Chapter 10 - Materials in Aeronautics

  • Chapter Overview: This chapter discusses materials peculiar to aeronautical engineering, focusing on lightweight, high-strength materials, primarily used in aircraft construction.

  • Key Properties of Aircraft Materials:

    • Strength vs. Weight: Strength allied to lightness is critical.
    • Additional Properties: Stiffness, toughness, corrosion resistance, fatigue resistance, environmental effects, fabrication ease, availability, and cost also influence material choice.

  • Main Material Groups:

    • Wood
    • Steel
    • Aluminum Alloys
    • Titanium Alloys
    • Fiber-Reinforced Composites

  • Aluminum Alloys:

    • Pure aluminum is flexible but low-strength; alloying with other metals improves strength significantly.
    • Types of Aluminum Alloys:
    • 1st Group: Alloyed with copper, magnesium, manganese, with good mechanical properties after heat treatment (e.g., yields 230-460 N/mm²).
    • 2nd Group: Retains strength at high temperatures (used in aero engines).
    • 3rd Group: High strength through zinc and magnesium; often leads to stress-corrosion failures.
    • The design consideration varies between military and civil aircraft regarding fatigue and corrosion resistance.

  • Steel:

    • Higher specific gravity limits use but still valuable for small components needing high tensile strength (e.g., undercarriage components).
    • Maraging Steels: High strength from nickel, cobalt, molybdenum, with excellent weldability and toughness.

  • Titanium Alloys:

    • Increase in use for combat aircraft, excellent fatigue strength, retains strength at high temperatures, but expensive and weighty.
    • Examples: Used in F15, F22, parts of Concorde.

  • Composite Materials:

    • Made from strong fibers (glass, carbon) in a plastic matrix; properties are directionally dependent (anisotropic).
    • Superior strength; usable in primary structures (now mostly carbon fiber-reinforced plastics).

  • Material Testing Techniques:

    • Tensile Tests: Measure ductility and yield strength.
    • Compression Tests: Important for brittle materials (e.g., concrete).
    • Bending Tests: Evaluate bending moments and plastic properties.
    • Impact Tests: Determine toughness under shock loading (Izod and Charpy tests).

  • Material Properties:

    • Ductility: Ability to undergo significant plastic deformation.
    • Brittleness: Little deformation before fracture.
    • Elasticity: Ability to return to original shape after load removal.
    • Plasticity: Permanent deformation remains after load removal.

  • Fatigue and Creep:

    • Fatigue: Reduces the endurance limit of materials under variable loads, especially in cyclic loading situations.
    • Creep: Deformation over time under constant load, important at high temperatures.
    • Minimized through design considerations to reduce stress concentrations and improve load distribution.

  • Properties Relevant to Aircraft Design:

    • Consideration of environmental impact, operational conditions, and the specific loading conditions experienced during service.

  • Material Selection and Application: The understanding of these materials is crucial for the design and safety of aircraft structures, ensuring they withstand various conditions during operation without failure.