Knowledge Levels 1, 2, and 3

Knowledge Levels

• Basic knowledge for categories A, B1, and B2 is indicated by knowledge level indicators 1, 2, or 3 against each subject, with Category C applicants required to meet either B1 or B2 basic knowledge levels.
• Level 1 objectives include familiarity with basic elements, simple descriptions using common words and examples, and usage of typical terms.
• Level 2 objectives include understanding theoretical fundamentals, giving general descriptions with typical examples, using mathematical formulae with physical laws, reading sketches and schematics, and applying knowledge practically with detailed procedures.
• Level 3 involves detailed theoretical and practical knowledge, combined with a capacity to apply separate elements of knowledge logically, with objectives.
• Level 3 objectives :
  • Knows the theory of the subject
  • Interrelationships with other subjects
  • Gives detailed descriptions using theoretical fundamentals and specific examples
  • Understands/ uses mathematical formula.
  • Reads, understands and prepares sketches
  • Applies knowledge practically using manufacturer's instructions
  • Interprets results and apply corrective action.

Metal Alloy Steels

• 'Metal characteristics' is a term identifying a material's feature or quality.
• Metals possess characteristics determining their use in manufacturing and construction.
• Characteristics include:
  • Strength, hardness, malleability, ductility, brittleness, conductivity, elasticity, toughness, fusibility, and density.
• 'Metal property' identifies an attribute, quality, or characteristic of a metal.
• Alloying changes material characteristics dramatically like adding carbon to steel for increased hardness.

Strength

• Classifying metals involves assessing their strength, determined by parent metal and alloying element percentages.
• Metals possess tensile, compressive, shear, torsional, bending, fatigue, and impact strength (toughness).

Metal Loading Forces

• Tensile Strength is the ability of sheet metal to withstand stress in tension and is defined by three components.
• Yield Strength is the stress where material strain transitions from elastic to plastic deformation, causing permanent deformation.
• Ultimate Strength is the maximum stress a material can endure under tension, compression, or shearing, representing the peak stress on the stress-strain curve.
• Breaking Strength is the stress at rupture and is the coordinate on the stress-strain curve at the point of rupture.
• Stress vs strain curve references include ultimate strength, yield strength (elastic limit), rupture (or fracture), strain-hardening region, and necking region.
• Compressive strength measures a metal's resistance to being pressed or squeezed.
• Shear strength quantifies a metal's capacity to withstand shear stress.
• Torsional strength is a metal's resistance to rotational shear, while bending strength measures resistance to bending.
• Fatigue strength (endurance strength) reflects a metal's ability to withstand repeated loading, and impact strength (toughness) indicates resistance to shock.

Hardness

• Hardness is a metal's ability to resist cutting, penetration, or abrasion
• Tensile strength directly correlates with hardness in steel, though this may not be constant with all metals.
• Metals harden through heat-treating or work hardening, and soften through annealing.

Malleability

• Malleability is a material's capability to be bent, formed, or shaped without cracking or breaking.
• Hardness and malleability are generally opposite properties
• Metals are often annealed or softened to increase malleability which allows complex shapes to be formed.
• After forming, the metal is heat-treated to increase strength.
• Hammering and shaping can harden a metal to a point where it requires re-annealing before forming can continue.
• Malleable metals can be hammered, pressed, or rolled into thin sheets without breaking and are highly ductile; non-malleable metals are brittle.

Ductility and Brittleness

• Ductility is the capacity of a metal to be drawn into wires, extrusions, or rods.
• Ductile metals are preferred in aircraft for their ease of forming and resistance to failure under shock loads, commonly for control cables
• Brittleness is a material's tendency to fracture or shatter when stressed, contrasting with ductility and malleability.
• Structural metals subjected to shock loads, should not be brittle.
• Cast iron and hardened steel are brittle ferous metals.

Elasticity, Toughness and Conductivity

• Elasticity is a metals ability to return to its original shape when bent or stretched, such as in the flexibility of spring steel or the expansion/contraction of aircraft skins due to pressure.
• A metal's elastic limit refers to the point after it cannot return to its original shape.
• Some non-ferrous metals have very low elastic limits, the elastic limit of hard spring steel is extremely high.
• Toughness is a material's ability to resist tearing or breaking when bent or stretched such as hammer faces and wrenches.
• Conductivity is a property dictating how well a metal transports heat or electricity, in which thermal and electrical conductivity are measures of a materials ability to transmit energy.
• Thermal conductivity also involves absorbing heat before transmitting it, which is referred to as heat exchange.

