Materials challenges and opportunities for enhancing the sustainability of automobiles
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Materials challenges and opportunities for enhancing the sustainability of automobiles Gregory A. Keoleian and John L. Sullivan Materials play a major role in defining the sustainability performance of automobiles throughout their materials-production, manufacturing, use, and end-of-life stages. Materials production and manufacturing raise many sustainability issues, including resource scarcity and materials sourcing, energy and carbon intensity, and materials efficiency in parts fabrication. In the use stage, materials properties such as density and strength directly affect materialsmass requirements, which influence two dominant sustainability parameters for vehicles: fuel economy and service life. For conventional vehicles, the operation segment of the use stage accounts for about 85% of the total life-cycle energy consumption and greenhouse-gas emissions. Consequently, powertrain technologies and efficiencies as well as fuel-cycle processes control these impacts. Future trends in vehicle electrification will shift the magnitude and distribution of life-cycle impacts and the effectiveness of materials strategies for improving sustainability, such as lightweighting. In many cases, the materials-production stage could become a greater determinant in life-cycle impacts. With current vehicle end-of-life management infrastructure, 85% of materials are recyclable, but recovery of plastics and segregation of metal alloys represent opportunities for improvement. Life-cycle assessment and cost analysis provide the most comprehensive methods for evaluating the sustainability of materials strategies. Using a life-cycle framework, this article highlights the current and future materials challenges and opportunities driving vehicle sustainability performance.
Introduction Automobiles provide tremendous mobility to consumers and have added considerably to the standard of living in the developed world. On the other hand, vehicles are resource-intensive products that significantly impact the environment throughout their lifetime. Each year in the United States, cars and light-duty trucks collectively consume about 17.3 EJ of energy during operation, comprising ∼60% of U.S. transportation energy use and ∼17% of total U.S. energy consumption. As of 2009, 684 million cars were registered worldwide, with 19.4% (132 million) in the United States, even though the United States represents only 4.5% of the world’s population.1 Vehicle ownership in 2009 was 828 vehicles per thousand people in the United States compared to around 46 per thousand in China.1 As automobile use grows in developing countries, this will pose even greater sustainability challenges in terms of materials and energy resources, as well as environmental impacts. This article explores the role materials play in influencing the sustainability of automobiles from a life-cycle perspective.
The life-cycle assessment framework shown in Figure 1 provides a systematic method and set of metrics for analyzing the environmental sustainability performance of vehicles over their u
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