MMEE 210

Materials Science

Dr Enoch N., OGUNMUYIWA

 Issues to Address…

➢ Types and general characteristics of engineering

materials.

➢ Materials repertoire and uses.

➢ Materials selection for engineering applications

 Some Important Materials Properties: Examples
➢ Chemical – relates to material's structure, its formation, and reactivity
with chemicals. Usually measured in a chemical laboratory.
➢ Examples include composition, microstructure, phases, grains,
inclusion, crystal structure, corrosion resistance, chemical
reactivity, etc.
➢ Physical – pertains to the interaction of materials with various forms
of energy and human senses. Can be measured without destroying or
changing a material.
➢ Examples include magnetic, electrical, optical, acoustic,
gravimetric, color, thermal properties, conductivity, specific heat,
heat distortion temperature (plastics), thermal expansion,
transition temperature (glass), elastic modulus – measures
stiffness, Poisson's ratio, use temperature, etc.
➢ Mechanical – associated to a material’s response to an applied force.
Often requires damage or destruction to a material. They usually
relate to elastic or plastic behavior.
➢ Examples include toughness, ductility, formability, strength
(tensile, compressive, impact, fatigue, shear, yield, rupture),
hardness, creep resistance, etc.
 Materials Types: General Characteristics
➢ Metals – are inorganic substances that are composed of one or more
metallic elements (may also contain some non-metallic elements).
➢ Metals are divided into two classes: Ferrous and Nonferrous.
➢ Their mechanical properties are of great practical importance in
engineering.
➢ Usage includes structural applications, biomedical applications,
aerospace, electronics, energy, transports, etc.
➢ Examples of metals include, Fe, Cu, Al, Ni, Ti, etc.

➢ General characteristics of metals:

➢ Have crystalline structures – atoms arranged in orderly manner.
➢ Relatively high stiffness, high strength and ductile at room
temperature.
➢ Some have good strength at high temperature.
➢ Most have relatively high electrical and thermal conductivities.
➢ Generally opaque and reflective – not transparent to visible light; a
polished metal surface has a lustrous appearance.
➢ Relatively heavier compared to other materials.
 Materials Types: General Characteristics
➢ Polymers – are compounds of non-metallic organic compounds
consisting of long molecular chains or networks based on carbon,
hydrogen, and other nonmetallic elements (i.e., O, N, and Si).
➢ Usage includes electrical insulations, automotive, power tool
housing, sporting goods, food packaging, etc.
➢ Examples include, rubber, adhesives, plastics, etc.

➢ General characteristics of polymers:

➢ They are relatively inert chemically and unreactive in a large
number of environments.
➢ They are soft, extremely ductile and pliable (easily formed into
complex shapes).
➢ Are poor electrical and thermal conductors.
➢ Most have low to medium strengths.
➢ Most have low densities.
➢ Most are relatively easy to process into final shape.
➢ Some are transparent, opaque and translucent.
 Materials Types: General Characteristics
➢ Ceramics – as inorganic crystalline compounds between metallic and
nonmetallic elements. they are most frequently oxides, nitrides, and
carbides.
➢ Usage includes cookware, cutlery, automobile engine parts,
electrical insulations, drill bits, etc.
➢ Examples include, beach sand, rocks, Al2O3, Si3N4, SiC etc.

➢ General characteristics of ceramics:

➢ Generally have high hardness, extreme brittleness (lack of
ductility) and are highly susceptible to fracture.
➢ They are relatively stiff and strong (stiffnesses and strengths are
comparable to those of the metals).
➢ Some have useful high temperature strength.
➢ Most have poor electrical and thermal conductivities.
➢ Are more resistant to high temperatures and harsh environments
than metals and polymers.
➢ Some are transparent, translucent, and opaque.
Materials Types: General Characteristics

Fig. 1: Transparent, translucent, and opaque – same material but

different structures.
 Materials Types: General Characteristics
➢ Composites – composed of two (or more) individual materials —
metals, ceramics, and polymers. The design goal of a composite is to
achieve a combination of properties that is not displayed by any
single material, and also to incorporate the best characteristics of each
of the component materials.
➢ Usage includes aircraft and aerospace applications, high-tech
sporting equipment (e.g., bicycles, golf clubs, tennis rackets, and
skis/snowboards), automobile bumpers, etc.
➢ Examples include, wood, bone, fiberglass, etc.

