E.8.15. Use a Limit stage to find materials with modulus E > 180 GPa and embodied energy Hm < 30 MJ. kg.
E.8.16. Use a Limit stage to find materials with yield strength ay > 100 MPa and a carbon footprint CO2 > 1 kg/kg.
E.8.17. Make a bar chart of embodied energy Hm. Add a tree stage to limit the selection to polymers alone. Which polymers have the lowest embodied energy?
E.8.18. Make a chart showing modules E and density p. Apply a selection line of slope 1, corresponding to the index p/E, positioning the line such that six materials are left above it. To what families do they belong?
E.8.19. A material is required for a tensile tie-rod to link the front and back walls of a barn to stabilize both. It must meet a constraint on strength and have as low an embodied energy as possible. To be safe, the material of the tie must have a fracture toughness K1c > 18 MPa. m172. The relevant index is
M = Hmp Ф ay
Construct a chart of ay plotted against Hm p. Add the constraint of adequate fracture toughness, meaning K1c > 18 MPa. m172, using a Limit stage. Then plot an appropriate selection line on the chart and report the three materials that are the best choices for the tie.
E.8.20. A company wants to enhance its image by replacing oil-based plastics in its products with polymers based on natural materials. Use the Search facility in CES to find biopolymers. List the materials you find. Are their embodied energies and CO2 footprints less than those of conventional plastics? Make bar charts of embodied energy and CO2 footprint to find out.
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