Materials in Mechanical Design and Product Design 1

Volume 1:

Material Selection in Mechanical Design and Product

Development

Materials in Mechanical Design and Product Design 2

1. REFERENCES:

Material Selection in Mechanical Design 4th Ed, Ashby

Material and Process Selection in Mechanical Design

Material Selection in Design, NPTEL

2. DESIGN:

Synthesis + Analysis + Creativity + Decision-making + Problem decomposition + complexity-to-

simplicity

Design Process: Need Identification > Concept Generation > Embodiment > System Design > Detail

Design

Need Identification – comes from customer, market need, etc.

Concept Generation – development of multiple solutions to meet the need

Embodiment -

Design constraints: (1) Qualitative – color, texture, etc. and (2) Quantitative – weight, size, etc.

2.1 Product Realization:

Product realization involves material selection. Materials chosen based on:

Performance characteristics – to meet functional requirements

Processing characteristics – to meet manufacturing and processing constraints

Sustainability characteristics – environmental impact constraints

Business considerations – to meet business constraints relative to cost and availability

Mechanical design is the design of components that carry mechanical loading including tensile/compressive

forces and bending/twisting moments

Evolution of engineering materials – from stone to ceramics, wood, plastics, iron, composites, etc.

2.1.1 Traditional materials:

- Wood good as a compressive and tensile load carrying material and has natural aesthetic beauty

- Ceramics based on sand (silica) is hard, abrasive, and a good thermal insulator

- Steel and aluminum are products of the industrial revolution (18th century)

Steel: Low Carbon, Medium Carbon, High Carbon, and stainless steel

- Low carbon steel (<0.25% carbon) used in structural reinforcements, car body panels, cans, and pressed

sheets

- Medium Carbon (0.25 – 0.50%) used in rail-road tracks and other low volume applications (cranks and

shafts)

- High Carbon Steel (0.5- 1.6%) used in tools, chisels, cables, and wires

- Stainless Steels: used in high end applications for high strength, corrosion, and high temperature

applications

2.1.2 Trends in material selection today:

- Increasing use of composites

- Increasing use of multifunctional materials: EMI interference, shock absorption, etc.

- Increasing use of plastics and polymer blends (more complex parts, design for assembly, etc.)

Materials in Mechanical Design and Product Design 3

- Eco-efficient design and reduction in material weights: design based on competitively priced

goods/services with minimum environmental impact

o Seven eco design principles – reduce material usage, reduce energy intensity, reduce toxicity,

enhance recyclability, maximize sustainability, extend product life/durability, increase service

life

2.1.3 Trends in material usage and reserves:

- Iron, steel, and aluminum are most widely used materials today

- Steel consumption is doubling every 20 years

- Aluminum consumption is doubling every 9 years

- Polymer consumption in increasing and doubling almost every 4 years

- Copper, Silver, Tungsten, Tin, and Mercury are rarely available today (becoming scarce)

2.1.4 Impact on the Designer:

- Material efficient design: use less material

- Substitute to different material – use more available material instead of scarce ones

- Recycling: stress recyclable material like Aluminum

2.1.5 Classification of materials:

Metals & Alloys

Ceramics & Glasses

Polymers

Composites = mixtures of above

2.1.6 Metal and Alloys

Iron and Steel

o Modulus of Elasticity Range = 180 – 210 GPa (rate of stress to strain)

o Yield Strength Range = 250 – 2250 MPa

o Service Temperature = -70 to 600 deg Celsius

o Application: concrete reinforcement, bridges, cables, shafts, gears, springs, bearings, car-bodies,

machines, equipment, ect.

