Case studies: use
14.1 Introduction and synopsis
Screening requires data sources with one structure, further information, sources with another. This
chapter illustrates what they look like, what they can do and what they cannot.
The procedure follows the flow-chart of Figure 13.2,
exploring the use of handbooks, databases,
trade-association publications, suppliers data sheets, the Internet, and, if need be, in-house tests.
Examples of the use of all of these appear in the case studies which follow. In each we seek
detailed data for one of the materials short-listed in various of the case studies of earlier chapters.
Not all the steps are reproduced, but the key design data and some indication of the level of detail,
reliability and difficulty are given. They include examples of the output of software data sources,
of suppliers data sheets and of information retrieved from the World-wide Web.
Data retrieval sounds a tedious task, but when there is a goal in mind it can be fun, a sort of
detective game. The problems in Appendix B at the end of this book suggests some to try.
14.2 Data for a ferrous alloy
An easy one first: finding data for a standard steel. A spring is required to give a closing torque
for the door of a dishwasher. The spring is exposed to hot, aerated water which may contain food
acids, alkalis and salts. The performance indices for materials for springs
M2 = :Ec;
A screening exercise using the appropriate charts, detailed in Case Study 6.8, led to a shortlist
which included elastomers, polymers, composites and metals. Elastomers and polymers are elimi-
nated here by the additional constraint on temperature. Although composites remain a possibility,
the obvious candidates are metals. Steels make good springs, but ordinary carbon steels would
corrode in the hot, wet, chemically aggressive environment. Screening shows that stainless steels
can tolerate this.
The detailed design of the spring requires data for the properties that enter M lor
M 2, -the
(in the case of a metal, the yield strength ay), the modulus E, the density p and
the cost C m -and
data for the resistance to corrosion. The handbooks are the place to start.