2.1.1.A AerospaceMaterials.pptx

PLTW Aerospace Materials

  • Overview of aerospace materials used in aircraft design and engineering.

Commonly Used Aerospace Materials

  • Wood: Once popular, now rarely used for production aircraft.

  • Steel: Cheap, easy to fabricate, strong; used for structural components.

  • Aluminum Alloys: Most widely used material due to good strength-to-weight ratio.

  • Titanium Alloys: High strength-to-weight ratio; used in high-stress components.

  • Magnesium Alloys: Lightweight and easy to make; used in various parts.

  • Nickel Alloys: Suitable for high-temperature applications and engine parts.

  • Fiber-reinforced Composites: Increasingly used for lightweight structures.

Factors for Selecting Materials

  • Function: Determines the application of the component.

  • Material Properties:

    • Strength to Weight Ratio: Critical for aerospace designs.

    • Stiffness: Ability to resist deformation.

    • Toughness: Resistance to impact and failure.

    • Corrosion Resistance: Essential for longevity in diverse environments.

    • Fatigue Resistance: Materials ability to withstand repeated loading.

    • Environmental Resistance: Withstanding temperature variations.

  • Production Factors:

    • Machinability: Ease of processing and shaping materials.

    • Availability and Consistency: Ensures reliable sourcing and performance.

Cyclic Stresses in Aircraft

  • Average commercial aircraft undergoes significant cyclic stresses over its lifespan:

    • Life Cycle: 30 years, approximately 60,000 flying hours.

    • Duration: Roughly 2,500 days of service, translating to 20,000 flights or 667 flights per year.

    • Operational Data: 100,000 miles of taxiing (around 4 times the Earth’s circumference).

    • Maintenance Costs: Average service cost may double the original purchase price.

Flight Stresses

  • Pressure Differential: Ranges from 0 kPa to 60 kPa (8.6 psi) between the fuselage and outside atmosphere.

  • Temperature Differential: Contrasts between ground temperature and -56 °C during cruise.

  • Impact Loads during Landing: Landing gear supports significant loads, wings flex under forces, and tires experience rapid acceleration.

Material Density Impact

  • Reducing material density directly reduces airframe weight, enhancing:

    • Fuel Efficiency

    • Climb Rate

    • G-force Loading

  • Effectiveness: Density reductions are 3 to 5 times more effective than enhancements in tensile strength or impact resistance.

Early Aircraft Materials

  • Wood: Used widely in early aircraft:

    • Wright Brothers predominantly used spruce for its availability, easy fabrication, and favorable strength-to-weight ratio.

    • Limitations: Sensitivity to moisture, rotting, and insect damage.

    • Now primarily found in homebuilt and specialty low-volume aircraft.

Aerospace Materials – Metal Alloy Forms

  • Forms of Metal Alloys:

    • Sheet: Formed sheets < 0.250 in, used in fuselage skin, and control surfaces.

    • Plate: Thickness > 0.250 in, machined into complex shapes and parts.

    • Forging: Deformation under high compressive forces to create strong, non-uniform parts.

    • Extrusion: Forcing material through dies to create a uniform cross-section; often used for stiffeners.

    • Casting: Liquid material solidified in molds to form various shapes.

Aerospace Materials – Aluminum Alloy

  • Characteristics: Widely used due to abundance, moderate cost, corrosion resistance, and excellent strength-to-weight ratio.

  • Common Alloys:

    • 2024 (24ST) includes aluminum, copper, manganese, and magnesium.

    • Different series based on principal alloying element (e.g., 1xxx, 2xxx, etc.).

  • Aluminum Lithium Alloys: Offer weight savings similar to composites but formed by traditional techniques.

Aerospace Materials – Steel Alloy

  • Cost-effective and easy to fabricate; initially used in early fuselage construction.

  • Properties: Varies by heat treatment; strength and ductility can be adjusted.

  • Typical Uses: High-strength applications, including fittings, firewalls, and engine mounts.

Aerospace Materials – Titanium

  • Advantages: Superior strength-to-weight ratio and stiffness compared to aluminum; resistant to high temperatures and corrosion.

  • Challenges: Difficult to form, influenced by impurity elements, and generally more expensive than aluminum.

  • Commonly used in jet engines, landing gear, and critical structural components.

Aerospace Materials – Magnesium

  • Offers good strength-to-weight ratio and high-temperature tolerance; often used in various components.

  • Concerns: Susceptible to corrosion and flammability; must have protective finishes and avoid difficult-to-inspect areas.

Aerospace Materials – High Temperature Nickel Alloys

  • Suitable for extreme applications in hypersonic aircraft; but heavier and harder to form than aluminum.

Aerospace Materials – Composites

  • Advanced materials like boron/epoxy and carbon fibers enhance structural performance; significant adoption in modern fighters to reduce weight.

  • Notable examples: Boeing 787 with >50% composite materials.

Aerospace Materials – Ceramics

  • Used for high-temperature applications; essential for parts needing heat resistance, such as engine exhaust nozzles.