SOCIETAL BENEFITS OF PLASTICS - Plastics and Environmental Sustainability - page 182

Table 5.1 Density, Modulus, and Strength of Materials Used in
Automobiles
Source: Based on Cheah (2010).
Material Density

(g/cm 3 )

Modulus
(GPa)

Tensile
strength
(MPa)

Embodied
energy (MJ/kg)

Mild steel 7.86 200 300 32

High-strength
steel

7.87 205 483 32

Aluminum 2.71 70 295 199

Magnesium 1.77 45 228 350

75 GRC a Polymer

composite

1.57 190 810

150 CRC b

a Glass-reinforced composite.

b Carbon-fiber-reinforced composite.

In a recent study, the steel assist step in Chevrolet TrailBlazer/GMC Envoy
was replaced by a functionally equivalent (slightly larger) but 51% lighter
plasticone(PEInternationalInc.,2012).Theimpactofthissubstitutionwas
studied over the vehicle lifetime using standard LCA methods. This single
replacement is estimated to have saved 2.7 million gallons of fuel over the
lifetimes of the full fleet of the 148,658 (2007 model year) vehicles. Fuel
savings also result in avoided emission of carbon into the atmosphere. All
environmental attributes did not improve as a result of the change: the
acidification potential was higher for the plastic part compared to the metal
step. Cost savings from the substitution of metals are readily apparent when
commercial fleets of vehicles are considered. In a redesigned prototype
delivery truck for a courier service, 4 the aluminum body panels were
replaced with ABS plastic panels. Fuel economy gained from this change
was shown to be about 40%. The savings in energy and emission accrued
on switching to the lighter functionally comparable panel is obviously very
significant.

National Highways Traffic Safety Administration (NHTSA) reported an
interesting study (NHTSA, 2012) on material substitution from steel to