1. MSE 401 Design in Material Engineering
Classes and Properties of Engineering Materials in Design

2. FAMILIES OF MATERIALS, PROPERTIES APPLICATIONS AND SELECTION CRITERIA
Historic evolution of Materials Science and Engineering
The Science and Engineering of Materials
Materials Classification
General properties of Materials
Going from Structure to Materials Properties
Materials Selection

3. Historic Evoluation of Material Science

4. The science and engineering of materials

5. Material classification

13. Material Properties
1. Mechanical properties: quantities that characterizes the behaviour of a material in response to external, or applied forces
2. Physical properties: quantities that characterize the behaviour of a material in response to physical phenomena other than mechanical forces such as heat, electricity, radiation)

16. Mechanical Properties
Strength: measure of the amount of tensile force per unit area that a material can withstand before it fails
Yield strength: the tensile stress (i.e. force/area) at which material yields
Ultimate tensile strength: the largest tensile stress a material can sustain
Shear strength: the largest stress a material can sustain under torsion before it yield or fractures
Compressive strength: a measure of the amount of compressive force per unit area that a material can withstand before it fails
Stiffness: the resistance to stretching, bending, or twisting loads.
Ductility: the ability of a material to plastically deform
Toughness: ability of a material to plastically deform before fracturing
Hardness: ability of a material to resist localized surface indentation or deformation
Fatigue strength: ability of a material to undergo a number of cyclic loads without fracturing
Creep resistance: ability of a material to resist stretching while under loads over long time periods at elevated temperatures
Impact strength: ability of a material to absorb sudden dynamic shocks or impacts without fracturing
Coefficient of friction: a relative measure of the amount of friction force between two surfaces
Wear coefficient: measure of the amount of surface removal due to rubbing and sliding.

18. When the material is difficult to grip (as is a ceramic), its strength can be measured in bending. The modulus of rupture or MoR (units: MPa) is the maximum surface stress in a bent beam at the instant of failure
Cyclic loading not only dissipates energy; it can also cause a crack to nucleate and grow, culminating in fatigue failure. For many materials there exists a fatigue or endurance limit

19. The hardness, H, of a material is a crude measure of its strength
The hardness, H, of a material is a crude measure of its strength. It is measured by pressing a pointed diamond or hardened steel ball into the surface of the material
The toughness and the fracture toughness measure the resistance of a material to the propagation of a crack. The fracture toughness is measured by loading a sample containing a deliberately-introduced crack of length 2c, recording the tensile stress at which the crack propagates.
The loss-coefficient measures the degree to which a material dissipates vibrational energy

20. Physical Properties Density : the amount of matter per unit volume
Coefficient of thermal expansion: a measure of the amount a material elongates in response to a change in its temperature
Melting point: the temperature at which a solid changes to a liquid
Specific heat: the amount of heat required to increase the temperature of a unit mass 1 degree
Corrosion resistance: the ability of a material to resist oxidation, direct chemical attack, or surface degradation by galvanic currents
Thermal conductivity: measure of heat flow across a surface
Electrical conductivity: measure of the ability to conduct electricity

21. Two temperatures, the melting temperature, Tm, and the glass temperature, Tg (units for both: K or C) are fundamental because they relate directly to the strength of the bonds in the solid. Crystalline solids have a sharp melting point, Tm. Non-crystalline solids do not; the temperature Tg characterizes the transition from true solid to very viscous liquid.
Most materials expand when they are heated. The thermal strain per degree of temperature change is measured by the linear thermalexpansion coefficient

22. 10-8 in units for good conductors to more than 1016 for the best insulators. The electrical conductivity is simply the reciprocal of the resistivity.
Optical properties of materials are broadly classed as
transparent:relatively little absorption and reflection
translucent:light scattered within the material (see right)
opaque:relatively little transmission

23. Fundamental properties

24. Fundamental properties

25. Material families / sub-families
Ceramics
Metals
Plastics
Composites
Materials
Family
(Ashby)
Non-ferrous
Ferrous
Elastomers
Thermosets
Thermoplastics
Sub-family

26. Material sub-families / classes
Family
Metals
Sub-family
Ferrous
Cast iron
Carbon steel
Alloy steel
Stainless steel
Classes

27. Metals Metals Ferrous Non-ferrous cast iron carbon steel alloy steel
stainless steel
aluminum
brass
bronze
copper
lead
magnesium
nickel
tin
titanium
tungsten
zinc

28. Metals
Ductile, strong, stiff, electrically conductive, thermally conductive, fatigue-resistant, creep-resistant, impact-resistant, heavy or massive, temperature-tolerant, medium-hard, not very corrosion-resistant
Ferrous: contains iron
Non-ferrous: do not contain iron

