Transcript New approaches in Materials and Manufacturing Education

Unit 8. Eco-selection:
environmentally informed
material choice
New approaches to Materials Education - a course authored by
Mike Ashby and David Cebon, Cambridge, UK, 2007
© MFA and DC 2007
Outline

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
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Material production
Natural fibers: cotton, silk, wool, jute
Man-made fibers: polyester, nylon, acrylic, cellulosics
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The product life-cycle
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Life cycle assessment (LCA)
Typical LCA output:
•
•
•
•
•
•
•
Resource consumption
Environmental
“stressors”
Energy consumption over life
Water consumption
Emission of CO2, NOx, SOx etc
Roll up into an
Eco-indicator ?
Particulates
Toxic residues
Acidification..Ozone depletion..
Full LCA time consuming, expensive, and requires great detail –
and even then is subject to uncertainty
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What is a designer supposed to do with these numbers?
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LCA is a product assessment tool, not a design tool
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LCA in the context of design
Market need
Problem statement
The need
Strategic tools
to guide design
Concept
Embodiment
Detail
Product specification
Manufacture,
distribution
Full LCA
A product-assessment tool
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Strategies for guiding design

Step 1: Seek method that combines acceptable cost burden with
adequate accuracy to guide decision making – a design tool
Increasing
Ecoscreening
Minutes
detail,
cost
and
time
Scoping
LCA
Streamline
LCA
Hours
Days
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Step 2: Seek single measure of stress
– energy or CO2
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Step 3: Separate life-phases
Complete
LCA
Months
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Strategies for guiding design (2)
 Why energy or CO2?
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Kyoto Protocol (1997): international agreement to reduce greenhouse gasses
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EU directives such as the EuP directive (2006)
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Practicality: CO2 and Energy are related and understood by the public

Cars: use-energy and CO2 cited
Appliances: use-energy cited
Official fuel economy figures:
Efficiency rating: A
Combined: 6 – 11 litre / 100km
Volume
CO2 emissions: 158 – 276 g / km
330 kWhr / year
0.3 m3
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Big picture: energy consumption of products
Which phase dominates?
Approximate breakdown (Bey, 2000., Allwood, 2006):
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Eco-scoping
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What should strategic tools do?
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Example: drink containers
Glass
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PE
PET
Aluminum
Steel
Aims:  to assess energy or CO2 burden quickly and cheaply
 to explore alternatives
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Eco-scoping

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
PET bottle

To assess, need both local and generic data.
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What is embodied energy?
Generic data
Material energy MJ / kg
 Database of embodied
energies for materials
Process energy MJ / kg
 Database of processing
energies for materials
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
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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
Generic data
Transport, MJ / tonne.km
 As before
Refrigeration, MJ/m3.day
 Refrigeration (4oC) 10.5
 Freezing (- 5oC)
13.0
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Disposal: recycling – the problems
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Recycle fractions for commodity materials
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Drink container: the scoping tool
INPUTS by user
Materials
 PET body
 PP cap
RETRIEVE from database
Material energy MJ / kg
38 g
5g
 Embodied energy, PET 85
 Energy to blow mould
11
Manufacture
 PET body moulded 38 g
 PP cap moulded
5g
Use
 Refrigeration
 Transport
 Sea freight
0.11
 Truck
1.3
5 days
200 km
Refrigeration, MJ / m3.day
Disposal
 Recycling ?
 Transport
Transport, MJ / tonne.km
Yes
15,000 km
 Refrigeration (4oC) 10.5
 Freezing (-5oC)
13.0
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CES Edu record for PET
Polyethylene terephthalate (PET)
General Properties
Density
Price
939 1.3 -
960 kg/m3
1.45 US $/kg
Mechanical Properties
Young's Modulus
Elastic Limit
Tensile Strength
Elongation
Hardness - Vickers
Fracture Toughness
0.6
17.9
20
200
5.4
1.4
-
0.9
29
45
800
8.7
1.7
GPa
MPa
MPa
%
HV
MPa.m1/2
Thermal Properties
Max Service Temp
100
Thermal Expansion 126
Specific Heat
1810
Thermal Conductivity 0.4
-
120
198
1880
0.44
C
10-6/K
J/kg.K
W/m.K
Electrical Properties
Resistivity
Dielectric constant
3x
2.2
Eco-properties: production
Production energy
Carbon dioxide
77 1.9 -
Recycle ?

