Stress and pressure

The SI unit of stress and pressure is the N/m2 or the Pascal (Pa), but from a materials point of view it is very small. The levels of stress large enough to distort or deform materials are measured in megaPascals (MPa). The table list the conversion factors relating MPa to measures of stress used in the older cgs and metric systems (dyne/cm2, kgf/mm2) by the Imperial system (lb/in2, ton/in2) and by atmospheric science (bar).

Conversion of units – stress and pressure

To ^






long ton/in2

From j

Multiply by




1.45 X 102



6.48 X 10~2




1.45 X 10-5

1.02 X 10-8


6.48 X 10-9


6.89 X 10-3

6.89 X 104


7.03 X 1Q-4

6.89 X 10-2

4.46 X 10“4



9.81 X 107

1.42 X 103



63.5 X 10~2





1.02 X 10~2


6.48 X 10~3

long ton/ in2


1.54 X 108

2.24 X 103


1.54 X 102


A.5 Energy and power

The SI units of energy is the Joule (J), that of energy the Watt (W = 1 J/ sec), or multiples of them like MJ or kW. If energy and power were always listed in these units, life would be simple, but they are not. First there are Imperial units Btu, ft. lbf, and ft. lbf/s. Then there are units of convenience: kWhr for electric power, hp for mechanical power. There are the units of the oil industry: barrels (7.33 barrels = 1 tonne, 1000 kg) and toe (tonnes of oil equivalent – the weight of oil with the same energy content). Switching between these units is simply a case of multiplying by the conversion fac­tors listed below.

Conversion of units – energy*

To ^





ft lbf


From 4

Multiply by






0.738 X 106

23.8 X 10~6





3.41 X 103

2.66 X 106

85.7 X 10~6


4.18 X 10-3

1.16 X 10~3



3.09 X 103

99.5 X 10~9


1.06 X 10-3

0.293 X 10-3



0.778 X 103

25.2 X 10-9

ft Ibf

1.36 X 10~6

0.378 X 10~6

0.324 X 10-3

1.29 X 10-3


32.4 X 10-12


41.9 X 103

11.6 X 103

10 X 106

39.7 X 106

30.8 X 109


MJ = megajoules; kWhr = kilowatt hour; kcal = kilocalorie; Btu = British thermal unit; ft Ibf = foot-pound force; toe = tonnes oil equivalent.

Conversion of units – power


To ^

kW (kJ/s)



ft lbf/s

From 4

Multiply by

kW (kJ/s)















ft lbf/s

1.36 X 10-3

5.68 X 10-3

1.82 X 10-3


kW = kilowatt; kcal/s = kilocalories per second; hp = horse power; ft lb/s = foot-pounds/second

A.6 Fuels

The energy content and CO2 emission of fossil fuels are listed in Table 6.5 of Chapter 6. Here we list alternative measures of quantity for oil and gas. Coal is always quantified in tonnes or short tons.

Measures of quantity

Crude oil

Natural gas

1 barrel = 35 Imperial gallons

1 billion m3 (109 m3) =

35.5 X 109 ft3

= 42 US gallons


6.29 X 106 boe*

= 159 liters


0.9 X 106 toe**

«135 kg


0.73 X 106 tonnes LNG***

‘boe = barrel of oil equivalent; "toe

= tonne of oil equivalent; ‘‘‘LNG =

liquid natural gas.

A.7 Energy prices (2007 data)

Energy prices fluctuate. All, ultimately, are tied to the price of oil, which in 2007 was $60 per barrel.

Approximate energy prices,

2007 data

Energy form

Price, usual units

Price per MJ

Electricity, industrial

$ 0.06/kWhr

$ 0.017/MJ

Electricity, grid

$ 0.11/kWhr

$ 0.031/MJ

Heavy fuel oil

$ 335/tonne

$ 0.0073/MJ

Industrial gas

$ 282/107 kilocals

$ 0.0067/MJ


$ 40/tonne

$ 0.0025

[1]Ashby, M. F., Materials selection in mechanical design, 3rd ed., Chapter 4, Butterworth Heinemann, 2005, ISBN 0-7506-6168-2. (A more advanced text that develops the ideas presented here in greater depth.)

[2]Ashby, M. F., and K. Johnson, Materials and design: the art and science of material selection in product design, Butterworth Heinemann, 2002, ISBN 0-7506-5554-2. (Materials and processes from and aesthetic point of view, emphasizing product design.)

[3] Eutrophication is the over-enrichment of a body of water with nutrients—phosphates, nitrates—resulting in excessive growth of organisms and depletion of oxygen concentration.

[4]Details can be found in EPS (1993), Idemat (1997), EDIP (1998), and Wenzel et al. (1997) Eco-indicator (1999).

[5] Graedel (1998); Todd and Curran (1999). See Further reading at the end of the chapter.

[6] Graedel lists an extensive protocol in the appendix to the book listed under Further reading.

[7]The Kyoto Protocol of 1997 and subsequent treaties and protocols, detailed in Chapter 5.

[8]Throughout this book carbon release to the atmosphere is measured in kg of CO2. One kg of elemental carbon is equivalent to 3.6 kg of CO2.

