Testing and introduction of new materials - Orthopaedic Biomaterials in Research and Practice - page 372

Design process

What is it? In the simplest form, engineering design is what engineers do. Despite

the use of mathematical tools, testing apparatus, and the other techni-
cal accouterments of engineering, it is at its heart a creative process,
no different from painting a picture or composing a modern dance. It
differs from these processes only in its goals and in the perception that
these goals may be set prospectively and their attainment measured
retrospectively.
Although the creative aspects of design are critical, the word pro-
cess is used with great emphasis. There is a tremendous need in design
to define a process that will be followed to complete a task and then
to rely on it, step by step, in achieving one's aim. The artistic ideal,
embodied in Mozart's alleged remark that he “did not compose music
but simply wrote it down,” is a romantic illusion. Design is a difficult,
painstaking process of drawing inspiration from initial objectives and
husbanding creative ideas as they are reduced to practice and confirmed
in operation.

Design cycle A structured design process consists of the consecutive execution of a

repetitive design cycle. The design of a simple device, such as a tongue
depressor, may be achieved in as little as three or four such cycles,
whereas a complex design, such as a powered hospital bed, may require
many more such cycles, some in parallel and others in series.
Materials, by their nature, are simpler in design aspects and tend
more to be designed in a single cycle. A cycle, with general applicability,
that may be used for design of materials has seven steps:

1. Define objectives

2. Set goals

3. Set specifications

4. Develop concepts

5. Select an approach

6. Complete the design

7. Test the design

Figure 15.1 shows how these steps fit together. The concept of con-
secutive use of such a cycle is clear if the objectives are thought to come
from issues raised by the result of a previous cycle and the output is used
to start another cycle. Thus, a materials design cycle may arise from a
previous device design that was unsuccessful owing to the lack of appro-
priate materials and may lead to a further cycle whose objectives might
be to improve some property of the designed material, to reduce its cost,
and so on.

Step 1: Define objectives A design cycle, like a journey, cannot begin
unless there is some reason for its existence. Thus, at the beginning, an
objective or objectives must be selected. The process of stating these in