➢ General characteristics of composites:

➢ Have a wide range of strength from low to very high.
➢ Some have very high strength-to-weight ratios (e.g. carbon-fiber
epoxy materials).
➢ Some have medium strength and are able to be cast or formed
into a variety of shapes e.g. fiberglass-polyester materials.
➢ Some have useable strengths at very low cost e.g. wood and
concrete.
 Engineering Materials: General Comparison of Properties

Fig 2: Bar chart of room

temperature density values for
various metals, ceramics,
polymers, and composite
materials.

Fig 3: Bar chart of room

temperature stiffness
(i.e., elastic modulus) values for
various metals, ceramics,
polymers, and composite
materials.
 Engineering Materials: General Comparison of Properties

Fig 4: Bar chart of room

temperature strength (i.e.,
tensile strength) values for
various metals, ceramics,
polymers, and composite
materials.

Fig 5: Bar chart of room

temperature resistance to
fracture (i.e., fracture toughness)
values for various metals,
ceramics, polymers, and
composite materials.
Engineering Materials: General Comparison of Properties

Fig 6: Bar chart of room temperature electrical

conductivity ranges for metals, ceramics, polymers, and semiconducting materials.
Engineering Materials: Functional Classifications – Examples

Fig 7: Functional classification of materials. Notice that metals, plastics, and ceramics occur in
different categories. A limited number of examples in each category are provided.
Materials Selection:
Simple Case Studies
 Materials Selection: Classes of Material 1

A certain application requires a material with the following

properties:

1. Lightweight,
2. Electrically non–conductive, and
3. Extremely stiff.

Suggest candidate class(es) of material suitable for such

application.
 Materials Selection: Classes of Material 2

A certain application requires a material with the following

properties:

1. Lightweight,
2. Electrically non–conductive, and
3. Extremely stiff.
4. Resistant to high temperatures.

Suggest candidate class(es) of material suitable for such

application.
 Materials Selection: Classes of Materials 3
A certain application requires a material with the following
properties:

Major requirement:
1. Very hard,
2. Corrosion resistant at room temperature and atmosphere
3. Extremely stiff.
Minor requirement:
1. Impact resistant

a. If you consider the major requirement, which class(es) of

materials would you suggest for such application?
b. If you consider both major and minor requirement, which
class(es) of materials would you suggest for such application?
c. Suggest a candidate material
 Materials Repertoire: Importance

➢ Thousands of materials to choose from for different applications

– competitions amongst materials.
➢ Working knowledge of engineering materials.
➢ Need to identify an exact material by using a globally
recognized designation system and designated required material
treatments.
➢ Over 100,000 engineering materials to choose from; over 15,000
plastics are commercially available worldwide and even more
metals and ceramics.
➢ No designer or engineer can be familiar with all those or know
the designation number for all.
➢ Be familiar with the common ones, e.g. steel, Al, Cu, etc.
➢ A repertoire of material will meet most design needs.
➢ Examples includes handbooks and in the modern days we have
software.
➢ ASTM handbook of Materials
➢ Granta Edupack, formerly CES Edupack, etc.
 Materials Repertoire: Example

Fig. 8: Strength vs. density (yield strength for metals and polymers, compressive strength for ceramics, tear
strength for elastomers, and tensile strength for composites). The guide lines are used in minimum weight,
yield-limited, design. © Materials Selection in Mechanical Design, Michael F. Ashby 4th Edition.
 Materials Repertoire: Example

Fig. 9: Strength vs. relative cost per unit volume. The design guide lines help selection to maximize strength
per unit cost. © Materials Selection in Mechanical Design, Michael F. Ashby 4th Edition.
 Materials Repertoire: Example

Fig. 10: The maximum service temperature—the temperature above which a material becomes
unusable. © Materials Selection in Mechanical Design, Michael F. Ashby 4th Edition.
 Materials Repertoire: Example

Fig. 11: Young’s modulus vs. strength. The design guide lines help with the selection of materials for
springs, pivots, knife-edges, diaphragms, and hinges. © Materials Selection in Mechanical Design,
Michael F. Ashby 4th Edition.
 Materials Repertoire: Example

Fig. 12: Strength vs. density (yield strength for metals and polymers, compressive strength for ceramics, tear
strength for elastomers, and tensile strength for composites). The guide lines are used in minimum weight,
yield-limited, design. © Materials Selection in Mechanical Design, Michael F. Ashby 4th Edition.
 Materials Selection: Relationships

Fig. 13: Interrelations of design, materials, and processing to produce a product.

