Material Selection

Material selection is a step in the process of designing any physical object. In the context of product design, the main goal of material selection is to minimize cost while meeting product performance goals. Systematic selection of the best material for a given application begins with properties and costs of candidate materials. For example, a thermal blanket must have poor thermal conductivity in order to minimize heat transfer for a given temperature difference.

The performance of an engineering component is limited by the properties of the material of which it is made, and by the shapes to which this material can be formed. Under some circumstances a material can be selected satisfactorily by specifying ranges for individual properties.

More often, however, performance depends on a combination of properties, and then the best material is selected by maximizing one or more ‘performance indices’. An example is the specific stiffness E/r (E is Young’s modulus and r is the density). Performance indices are governed by the design objectives.

Component shape is also an important consideration. Hollow tubular beams are lighter than solid ones for the same bending stiffness and I–section beams may be better still. Information about section shape can be included in the performance index to enable simultaneous selection of material and shape.

We tackle material selection in four steps:

  1. Translation—reinterpreting the design requirements in terms of function, constraints, objectives, and free variables.
  2. Screening—deriving attribute limits from the constraints and applying these to isolate a subset of viable materials.
  3. Ranking—ordering the viable candidates by the value of a material index, the criterion of excellence that maximizes or minimizes some measure of performance.
  4. Documentation—seeking documentation for the top-ranked candidates, exploring aspects of their history, their established uses, their behavior in relevant environments, their availability, and more, until a sufficiently detailed picture is built up that a final choice can be made.