Materials and Hardware
What you must know
This domain covers aircraft materials (aluminium alloys, titanium, steel, composites), their properties and heat treatment, corrosion types and prevention, fasteners (rivets, bolts, screws, nuts, locking devices), bearings, springs, pipes and unions, and control cables. You must recognise standard hardware markings, thread types, grip length selection for bolts, and the difference between close-tolerance and interference-fit fasteners.
Traps to watch
- Bolt grip length: the unthreaded shank should lie within the joint; threads must not bear on the shear plane.
- Rivet identification: head markings indicate alloy and temper; a dimple or raised dot means a specific alloy, not a defect.
- Corrosion types: galvanic corrosion needs dissimilar metals plus an electrolyte; stress corrosion needs tensile stress plus a corrosive environment.
- Heat treatment: solution treatment and precipitation hardening (ageing) are distinct steps for aluminium alloys.
- Locking devices: tab washers, split pins, and self-locking nuts each have specific approved applications; never reuse a self-locking nut beyond limits.
Worked example
A joint stack measures 12 mm thick. A bolt with a grip length of 12 mm is correct; adding a washer increases the stack, so grip must be rechecked. If the bolt is too long, threads fall inside the bearing (shear) area, reducing strength; if too short, the nut may not fully engage.
Rule of thumb
Select bolt grip so the thread starts just beyond the joint face, and never allow threads to carry shear load in a structural joint.