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Unit 8. Eco-selection: environmentally informed material choice. Outline. Material consumption and the material life-cycle. LCA, problems and solutions. Analysis of products. Strategy for materials selection. Exercises. More info:

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Unit 8. Eco-selection: environmentally informed material choice

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Unit 8 eco selection environmentally informed material choice
Unit 8. Eco-selection:environmentally informed material choice


  • Material consumption and the material life-cycle

  • LCA, problems and solutions

  • Analysis of products

  • Strategy for materials selection

  • Exercises

More info:

  • “Materials: engineering, science, processing and design”, Chapter 20

  • “Materials Selection in Mechanical Design”, Chapter 16

Material production
Material production

Natural fibers: cotton, silk, wool, jute

Man-made fibers: polyester, nylon, acrylic, cellulosics

Life cycle assessment lca

  • Typical LCA output:

  • Resource consumption

  • Energy consumption over life

  • Water consumption

  • Emission of CO2, NOx, SOx etc

  • Particulates

  • Toxic residues

  • Acidification..Ozone depletion..

Roll up into an

Eco-indicator ?

Life cycle assessment (LCA)



  • Full LCA time consuming, expensive, and requires great detail – and even then is subject to uncertainty

  • What is a designer supposed to do with these numbers?

  • LCA is a product assessment tool, not a design tool

Lca in the context of design

Market need

Problem statement


The need


Strategic tools

to guide design


Product specification

Full LCA



A product-assessment tool

LCA in the context of design

Strategies for guiding design

Increasing detail, cost and time









Minutes Hours Days Months

Strategies for guiding design

  • Step 1: Seek method that combines acceptable cost burden with adequate accuracy to guide decision making – a design tool

  • Step 2: Seek single measure of stress

  • – energy or CO2

  • Step 3: Separate life-phases

Strategies for guiding design 2

Appliances: use-energy cited

Official fuel economy figures:

Combined: 6 – 11 litre / 100km

CO2 emissions: 158 – 276 g / km

Efficiency rating: A

Volume0.3 m3

330 kWhr / year

Strategies for guiding design (2)

  • Why energy or CO2?

  • Kyoto Protocol (1997):international agreement to reduce greenhouse gasses

  • EU directives such as the EuP directive (2006)

  • Practicality:CO2andEnergy are related and understood by the public

Big picture energy consumption of products
Big picture: energy consumption of products

Which phase dominates? Approximate breakdown (Bey, 2000., Allwood, 2006):

Eco scoping

Glass PE PET Aluminum Steel


  • What should strategic tools do?

  • Example: drink containers

  • Aims:  to assess energy or CO2 burden quickly and cheaply

  •  to explore alternatives

Eco scoping1

PET bottle Aluminum Steel


  • Separate the phases of life

1. Material production: the embodied energy

2. Bottle manufacture: the processing energy

3. Delivery and use: transport and refrigeration

4. Disposal: collection, recycling, energy recovery

  • To assess, need both local and generic data.

What is embodied energy

Generic data Aluminum Steel

  • Material energy MJ / kg

  • Database of embodied energies for materials

  • Process energy MJ / kg

  • Database of processing energies for materials

What is embodied energy?

  • Transport, MJ / tonne.km

  • Sea freight 0.11 – 0.15

  • Barge (river) 0.75 – 0.85

  • Rail freight 0.80 – 0.9

  • Truck 0.9 – 1.5

  • Air freight 8.3 – 15

Use delivery and refrigeration and disposal

Generic data Aluminum Steel

  • Transport, MJ / tonne.km

  • As before

Use (delivery and refrigeration) and disposal

1. Material production: the embodied energy

2. Bottle manufacture: the processing energy

3. Delivery and use: transport and refrigeration

4. Disposal: collection, recycling, energy recovery

  • Refrigeration, MJ/m3.day

  • Refrigeration (4oC)10.5

  • Freezing (- 5oC) 13.0

Drink container the scoping tool

RETRIEVE from database Aluminum Steel

INPUTS by user

  • Material energy MJ / kg

  • Embodied energy, PET 85

  • Energy to blow mould 11

  • Manufacture

  • PET body moulded 38 g

  • PP cap moulded 5 g

  • Use

  • Refrigeration 5 days

  • Transport 200 km

  • Disposal

  • Recycling ? Yes

  • Transport 15,000 km

  • Materials

  • PET body 38 g

  • PP cap 5 g

Drink container: the scoping tool

  • Transport, MJ / tonne.km

  • Sea freight0.11

  • Truck1.3

  • Refrigeration, MJ / m3.day

  • Refrigeration (4oC)10.5

  • Freezing (-5oC) 13.0

Ces edu record for pet

Eco-properties: production Aluminum Steel

Production energy77-85 MJ/kg

Carbon dioxide1.9 -2.2kg/kg

Recycle ?

Eco-properties: manufacture

Injection / blow moulding 12 - 15 MJ/kg

Polymer extrusion 3 - 5 MJ/kg

Environmental notes. PE is FDA compliant - it is so non-toxic that it can be embedded in the human body (heart valves, hip-joint cups, artificial artery).

