Aircraft Material Selection: Composites, Metal Alloys, and Corrosion

The selection of materials for aircraft construction is a critical decision that balances various properties such as strength, weight, cost, and resistance to environmental factors. While traditional metal alloys remain dominant, composite materials are increasingly used for their superior performance characteristics.

Composite Materials

Composites, such as carbon fibre, aramid (Kevlar), and fibreglass, offer significant advantages in aircraft design:

• Strength-to-Weight Ratio: Composites typically have a much higher strength-to-weight ratio than metal structures, making them ideal for creating lighter, more efficient aircraft.
• Directional Strength: The strength of a composite component can be tailored to the direction of the load by orienting the fibres. This specific alignment allows engineers to maximize strength exactly where it is needed, unlike in isotropic metals.

Metal Alloys

Despite the rise of composites, metal alloys (like aluminium and titanium) still form the bulk of the aviation industry's structures.

• Properties: Metals generally have a high strength-to-weight ratio, though lower than that of modern composites. They are versatile and their properties can be tailored through alloying (e.g., using heat-resistant titanium in hot engine sections).
• Corrosion Susceptibility: A significant disadvantage of metal is its high susceptibility to corrosion, which requires constant monitoring and maintenance.

Maintenance of Metal Parts

When corrosion is detected on metal parts, the appropriate action is to repair, prime, and paint the damaged parts.

• Incorrect Maintenance Practices:
  • Painting over corrosion: This is not recommended as it merely masks the issue while the corrosion continues to weaken the structural integrity.
  • Replacing with plastic/composites: While theoretically an option, this is often expensive and may not be technically feasible for all components.
  • Excessive washing: While cleaning is important, washing the aircraft after every flight is not the primary solution and can, in some cases, promote water-based corrosion if not dried properly.

Material Selection Factors

Engineers select materials based on specific criteria to ensure safety and efficiency:

• High Strength-to-Weight Ratio: The most desirable property for aviation materials.
• Other Factors: Elasticity, resistance to corrosion, cost, and heat resistance.
• Brittleness: Brittle materials are avoided as they are likely to snap or shatter under load rather than flex.