizing
• Priming
BondingPretreatment
25Structural joints | 27
• Relevant bonded structures
• Doublers
• Clips/frames/stringers
• Patch repairs
• Failure possible in
• Substrate
• Adhesive
BondingFailure modes
doubler/patch
substrate
bondline fillet
repair patch
damaged substrate
bondline fillet
damage
clip/frame
substrate
bondline
fillet
26Structural joints | 27
Bonding
• Bonded joint
• Scarf joint
• Stepped lap-joint
Composites
27Structural joints | 27
Summary
• Different joint types
• Mechanically fastened joints
• Tension and shear joints
• Load transfer mechanisms
• Failure modes
• Welded joints
• Adhesive bonded joints
Structural joints