Life Cycle Impact of Different Joining Decisions on Vehicle Recycling

Abstract

Stricter vehicle emission legislation has driven significant reduction in environmental impact of the vehicle use phase through increasing use of lightweight materials and multi-material concepts to reduce the vehicle mass. The joining techniques used for joining multi-material designs has led to reduction in efficiency of the current shredder-based recycling practices. This thesis quantifies this reduction in efficiency using data captured from industrial recycling trials. Life Cycle Assessment has been widely used to assess the environmental impact throughout the vehicle life cycle stages. Although there is significant research on material selection or substitution to improve the vehicle’s carbon footprint, the correlation between multi-material vehicle designs and the material separation through commonly used shredding process is not well captured in the current analysis. This thesis addresses this gap using data captured from industrial trials to measure the influence of different joining techniques on material recycling efficiencies. The effects of material degradation due to joining choices are examined using the life cycle analysis including exergy losses to account for a closed-loop system. The System Dynamics approach is then performed to demonstrate the dynamic life cycle impact of joining choices used for new multi-material vehicle designs. Observations from the case studies conducted in Australia and Europe showed that mechanical fasteners, particularly machine screws, are increasingly used to join different material types and are less likely to be perfectly liberated during the shredding process. The characteristics of joints, such as joint strength, material type, size, diameter, location, temperature resistance, protrusion level, and surface smoothness, have an influence on the material liberation in the current sorting practices. Additionally, the liberation of joints is also affected by the density and thickness of materials being joined. The life cycle analysis including exergy losses shows a significant environmental burden caused by the amount of impurities and valuable material losses due to unliberated joints. By measuring the influence of joints quantitatively, this work has looked at the potential of improving the quality of materials recycled from ELV to be reused in a closed-loop system. The dynamic behaviours between the joining choices and their delayed influence on material recycling efficiencies from the life cycle perspective are performed using the data from case studies. It shows that the short-term reduction in environmental impact through multi-material structures is offset over the long-term by the increasing impurities and valuable material losses due to unliberated joints. The different vehicle recycling systems can then be resembled using two widely known system archetypes: “Fixes that Fail” and “Shifting the Burden”. Despite the adoption of more rigorous recycling approaches, the life cycle impact of different joining techniques on vehicle recycling continue to exist. The enactment of strict regulations in current ELV recycling systems is unable to solve the underlying ELV waste problem, and only prolongs the delay in material degradation due to joining choices. This work shows that the choice of joining techniques used for multi-material vehicle designs has a significant impact on the environmental performance during the ELV recycling phase.