section epub:type=”chapter”> The status of steel as the raw material of choice for the manufacture of car bodies rests principally on its price. It has always been the cheapest material that meets the necessary strength, stiffness, formability, and weldability requirements of large-scale car body production. Until recently, the fact that steel has a density two-thirds that of lead accorded little significance. But increasing sustainability awareness and legislative requirements concerning carbon emissions are now changing that view. Car makers are looking hard at alternative materials. Energy is used to build a car and energy is used to run it. High oil prices mean that the cost of the gas consumed during the life of a car is comparable with the cost of the car itself. Consumers now want more fuel-efficient cars, and more fuel-efficient cars have lower carbon emissions. This chapter addresses these concerns. The chapter discusses various ways of achieving energy economy. The chapter also focuses on alternative materials that can be used, which is divided into primary mechanical properties and secondary properties. Although resistance to deflection and plastic yielding are obviously of first importance in choosing alternative materials, other properties too enter into the selection. The chapter concludes with a discussion of various production methods of cars. The status of steel as the raw material of choice for the manufacture of car bodies rests principally on its price. It has always been the cheapest material that meets the necessary strength, stiffness, formability, and weldability requirements of large-scale car body production. Until recently, the fact that steel has a density two-thirds that of lead was accorded little significance. But increasing sustainability awareness and legislative requirements concerning carbon emissions are now changing that view. Car makers are looking hard at alternative materials. Energy is used to build a car, and energy is used to run it. Oil prices mean that the cost of the gas consumed during the life of a car is comparable with the cost of the car itself. Consumers want more fuel-efficient cars, and more fuel-efficient cars have lower carbon emissions. This trend is magnified by the taxation policies of governments. Fuel duties have increased, so one way in which the motorist can offset the effects of additional fuel taxation is to reduce fuel consumption per mile. However, this strategy can be partly countered by imposing annual taxes on vehicles that relate to their carbon emissions. This acts as a driver to reduce engine power—effectively vehicle size. The extent to which governments really care about sustainability and carbon emissions—or are using these as a front for generating yet further taxation revenues—is open to question. But the way in which the economics are felt at consumer level is the same, and likely to get much worse in the longer term. It is clear from Table 33.1 that the energy content of the car itself—the steel, rubber, glass, and manufacturing process—is small: less than 10% that required to move the car. This means there is little point trying to save energy here; indeed (as we shall see) it may pay to use more energy to make the car (using, for instance, aluminum instead of steel) if this reduces fuel consumption. Table 33.1 We must focus, then, on reducing the energy used to move the car. The following are the two routes. We can reduce the size of cars, but the consumer does not like that. Or we can reduce the weight of the car by substituting lighter materials for those used now. Lighter cars not only use less fuel, but they also have lower carbon emissions—hence, the interest in producing lighter vehicles, reversing a consistent trend in the opposite direction. As Figure 33.1 suggests, most cars weigh between 400 kg and 2500 kg. In a typical modern production car (Figure 33.2), this is made up as shown in Table 33.2. Table 33.2 Candidate materials for substitutes must be lighter than steel, but structurally equivalent. For the engine block, the choice is obvious: aluminum (density 2.7 Mg m–3) or possibly magnesium (density 1.8 Mg m–3) replace an equal volume of cast iron (density 7.7 Mg m–3) with an immediate weight reduction on this component of 2.8 to 4.3 times. The production methods remain almost unchanged. Most manufacturers have made this change; cars like the one shown in Figure 33.3 are a thing of the past. The biggest potential weight saving, however, is in the body panels, which make up 60% of the weight of the vehicle. Here the choice is more difficult. Candidate materials are given in Table 33.3.
Final Case Study: Materials and Energy in Car Design
Publisher Summary
33.1 Introduction
33.2 Energy and Carbon Emissions
33.3 Achieving Energy Economy
Energy to produce cars, per year
=
0.8% to 1.5% of total energy consumed by nation
Energy to move cars, per year
=
15% of total energy consumed by nation
Transportation of people and goods, total
=
24% of total energy consumed by nation
33.4 Material Content of a Car
Material
Component
71% steel
Body shell; panels
15% cast iron
Engine block; gear box; rear axle
4% rubber
Tires; hoses
Balance
Glass, zinc, copper, aluminum, polymers
33.5 Alternative Materials
Primary mechanical properties
