Solution manual for exercises - MAELabs UCSD

E8.13. Use the chart E − H m ρ chart of Figure 8.13 to find the metal with a modulus E greater than
100 GPa and the lowest embodied energy per unit volume.
Answer. The construction is shown below. The metal with a modulus greater than 100 GPa and the
lowest embodied energy is cast iron.
The Modulus – Embodied energy chart: the one for stiffness at minimum embodied energy.
8.14. A maker of polypropylene (PP) garden furniture is concerned that the competition is stealing part
of his market by claiming that the “traditional” material for garden furniture, cast iron, is much less
energy and CO2 intensive than the PP. A typical PP chair weighs 1.6 kg; one made of cast iron weighs
11 kg. Use the data sheets for these two materials in Chapter 12 of the book to find out who is right –
are the differences significant? (Remember the warning about precision at the start of Chapter 12).
If the PP chair lasts 5 years and the cast iron chair lasts 25 years, does the conclusion change?
Answer. The table lists mean values of embodied energy and carbon footprint, per kg, for the two
materials. The last two columns show the values per chair. If the difference in lifetime is ignored, the
two chairs do not differ significantly in embodied energy, but they do in carbon release. If the longer
life of the cast iron chair is recognized by dividing the values by the life in years (to give energy and
carbon per chair.year) the cast iron chair wins easily.
Material Embodied energy*
MJ/kg
CO 2 *
kg/kg
Embodied energy
MJ/chair
Eco text: solution manual 47 MFA, 08/12/2008
CO 2
kg/chair
Cast iron 17 1.05 187 11.6
Polypropylene 103 2.7 165 4.32
* From the data sheets of Chapter12.
Lower embodied
energy
Modulus
E = 100 GPa