Page 465 - Corrosion Engineering Principles and Practice

432 C h a p t e r 1 1 M a t e r i a l s S e l e c t i o n , Te s t i n g , a n d D e s i g n C o n s i d e r a t i o n s 433

In the Materials Selector software system developed following
Ashby’s principles, this is achieved by first screening and ranking the
candidates to give a shortlist, and then seeking detailed supporting
information for each short-listed candidate, allowing a final choice.
It is important to start with a full menu of materials in mind; failure
to do so may mean a missed opportunity. If an innovative choice is to
be made, it must be identified early in the design process. Later, too
many decisions have been taken and commitments made to allow
radical change: it is now or never.
The immensely wide choice is narrowed, first, by applying prop-
erty limits which screen out the materials which cannot meet the
design requirements. Further narrowing is achieved by ranking
the candidates by their ability to maximize performance. Perfor-
mance is generally limited not by a single property, but by a com-
bination of them. The results of a search with Materials Selector in
its supporting databases can be presented in a convenient selec-
tion chart such as shown in Fig. 11.1 for two basic mechanical
properties, that is, strength and Young’s modulus.
However, there is no obvious provision to include corrosion
resistance considerations in Ashby’s model. The main reason for this
may be that unlike other design considerations such as fatigue, designing
with corrosion in mind is far from being a straightforward process since
each form of corrosion is essentially a separate failure mode that needs

1000
Technical
ceramics
Metals
100 Non-technical
ceramics
Young’s modulus (GPa) 10 1 Foams Composites strain

Yield

0.1 Polymers
Elastomers

0.01
0.1 1 10 100 1000
Strength (MPa)

FIGURE 11.1 Ashby materials selection chart based on strength properties.