NTSB - AA587

Pilot? Accident Reconstruction Construction Site Tollbooth Cameras

Accident Reconstruction Movie

Pilot Error? A 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

Modulus (GPa) carbon nanotubes whiskers fibers wires Diameter Types of Fiber Reinforcement Whiskers: smallest, nearly perfectly crystalline, extremely strong and stiff (e.g. graphite, SiC, Al 2 O 3, 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

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

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 E cs =cos  *(E m V m + E f V f ) Usually concerned with tubes in bending - minimize deflection 3-point bending problem L dodo didi F

Applications of Filament Winding

Applications of Filament Winding

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

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

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

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)skis

Applications of Laminates

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 K t  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 1000x500x Matrix Overheat Exit Side Debond 200x 500x