Composites For Aerospace Applications

Materials

Lecture Topics • Wood and fabric • Metals • Composites • Other considerations

Reading Sorry, 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 pieces varied (no manufacturing control)

Post WWI • Wire Braced Metallic Space Frame with Fabric 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

Failure Modes

buckling

Yield (ductile)

Fracture (brittle)

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 iron

Aluminum Alloys

Aircraft Metals • Steel alloys: too heavy now but used for landing gear • Aluminum alloys: used for modern aircraft • Titanium alloys: y g good for high g temperatures 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/ 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 forces “overbuilding” which negates weight advantage • Engineers are still learning about fatigue properties p p of composites p • Environmental Sensitivity (Temp., UV, Lightning) • Cost

Composite Materials • Fiber reinforced composite materials consist of fibers & matrix – M Matrix t i (glue) ( l ) – provides id lload d ttransfer f between fibers, support & protection

– Fiber – provides the strength and stiffness

Aerospace Composite Materials • Fibers: – Aramid (Kevlar™) – Glass (E, S,…) – Carbon (Graphite) – ….

• Matrix: – Polyester y – Epoxy – ….

Fiberglass

Carbon Fiber Aramid

Why Thin Fibers? • Smaller diameter has fewer number of internal flaws • More bonding surface area • Molecular alignment • More flexibility strength

Composites Applications

Composites in Airplanes • Plywood – WWII y matrix composites p • Polymer – Graphite/Epoxy – Aramid/Epoxy – Fiberglass

• Metal matrix composites

The de Haviland Mosquito with Balsa plywood skin (1940)

• Ceramic matrix composites

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 – Cotton

• Metals – Steel – Aluminum & Titanium alloys

• Composites – – – –

Fiberglass Carbon Kevlar, Plywood