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NTSB - AA587
NTSB - AA587
NTSB - AA587
NTSB - AA587
NTSB - AA587
NTSB - AA587
NTSB - AA587
NTSB - AA587
NTSB - AA587
Pilot? Accident Reconstruction
Construction Site
Tollbooth Cameras
Accident Reconstruction
Movie
Pilot Error?• A300-600 is not fly-by-wire• Maximum rudder deflection at 250 knots (VA)
• Pedal force = 10 lbs• Pedal Travel = 1.25 inches
• AA Training Guide• FAA Pilot’s Handbook of Aeronautical Knowledge
• “any combination of flight control usage, including full deflection of the controls, or gust loads should not create an excessive air load if the airplane is operated below mauneuvering speed”
• “The Myth of Maneuvering Speed”, Flying Magazine
Mod
ulus
(GPa
)
10
100
1000 carbon nanotubes
whiskers
fibers
wires
Diameter
Types of Fiber Reinforcement• Whiskers: smallest, nearly perfectly crystalline, extremely
strong and stiff (e.g. graphite, SiC, Al2O3, etc.)• Fibers: small diameter, polycrystalline or amorphous (e.g.
aramids, glass, carbon, SiC, etc.)• Wires: relatively large diameter (e.g. steel, tungsten,
molybdenum, etc.)
Fiber Weave Patterns
More Complex Fiber Weaves
Prepreg Production• Prepreg: Tape of thermoset polymer and fiber
reinforcement pre-impregnated with curing agent• Must be stored below room temp to slow curing
• Parts made by “lay-up” of tape• Hand cut to shape• Manually control orientation
• High temperatures and pressures to cure• Vacuum bag in autoclave
Hand Lay-up
Lay-up Steps (simple panel)
Tape Placement (7-axis!!)
Applications of Hand Lay-up
www.owenscorning.com/composites/applications
Warpage
Pultrusion
• Used to fabricate • Long, continuous parts • Constant cross-section
• Rovings or tows • Impregnated with matrix• Pulled through steel die for shape
• Properties often highly unidirectional
Applications of Pultrusion
www.owenscorning.com/composites/applications/www.pultruders.com/
Filament Winding • Used to fabricate
• Hollow parts • Usually radial symmetry
• Fibers or tows • Impregnated with matrix• Continuously wound onto
mandrel
• Usually automated winding equipment
• Various winding patterns used• Excellent strength-to-weight• Very economically attractive
Properties vs. Winding Angle
• Modulus of Elasticity• Rule of mixtures estimate• Ecs=cos q*(EmVm+ EfVf)
• Usually concerned with tubes in bending - minimize deflection• 3-point bending problem•
4i
4o
3dd
64I
EI48FLy
L
dodi
F
Applications of Filament Winding
www.owenscorning.com/composites/applications/www.advancedcomposites.com
Applications of Filament Winding
www.owenscorning.com/composites/applications/www.advancedcomposites.com
Resin Transfer Molding• Used to fabricate
– Intricate 3-D shapes• Fiber preform captured in
closed steel mold • Matrix is injected• Preform may be complex
– Braided,– Woven, or– Simple random mat
(SRIM)• Closed tooling provides
good dimensional stability
Applications of RTM
www.owenscorning.com/composites/applications/consumer/sports.html
Press Forming (Compression Molding)
• Similar to compression molding polymers– Mold heated– Mold closes and
applies pressure– Plastic becomes
viscous – Conforms to mold
shape• May be used for
thermoplastic matrices• Geometry usually limited
Applications of Press Forming
www.owenscorning.com/composites/applications
Injection Molding• Very similar to injection molding polymers
• Can inject chopped fibers with matrix into closed die• Fibers usually rather short due to screw
Applications of Injection Molding
www.owenscorning.com/composites/applications
Structural & Laminated Composites
• Laminate composite:• 2-D layered structure designed for high strength in preferred
directions• Sandwich panel:
• Structure with strong outer layers and rigid but light inner core (e.g. skis)
Applications of Laminates
www.owenscorning.com/composites/applicationshttp://www.hexcelcomposites.com/Markets/Markets/Sports
www.nikebiz.com
Machining Problems• Usually must use secondary operations on
composites• Trim edges• Cut holes
• Fasteners• Attachments• Access for wiring, assembly, maintenance
• Holes will always act as stress concentrations• Kt 3• Fatigue often initiated from these points• Holes need to be drilled as “damage free” as possible
such that concentration does not increase
Machining Problems
• For machining parameters to choose:• Tool speed• Feed rate• Tool geometry• Coolant
• For polymer composites this is difficult• Matrix: soft, ductile, hygroscopic
• Want to absorb water in coolant• Fiber: hard, brittle, abrasive
• Tools wear very quickly
• Hard to achieve damage free holes and edges
Common Composite Damage• Fiber breakage
• Broken fibers do not carry load effectively near the hole
• Matrix chip-out• Geometric discontinuity near hole
• Delamination• Tool feeds perpendicular to ply, separating from bulk• Local fiber reinforcement is not balanced
• Matrix overheating• Locally melt surface• Results in rough finish, clogged tool
• In some applications load carrying capacity not important• Visual rejection still a possibility!
Composite Machining Damage(SEM Images)
Fiber Breakage and Chipout Matrix Chipout
1000x 500x
Matrix Overheat
Exit Side Debond
200x500x