Why is a materials selection methodology needed?
Because material properties vary enormously, and design choices are complicated by multiple factors like function, commercial aspects, and environmental impact.
The three-way relationship that defines a final product.
Structure, Properties, and Processing.
What are the four main steps of the materials selection process?
- Translation, 2. Screening, 3. Ranking, 4. Refining.
What is ‘Translation’ in the context of materials selection?
It is the process of expressing design requirements as specific ‘Constraints’ and ‘Objectives’ for the material.
What are ‘Constraints’?
These are essential conditions that must be met, for example, the maximum service temperature must be greater than 200°C.
What are ‘Objectives’?
These are the properties that need to be maximised or minimised, for example, minimising weight or cost.
What is ‘Screening’?
It is the elimination of materials that do not meet the set threshold constraints.
What is ‘Ranking’?
It is the process of ordering the materials that passed screening based on their performance indices to maximize or minimize objectives.
Example requirements for a heat sink material in power electronics.
Must operate at 200°C, be a good electrical insulator, a good thermal conductor, and be lightweight.
What material was identified for the heat sink in the example?
Aluminum nitride.
The unique combination of properties of Aluminum Nitride.
It is an electrical insulator but an excellent conductor of heat.
Definition of Electrical Resistivity.
A measure of a material’s strength of resistance to the flow of electric current.
The formula is ρ=R L A.
Definition of Thermal Conductivity.
A measure of a material’s ability to conduct heat.
The formula for heat flux is q=−k L ΔT.
What is the correlation between thermal and electrical properties in metals?
Metals with higher thermal conductivity also tend to have lower electrical resistivity (i.e., better electrical conductivity).
How does materials selection fit into the overall engineering design process?
It is an iterative process; material choice is considered and refined during the conceiving, developing, and evaluating stages of a solution.
