Aircraft Materials (Metallic)

• Metal Alloy Steels


  Ferrous Metal Characteristics and Properties
• Strength


  One way to classify metals is according to the amount of strength they possess. A metal's strength is determined by the percentages of the parent metal and other elements used to make an alloy. There are many different types of strength, including: Tensile strength, Compressive strength, Shear strength, Torsional strength, Bending strength, Fatigue strength, Impact strength (also known as toughness).
• Metal Loading Forces


  Tensile strength, Compressive strength, Shear strength, Torsional strength, Bending strength, Fatigue strength, Impact strength (toughness)
• Tensile strength


  The ability of a piece of sheet metal to withstand stress in tension. There are three definitions: Yield strength, Ultimate strength, Breaking strength.
• Reference numbers on the stress vs strain curve for structural steel include: Ultimate strength, Yield strength (elastic limit), Rupture (or fracture), Strain-hardening region, Necking region.
• Compressive strength


  A metal's ability to withstand being pressed or squeezed.
• Shear strength


  A metal's ability to withstand shear stress.
• Torsional strength


  A metal's ability to resist rotational shear.
• Bending strength


  A metal's bending strength.
• Fatigue strength


  A metal's ability to resist repeated loading.
• Impact strength (toughness)


  A metal's ability to resist shock.
• Hardness


  A metal's ability to resist cutting, penetration or abrasion.
• Malleability


  A material's ability to be bent, formed or shaped without cracking or breaking.
• Ductility


  The ability of metal to be drawn into wire stock, extrusions or rods.
• Brittleness


  A material's tendency to break or shatter when exposed to stress, and is the opposite of ductility and malleability.
• Elasticity


  A metal's tendency to return to its original shape after normal stretching and bending.
• Toughness


  A material's ability to resist tearing or breaking when it is bent or stretched.
• Conductivity


  The property which enables a metal to carry heat or electricity.
• Thermal Expansion


  The ability of a metal to expand when heated and shrink when cooled.
• Fusibility


  The ability of metal to be joined by heating and melting.
• Ferrous Metals


  Any alloy containing iron as its chief constituent.
• Iron (Ferrite)


  The most common ferrous metal in aircraft structures is steel, an alloy of iron with a controlled amount of carbon added.
• Steel Composition


  Steel is a material composed primarily of iron. All types of steel contain a second element: carbon. Many other alloying elements are used to produce different types of steel.
• Cast iron has few aircraft applications because of its low strength-to-weight ratio. However, it is used in engines for items such as valve guides, where its porosity and wear characteristics allow it to hold a lubricant film. It is also used in piston rings.
• Steel


  An alloy of iron with a controlled amount of carbon added
• Iron


  • Fairly soft, malleable and ductile in its pure form
  • Silvery white in colour and quite heavy
  • Combines readily with oxygen to form iron oxide (rust)
• Cast iron


  Iron poured from a furnace into moulds, normally contains more than 2% carbon and some silicon
• Cast iron has few aircraft applications because of its low strength-to-weight ratio
• Cast iron is used in engines for items such as valve guides, where its porosity and wear characteristics allow it to hold a lubricant film
• Cast iron is also used in piston rings
• Steel


  A material composed primarily of iron, with carbon as the second element
• Difference between steel, cast iron and wrought iron

  Primarily based on the carbon content

  
• SAE steel numbering system

  • Four-digit numerical index system to represent chemical composition standards for steel specifications
  • First digit identifies the principal alloying element
  • Second digit indicates the percentage of the principal alloying element
  • Last two digits indicate the average carbon content in hundredths of a percent

  
• SAE designations for major classifications of steel

  • 1xxx - Carbon steels
  • 2xxx - Nickel steels
  • 3xxx - Nickel-chromium steels
  • 4xxx - Molybdenum steels
  • 5xxx - Chromium steels
  • 6xxx - Chromium-vanadium steels
  • 7xxx - Tungsten steels
  • 8xxx - Nickel-chromium-molybdenum steels
  • 9xxx - Silicon-manganese steels
• Purpose of ferrous metal alloys

  Iron has few practical uses in its pure state, but adding small amounts of other materials to molten iron dramatically changes its properties
• Carbon


  • The most common alloying element found in steel, forms iron carbides called cementite
  • Allows steel to be heat-treated to obtain varying degrees of hardness, strength and toughness
  • The greater the carbon content, the more receptive steel is to heat treatment and the higher its tensile strength and hardness
  • Higher carbon content decreases the malleability and weldability of steel
• Ferrous materials classified by carbon content

  • Low-carbon or mild steel
  • Medium-carbon steels
  • High-carbon steels
• Low-carbon or mild steel


  • Primarily used in non-structural areas, easily welded, machines readily, does not accept heat treatment
• Medium-carbon steels


  • Will accept heat treatment, especially adaptable for machining or forging, used where surface hardness is desirable
• High-carbon steels


  • Very hard, primarily used in springs, files and some cutting tools