30. Polymer Elastomers Thermosets Thermoplastics Polymers butyl
fluorocarbon
neoprene
nitrile
polysulfide
rubber
silicone
alkyd
epoxy
melamine
phenolic
polyester
urethane
ABS
acetal
acrylic
nylon
polycarbonate
polyethylene
polypropylene
polystyrene
vinyl

31. Polymers
Strong, flexible, electrically and thermally insulating, not creep-resistant, impact-resistant, lightweight, temperature-sensitive, soft, corrosion-resistant
Thermoplastic: polymers repeatedly softened by heating and hardened by cooling
Thermoset: polymers hardened by curing
Elastomers : ‘elastic polymers’, can either be thermoplastic or thermoset polymers

33. Ceramics
Strong in compression, weak in tension, brittle, stiff, electrically and thermally insulating, not impact-resistant, medium weight, very temperature tolerant, very hard, corrosion-resistant
Ceramics
alumina
beryllia
diamond
magnesia
silicon carbide
silicon nitride
zirconia

34. Silicon carbide Excellent corrosion resistant Low density
Resistant to high temperatures
High electrical resistance
High hardness
Low tensile strength
Low toughness difficult to shape
Products: electrical insulators, cutting tools, grinding wheels

36. Composites
Stiff, strong, light, non-conducting, moderately corrosion-resistant, sensitive to temperature
carbon fiber
cermet matrix
glass fiber
Kevlar fiber
Composites

38. Glass Transparent, or easily coloured High resistance to corrosion
Easy to shape
Low tensile strength
Low toughness
Costs a lot to make so more economical to recycle
Products : windows, bottles, ovenware, optical fibres

39. Property profiles by family

41. How do we choose a material?
Product function depends upon…
material, manufacturing process, geometry
We have to consider all three
Do we select a few feasible materials first…
then select the specific mfg process? or
Do we select a few feasible mfg processes…
then select the specific material?

42. Interdependence

43. Product function is interdependent
Material
Properties
Product
Function
Manufacturing
Processes
Product
Geometry

44. Material selection methods
1. Screening Methods:
Materials-first approach
Manufacturing-processes-first approach
2. Rating/Ranking Method:
Matrix indices
Ashby Plot
Screening methods means that we disregard material/processes that is not possible/ unfeasible to be used.

45. Materials approach Application Information Applied loads
magnitude
cyclic nature (steady, fatigue)
rate (slow, impact)
duration (creep)
Ambient conditions
temperature
moisture
sunlight
chemical liquids/vapors
Safety
Cost

46. Process Approach Part Information Production volume
Part size (overall)
Shape capability (features)
boss/depression 1D
boss/depression >1D
holes
undercuts (internal/external)
uniform walls
cross sections (uniform /regular)
rotational symmetry
captured cavities

47. Material indices Given the same cost/volume… which is stronger?
index = Strength/cost
Given the same cost/volume… which is stiffer?
index = Young’s modulus/cost
You list out the properties that your are after. Compare it with some other factors that is to be considered such as cost per unit volume etc.

48. Ashby Chart
How can we use it?

49. Materials selection prospective materials and processes functional?
manufacturable?
rejected
materials and processes
screening
feasible
materials and
processes
relative
performance?
rating
best
material(s) and processes

54. Case Studies

55. Hats
Helmets
Hard hats
Climbing hat
Cycling hats

56. 1500s helmet in forged steel
What is the
problem with
this hat?
What is the problem with this hat?

57. Work safety helmet with visor

58. Rock climbing helmet

59. Bicycle helmet

60. Bags
Fashion handbags
School bags
Mountaineering backpacks

61. picture by Dan Smith: www.wikipedia.com
Fashion bags
picture by Dan Smith:

62. picture Berghaus Vulcan: www.wikipedia.com
Backpacks
picture Berghaus Vulcan:

63. Kitchen utensils
Spatulas
Disposable cups
Ovenware

64. Spatulas

65. Ovenware

66. Aero-engine
Requires materials which can operate at temperatures between 600° C to 1000° C.

67. Summary Product function interdependence Mechanical properties
Physical properties
Families, sub, classes of materials
Ashby charts
Materials first approach
Process first approach

68. EXERCISE
Choose from one of the items shown before and write a short essay (of not less than 300 words) on:
- The materials that can be used to make the item chosen (please be specific).
- Why those particular materials are chosen (relate to the function of the product) including the mechanical and physical properties that enables the item/product to achieve its intended function.
- Suggest the most appropriate material and why?