Part-66 Module 6 — Materials and Hardware Flashcards

Vocabulary practice flashcards covering materials, hardware, and maintenance concepts for the UK CAA Part-66 Module 6 exam.

Proportional Limit

The highest stress at which stress is proportional to strain, where Hooke's law is valid and the line on the stress–strain curve is straight.

Elastic Limit / Yield Point

The stress at which permanent (plastic) deformation begins; it is the point above the proportional limit.

SAE 4130

A common aircraft chrome-molybdenum steel containing approximately $0.30\%$ carbon.

SAE Steel Code First Digit

Indicates the major alloying element, such as 1 for carbon, 4 for molybdenum, and 8 for Ni-Cr-Mo.

Martensite

A hard, brittle structure formed by heating steel above the upper critical temperature and soaking, followed by quenching in water or oil.

Annealing

A heat treatment involving heating and slow-cooling in a furnace to produce the softest, stress-free, and machinable state of the metal.

Normalising

A process of heating and air-cooling that refines grain structure and relieves forging stresses.

Brinell (HB)

A hardness test using a hardened-steel or tungsten-carbide ball indenter to measure the indentation diameter.

Rockwell (HRB/HRC)

A common hardness test using a steel ball (B scale) or diamond cone (C scale) that measures the depth of indentation.

Vickers (HV)

A precise hardness test using a square-based diamond pyramid indenter, measuring the diagonals optically.

Alclad

$2xxx$ or $7xxx$ aluminium sheet clad with a thin layer of pure aluminium for corrosion protection.

Aluminium Temper T3

Solution heat-treated, cold-worked, and naturally aged (e.g., $2024-T3$).

Aluminium Temper T6

Solution heat-treated and artificially aged to achieve maximum strength (e.g., $7075-T6$).

Aluminium Temper T73

Solution heat-treated and over-aged to provide resistance to stress-corrosion cracking and exfoliation.

Ti-6Al-4V

An aerospace workhorse titanium alloy consisting of $6\%$ aluminium and $4\%$ vanadium.

Magnesium Fire Protocol

Extinguish only with Class D dry powder; never use water or $CO_2$ as magnesium reacts violently.

Carbon Fibre (CFRP)

A black, electrically conductive composite with the highest strength and stiffness, which can galvanic-couple with aluminium to cause corrosion.

Aramid (Kevlar®)

A yellow reinforcing fibre known for high toughness and impact resistance that absorbs moisture.

Composite Matrix

The resin (thermosetting or thermoplastic) used to bind reinforcing fibres in a composite material.

Tap Test (Coin Tap)

A screening tool where a dull/dead tone indicates a disbond or delamination, while a clear tone indicates sound structure.

BVID

Barely Visible Impact Damage, a common defect in composite structures.

Sitka Spruce

The standard reference timber for aircraft wooden structures against which other species are compared.

Grain Slope Limit

For any structural wooden member, the slope of the grain must not exceed a ratio of $1:15$.

Compression Failure (Wood)

Characterised by buckled fibres appearing as fine lines or streaks at right angles to the wood grain.

Maule Tester

A push-type punch tester used to non-destructively check the strength of cotton or linen fabric.

Nitrate Dope

The initial dope coat used on aircraft fabric for adhesion; it is highly flammable.

Corrosion Essentials

Requires four elements: an anode, a cathode, an electrolyte (moisture/salt), and a metallic path.

Exfoliation

An advanced form of intergranular corrosion occurring in wrought products where grains lift or flake like book pages.

Stress Corrosion Cracking (SCC)

Cracking caused by the combination of sustained tensile stress and a corrosive environment.

Filiform Corrosion

Worm-like traces appearing under organic coatings (paint) when relative humidity is between $78–90\%RH$.

Thread Pitch (P)

The distance between adjacent thread crests.

Thread Lead (L)

The axial distance a thread advances in one full turn, calculated as $L = n \times P$.

AN Bolt Diameter

Indicated by the first number after the AN code in sixteenths of an inch (e.g., AN4 is $\frac{4}{16}$ or $\frac{1}{4}$ inch).

AN Bolt "A" Suffix

Indicates an undrilled shank intended for use with a self-locking nut.

AN Bolt "H" Suffix

Indicates a drilled head for installing lockwire.

MS21044 Nut

A common self-locking nut with a fibre/nylon insert, temperature limited to approximately $120\text{ °C}$.

AN310 Nut

A full-strength castellated nut used with drilled-shank bolts for tension applications.

AD Rivet (2117-T)

Known as the "field rivet," it has a dimple head marking and is driven as received.

DD Rivet (2024-T)

An "ice-box" rivet with a raised double-dash marking that must be refrigerated after heat treatment and driven soon after.

Rivet Code Diameter (e.g., MS20470AD4-8)

The first number represents the diameter in thirty-seconds of an inch (e.g., $4 = 4/32$ inch).

Rivet Code Length (e.g., MS20470AD4-8)

The second number represents the length in sixteenths of an inch (e.g., $8 = 8/16$ inch).

AN Flare Angle

Standardised at $37\text{ °}$ for aircraft flared fittings.

Flexible Hose Sizing

Indicated by the inside diameter (ID) in sixteenths of an inch.

Gear Ratio

Calculated as the number of teeth on the driven gear divided by the number of teeth on the driving gear (teeth on driven $\div$ teeth on driver).

Worm Gear Self-locking

Generally occurs when the lead angle is below approximately $5\text{ °}$ and the efficiency is below about $40\%$.

Spring Slenderness Ratio

The ratio of free length to mean coil diameter ($L_f / D$); if greater than $4$, the spring is likely to buckle.

Tapered Roller Bearing

A bearing designed to handle heavy combined radial and thrust loads, commonly used in wheels.

7x19 Control Cable

The most flexible control cable construction, consisting of 7 strands of 19 wires each, used for running over pulleys.

Turnbuckle

A device with one left-hand and one right-hand threaded steel end in a brass barrel used to adjust cable tension.

AWG (American Wire Gauge)

An inverse scale for wire diameter where a larger number indicates a thinner wire.

MIL-C-5015 Shell Size

A number representing the coupling-thread diameter in sixteenths of an inch (e.g., size 20 is approximately $1 \frac{1}{4}$ inch).