Metal Foams: A Design Guide

Cost estimation and viability 211
increased payload that this allows (Table 16.2). The value of heat transfer can
be derived from the value of the energy transmitted or saved by unit change in
the heat flux per unit area. Approximate exchange constants can sometimes be
derived from historical pricing data; thus the value of weight saving in bicycles
can be found by plotting the price Ł P of bicycles against their mass m, using
the slope dP/dm as a measure of ˛. Finally, exchange constants can be found
by interviewing techniques (Field and de Neufville, 1988; Clark et al., 1997),
which elicit the value to the consumer of a change in one performance metric,
all others held constant.
Table 16.2 Exchange constants ˛ for transport systems
Sector: Transport Basis of estimate Exchange constant
systems £/kg ($/lb)
Car, structural
components
Truck, structural
components
Civil aircraft,
structural
Military vehicle,
structural
Space vehicle,
structural
Bicycle, structural
components
Fuel saving 0.5 to 1.5 (0.4 to 1.1)
Payload, fuel saving 5 to 10 (4 to 8)
Payload 100 to 500 (75 to 300)
Payload, performance 500 to 1000 (350 to 750)
Payload 3000 to 10 000 (2000 to 75 000)
Perceived value
(derived from data for
price and mass of
bicycles)
80 to 1000 (50 to 700)
The values of ˛ in Table 16.2 describe simple trade-offs between cost and
performance. Circumstances can change these, sometimes dramatically. The
auto-maker whose vehicles fail to meet legislated requirements for fleet fuel
consumption will assign a higher value to weight saving than that shown in
Table 16.2; so, too, will the aero-engine maker who has contracted to sell an
engine with a given power-to-weight ratio if the engine is overweight. These
special cases are not uncommon, and can provide the first market opportunity
for a new material.
Ł For any successful product the cost, C, the price, P, and the value, V, are related by CVno one will buy it. Thus P can be viewed
as a lower limit for V.