Exploring the potential of variable stiffness design in reducing the life-cycle impact of composite aircraft parts

In 2022 Airbus and Boeing combined delivered 1203 commercial aircraft. With an annual predicted growth of 4.3% for the coming 20 years there is an urgent need for end of life solutions that go beyond down-cycling of parts that cannot be reused. Especially carbon fibre reinforced composites are hard to recycle, and attempts to deliver recyclable short fibre reinforced thermoplastic materials see a reduction in specific properties. This is a problem because, the life cycle impact of an aircraft part is predominantly determined by its weight, which drives cumulative CO2-emissions over its lifetime. The transition to renewable energy sources by the aviation sector has the potential to change this relationship drastically. Therefore, it is necessary to begin developing methods to account for life cycle impact already at the start of the mechanical design of an aircraft part. This study proposes to apply variable stiffness laminate design to compensate for relatively lower mechanical performance of a recyclable short fibre reinforced composite laminate. This is successfully demonstrated using the example of a rectangular plate under uniaxial compression with the ATR72 as case study. The results furthermore clearly show that moving from conventional to renewable energy sources, reduces the impact of part-weight on the accumulated CO2-emissions for the life span of the aircraft very significantly, bringing recycling considerations more into focus.