[9]The data sheets are a subset of those contained in the CES (2009) software, which also implements both the tools described here.

[10]Pre Consultants estimate that the time needed to perform a “screening” LCA is about eight days and for a full LCA is about 22 days.

[11] This list is a slightly extended version of one presented by D. G. Woodward, Life-cycle costing, Int. J. Project Management, 1997, Vol. 15, 335-344.

[12] What most of us see as waste can become the material of invention to the artist. For remarkable examples of this idea, visit the Musee International des Arts Modestes, 23 quai du Marechal de Lattre de Tassigny, 34200 Sete, France (www. miam. org).

[13] I remember a sign above a store in an English town: "we buy junk. We sell antiques.”

[14] See, for instance, The Packaging Federation, www. packagingfedn. co. uk, or the Flexible Packaging Association, www. flexpack. org.

[15] For an organization with such an ideal, see www. eternally-yours. nl.

[16] Detailed in books on industrial ecology such as Ayres and Ayres (2002); see Further Reading.

[17] A protocol is defined as "a memorandum of resolutions arrived at in negotiation, signed by the negotiators, as a basis for a final convention or treaty.” In fact, the Kyoto Protocol is more than that, being a binding treaty to meet certain agreed objectives. The distinction between the Protocol and the Convention, in current usage, is that though the Convention encourages countries to stabilize emissions, the Protocol commits them to do so.

[18] See www. uk/iso-14040 for a summary.

[19]For the more intimate details, see www. environdec. com

[20]U. K. Department for Environment, Food, and Rural Affairs (DEFRA), www. defra. gov. uk/ environment/index. html.

[21]"Nothing is certain but death and taxes”—that was Benjamin Franklin writing 250 years ago.

[22]See www. emitconsortium. com for an example.

throughout this book, atmospheric carbon is measured as CO2 One kg of elemental carbon is equivalent to 3.6 kg of CO2.

[24] Logarithmic means that the scale goes up in constant multiples, usually of 10. We live in a logarithmic world; our senses, for instance, all respond in that way.

[25] Further descriptions and a wide range of charts can be found in Ashby (2005) and Ashby et al. (2006).

[26] Materials. A bill of materials is drawn up, listing the mass of each component used in the product and the material of which it is made, as on the left of Table 7.1. Data for the embodied energy (MJ/kg) and CO2 (kg/kg) per unit mass for each material are

[27]Elsam Engineering A/S, Life-cycle assessment of offshore and onshore sited wind farms, October 2004. This document lists the quantities of the more significant materials and the weight of each subsystem. The nacelle itself is made up of a number of smaller parts, some of which are difficult to assess due to the limited information contained in the report.

[28]Nordex N90 Technical Description, Nordex Energy GmbH, April 2004.

[29]Vestas, Life-cycle assessment of offshore and onshore sited wind turbines, Vestas Wind Systems A/S, 2005, www. vestas. com.

[30]Wind Energy Weekly, Vol. 18, Number 851, June 1999.

[31]A study of Danish wind turbines located in particularly favorable sites found a capacity factor of 54%, but this is unusual. A value of 25% is more realistic.

[32]The CES Eco Audit tool is a standard part of the CES Edu Package developed by Granta

Design, Cambridge, U. K., www. GrantaDesign. com.

[34] Also called a value function or utility function. The method allows a local minimum to be found. When the search space is large, it is necessary to recognize that the values of the exchange constants a,■ may themselves depend on the values of the performance metrics Pi

[35] Very low-density foams and gels (which can be thought of as molecular-scale, fluid-filled

foams) can have lower moduli than this. For example, gelatin (as in Jell-O) has a modulus of

about 10~5 GPa.

[38] The CES material selection software is a product of Granta Design, Cambridge, U. K. (www. grantadesign. com).

[39] The annual GDP is an indicator used to gauge the health of a country’s economy. It is the total value of all goods and services produced over a given year. Think of it as the size of the economy. GDP per capita is a measure of average individual income.

[40] Frosch and Gallopoulos, 1989; Regge and Pallante, 1996, cited by Guidice et al., 2006.

[41] 1 kW. hr = 3.6 MJ; thus 1 GJ/year per person = 3,600 kW. hr/year per person. 1 kW. hr per day = 0.042 kW.

[42] Weighted average of six metals and six nonmetallic commodities. Source: market indicators, Economist, Jan. 15, 2000, cited by Lomberg, 2001.

[43] Source: annual energy reviews of the Energy Information Agency (EIA) of the U. S. Department of Energy (www. eia. doe. gov).

[44] GDP per capita in constant 2000$, replotted from data assembled by Lomberg (2001).

[45] Correcting for inflation is not simple. For conversion factors, see www. measuringworth. com.

[46] The HDI is a compound index that combines provision of education, level of health care, opportunity for individual development, and personal freedom.

[47] For full documentation and analysis of the facts listed in this section, see the book by Nielsen (2005) and the IPCC (2007) report listed under Further Reading.

[48]See, for example, the provocative but well-researched book by Lomberg (2001).

[49]See, for example, Hardin (1968).

[50]The geometric mean of two numbers Xand Yis [XY.