CES Edu record for PET

Polyethylene terephthalate (PET)

  • General Properties

  • Density939-960kg/m3

  • Price1.3-1.45US $/kg

  • Mechanical Properties

  • Young's Modulus0.6-0.9GPa

  • Elastic Limit17.9-29MPa

  • Tensile Strength20-45MPa

  • Elongation200-800%

  • Hardness - Vickers5.4-8.7 HV

  • Fracture Toughness1.4-1.7MPa.m1/2

  • Thermal Properties

  • Max Service Temp100- 120C

  • Thermal Expansion126- 19810-6/K

  • Specific Heat1810- 1880J/kg.K

  • Thermal Conductivity0.4- 0.44W/m.K

  • Electrical Properties

  • Resistivity3 x 1022-3 x 1024.cm

  • Dielectric constant2.2-2.4

Energy/CO2 efficient design

Thermo-mechanical design

Energy breakdown for pet bottle

Material Aluminum Steel

Energy breakdown for PET bottle

Applying the strategy

2. Strategy Aluminum Steel





  • Select:

  • recyclable

  • non- toxic


  • Minimize:

  • process energy

  • CO2/kg

  • Minimize:

  • weight

  • heat loss

  • electrical loss

  • system

  • Minimize:

  • embodied energy

  • CO2/ kg

Applying the strategy

1. Analysis

Assess energy

use over life






Embodied energy of materials per kg

Hybrids Aluminum Steel

Embodied energy of materials per kg

CES Edu Level 2 DB

Embodied energy of materials per m 3

Hybrids Aluminum Steel

Embodied energy of materials per m3

CES Edu Level 2 DB

Embodied energy per unit of function

Glass PE PET Aluminum Steel

Embodied energy per unit of function

Function: contain 1 litre of fluid

Mass 325 38 25 20 45 g

Mass/litre 433 38 62 45 102 g/litre

Emb. energy14 80 84 200 23 MJ/kg

Energy/litre 8.2 3.2 5.4 9.0 2.4MJ/litre

  • Steelwins on material embodied energy

  • Processing?

  • Recycling?

  • Toxicity?

Material choice depends on function and system

Mobile barrier Aluminum Steel

Static barrier


M Mf U D

M Mf U D

Bending strength

per unit material energy


Material choice depends on function and system

Function Absorb impact, transmit load to energy-absorbing units or supports


phase of life

Bending strength

per unit mass

Selected materials

CFRP, Ti-alloy, Al-alloy

Cast iron, steel

Concept embodiment detail

Supercars Aluminum Steel




Concept, embodiment, detail

The main points
The main points Aluminum Steel

  • Scoping LCA gives quick, approximate “portrait” of energy / CO2burden of products. A practical tool for assessing eco-burden and guiding (re)-design.

  • Separate the life-phases

    • Material

    • Manufacture

    • Use

    • Disposal

Base material choice on relative contributions to stress

  • Consider system dependence

    • Optimise within one concept

    • Explore alternative concepts

The CES EduPack provides data to help with this

Unit 8 eco selection environmentally informed material choice
Demo Aluminum Steel

Exercises eco comparisons 1
Exercises: Eco-comparisons (1) Aluminum Steel

  • 8.1 Rank the commodity materials

  • Low carbon steel

  • Age hardeing aluminum alloys

  • Polyethylene

  • by embodied energy/kg and embodied energy/m3. Use the means of the ranges given in the database.

  • (Energy per unit volume is that per unit weight multiplied by the density)



Density 939 – 960 kg/m3

Embodied energy 76.9 – 85 MJ/kg

The Al alloy has the highest energy content, by far, by both measures. Per kg, steel has the lowest energy content; by volume, it is polyethylene.

Exercises eco comparisons 2
Exercises: Eco-comparisons (2) Aluminum Steel

8.2.Plot a bar chart for the embodied energies of metals and compare it with one for polymers, on a a “per unit yield strength” basis. Use the “Advanced” facility to make the function

Which materials are attractive by this measure?


The most attractive, from an embodied energy per unit strength perspective are carbon steels and cast irons. Among polymers, biopolymers like Polylactide (PLA) and starch based polymers perform well.

Exercise the nature of embodied energy
Exercise: the nature of embodied energy Aluminum Steel

8.3Iron is made by the reduction of iron oxide, Fe2O3, with carbon, aluminum by the electro-chemical reduction of Bauxite, basically Al2O3. The enthalpy of oxidation of iron to its oxide is 5.5 MJ/kg, that of aluminum to its oxide is 16.5 MJ/kg.

Compare these with the embodied energies of cast iron, of carbon steel, and of aluminum, retrieved from the CES database (use means of the ranges given there).

What conclusions do you draw?

Cast iron, grey

Embodied energy 16.4 – 18.2 MJ/kg

The embodied energies are between 3 and 12 times larger than the thermodynamically necessary to reduce the oxide to the metal. There are several reasons. The largest is that industrial processes, at best, achieve an energy-efficiency of around 33% (the blast furnace, used to make iron, is remarkably efficient). Then there is transport, the energy to run, heat, light and maintain the plant in which the metal is made, and many other small contributions to the total energy input per unit of output.

Aluminum alloys

Embodied energy 184 – 203 MJ/kg

End of unit 8
End of Unit 8 Aluminum Steel

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