Aluminum-Based Solutions for Tomorrow’s Airframe Structures

Tomorrow’s airframe structures will have to meet an ever-widening set of expectations:  low weight and low cost remain key drivers, but increased maintenance intervals are now the industry norm.  In addition technology robustness, reduced lead time and ecologically responsible manufacturing are increasingly required.  Aluminum-based solutions have significant potential with regard to these expectations, both through the traditional route of improved alloy performance and via improved design and manufacturing approaches.  

The major aluminum suppliers have a strong track record in focused new alloy development.  Recent development emphases have included Al-Cu-Li alloys, giving rise for example to Constellium’s AIRWARE™ technology.  These alloys combine the intrinsically improved density and stiffness due to Li addition with a significant step in strength-damage tolerance balance.  The intrinsically good corrosion resistance of Al-Cu-Li alloys brings further potential, either with regard to reducing the cost of corrosion protection systems or by facilitating increased inspection intervals.  The economic and environmental viability of such solutions also depends on the industry’s ability to recycle the scrap material efficiently; major progress in this field has been made over the last several years. 

However, alloy developments only represent about half the potential improvements currently accessible with metallic structures, the remainder being associated with more efficient design and manufacturing approaches.  For example, the cost of riveted skin-stringer panels can be improved by application of welding or bonding, thereby eliminating much of the complexity and cost of assembly.  Moreover, moving from riveting to welding or bonding reduces the number of fatigue initiation sites associated with local stress risers and can thus bring significant weight benefits.

Over and above the technologies mentioned above, metallic solutions that explore higher potential but lower maturity technologies are being investigated.  Examples include incorporating structural health monitoring capable features in wrought aluminum products, tailored property parts, and aeroelastic tailoring.  All these have been demonstrated at relatively small scale in aluminum structures, and now need to be brought to a higher technology readiness level.

Illustrations of the aforementioned technologies will be presented, along with both calculated benefits in terms of airframe weight and estimates of their technology readiness dates.