1. Selection Criteria Properties Availability Cost Manufacturability
Most designers select materials considering
Properties
Availability
Cost
Manufacturability

2. Properties Mechanical
Yield strength (ductile) / Ultimate strength (brittle)
Fatigue (endurance limit)
Stiffness or rigidity (modulus of elasticity)
Hardness (Rockwell, Brinell)
Impact strength (fracture toughness)
Toughness (sharpy test)
Ductility (% reduction is area)
Hardenability
Creep (elevated temperature properties)
High/Low temperature properties
Wear characteristics

3. Properties Physical Chemical Corrosion resistance Oxidation resistance
Density
Electrical properties
Thermal properties (conductivity)
Magnetic
Melting point
Thermal expansion
Flamability
Optical
Chemical
Corrosion resistance
Oxidation resistance
Toxicity
Resistance to radiation
Resistance to elements
Dimensional
Dimensional stability
Surface finish

4. Availability Important questions:
Is the supply plenty, stable, and predictable
Is the material available in the desired form?
Gage 10 sheets of 304L stainless steel?
Do we have to order 100,000 lbs?
Is the material available from company-certified vendors and multiple suppliers?

5. COST The primary factor in material selection in industry
Comparative cost of engineering metals per pound
Hook design: Tungsten
In school: Properties important / cost no issue
In industry: Cost also very important

6. COST
Cost per volume may be a better choice. The following table is $/in3

7. Other Cost Factors
What is the cost of material in relation to the production cost or selling price?
Is it an orbiting satellite, B1 bomber, or a hammer?
What is the production volume?
A one of a kind design, or Garden Weasel?
What are the manufacturing processes?

8. Manufacturability Primary processes Forming Machining Casting Welding
Rolling (hot or cold) + forging + upsetting + bending + drawing
Machining
Turning + milling + drilling + broaching + sawing
Casting
Sand casting, investment casting, die casting
Welding
Laser cutting + water jet cutting
PM technology

9. Manufacturability Secondary processes Forming Machining Heat treatment
Finish forming
Machining
Turning + milling + reaming + grinding
Heat treatment
Deburring
Plating + coating

10. Manufacturing Machinability Weldability Formability Castability
Hardenability

11. Designer’s Choices Know about the properties of a few carbon steels
Know about the properties of a few cast irons
Class 20, Class 60, Ductile
Know about the properties of a few alloy steel
4140, 4340, 9310
Know about the properties of a few tool steels
01, A2, D2, S1, H13, M2
Know about the properties of a few stainless steels
304, 304, 316,420,440C, 17-4 PH

12. Designer’s Repertoire
Know about the properties of a few Aluminum alloys:
3003, 5052, 6061, 7075
Know about the properties of a few nickel alloys:
Monel, Inconel
Know about the properties of a few copper alloys:
C36000 yellow brass, C52100 phosphor bronze
Know about the properties of a few titanium alloys
Know about the properties of a few Magnesium alloys

13. Designer’s Repertoire
Know about the properties of a few ceramics
Aluminum oxides
Silicon nitride / Silicon carbide
Cemented carbides
Carbon products
Ceramic coatings (Chromium oxide, Tungsten carbide)
Know about the properties of a few plastics:
Polyethylene / Polyimides / Polyamides
Polycarbonate
PVC /ABS
Nylons
Elastomers

14. Example
Suppose a designer has created a drawing for a shaft of a hypothetical device. The list of operational conditions have been determined as follows:
1.25” diameters are to fit ball bearings
The shaft is subjected to maximum shear stress of 10 ksi
There is possibility of moderate shock load
Small end must resist damage from frequent removal of a keyed gear.
There are no inertial requirements.
Surface roughness to be 32 micro inches max.
Diameters must be concentric to inch.

15. Example
Based on the operational requirements, time constraint, and cost, the following selection factors have been established:
Hardness of at least 30 HRC
Fatigue strength of 30 ksi
Impact strength must be high
Stiffness must be high
The part must not rust in 50% RH room air.
Must be dimensionally stable.
Parts are needed in one week.
Three units are required.
Expected service life is 5 years