Choice and use of materials

When designing an industrial product, it is always necessary to choose the material from which the object will be made and the process used to produce it. This choice is both crucial and difficult. Crucial because the performance of the design and its economic viability depend on it, difficult because of both the diversity of possible materials and processes, and the variety of requirements demanded by the design.

There are an estimated 60,000 materials available, and around 6,000 possible processes. It is unthinkable that the designer should be familiar with more than a small fraction of this immense diversity, and the difficulty of choosing materials is partly due to this hyperchoice of materials. However, the variety of requests and their often contradictory nature add to the complexity of the multitude of possibilities, the difficulty of objectively stating the desired performance and, perhaps even more, the difficulty of managing a multi-criteria choice.

It is therefore clearly useful to have a systematic procedure for selecting the most suitable process and material for a given function or part, in order to be able to guide oneself effectively through the variety of possible choices. This systematic procedure must be sufficiently general to be applied to a wide variety of designs, and sufficiently transparent to allow the user to retain control, intervene in the selection process and let his creativity, imagination and experience do the work.

The selection method we present in this article should not be understood as a rigid structure, but rather as a guide to ensure that interesting but unusual solutions are not dismissed a priori, as a method for objectively clarifying the requirements of the specifications and comparing the performance of very different materials for a given function. The paradigmatic question of material selection might be: how is it that springs can be made from materials as different as rubber and steel? To answer this question, we need to be able to define a performance index associated with the spring's function, a performance index that enables us to objectively compare two such different materials, and to choose between them on the basis of other design requirements.

The selection method itself must be sufficiently simple and flexible for the designer to be able to implement it with a few quick calculations, but to be able to choose effectively from a large number of materials and processes, it is natural to have recourse to data banks and selection aid software. In this article, we look at both selection methods and existing software aids, and illustrate them with a few case studies.

There are many books on industrial product design and material selection...