Aluminum and Alloys

o Modulus of Elasticity Range = 65 – 90 GPa (~1/3 that of steel)

o Yield Strength Range = 30 - 510 MPa

o Service Temperature = -270 to 200 deg C

o Application: lightweight to strength, excellent thermal and electrical properties, Aerospace, car

bodies, packaging, thermal and electrical applications

Copper & Alloys

o Modulus of Elasticity Range =

o Yield Strength Range =

o Service Temperature =

o Application:

Nickel & Alloys

o Modulus of Elasticity Range = 125 – 245 GPa (comparable to Steel)

o Yield Strength Range = 20 – 2100 MPa (comparable to Steel)

o Service Temperature = up to 1200 deg C

Materials in Mechanical Design and Product Design 4

o Application: high temperature application like turbine blades and aerospace

Titanium & Alloys

o Modulus of Elasticity Range = 90 – 140 GPa (slightly lower than Steel)

o Yield Strength Range = 170 – 1250 MPa (slightly lower than Steel)

o Service Temperature = -50 t0 500 deg C (good service temperature)

o Application: lighter than steel so used in aerospace applications and for nuclear applications

given its good irradiated properties

2.1.7 Polymers – Thermoplastics, Thermosets, and Elastomers

Thermoplastics – can be reused by melting

o Polyethylene (PE) – elastic modulus = 0.03-1.4 GPa; service temperature limited to ~100 deg C;

PE fibre popular in composities, LDPE and HDPE are popular in containers

o Polymethyl Methacrylate (PMMA or Acrylic) – transparent w/ higher elastic modulus than PE;

good stiffness and low density and good optical properties; tensile strength ~53 to74 MPa;

aerospace applications as cockpit canopies and in lenses and CDs

o Polymide (Nylon) – good tensile strength and good for molding applications; tensile strength

~830 MPa; low coefficient of friction (bearing applications); service temperature between (-80 to

120 deg C)

o Polystyrene (PS) – available in thin film, blended and foam forms; tensile strength ~ 30 to 60

MPa; widely used for disposable cups and utensils

o Polyvinyl Chloride (PVC) – cheap yet attractive polymer; similar strength to PS; good corrosion

resistance and UV resistance; used extensively in pipes, fittings, and floorings

Thermosets – cannot be reused using heat

o Polyurethane (PU) – generally available as foams; used in crash protection and vibration

dampening; low strength modulus; superior material for energy dissipation

o Epoxy – used in mechanical joints; good strength and widely used in glass-reinforced and fibre

reinforced plastics

Elastomers – superior strain resistance (good stretch-ability)

o Butyl Rubbers – good energy dissipation; good resistance to abrasion and tearing; can be used @

temps up to 150 deg C; used for tubes, belts, and hoists

o Silicone Rubbers – service temps up to 300 deg C; can be reinforced with fillers to improve

strength; used for seals, gaskets, o-rings, and food processing equipment

2.2 Relative Cost of Materials:

Material Relative Cost (x 10-4)

CFRP 6060 Multiply index by $330, 000 (US$/ton) to get absolute

price ($330, 000 is cost of Boron Epoxy composite

previously used on the Space Shuttle designs. Tungsten 787

Cobalt 521

Titanium Alloy 385

Polyamide 306

PMMA 160

High Speed Steel 121

Nylon 96

GFRP 100

Stainless Steel 93

Polycarbonate 77

Aluminium Alloy 73

Materials in Mechanical Design and Product Design 5

Epoxy 50

Rubber 43

HDPE 37

PS 39

Mild Steel 14

Soft Wood 13

Cement 01

Source: Roymech (http://www.roymech.co.uk/Useful_Tables/Matter/Costs.html)

Metal Price $

1000/tonne

1000/m3

Relative cost

(weight)

Relative cost

(volume)

Steel HR (A56) 6 3,2 24,7 1 1

Steel CD (12L40) 7,4 3,9 30,5 1.23 1.23

Alloy Steel (4130) 9,99 5,3 41,2 1.66 1.66

St.Stl (304L) 15,34 8,1 63,2 2.6 2.56

St.Stl (316L) 20,61 10,9 84,9 3.4 3.44

Aluminium (2011-T3) 8,58 13,1 35,4 4.2 1.43

Copper (C110) 37,91 17,5 156,2 5.6 6.32

Brass (C360) 25,3 11,7 104,3 3.7 4.22

Bronze 42,09 19,5 173,5 6.2 7.0

Titanium (6AL-4VG5) 107 98 441 31 17.8