Thermal Expansion and Fusibility

• Thermal Expansion is the ability of a metal to expand when heated and contract when cooled.
• Coefficient of expansion is the amount of expansion or contraction at specific temperatures which all aircraft experience as ambient temperature changes.
• Fusibility is the ability of metal to be joined by heating and melting two compatible pieces of metal into a continuous section.
• Fusion joining or welding, is the correct term for this process.

Ferrous metals

• A ferrous metal is any alloy with iron as chief constituent, including steel, cast iron, titanium, and iron alloys with metals such as stainless steel.
• Steel is the most common ferrous metal in aircraft structures, which is an iron alloy with controlled carbon.
• Iron is a soft, malleable, ductile, silvery-white chemical element that combines readily with oxygen, forming iron oxide, or rust.
• Iron is commonly mixed with carbon and other alloying agents/impurities.
• Cast iron is from pouring iron from a furnace and normally contains over 2% carbon and some silicon.
• Cast iron has few aircraft applications because of its low strength-to-weight ratio; however, its used as valve guides, with porosity/wear characteristics to hold lubricant film, and piston rings.

Steel Composition and Identification

• A material composed primarily of iron is steel.
• While most steels contain other alloying elements, all steels contain carbon.
• Carbon content primarily dictates the differences between steel, cast iron, and wrought iron.
• General SAE uses a four-digit numerical index system to represent chemical composition standards.
  • First digit identifies principal alloying element
  • Second digit is the principal alloying element percentage
  • Last two digits are the carbon content in hundredths of a percent

SAE Steel Major Classifications

• 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

Alloying Agents in Steel: Purpose

• In its pure form, iron is used with very little practical application
• However, molten iron dramatically changes once a small amount of materials are added
• More common materials added include carbon, sulphur, silicon, phosphorous, nickel, and chromium

Carbon

• Most common alloying element when found in steel
• When carbon is mixed with iron forms compounds of iron carbides that are called cementite
• Steel containing carbon allows obtaining varying degrees hardness, toughness, and strength if heat treated
• More receptive steel is to heat treatment when greater carbon content
• Higher tensile strength and hardness in higher contents
• Higher carbon content = decrease in malleability and weldability
• Designations of metal hardness or its temper is indicated by a letter to separate the designation of alloy by a dash

Ferrous Materials Classifications

• Low-Carbon or Mild Steel
  • Used in non-structural areas, such as steel-tube construction in the past
  • Easily welded
  • Machines readily
  • Does NOT accept heat treatment
• Medium-Carbon Steels
  • Will accept heat treatment
  • Adaptable for forging and machining
  • Used when surface hardness is desired
• High-Carbon Steels
  • Very hard
  • Used in making some cutting tools, springs, and files

Silicon, Manganese, and Sulphur

• Silicon: When alloyed with steel acts as a hardener, in small quantities improves ductility.
• Manganese: Unique non-magnetic steel with extreme anti-wear properties that is present in mangalloy (manganese steel).
  • Material very resistant to abrasion, will achieve up to 3 times surface hardness during impact, without any increase in brittleness
• Sulphur: An undesirable impurity added to steel that makes it brittle when forged and rolled
  • Sulphur must be removed entirely during refining
  • If not manganese can be added to counter its effects

Effects from Phosphorous, Nickel, & Chromium

• Phosphorous can raise the yield strength of steel and improve low-carbon steel's resistance to atmospheric corrosion.
• Nickel added to strength and hardness of steel, also increases it's yield strength, and slows the rate of hardening when hardened, which increases the depth of hardening and produces a finer grain structure.
  • The finer grain reduces steel's tendency to warp and scale when it is heat treated
• Chromium will increase strength and hardness as well as improve wear/corrosion resistance.
  • Because of its characteristics it is used in balls and rollers of antifriction bearings
  • Also used as alloying element in steel
  • Electrolytically deposited on cylinder walls & bearing journals for a hard, wear-resistant surface

