Materials and Hardware
Core concepts
Ferrous and non-ferrous metals and their alloys: properties, heat treatment (annealing, normalising, hardening, tempering), and the reason aircraft use aluminium alloys, titanium and magnesium. Composite materials - fibres, matrices, lay-up, and the inspection issues they create. Corrosion types: surface, galvanic, stress, intergranular and fretting, with their causes and prevention. Then hardware: aircraft bolts (AN, MS, close-tolerance), nuts, washers, pins, keys, screws, and rivets - solid, blind and special - with their identification codes, plus fasteners for composites. Also pipes, unions, bearings, springs, transmissions, cables, and control-surface fittings.
Traps in questions
- Rivet part numbers are read left to right: material, head type, diameter in 1/32 inch, length in 1/16 inch. A dash number is not a diameter in millimetres.
- AN versus MS numbering systems are different; do not assume interchangeability.
- Galvanic corrosion needs an electrolyte and two dissimilar metals; carbon fibre against aluminium is a classic trap.
- Aluminium alloys are not strengthened by quenching alone - ageing or precipitation treatment completes the process.
- Self-locking nuts have a limited number of reuses; check the specification.
Worked example
Read MS20470AD4-5: MS20470 is the universal-head solid rivet specification; AD is 2117-T3 aluminium alloy; 4 means 4/32 = 1/8 inch diameter; 5 means 5/16 inch length. For a grip of two 0.05 in sheets (0.10 in total), the length required is grip plus about 1.5 diameters for the upset head: 0.10 + 1.5 × 0.125 ≈ 0.29 in, so a dash-5 rivet is selected.
Rule of thumb
Rivet diameter is the dash number over 32; length is the second dash number over 16, in inches.