Materials- Materials Selection

Question 1

What factors for initial design influence the choice of material?

Answer 1

Physical factors- size, shape and weight (processing criteria).
Mechanical factors- strength, modulus, toughness (property criteria).
Costa and availability (processing)

Question 2

What factors for manufacturing influence the choice of material?

Answer 2

Forming and shaping- casting, forming, etc (processing).

Question 3

What factors for life of component influence the choice of material?

Answer 3

Structural integrity (property criteria)

Question 4

What factors for recycling influence the choice of material?

Answer 4

Reuse or disposal (environmental criteria)

Question 5

General properties of metals

Answer 5

High elastic moduli and toughness. Vulnerable to fatigue and corrosion.

Question 6

General properties of ceramics

Answer 6

High moduli, brittle

Question 7

General properties of glasses

Answer 7

Amorphous, brittle and hard

Question 8

General properties of elastomers (type of polymer)

Answer 8

Enormous elastic extension

Question 9

General properties of polymers

Answer 9

Easy to shape, resistance to corrosion

Question 10

General properties of hybrids

Answer 10

Easy to shape

Question 11

What happens to polymers above Tg?

Answer 11

Chains vibrate enough to overcome Van der Waals

Question 12

What features do materials of a family have in common?

Answer 12

Similar properties, processing routes and often applications.

Question 13

What does a property profile include?

Answer 13

The attributes (properties) of a specific material. It is a member of a sub-class of a class of a family of materials.

Question 14

What does an Ashby diagram include?

Answer 14

Measure of one property on y-axis (sometimes log scale) against measure of another property on x-axis. Has regions of each type of material on the diagram. Ellipses in these regions represent individual materials of the family to account for their property ranges due to different processing, microstructure and defects present.

Question 15

4 steps of materials selection strategy

Answer 15

Translation, screening, ranking, supporting information

Question 16

Translation step

Answer 16

Consider all materials. Express design requirements as a function. Identify the function (what does component do). Consider constraints (non-negotiable or desirable conditions that must be met). Think about objective (what is to be maximised/minimised). Identify free variables (what parameters of problem designer free to change).

Question 17

Screening and ranking steps

Answer 17

Screening isolates materials capable of doing job. Ranking identifies those among them that can do the job best

Question 18

Example of cork remover: function, constraints, free variables

Answer 18

Function: ensure linear pull of cork
Constraints: doesn’t break, elongate, corrode, is light, cheap
Free variable: material used

Question 19

Example of cork remover: quantity constraints

Answer 19

Doesn’t break: high yield strength
Doesn’t elongate: high YM
Doesn’t corrode: resistant materials to water, cleaning fluid, etc
Cheap: cost per kg

Question 20

Using an Ashby diagram with known constraints

Answer 20

Plot 2 properties you want specifics of on the axes. Draw vertical or horizontal line at min/max value for each. Look at materials in region that satisfies constraints for both properties.

Question 21

Supporting information step

Answer 21

Research history of top-ranked candidates. Compare them to choose the single best material.