 Materials Selection: General Criteria
Materials are selected on the basis of four general criteria:

1. Performance characteristics (properties) – the process of matching

values of the properties of the material with the requirements and
constraints imposed by the design.
2. Processing (manufacturing) characteristics – means finding the
process that will form the material into the required shape with a
minimum of defects at the least cost.
3. Environmental profile – focused on predicting the impact of the
material throughout its life cycle on the environment. environmental
considerations are growing in importance because of the dual
pressures of greater consumer awareness and governmental
regulation.
4. Business considerations – cost of the parts that is made from the
material! This considers both the purchase cost of the material and the
cost to process it into a part. A more exact basis for selection is life-
cycle cost, which includes the cost of replacing failed parts and the
cost of disposing of the material at the end of its useful life.
 Materials Selection Process: Overview
Materials selection, like other aspects of engineering design, is a decision-
making process. The steps in the process are as follows:

1. Analysis of the materials requirements. Determine the conditions of

service and environment that the product must withstand. Translate them
into material properties.
2. Screening for candidate materials. Compare the needed properties with
a large materials property database to select a few materials that look
promising for the application.
3. Analysis of candidate materials in terms of trade-offs of product
performance, cost, manufacturability, and availability to select the best
material for the application. This is done in the embodiment phase of
design.
4. Development of design data for critical systems or components*.
Determine experimentally the key material properties for the selected
material to obtain statistically reliable measures of the material
performance under the specific conditions expected to be encountered
in service.
 Materials Selection: General Procedure

Engineers are often required solve materials selection problems.

Procedure:

1. For a Specific Application Determine Required Properties

• Properties: mechanical, electrical, thermal,
magnetic, optical, deteriorative.

2. From List of Properties Identify Candidate Material(s)

3. Best Candidate Material Specify Processing technique(s)

• To provide required set of properties
• To produce component having desired shape and size
• Example techniques: casting, mechanical forming, welding,
heat treating
4. Consider the Cost Life–cycle Cost!
 Materials Selection: Case Study
Artificial Hip Replacement

Fig. 14: Anatomy of a human hip joint and adjacent skeletal features
 Materials Selection: Case Study
Artificial Hip Replacement
Hip joint problems can be painful and disabling
➢ Joint deterioration (loss of cartilage) as one ages
➢ Joint fracture

(a) (b)

Arrows point to
ends of fracture line

Fig. 15: X-ray of (a) normal hip joint, and (b) fractured hip joint
 Materials Selection: Case Study

Artificial Hip Replacement

➢ Damaged and diseased hip joints can be replaced with

artificial ones!

➢ Materials requirements for artificial joints

➢ Biocompatible – minimum rejection by surrounding
body tissues
➢ Chemically inert to body fluids
➢ Mechanical strength to support forces generated
➢ Good lubricity and high wear resistance between
articulating surfaces.
 Materials Selection: Case Study

Artificial Hip Replacement

➢ Femoral stem — inserted into
Head
top of hip bone (femur) (Ball)
➢ Head (Ball) — affixed to
femoral stem
➢ Shell — attached to pelvis
➢ Liner — into which head fits Liner & Shell
(Acetabular)
Materials Used Femoral
Stem
➢ Femoral stem — Titanium or
CoCrMo alloy
➢ Head (Ball) —CoCrMo alloy
or Al2O3
➢ Shell — Titanium alloy Fig. 16: © Photograph
courtesy of Zimmer,
➢ Liner — PE or Al2O3. Inc., Warsaw, IN, USA.
 Materials Selection: Hip Replacement

Fig. 17: Schematic diagram of an

artificial hip Fig. 18: X-ray of an implanted
artificial hip
Materials Selection: Incorrect Prediction Factors

➢ War – e.g., unrest, etc.

➢ In–service defects
➢ New major discovery
➢ Others?
 Summary

➢ Appropriate materials and processing decisions

require engineers to understand materials and their
properties.
➢ Materials' properties depend on their structures;
structures are determined by how materials are
processed.
➢ In terms of chemistry the classifications of materials
are metals, ceramics, polymers, and composites.
➢ Most properties of materials fall into the following
six categories: mechanical, physical, and chemical.
➢ An important role of engineers is that of materials
selection.
Ask that burning question now!