composites for aerospace applications

Materials

Lecture Topics• Wood and fabric

• Metals• Metals

• Composites

• Other considerations

ReadingSorry, not covered in book

Early Airplanes• Pre-1930’s most airplanes were

made with wood and fabric - organic

• Wood is strong, easy to work, and plentiful

• Cotton fabric covered airframe and shaped airfoil

Pre WWI & WWI• Wire-Braced Wood

Frames / Fabric Covered

• Wood had to have very straight grain

• Wood can rot

• Properties of wood• Properties of wood pieces varied (no manufacturing control)

Post WWI• Wire Braced Metallic

Space Frame with Fabric CoverFabric Cover

• Steel tubing replaced wood

• Welded joints are critical

• Aluminum wasn’t strong enough

Pre WWI & WWII• Duralumin (invented in Germany - 1909)

started to be used

• More knowledge of materials allowed engineers to create stronger yet non-brittle metals

• Monocoque and stressed skin construction• Monocoque and stressed skin construction

Failure Modes

Yield(ductile)

Fracture(brittle)

buckling

Alloys• Alloys are mixtures of basic metals with

other elements

• Duraluminum = small parts of copper and magnesium added to aluminum

• Steel = varying amounts of carbon in ironiron

Aluminum Alloys

Aircraft Metals• Steel alloys: too heavy now but used

for landing gear

• Aluminum alloys: used for modern aircraft

• Titanium alloys: good for high y g gtemperatures but very $$$

Composite Materials

• A material system composed of two or more distinct constituents that are mechanically combined to possess unique and desired properties

Can you name any?

Examples:

• Natural Wood (fibrocellulosic in lignin)

• Plywood (lignin fibers/ phenolic)

• Fiberglass (glass fiber/ polyester)

• Carbon fiber or Kevlar fiber/ epoxyCarbon fiber or Kevlar fiber/ epoxy

Why Composites ?High strength-to-density ratio

High modulus-to-density ratio

Advantages of Composites

Strength per unit mass

Stiffness per unit mass

Advantages of Composites• Composites last longer – less fatigue

Advantages of Composites• Less Thermal Expansion

Advantages of Composites• Performance improvements (lower weight)

– Lower D.O.C.’s (incl. fuel savings)– More cargo revenue

• Reduced maintenance– Large reduction in fatigue and corrosion

maintenance• Potential manufacturing cost reduction

– Better material usage– Reduced assembly/ part count

• Increased Design freedom– Tailored to a specific application– Complex shapes can be manufactured

Disadvantages of Composites• Difficult to predict strength

• Less knowledge of material forcesLess knowledge of material forces “overbuilding” which negates weight advantage

• Engineers are still learning about fatigue properties of compositesp p p

• Environmental Sensitivity (Temp., UV, Lightning)

• Cost

Composite Materials• Fiber reinforced composite materials

consist of fibers & matrixM t i ( l ) id l d t f– Matrix (glue) – provides load transfer between fibers, support & protection

– Fiber – provides the strength and stiffness

Aerospace Composite Materials• Fibers:

– Aramid (Kevlar™)– Glass (E, S,…)– Carbon (Graphite)– ….

• Matrix:– Polyester Fiberglassy– Epoxy– ….

Fiberglass

Aramid

Carbon Fiber

Why Thin Fibers?• Smaller diameter has fewer number of internal flaws

• More bonding surface area

• Molecular alignment

• More flexibilitystrength

Composites Applications

Composites in Airplanes• Plywood – WWII

• Polymer matrix compositesy p

– Graphite/Epoxy

– Aramid/Epoxy

– Fiberglass

• Metal matrix composites

• Ceramic matrix composites

The de Haviland Mosquito with Balsa plywood skin (1940)

Aerospace Applications• Military aircraft

Aerospace Applications• General aviation: Complete composite fuselages

Raytheon Premier I Raytheon Horizon

AASI Jetcruzer 500

Visionaire Corp. VA10 (Vantage)

Aerospace Applications• Transports

Boeing 787 Dreamliner

Boeing 787 Dreamliner

Summary• Early materials – “organic”

– Wood– CottonCotton

• Metals – Steel– Aluminum & Titanium alloys

• CompositesFiberglass– Fiberglass

– Carbon– Kevlar,– Plywood