85 MJ/kg
2.2 kg/kg
Eco-properties: manufacture
Injection / blow moulding 12 - 15 MJ/kg
Polymer extrusion
3 - 5 MJ/kg
Environmental notes. PE is FDA compliant - it is
1022-
3x
2.4
1024
Thermo-mechanical design
.cm
so non-toxic that it can be embedded in the human
body (heart valves, hip-joint cups, artificial artery).
Energy/CO2 efficient design
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Energy breakdown for PET bottle
Material
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Applying the strategy
1. Analysis
Assess energy
use over life
Manufacture
Use
Disposal
Energy
Production
2. Strategy
Material
Minimize:
• embodied energy
• CO2 / kg
Manufacture
Minimize:
• process energy
• CO2/kg
Disposal
Use
Minimize:
• weight
• heat loss
• electrical loss
• system
Select:
•
•
recyclable
non- toxic
materials
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Embodied energy of materials per kg
CES Edu Level 2 DB
Hybrids
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Embodied energy of materials per m3
CES Edu Level 2 DB
Hybrids
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Embodied energy per unit of function
Function: contain 1 litre of fluid
Glass
PE
PET
Aluminum
Steel
Mass
325
38
25
20
45
g
Mass/litre
433
38
62
45
102
g/litre
Emb. energy
14
80
84
200
23
MJ/kg
Energy/litre
8.2
2.4
MJ/litre
3.2
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5.4
9.0
Steel wins on material embodied energy
Processing?
Recycling?
Toxicity?
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Material choice depends on function and system
Mobile barrier
Static barrier
Dominant
phase of life
Absorb impact, transmit load to energy-absorbing units or supports
Energy
Function
M Mf U
Criterion
Selected
materials
D
Bending strength
per unit material energy
Cast iron, steel
M Mf U
D
Bending strength
per unit mass
CFRP, Ti-alloy, Al-alloy
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Concept, embodiment, detail
Supercars
Petrol
Diesel
Hybrid
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The main points
Scoping LCA gives quick, approximate “portrait” of energy / CO2 burden 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
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Demo
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Exercises: Eco-comparisons (1)
File
8.1 Rank the commodity materials
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Low carbon steel
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Age hardeing aluminum alloys
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Polyethylene
View
Browse
Select
Select
Tools
Search
Table:
Table: MaterialUniverse
MaterialUniverse
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)
Subset:
Subset: Edu
Edu Level
Level 22
MaterialUniverse
Answer
Material
Edit
+
Ceramics and glasses
+
Hybrids: composites etc
+
Metals and alloys
+
Polymers and elastomers
Embodied
energy MJ/kg
Density
kg/m3
Embodied
energy GJ/m3
Low carbon steel
23.6
7850
185
Age hardening Al alloy
194
2700
523
Density
Polyethylene
83
950
79
Embodied energy 76.9 – 85 MJ/kg
Polyethylene
939 – 960 kg/m3
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.
© MFA and DC 2007
Exercises: Eco-comparisons (2)
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
Energy per unit strength 
Browse
Emodied energy x Density
Search
1. Selection data
Yield strength
Edu
Edu Level
Level2:
2: Materials
Materials
Which materials are attractive by this measure?
2. Selection Stages
Answer.
[Embodied energy] * [Density] / [Yield strength]
Select
Graph
Limit
Tree
100000
Lead
Titanium
Copper
Al-alloys
Nickel
PTFE
Embodied energy*
Density / Yield strength
Ionomers
Mg alloys
Polyurethane
PS
10000
Bronze Brass
PC
PP
Zinc alloys
PET
Nylon
PE
1000
Epoxies
Starch-based thermoplastics
Low carbon steel
Medium carbon steel
Cast iron, ductile (nodular)
Polylactide (PLA)
Low alloy steel
High carbon steel
MaterialUniverse:\Metals and alloys
MaterialUniverse:\Polymers and elastomers
Material class
+
-
/
*
^ (
)
List of properties
 Density
 Modulus
 Yield strength
 Embodied energy
 etc
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.
© MFA and DC 2007
Exercise: the nature of embodied energy
File
8.3 Iron 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?
Material
Enthalpy of
oxidation MJ/kg
Embodied
energy MJ/kg
Cast iron
5.5
17.1
Carbon steel
5.5
23.6
Aluminum
16.5
194
Edit
View
Browse
Select
Select
Tools
Search
Table:
Table: MaterialUniverse
MaterialUniverse
Subset:
Subset: Edu
Edu Level
Level 22
MaterialUniverse
+
Ceramics and glasses
+
Hybrids: composites etc
+
Metals and alloys
+
Polymers and elastomers
Cast iron, grey
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.
Embodied energy 16.4 – 18.2 MJ/kg
Aluminum alloys
Embodied energy 184 – 203 MJ/kg
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End of Unit 8
© MFA and DC 2007