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Lightweight structures are increasingly necessary to meet current engineering requirements. Weight reduction in diverse applications such as automobiles or machine tools is achieved either by using less material or by substituting material with a lighter one, which provides more functionality per unit of weight. To be an effective enabler for sustainability, lightweight structures should result in lower environmental impacts per functional unit when compared to conventional structures on a life cycle basis. However, applying new materials and manufacturing processes often leads to an increase in environmental impacts from the raw materials and production stage of the life cycle. Furthermore, end-of-life disassembly and recycling may become more difficult. In addition, the expected efficiency gains from the use of lightweight structures depend on how the overall market and technical systems respond to them. Consequently, the environmental evaluation of lightweight structures in engineering entails various methodological challenges. Organised around a life cycle engineering framework with a focus on eco-effectiveness, this paper provides a comprehensive review of lightweight structure applications and the challenges and opportunities they present in a life cycle engineering context.

Making, driving, and disposing of U.S. light-duty vehicles (LDVs) account for 3% of global greenhouse gas emissions related to energy and processing. This study calculates future emissions and global temperature rises attributable to U.S. LDVs. We examine how 2021−2050 U.S. LDV cumulative emissions can be limited to 23.1 Gt CO 2equiv , helping to limit global warming to less than 2 °C. We vary four vehicle life cycle parameters (transport demand, sales share of alternative fuel vehicles, vehicle material recycling rates, and vehicle lifespans) in a dynamic fleet analysis to determine annual LDV sales, scrappage, and fleet compositions. We combine these data with vehicle technology and electricity emission scenarios to calculate annual production, use, and disposal emissions attributable to U.S. LDVs. Only 3% of the 1512 modeled pathways stay within the emission limit. Cumulative emissions are most sensitive to transport demand, and the speed of fleet electrification and electricity decarbonization. Increasing production of battery electric vehicles (BEVs) to 100% of sales by 2040 (at the latest) is necessary, and early retirement of internal combustion engine vehicles is beneficial. Rapid electricity decarbonization minimizes emissions from BEV use and increasingly energy-intensive vehicle production. Deploying high fuel economy vehicles can increase emissions from the production of BEV batteries and lightweight materials. Increased recycling has a small effect on these emissions because over the time period there are few postconsumer batteries and lightweight materials available for recycling. Without aggressive actions, U.S. LDVs will likely exceed the cumulative emissions budget by 2039 and contribute a further 0.02 °C to global warming by 2050, 2.7% of the remaining global 2 °C budget.

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