Material choice locks duty, cost, and process together.

Choose it from the duty, the environment and the process, together. Write what the part must survive, where, and how it will be made. Then shortlist families that can do those three at once. A material that machines beautifully and moulds badly is the wrong choice if you will mould. A material that shrugged off a bench drop in a printed stand-in has not been chosen. It has been postponed.

The strain sum below is hypothetical teaching maths. The allowable strains are assumed for the exercise. They are not a grade datasheet, not a BrahmWorks test and not a permissible limit you can copy onto a drawing. The grade supplier’s data, read for the temperature and the chemical you actually have, replaces them.