Other Alloying Agents

• Nickel-chromium
  • Nickel gives material to steel, chromium hardens it
  • Both alloys give steels great characteristics for high strength structural applications
• Molybdenum
  • Commonly used
  • Reduces the grain size of steel
  • Increases both impact strength plus elastic unit
  • Possesses a great deal of fatigue strength/very wear resistant
• Chrome-molybdenum
  • Ready readily
  • Easily welded by and gas or electric arc
  • Responds well to heat treatment
  • Ideal choice for landing gear structures/engine mounts because wear resistance make material engine cylinders/highly stressed parts
• Vanadium
  • Combined with chromium produces strong, tough, ductile steel alloy
  • Ball bearings typically made of chrome-vanadium steel
• Tungsten
  • This is used to add a extremely melting point characteristic to alloyed steel
  • These steels have high density (high mass)
  • Retain hardness at elevated operating Temps, for breaker, contacts in magnetos, and control surface balance weights

Titanium and Stainless Steel

• Titanium alloys have very high tensile strength/toughness at elevated temperatures
  • Lightweight and high corrosion resistance
  • Ability to withstand extreme temperatures
• Large amounts of both nickel and chromium in type of corrosion resistant steel known as Stainless Steel
  • Strength/resistance to corrosion make steel suitable for high temperature
  • Found in firewalls and exhaust components.

Heat Treatment of Steel and Its Purpose

• Pure iron is too ductile, soft,weak, and won't respond to heat
• 10's percent of alling elements, Iron alloyed to cartbon equals steel which is easy to heat treat producing strengths, and ductilities
• Carbon is most important of these/most steel eat treatment methods are based on controlling and distribution
• The process of is and coling carbon steel without canging the shape
• Can also be used to alter manufacturers
• High-carbon steel respond very well

Annealing & Normalising

• Annealing involved heating soaking then allowing it to cool, which softens
• Allowing it to cool can include leaving in a furnance or surrounding it with ash or hot sand for even heat displacement
• Normalizing realives stresses from forging, welding, or machining that lead to failure
• Process involve maintaining soak temp until evenly heat soaked.
• Cooling is done with still open air from oven
• Carbon can precipitate out, less than annealing
• Useful on welded parts to set up internal stresses/ strains in adjacent material

Hardening & Tempering

• Hardening is readily done on carbon steel where hardness attained depends on carbon content.
• Hardening requires heating steel so the carbon disperse's uniformly
• Alloy is rapidly cooled through quenching in brine (water w/ salt content), oil, etc
• Quench speed depends on the quenching medium
• Tempering is using heat to reduce undesirable qualities of steel such as brittleness
• Tempering can reduce metal temperature, and holding it to becomes heat soaked
• Then cooled to room temperature in still air which not only reduces brittleness but also relieves stress, then improves ductility/toughness.

Case Hardening

• Case hardening is processing metal requiring hard durable surfaces/core material and remains toigh for air craft components such as bearing/s
• Suited for alloy and low carbon which won't penetrate the core.
• If high carbon steel is case hardened, it may cause increased hardness

Aircraft Materials: Non-Ferrous

• Non-Ferrous Materials
  • Characteristics/properties of nonferrus metals
    • Identification/heat thearment of nonferrus metals
    • Level 2

Non-Ferrous Metals, Properties and Identifying Aluminum

• Aluminum, copper,titanium, and magnesium are some of many commen non-ferrus metals for aircraff construction and repair.
• Aluminum, a white-silver matallic.element, is obtained at alectrolysing buxite.
• Lacking sufficient strength by itself, pure aluminum is alloyed or mixed with compatible metals like copper or zinc

Wrought Aluminum and Alloys

• Aluminum will be made made for more types -Strainhardenble -Commercially/Chemical applications
• 1XXX Series - pure aluminum ingot Alloys with (2XXX series) will utilize the cu as agent when mixed with c/metallic charges in grain. -Susceptible to inter granilar corrosion if improperly treated
• Alloy used in aircraft is copper aluminium, mainly 2017 and 2024

Series Continued

• Allolys with (3xxx series) is will be manganese as principle aying
  • non-heat-treatable
  • common variation has good workability
• (4XXX series)
  • will be alloy aluminium silicon which lowers melting and results in good brazing
• (5XXX series)
  • good welding/corrosion resistance
  • If exposed to high/cold Temps the susceptbility can be increased
• Alloy that contains (6XXX series)
  • has medium strength combined with corrosion/forming properties
• (7xxx series)
  • Made from harder/stronger aluminium like 7075/7178 Passenger aircraft examples
  • Strings/Kill/Floor be/wing
  • bulkhead/window/gear beam
  • wing upper skin pars/ beam
  • landing been gear
  • Wing lower skin
• The Series 8xxx exceptionally provides a high stren,gth increases combines aerospace/weight/stiffness