Föreläsning 2 - material selection

Question 1

Describe the design process

Answer 1

1. Market need
2. Problem statement: What is the purpose of the product?
3. Concept: data for material family (ex metals), choice of process family
4. Embodiment: data for material class (ex steel), how will it work, shape? Choice of process class
5. Detail: data for single material (ex Al-2040), choice of single process
6. Product specification: specifications => manufacture

Question 2

1. What is translation?

Answer 2

Demands on component to demands on material.

-Function:
Main function of the component, e.g., conduct heat,
insulate electricity, beam in bending that does not
plasticize.

-Constraints:
Must be met for the component to work, e.g. operating
temp, sustain water, fracture toughness

-Objective:
Properties we want to optimize: weight, price,
environmental.

-Free variables:
Variables we are free to choose, e.g. section area,
material

Question 3

2. What is screening?

Answer 3

Removing all materials that do not fulfill all constraints. (the product will not work properly if we are using these materials).

We can take away material properties that are included in the objective. (no constraint on density if the objective is low weight).

Question 4

3. How do we optimize?

Answer 4

• Rank the remaining materials based on objective.
• Use function, objective and free variables to determine a performance index.

Performance index = numerical value, one property or function of properties.

Example of performance index: E/density

Question 5

4. Why do we find documentation on the materials?

Answer 5

We find documentation in books, articles, standards etc to find experiences or useful information.

Question 6

How do we iterate?

Answer 6

The materials selection usually has to be done in several steps. Start with material groups.

Question 7

Describe the material selection process

Answer 7

All materials
–>
Translate requirements: express as function, constraints, objectives and free variables.
–>
Screen using constraints: eliminate materials that cannot do the job
–>
Rank using objective: find the screened materials that do the job best.
–>
Seek documentation: research the family history of top-ranked candidates
–>
Final material choice!

Question 8

Name some common constraints

Answer 8

Stiffness
Strength
Fracture toughness
Thermal conductivity
Electrical resistivity
Cost
Mass

Question 9

Name some common objectives

Answer 9

Minimise:
Cost
Mass
Volume
Environmental impact
Heat loss

Maximise:
Energy storage
Heat flow