Engineering material selection is a constrained decision problem rather than a search for the material with the largest single property.

Start by translating the design into four categories:

• function: what the component must do;
• constraints: requirements that must be satisfied, such as service temperature, electrical insulation or minimum fracture toughness;
• objective: what should be minimized or maximized, such as mass, cost or environmental burden;
• free variables: choices the designer may change, such as material, section size or manufacturing process.

Screening

Eliminate candidates that violate a hard constraint. A material that cannot survive the service temperature should not remain in the ranking merely because it is light.

Ranking

Among survivors, rank performance using a justified metric or derived performance index. Property charts can reveal families that occupy favorable combinations of stiffness, density, strength, conductivity or other properties.

Supporting information

A numerical ranking is not the final decision. Check fracture mode, fatigue, creep, corrosion, availability, joining, manufacturability, variability, inspection, repair, regulatory constraints and cost data relevant to the real component.

Material and process choices are coupled: selecting a polymer, casting alloy, ceramic or composite implicitly changes feasible shapes and manufacturing routes.

A defensible selection therefore records why candidates were screened out, what objective ranked the survivors, and which non-numerical risks determined the final choice.