Take, make, use, dispose

According to Atkins’ senior engineer James Domone, assistant engineer Philippa Bliss and engineer Matt Copus, aerospace must consider production in its move towards a carbon net zero target by 2050.

While the majority of carbon emissions from commercial aerospace occur during flight operations, to truly meet carbon Net Zero targets, the industry must also tackle emissions resulting from production. Could a circular economy – the reuse, refurbishment, repurposing and recycling of aircraft components – be the answer?

Aircraft production is estimated to contribute 1% of commercial aviation’s total greenhouse gas emissions. These come from raw material extraction, material processing, manufacturing and transportation. While this is a small proportion of emissions compared with aircraft operations, for aviation to achieve a carbon Net Zero target by 2050, production-related strategies are required.

Traditional aerospace manufacturing processes follow a linear path simply described as ‘take – make – use – dispose’, with economic growth directly linked to increasing use of natural materials. But raw materials are finite in nature, and their cost is rising.

Instead, adopting a circular process that puts reuse and recycling as central tenets is environmentally attractive and is becoming increasingly economically attractive. This is described as the circular economy and adopting it as a strategy requires a ‘reduce – reuse – recycle’ philosophy that requires less energy and therefore supports a reduction in emissions.

In short, a circular economy system aims to minimise inputs and outputs. For aerospace production, the inputs are raw materials and the outputs are typically either landfill waste or materials recycled into other industries, with very little brought back into the aerospace production chain. With initial raw material extraction one of the biggest sources of carbon emissions during production, using a circular strategy could eliminate the need for inputting new raw material.

To make this feasible, moving towards a circular economy would require a shift in design approach, enabled by novel manufacturing technologies and supported by a change in business approach. Reducing initial material use, reusing components where possible, increasing use of recycled material and designing for recyclability are key strategies to change to a circular economy. Enabling technologies to achieve these aims are additive manufacturing, advanced recycling processes and digital twins.

Additive manufacturing in particular holds significant potential for reducing the amount of raw material required, both through optimisation for lightweight design and reduced waste during manufacture. The material inputs could also come directly from recycling end-of-life aerospace parts materials, further reducing the need for raw material input. Certification of components manufactured, repaired or remanufactured through an additive process presents challenges – but this has been noted, and they’re already being addressed and overcome.

Design for recycling

When it comes to aerospace material recycling, a big challenge comes from quality requirements. To fix this, the quality and cost of recycled materials could be improved significantly through ‘design for recycling’, which would entail a greater concentration on feature details and assemblies that allow easy dismantling, and making use of materials that can be recycled more easily. Improved material separation technologies are also important and metal additive processes can more readily accept the powdered or wire forms recycled metal is typically available in, which themselves are less prone to quality problems.

While recycling metal alloys presents a difficult recycling situation, reinforced plastic composite materials are a larger obstacle. These form a large proportion of aircraft structures and are likely to be increasingly necessary as greater weight savings in the aircraft of the future are required. Although trickier, there are processes and techniques for recycling these materials. Thermoset resin composites are typically recycled by removing the resin through pyrolysis and recovering fibres. The fibres can then be made into chopped matting or used as short reinforcing fibres within plastics. These materials are not as strong and stiff, reducing their uses. But composite materials do benefit from high fatigue resistance, increasing reuse, remanufacture and repurpose opportunities for these components.

Finally, digital twins could be used as a means to track components through life, providing details on original material composition and usage. Hazardous materials could be tagged as such, to help minimise risk to process operators, while parts available for reuse could be identified quickly along with optimal repair, remanufacture and recycling pathways.

When circular strategies are available, aircraft and their components have an increased value at the end of their initial life. If current aircraft operator models are followed, this value is held by airlines and could support the purchase costs resulting from the development and implementation of this new approach. However, a circular economic approach also lends itself to an aircraft-as-a-service business model whereby the aircraft manufacturer retains ownership. They are then further incentivised to produce aircraft best suited to circular processes and further increase the end-of-life value ready for the next cycle. It also becomes much easier to identify parts for reuse and remanufacture, with recycling processes tailored to the specific materials used and developed to support recycling back into the aircraft production chain.

By developing and implementing circular economy strategies and processes, the energy required for production of aircraft can be massively reduced. The energy saving predominately comes from removing the need to extract raw materials from the earth. This is achieved by extending the life of aircraft and their constituent components through a hierarchy of reuse, repair, remanufacture and recycling processes. By reducing the energy required for aircraft production, the CO₂ output is proportionately reduced and more of the remaining energy input can be sourced from renewables, supporting the global imperative to achieve Net Zero.

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