Properties and Selection of Engineering Materials

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Materials Selection in Mechanical Design M.F.
Ashby, Butterworth-Heinemann, 1992
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2.1 The vast materials worldVast in number

• 102 of chemical elements
• 103 of steel
• 103 of polymers.
• 10 of Al alloys

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Wide range in properties

• Melting temps from 0 to 3000 oC
• Density from 0.1 to 20 g/cm3
• Yield strength from 1 to 2000 MPa
• Cost from 0.1 to 106 per kg
• Resistivity from 10-6 to 1020 ??cm

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Numerous processing methods Metals

• Cast
• Powder processed
• Cold/hot working
• Surface treatment
• Heat treatment, various methods
• Joining methods

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Processing methods of polymers

• Injection molding
• Extrusion
• Blow molding
• Plasticizers
• Fiber reinforcement
• Foaming

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Subgroups

• Steels
• Low-carbon steels
• High-carbon steels
• Stainless steels
• Tool steels
• Cast irons
• Grey iron
• White iron

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Numerous in applications

• Automotive
• Aerospace
• Chemical
• Power generation
• Infrastructure
• Electronic
• Domestic
• Biomedical

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2.2 Properties and selection

• Selection of a material is based on many
  properties.

• Example-1 car body panel

• Stiffness
• Strength (dent resistance)
• Corrosion resistance
• Formability/Joining/Weldability
• Cost
• Recyclibility.

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• Example 2 Jet engine turbine blade
• Stiffness
• High temperature strength
• Thermal expansion
• Thermal conductivity
• Oxidation resistance
• Impact resistance
• Fatigue resistance
• Cost

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Primary properties in selection
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2.3 Aspects of materials properties

• Presentation
• Measurement
• Dependence of the properties on external
  conditions
• Treatment to regulate the properties
• Underlying mechanisms

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Example corrosion resistance
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2.4 Tools for navigating the vast materials
world

• Classification of materials
• Subgroups of materials
• Materials property charts
• Handbooks and computerized data bases
• Awareness and understanding of materials
  properties

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2.5 Approach of this course

• Structure the course around materials property
  charts
• Zoom-out for global view of properties
• Zoom-in to examine individual materials
• Build an understanding around property charts.

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• Example 1

E vs ? Global view
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• E vs ? zoom-in

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E vs ? zoom in further

• Polymers
• A given polymer has a wide range of E and ?
• Types of atomic bonding in polymers
• Effect of molecular weight and processing on
  Youngs modulus

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• Metals
• A given metal has a relatively narrow range in E
  and ?
• Nature of atomic bonding
• Relation with other properties